Loop-and-allied QG bibliography

[John86]

http://arxiv.org/abs/1001.1310

Acoustic geometry for general relativistic barotropic irrotational fluid flow
Authors: Matt Visser (Victoria University of Wellington), Carmen Molina-Paris (Leeds University)
(Submitted on 8 Jan 2010)
Abstract: "Acoustic spacetimes", in which techniques of differential geometry are used to investigate sound propagation in moving fluids, have attracted considerable attention over the last few decades. Most of the models currently considered in the literature are based on non-relativistic barotropic irrotational fluids, defined in a flat Newtonian background. The extension, first to special relativistic barotropic fluid flow, and then to general relativistic barotropic fluid flow in an arbitrary background, is less straightforward than it might at first appear. In this article we provide a pedagogical and simple derivation of the general relativistic "acoustic spacetime" in an arbitrary (d+1) dimensional curved-space background.

http://arxiv.org/abs/1001.1180

The quantum interest conjecture in (3+1)-dimensional Minkowski space
Authors: Gabriel Abreu (Victoria University of Wellington), Matt Visser (Victoria University of Wellington)
(Submitted on 7 Jan 2010)
Abstract: The quantum inequalities, and the closely related quantum interest conjecture, impose restrictions on the distribution of the energy density measured by any time-like observer, potentially preventing the existence of exotic phenomena such as Alcubierre warp-drives or traversable wormholes. It has already been proved that both assertions can be reduced to statements concerning the existence or non-existence of bound states of a certain 1-dimensional quantum mechanical Hamiltonian. Using this approach, we will informally review a simple variational proof of one version of the Quantum Interest conjecture in (3+1)-dimensional Minkowski space.

 

[marcus]

http://arxiv.org/abs/1001.1758
Weak lensing, dark matter and dark energy
Dragan Huterer (University of Michigan)
Invited review article for the GRG special issue on gravitational lensing (P. Jetzer, Y. Mellier and V. Perlick Eds.). 17 pages, 8 figures
(Submitted on 11 Jan 2010)
"Weak gravitational lensing is rapidly becoming one of the principal probes of dark matter and dark energy in the universe. In this brief review we outline how weak lensing helps determine the structure of dark matter halos, measure the expansion rate of the universe, and distinguish between modified gravity and dark energy explanations for the acceleration of the universe. We also discuss requirements on the control of systematic errors so that the systematics do not appreciably degrade the power of weak lensing as a cosmological probe."

http://arxiv.org/abs/1001.1838
Spacetime geometry in (2+1)-gravity via measurements with returning lightrays
C. Meusburger
Talk given at the XXV Max Born Symposium: The Planck Scale (Wroclaw, June 29-July 3 2009) 10 pages, 4 figures
(Submitted on 12 Jan 2010)
"We consider an observer in a (2+1)-spacetime without matter and cosmological constant who measures spacetime geometry by emitting lightrays which return to him at a later time. We investigate several quantities associated with such lightrays: the return time, the directions into which light needs to be emitted to return and the frequency shift between the lightray at its emission and its return. We derive explicit expressions for these quantities as functions on the reduced phase space and show how they allow the observer to reconstruct the full geometry of the spacetime in finite eigentime. We comment on conceptual issues. In particular, we clarify the relation between these quantities and Dirac observables and show that Wilson loops arise naturally in these quantities."

http://arxiv.org/abs/1001.1842
Global Lorentzian geometry from lightlike geodesics: What does an observer in (2+1)-gravity see?
C. Meusburger
Talk given at the workshop Chern-Simons Gauge Theory: 20 years after, August 3-7 2009, Hausdorff Center for Mathematics, 18 pages, 9 figures
(Submitted on 12 Jan 2010)
"We show how an observer could measure the non-local holonomy variables that parametrise the flat Lorentzian 3d manifolds arising as spacetimes in (2+1)-gravity. We consider an observer who emits lightrays that return to him at a later time and performs several realistic measurements associated with such returning lightrays: the eigentime elapsed between the emission of the lightrays and their return, the directions into which the light is emitted and from which it returns and the frequency shift between the emitted and returning lightray. We show how the holonomy variables and hence the full geometry of these manifolds can be reconstructed from these measurements in finite eigentime."

 

[John86]

http://arxiv.org/abs/1001.2007

The Holographic Universe
Authors: Paul McFadden, Kostas Skenderis
(Submitted on 13 Jan 2010)
Abstract: We present a holographic description of four-dimensional single-scalar inflationary universes in terms of a three-dimensional quantum field theory. The holographic description correctly reproduces standard inflationary predictions in their regime of applicability. In the opposite case, wherein gravity is strongly coupled at early times, we propose a holographic description in terms of perturbative QFT and present models capable of satisfying the current observational constraints while exhibiting a phenomenology distinct from standard inflation. This provides a qualitatively new method for generating a nearly scale-invariant spectrum of primordial cosmological perturbations.

http://arxiv.org/abs/0912.2678

New Physics at Low Accelerations (MOND): an Alternative to Dark Matter
Authors: Mordehai Milgrom (Weizmann Institute)
(Submitted on 14 Dec 2009)
Abstract: I describe the MOND paradigm, which posits a departure from standard physics below a certain acceleration scale. This acceleration as deduced from the dynamics in galaxies is found mysteriously to agree with the cosmic acceleration scales defined by the present day expansion rate and by the density of `dark energy'. I put special emphasis on phenomenology and on critical comparison with the competing paradigm based on classical dynamics plus cold dark matter. I also describe briefly nonrelativistic and relativistic MOND theories.

http://arxiv.org/abs/0912.0790

Bimetric MOND gravity
Authors: Mordehai Milgrom
(Submitted on 4 Dec 2009)
Abstract: A new relativistic formulation of MOND is advanced, involving two metrics as independent degrees of freedom: the MOND metric g_mn, to which alone matter couples, and an auxiliary metric g*_mn. The main idea hinges on the fact that we can form tensors from the difference, C^a_bc, of the Levi-Civita connections of the two metrics, and these act like gravitational accelerations. In the context of MOND we can form dimensionless `acceleration' scalars, and functions thereof, from contractions of C^a_bc/a0. I look at a class of bimetric MOND theories governed by an action with the gravitational Lagrangian density b sqrt(g)R+a sqrt(g*) R* -2(gg*)^{1/4}f(k)a0^2M(U/a0^2), and with matter actions I(g_mn,psi)+I*(g*_mn,chi), with U a scalar quadratic in the C^a_bc, k=(g/g*)^{1/4}, and allowing for the existence of twin matter, chi, that couples to g*_mn alone. In particular, I concentrate on one interesting and simple choice of the scalar U. This theory introduces only one new constant, a0; it tends simply to General Relativity in the limit a0 goes to 0, and to a phenomenologically valid MOND theory in the nonrelativistic limit. The theory naturally gives MOND and "dark energy" effects from the same term in the action, both controlled by the MOND constant a0. As regards gravitational lensing by nonrelativistic systems--a holy grail for relativistic MOND theories--the theory predicts that the same potential that controls massive-particle motion also dictates lensing in the same way as in GR. This last result can be modified with other choices of U, but lensing is still enhanced and MOND-like, with an effective logarithmic potential.

 

[MTd2]

http://arxiv.org/abs/1001.2748

Twisted geometries: A geometric parametrisation of SU(2) phase space

Laurent Freidel, Simone Speziale
(Submitted on 15 Jan 2010)
A cornerstone of the loop quantum gravity program is the fact that the phase space of general relativity on a fixed graph can be described by a product of SU(2) cotangent bundles per edge. In this paper we show how to parametrize this phase space in terms of quantities describing the intrinsic and extrinsic geometry of the triangulation dual to the graph. These are defined by the assignment to each triangle of its area, the two unit normals as seen from the two polyhedra sharing it, and an additional angle related to the extrinsic curvature. These quantities do not define a Regge geometry, since they include extrinsic data, but a looser notion of discrete geometry which is twisted in the sense that it is locally well-defined, but the local patches lack a consistent gluing among each other. We give the Poisson brackets among the new variables, and exhibit a symplectomorphism which maps them into the Poisson brackets of loop gravity. The new parametrization has the advantage of a simple description of the gauge-invariant reduced phase space, which is given by a product of phase spaces associated to edges and vertices, and it also provides an abelianisation of the SU(2) connection. The results are relevant for the construction of coherent states, and as a byproduct, contribute to clarify the connection between loop gravity and its subset corresponding to Regge geometries.

 

[marcus]

http://arxiv.org/abs/1001.2663
Cosmic recall and the scattering picture of Loop Quantum Cosmology
Wojciech Kaminski, Tomasz Pawlowski
19 pages, 3 figures
(Submitted on 15 Jan 2010)
"The global dynamics of a homogeneous universe in Loop Quantum Cosmology is viewed as a scattering process of its geometrodynamical equivalent. This picture is applied to build a flexible (easy to generalize) and not restricted just to exactly solvable models method of verifying the preservation of the semiclassicality through the bounce. The devised method is next applied to two simple examples: (i) the isotropic Friedman Robertson Walker universe, and (ii) the isotropic sector of the Bianchi I model. For both of them we show, that the dispersions in the logarithm of the volume ln(v) and scalar field momentum ln(p_phi) in the distant future and past are related via strong triangle inequalities. This implies in particular a strict preservation of the semiclassicality (in considered degrees of freedom) in both the cases (i) and (ii). Derived inequalities are general: valid for all the physical states within the considered models."

http://arxiv.org/abs/1001.2702
Emergent matter from 3d generalised group field theories
Alessandro Di Mare, Daniele Oriti
14 pages, 1 figure
(Submitted on 15 Jan 2010)
"We identify classical solutions of a generalised group field theory model in 3 dimensions, and study the corresponding perturbations, deriving their effective dynamics. We discuss their interpretation as emergent matter fields. This allows us, on the one hand to test the proposed mechanism for emergence of matter as a phase of group field theory, and on the other hand to expose some limitations of the generalised group field theory formalism."

http://arxiv.org/abs/1001.2699
Gravity in presence of fermions as a SU(2) gauge theory
F. Cianfrani, G. Montani
5 pages
(Submitted on 15 Jan 2010)
"The Hamiltonian formulation of the Holst action in presence of a massless fermion field with a non-minimal Lagrangian is performed without any restriction on the local Lorentz frame. It is outlined that the phase space structure does not resemble that one of a background independent Lorentz gauge theory, because some additional constraints are present. Proper phase space coordinates are introduced, such that SU(2) connections can be defined and the vanishing of conjugate momenta to boost variables is predicted. Finally, it is outlined that for a particular value of the non-minimal parameter the kinematics coincides with that one of a background independent SU(2) gauge theory and the Immirzi parameter becomes the coupling constant of such an interaction between fermions and the gravitational field."

 

[John86]

http://arxiv.org/abs/1001.2725

The Scalar Curvature of a Causal Set
Authors: Dionigi M.T. Benincasa, Fay Dowker
(Submitted on 15 Jan 2010 (v1), last revised 16 Jan 2010 (this version, v2))
Abstract: A one parameter family of retarded linear operators on scalar fields on causal sets is introduced. When the causal set is well-approximated by 4 dimensional Minkowski spacetime, the operators are Lorentz invariant but nonlocal, are parametrised by the scale of the nonlocality and approximate the continuum scalar D'Alembertian, $\Box$, when acting on fields that vary slowly on the nonlocality scale. The same operators can be applied to scalar fields on causal sets which are well-approximated by curved spacetimes in which case they approximate $\Box - {{1/2}}R$ where $R$ is the Ricci scalar curvature. This can used to define an approximately local action functional for causal sets.

http://arxiv.org/abs/1001.2758

Beyond the Quantum
Authors: Antony Valentini
(Submitted on 15 Jan 2010)
Abstract: At the 1927 Solvay conference, three different theories of quantum mechanics were presented; however, the physicists present failed to reach a consensus. Today, many fundamental questions about quantum physics remain unanswered. One of the theories presented at the conference was Louis de Broglie's pilot-wave dynamics. This work was subsequently neglected in historical accounts; however, recent studies of de Broglie's original idea have rediscovered a powerful and original theory. In de Broglie's theory, quantum theory emerges as a special subset of a wider physics, which allows non-local signals and violation of the uncertainty principle. Experimental evidence for this new physics might be found in the cosmological-microwave-background anisotropies and with the detection of relic particles with exotic new properties predicted by the theory.

 

[atyy]

http://arxiv.org/abs/1001.2706
Matrix Models, Emergent Spacetime and Symmetry Breaking
Harald Grosse, Fedele Lizzi, Harold Steinacker
(Submitted on 15 Jan 2010)
We discuss how a matrix model recently shown to describe emergent gravity may contain extra degrees of freedom which reproduce some characteristics of the standard model, in particular the breaking of symmetries and the correct quantum numbers of fermions.

http://arxiv.org/abs/1001.2703
Noncommutative gauge theory and symmetry breaking in matrix models
Harald Grosse, Fedele Lizzi, Harold Steinacker
(Submitted on 15 Jan 2010)
We show how the fields and particles of the standard model can be naturally realized in noncommutative gauge theory. Starting with a Yang-Mills matrix model in more than 4 dimensions, a SU(n) gauge theory on a Moyal-Weyl space arises with all matter and fields in the adjoint of the gauge group. We show how this gauge symmetry can be broken spontaneously down to SU(3)_c x SU(2)_L x U(1)_Q (resp. SU(3)_c x U(1)_Q), which couples appropriately to all fields in the standard model. An additional U(1)_B gauge group arises which is anomalous at low energies, while the trace-U(1) sector is understood in terms of emergent gravity. A number of additional fields arise which we assume to be massive, in a pattern that is reminiscent of supersymmetry. The symmetry breaking might arise via spontaneously generated fuzzy spheres, in which case the mechanism is similar to brane constructions in string theory.

 

[MTd2]

http://arxiv.org/abs/1001.2919

A Deformed Poincare Invariance for Group Field Theories

Florian Girelli, Etera R. Livine
(Submitted on 17 Jan 2010)
In the context of quantum gravity, group field theories are field theories that generate spinfoam amplitudes as Feynman diagrams. They can be understood as generalizations of the matrix models used for 2d quantum gravity. In particular Boulatov's theory reproduces the amplitudes of the Ponzano-Regge spinfoam model for 3d quantum gravity. Motivated by recent works on field theories on non-commutative flat spaces, we show that Boulatov's theory (and its colored version) is actually invariant under a global deformed Poincare symmetry. This allows to define a notion of flat/excited geometry states when considering scalar perturbations around classical solutions of the group field equations of motion. As a side-result, our analysis seems to point out that the notion of braiding of group field theories should be a key feature to study further in this context.

 

[MTd2]

http://arxiv.org/abs/1001.3282

Non-standard loop quantum cosmology

Wlodzimierz Piechocki
(Submitted on 19 Jan 2010)
We present results concerning the nature of the cosmological big bounce(BB) transition within the loop geometry underlying loop quantum cosmology (LQC). Our canonical quantization method is an alternative to the standard LQC. An evolution parameter we use has clear interpretation both at classical and quantum levels. The physical volume operator has discrete spectrum which is bounded from below. The minimum gap in the spectrum defines a quantum of the volume. The spectra of operators are parametrized by a free parameter to be determined.

 

[marcus]

http://arxiv.org/abs/1001.3292
On the regularization of the constraints algebra of Quantum Gravity in 2+1 dimensions with non-vanishing cosmological constant
Alejandro Perez, Daniele Pranzetti
(Submitted on 19 Jan 2010)
"We use the mathematical framework of loop quantum gravity (LQG) to study the quantization of three dimensional (Riemannian) gravity with positive cosmological constant (Lambda>0). We show that the usual regularization techniques (successful in the Lambda=0 case and widely applied in four dimensional LQG) lead to a deformation of the classical constraint algebra (or anomaly) proportional to the local strength of the curvature squared. We argue that this is an unavoidable consequence of the non-local nature of generalized connections."

http://arxiv.org/abs/1001.3380
Why Does the Universe Expand?
T. Padmanabhan
5 pages
(Submitted on 19 Jan 2010)
"The purpose of the paper is five-fold: (a) Argue that the question in the title can be presented in a meaningful manner and that it requires an answer. (b) Discuss the conventional answers and explain why they are unsatisfactory. (c) Suggest that a key ingredient in the answer could be the instability arising due to the 'wrong' sign in the Hilbert action for the kinetic energy term corresponding to expansion factor. (d) Describe how this idea connects up with another peculiar feature of our universe, viz. it spontaneously became more and more classical in the course of evolution. (e) Provide a speculative but plausible scenario, based on the thermodynamic perspective of gravity, in which one has the hope for relating the thermodynamic and cosmological arrows of time."

 

[qsa]

I think this guy is very ,very close to the final TOE

http://arxiv.org/PS_cache/arxiv/pdf/0711/0711.4232v5.pdf

Properties of the Curved Spaetime Dirac Equation
G. G. Nyambuya

Abstract. This paper is a continuation of the earlier paper (Nyambuya 2008) the
Curved Spacetime Dirac Equation has been derived. This equation has been developed
mainly to account in a natural way for the observed anomalous gyromagnetic ratio of
fermions and the suggestions is that particles including the Electron, which is thought
to be a point particle, do have a finite spatial size which is the reason for the observed
anomalous gyromagnetic ratio. Combining the idea Nyambuya 2008a and the
proposed Unified Field Theory (Nyambuya 2007), a total of 12 equations each with 16
sub-components are generated thus totaling 192 equations for the Curved Spacetime
Dirac Equation. Four symmetries of these equation are investigated, that is the Lorentz
symmetry, charge conjugation symmetry (C), time reversal symmetry (T) and Space
reversal (P). It is shown that these equations are Lorentz invariant, obey C invariance
symmetry and that some violate T and P symmetry while others do not and that they
all obey TP symmetry. These symmetries show that anti-particles have positive mass and
energy but a negative rest mass and the opposite sign in electronic charge. A suggestion is made that the rest mass of a particle must be related to the electronic charge of that particle.

 

[qsa]

here is a more recent paper

http://arxiv.org/PS_cache/arxiv/pdf/0807/0807.1754v3.pdf


Abstract. (Dated: May 5, 2009) The original Dirac Equation is modified in the simplest imaginable and
most trivial manner to include a universal 4-Vector Cosmological Field term in the space and
time dimensions. This cosmological field leads to a modified Dirac Equation capable of
explaining why the Universe appears to be made up chiefly of matter. It is seen that
this 4-Vector Cosmological Field is actually a particle field and this particle field can possibly
be identified with the darkmatter and darkenergy field. Further, this 4-Vector Cosmological
Field is seen to give spacetime the desired quantum mechanical properties of randomness.
Furthermore, it is seen that in the emergent Universe, the position coordinates of a particle
in space – contrary to the widely accepted belief that the position of a particle in space
has no physical significance, we see that that opposite is true – namely that the position
of a particle has physical significance. We further note that the 4-Vector Cosmological Field
modification to the Dirac Equation leads us to a vacuum model redolent but differrent
from that of Quantum Electrodynamics (QED). This new vacuum model is without virtual
particles but darkparticles. We dare to make the suggestion that these darkparticles may
possibly explain the current mystery of what really is darkmatter and darkenergy.

 

[gadzirai]

Have you found any thing with the paper:

http://arxiv.org/PS_cache/arxiv/pdf/...807.1754v3.pdf

 

[marcus]

http://arxiv.org/abs/1001.3505
Polymer quantization of the free scalar field and its classical limit
Alok Laddha, Madhavan Varadarajan
58 pages
(Submitted on 20 Jan 2010)
"Building on prior work, a generally covariant reformulation of free scalar field theory on the flat Lorentzian cylinder is quantized using Loop Quantum Gravity (LQG) type 'polymer' representations. This quantization of the continuum classical theory yields a quantum theory which lives on a discrete spacetime lattice. We explicitly construct a state in the polymer Hilbert space which reproduces the standard Fock vacuum- two point functions for long wavelength modes of the scalar field. Our construction indicates that the continuum classical theory emerges under coarse graining. All our considerations are free of the 'triangulation' ambiguities which plague attempts to define quantum dynamics in LQG. Our work constitutes the first complete LQG type quantization of a generally covariant field theory together with a semi-classical analysis of the true degrees of freedom and thus provides a perfect infinite dimensional toy model to study open issues in LQG, particularly those pertaining to the definition of quantum dynamics."


http://arxiv.org/abs/1001.3668
Newtonian gravity in loop quantum gravity
Lee Smolin
16 pages
(Submitted on 20 Jan 2010)
"We apply a recent argument of Verlinde to loop quantum gravity, to conclude that Newton's law of gravity emerges in an appropriate limit and setting. This is possible because the relationship between area and entropy is realized in loop quantum gravity when boundaries are imposed on a quantum spacetime."

 

[John86]

http://arxiv.org/abs/1001.3538

At the Frontier of Knowledge
Authors: Sabine Hossenfelder
(Submitted on 20 Jan 2010)
Abstract: At any time, there are areas of science where we are standing at the frontier of knowledge, and can wonder whether we have reached a fundamental limit to human understanding. What is ultimately possible in physics? I will argue here that it is ultimately impossible to answer this question. For this, I will first distinguish three different reasons why the possibility of progress is doubted and offer examples for these cases. Based on this, one can then identify three reasons for why progress might indeed be impossible, and finally conclude that it is impossible to decide which case we are facing.

http://arxiv.org/abs/1001.3391

Quantum theory, gravity, and the standard model of particle physics : using the hints of today to build the final theory of tomorrow
Authors: T. P. Singh
(Submitted on 19 Jan 2010)
Abstract: When a mountaineer is ascending one of the great peaks of the Himalayas she knows that an entirely new vista awaits her at the top, whose ramifications will be known only after she gets there. Her immediate goal though, is to tackle the obstacles on the way up, and reach the summit. In a similar vein, one of the immediate goals of contemporary theoretical physics is to build a quantum, unified description of general relativity and the standard model of particle physics. Once that peak has been reached, a new (yet unknown) vista will open up. In this essay I propose a novel approach towards this goal. One must address and resolve a fundamental unsolved problem in the presently known formulation of quantum theory : the unsatisfactory presence of an external classical time in the formulation. Solving this problem takes us to the very edge of theoretical physics as we know it today!

http://arxiv.org/abs/1001.3419

Quantum Darwinism of Scattering Radiation
Authors: C. Jess Riedel, Wojciech H. Zurek
(Submitted on 19 Jan 2010)
Abstract: We study Quantum Darwinism--the redundant recording of information about the preferred states of a decohering system by its environment--in the case of an object that is illuminated by photons. We calculate the linear quantum mutual information between the object and its photon environment for both monochromatic and thermal radiation. Then, we compare this to a semi-classical treatment of the monochromatic radiation and calculate the exact Shannon mutual information. We demonstrate that these realistic models exhibit fast and extensive proliferation of information about the object into the environment and result in redundancies orders of magnitude larger than the exactly soluble models considered to date.

 

[czes]

http://arxiv.org/abs/1001.3668
Newtonian gravity in loop quantum gravity
Lee Smolin
16 pages
(Submitted on 20 Jan 2010)
"We apply a recent argument of Verlinde to loop quantum gravity, to conclude that Newton's law of gravity emerges in an appropriate limit and setting. This is possible because the relationship between area and entropy is realized in loop quantum gravity when boundaries are imposed on a quantum spacetime."

Have you seen that I wrote the same 2 days earlier (18 Jan) but without high mathematic ?
They start to use Compton wave length but still do calculate by Shannon entropy using Boltzmann constant. Compton wave length does it much easier.

 

[marcus]

Czes,
This thread is primarily bibliography. I hope you continue this discussion, not here (where it interferes with the bibliography) but in a separate "Czes discussion thread" or wherever else is agreeable to you.

 

[marcus]

http://arxiv.org/abs/1001.3808
Notes Concerning "On the Origin of Gravity and the Laws of Newton" by E. Verlinde (arXiv:1001.0785)
Jarmo Mäkeä
6 pages, 1 figure
(Submitted on 21 Jan 2010)
"We point out that certain equations which, in a very recent paper written by E. Verlinde, are postulated as a starting point for a thermodynamical derivation of classical gravity, are actually consequences of a specific microscopic model of spacetime, which has been published earlier."

 

[marcus]

http://lanl.arxiv.org/abs/1001.3999
Observables for FRW model with cosmological constant in the framework of loop cosmology
Jakub Mielczarek, Wlodzimierz Piechocki
7 pages, 4 figures
(Submitted on 22 Jan 2010)
"We consider a flat cosmological model with a free massless scalar field and the cosmological constant Lambda in the framework of loop quantum cosmology. The scalar field plays the role of an intrinsic time. We apply the reduced phase space approach. The dynamics of the model is solved analytically. We identify elementary observables and their algebra. The compound physical observables like the volume and the energy density of matter field are analysed. Both compound observables are bounded and oscillate in the Lambda<0 case. The energy density is bounded and oscilltes in the Lambda>0 case. However, the volume is unbounded from above, but periodic."

http://lanl.arxiv.org/abs/1001.4041
Causal Sets: Quantum gravity from a fundamentally discrete spacetime
Petros Wallden
10 pages, review of causal sets based on talk given at the 1st MCCQG conference
(Submitted on 22 Jan 2010)
"In order to construct a quantum theory of gravity, we may have to abandon certain assumptions we were making. In particular, the concept of spacetime as a continuum substratum is questioned. Causal Sets is an attempt to construct a quantum theory of gravity starting with a fundamentally discrete spacetime. In this contribution we review the whole approach, focusing on some recent developments in the kinematics and dynamics of the approach."

http://lanl.arxiv.org/abs/1001.3876
Alternatives to dark matter: Modified gravity as an alternative to dark matter
Jacob D. Bekenstein
20 pages, 4 figures
(Submitted on 21 Jan 2010)
"The premier alternative to the dark matter paradigm is modified gravity. Following an introduction to the relevant phenomenology of galaxies, I review the MOND paradigm, an effective summary of the observations which any theory must reproduce. A simple nonlinear modified gravity theory does justice to MOND at the nonrelativistic level, but cannot be elevated to the relativistic level in a unique way. I go in detail into the covariant tensor-vector-theory (TeVeS) which not only recovers MOND but can also deal in detail with gravitational lensing and cosmology. Problems with MOND and TeVeS at the level of clusters of galaxies are given attention. I also summarize the status of TeVeS cosmology."

 

[MTd2]

http://arxiv.org/abs/1001.4188

Loop quantum gravity - a short review

Hanno Sahlmann
(Submitted on 23 Jan 2010)
In this article we review the foundations and the present status of loop quantum gravity. It is short and relatively non-technical, the emphasis is on the ideas, and the flavor of the techniques. In particular, we describe the kinematical quantization and the implementation of the Hamilton constraint, as well as the quantum theory of black hole horizons, semiclassical states, and matter propagation. Spin foam models and loop quantum cosmology are mentioned only in passing, as these will be covered in separate reviews to be published alongside this one.

http://arxiv.org/abs/1001.4364

Holographic actions from black hole entropy

Francesco Caravelli, Leonardo Modesto
(Submitted on 25 Jan 2010)
Using the Wald's relation between the Noether charge of diffeomorphisms and the entropy for a generic spacetime possessing a bifurcation surface, we introduce a method to obtain a family of higher order derivatives effective actions from the entropy of black holes. Our point of view is to consider fundamental the black hole entropy and the action an emerged object. We then specialize to a particular class of effective theories: the f(R) theories. We apply the idea, using a simple mind ansatz, to loop quantum gravity and to a general class of log-corrected entropy formulas.

http://arxiv.org/abs/1001.4364

Quantum Tetrahedra

Mauro Carfora, Annalisa Marzuoli, Mario Rasetti
(Submitted on 25 Jan 2010)
We discuss in details the role of Wigner 6j symbol as the basic building block unifying such different fields as state sum models for quantum geometry, topological quantum field theory, statistical lattice models and quantum computing. The apparent twofold nature of the 6j symbol displayed in quantum field theory and quantum computing -a quantum tetrahedron and a computational gate- is shown to merge together in a unified quantum-computational SU(2)-state sum framework.

 

[MTd2]

http://arxiv.org/abs/1001.4581

Geometry of the quantum universe

J. Ambjorn, A. Goerlich, J. Jurkiewicz, R. Loll
(Submitted on 26 Jan 2010)
A universe much like the (Euclidean) de Sitter space-time appears as background geometry in the causal dynamical triangulation (CDT) regularization of quantum gravity. We study the geometry of such universes which appear in the path integral as a function of the bare coupling constants of the theory.

 

[marcus]

http://arXiv.org/abs/1001.4538
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
E. Komatsu, K. M. Smith, J. Dunkley, C. L. Bennett, B. Gold, G. Hinshaw, N. Jarosik, D. Larson, M. R. Nolta, L. Page, D. N. Spergel, M. Halpern, R. S. Hill, A. Kogut, M. Limon, S. S. Meyer, N. Odegard, G. S. Tucker, J. L. Weiland, E. Wollack, E. L. Wright
48 pages, 19 figures. Submitted to Astrophysical Journal Supplement Series
(Submitted on 25 Jan 2010)
"(Abridged) The 7-year WMAP data and improved astrophysical data rigorously tests the standard cosmological model and its extensions. By combining WMAP with the latest distance measurements from the Baryon Acoustic Oscillations (BAO) and the Hubble constant (H0) measurement, we determine the parameters of the simplest LCDM model. The power-law index of the primordial power spectrum is n_s=0.963+-0.012, a measurement that excludes the scale-invariant spectrum by more than 3-sigma. The other parameters, including those beyond the minimal set, are also improved from the 5-year results. ...We report a significant detection of the SZ effect at the locations of known clusters, and show that the current simulations and analytical calculations overestimate the gas pressure, and do not reproduce the observed gas pressure in clusters of galaxies. This result is consistent with the lower-than-expected SZ power spectrum recently measured by the SPT collaboration."

For the whole series of 7-year WMAP reports see:
http://lambda.gsfc.nasa.gov/product/map/dr4/map_bibliography.cfm[/QUOTE]

http://arxiv.org/abs/1001.4758
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Are There Cosmic Microwave Background Anomalies?
C. L. Bennett (JHU), R. S. Hill (ADNET), G. Hinshaw (NASA/GSFC), D. Larson (JHU), K. M. Smith (Princeton), J. Dunkley (Oxford), B. Gold (JHU), M. Halpern (UBC), N. Jarosik (Princeton), A. Kogut (NASA/GSFC), E. Komatsu (U. Texas), M. Limon (Columbia), S. S. Meyer (U. Chicago), M. R. Nolta (CITA), N. Odegard (ADNET), L. Page (Princeton), D. N. Spergel (Princeton), G. S. Tucker (Brown), J. L. Weiland (ADNET), E. Wollack (NASA/GSFC), E. L. Wright (UCLA)
19 pages, 17 figures, also available with higher-res figures on this http URL; submitted to Astrophysical Journal Supplement Series
(Submitted on 26 Jan 2010)
"A simple six-parameter LCDM model provides a successful fit to WMAP data, both when the data are analyzed alone and in combination with other cosmological data. Even so, it is appropriate to search for any hints of deviations from the now standard model of cosmology, which includes inflation, dark energy, dark matter, baryons, and neutrinos. The cosmological community has subjected the WMAP data to extensive and varied analyses. While there is widespread agreement as to the overall success of the six-parameter LCDM model, various "anomalies" have been reported relative to that model. In this paper we examine potential anomalies and present analyses and assessments of their significance. In most cases we find that ...
...We examine several potential or previously claimed anomalies in the sky maps and power spectra, including cold spots, low quadrupole power, quadropole-octupole alignment, hemispherical or dipole power asymmetry, and quadrupole power asymmetry. We conclude that there is no compelling evidence for deviations from the LCDM model, which is generally an acceptable statistical fit to WMAP and other cosmological data."

Until now we have only had reports based on the 5-year WMAP data. These are the first I have seen based on 7-year data.

There has been a lot of fast reaction to the Verlinde paper. This is just a sample. The author has a decent publication track record---several Phys. Rev. D, and comparable:

http://arxiv.org/abs/1001.4585
Modified Entropic Force
Changjun Gao
3 pages, 2 figures
(Submitted on 26 Jan 2010 (v1), last revised 27 Jan 2010 (this version, v2))
The theory of thermodynamics tells us the equipartition law of energy does not hold in the limit of very low temperature. It is found the Debye model is very successful in explaining the experimental results. Motivated by this fact, we modify the entropic force formula which is proposed very recently. Since the Unruh temperature is proportional to the strength of gravitational field, so the modified entropic force formula is an extension of the Newtonian gravity to weak field. On the contrary, General Relativity extends Newtonian gravity to strong field case. Corresponding to Debye temperature, there exists a Debye acceleration g_D. It is found the Debye acceleration is g_D=10^{-14}\textrm{N}\cdot \textrm{{kg}}^{-1}. This acceleration is very much smaller than the gravitational acceleration 10^{-4}\textrm{N}\cdot \textrm{{kg}}^{-1} which is felt by the Neptune. Therefore, the modified entropic force can be very well approximated by the Newtonian gravity in solar system. With this Debye acceleration, we also find the current cosmic speeding up can be explained without invoking any kind of dark energy."

 

[marcus]

Renate Loll video lectures on quantum gravity
http://pirsa.org/10010094/
http://pirsa.org/10010095/
http://pirsa.org/10010096/
These are the first three lectures of the series, given Monday-Wednesday, the 25-27 of January 2010.

Planned as a 3-week series of daily one-hour lectures, part of the Perimeter Scholars program at Perimeter Institute. Loll will give some of the history of the subject and perspective on how the two main approaches to nonperturbative QG arose: the canonical and the path integral approaches.
She will cover both canonical LQG and her own triangulations path integral approaches as examples of the two main ways of doing nonperturbative QG.

http://arxiv.org/abs/1001.4823
Extended Horava gravity and Einstein-aether theory
Ted Jacobson
4 pages
(Submitted on 27 Jan 2010)
"Einstein-aether theory is general relativity coupled to a dynamical, unit timelike vector. If this vector is restricted in the action to be hypersurface orthogonal, the theory is identical to the IR limit of the extension of Horava gravity proposed by Blas, Pujolàs and Sibiryakov. Hypersurface orthogonal solutions of Einstein-aether theory are solutions to the IR limit of this theory, hence numerous results already obtained for Einstein-aether theory carry over."

http://arxiv.org/abs/1001.4929
Post-Inflationary Evolution via Gravitation
N. C. Tsamis (U. of Crete) R. P. Woodard (U. of Florida)
16 pages, 1 figure
(Submitted on 27 Jan 2010)
"We study a class of non-local, purely gravitational models which have the correct structure to reproduce the leading infrared logarithms of quantum gravitational back-reaction during the inflationary regime. These models end inflation in a distinctive phase of oscillations with slight and short violations of the weak energy condition and should, when coupled to matter, lead to rapid reheating. By elaborating this class of models we exhibit one that has the same behaviour during inflation, goes quiescent until the onset of matter domination, and induces a small, positive cosmological constant of about the right size thereafter."

http://arxiv.org/abs/1001.4960
On the impossibility of superluminal travel: the warp drive lesson
Carlos Barceló, Stefano Finazzi, Stefano Liberati
Second prize of the 2009 FQXi essay contest "What is Ultimately Possible in Physics?"
(Submitted on 27 Jan 2010)
"The question of whether it is possible or not to surpass the speed of light is already centennial. The special theory of relativity took the existence of a speed limit as a principle, the light postulate, which has proven to be enormously predictive. Here we discuss some of its twists and turns when general relativity and quantum mechanics come into play. In particular, we discuss one of the most interesting proposals for faster than light travel: warp drives. Even if one succeeded in creating such spacetime structures, it would be still necessary to check whether they would survive to the switching on of quantum matter effects. Here, we show that the quantum back-reaction to warp-drive geometries, created out of an initially flat spacetime, inevitably lead to their destabilization whenever superluminal speeds are attained. We close this investigation speculating the possible significance of this further success of the speed of light postulate."

 

[MTd2]

http://arxiv.org/abs/1001.4965

The Coulomb Force as an Entropic Force

Tower Wang
(Submitted on 27 Jan 2010)
Motivated by Verlinde's theory of entropic gravity, we give a tentative explain to the Coulomb's law with an entropic force. When trying to do this, we find the equipartition rule should be extended to charges and the concept of temperature should be reinterpreted. If one accepts the holographic principle as well as our generalizations and reinterpretations, then the coulomb's law, the Poisson's equation and the Maxwell's equations can be derived smoothly. Our attempt can be regarded as a new way to unify the electromagnetic force with gravity, from the entropic origin. Possibly some of our postulate are related to the D-brane picture of black hole thermodynamics.

 

[MTd2]

http://arxiv.org/abs/1001.5032

Ghost wave-function renormalization in Asymptotically Safe Quantum Gravity

Kai Groh, Frank Saueressig
(Submitted on 28 Jan 2010)
Motivated by Weinberg's asymptotic safety scenario, we investigate the gravitational renormalization group flow in the Einstein-Hilbert truncation supplemented by the wave-function renormalization of the ghost fields. The latter induces non-trivial corrections to the beta-functions for Newton's constant and the cosmological constant. The resulting ghost-improved phase diagram is investigated in detail. In particular, we find a non-trivial ultraviolet fixed point in agreement with the asymptotic safety conjecture, which also survives in the presence of extra dimensions. In four dimensions the ghost anomalous dimension at the fixed point is $\eta_c^* = -1.8$, supporting space-time being effectively two-dimensional at short distances.

http://arxiv.org/abs/1001.5033

Ghost anomalous dimension in asymptotically safe quantum gravity

Astrid Eichhorn, Holger Gies
(Submitted on 27 Jan 2010)
We compute the ghost anomalous dimension within the asymptotic-safety scenario for quantum gravity. For a class of covariant gauge fixings and using a functional RG scheme, the anomalous dimension $\eta_c$ is negative, implying an improved UV behavior of ghost fluctuations. At the non-Gaussian UV fixed point, we observe a maximum value of $\eta_c\simeq -0.78$ for the Landau-deWitt gauge within the given scheme and truncation. Most importantly, the backreaction of the ghost flow onto the Einstein-Hilbert sector preserves the non-Gaussian fixed point with only mild modifications of the fixed-point values for the gravitational coupling and cosmological constant and the associated critical exponents; also their gauge dependence is slightly reduced. Our results provide further evidence for the asymptotic-safety scenario of quantum gravity.

http://arxiv.org/abs/1001.5238

Friedmann equation of FRW universe in deformed Horava-Lifgarbagez gravity from entropic force

Shao-Wen Wei, Yu-Xiao Liu, Yong-Qiang Wang
(Submitted on 28 Jan 2010)
It is generally thought that there exists a logarithmic term in the entropy/area relation for the deformed Horava-Lifgarbagez gravity. With the entropy/area relation, we obtain the modified Friedmann equations from the first law of thermodynamics and the entropic force, respectively. Although the modified Friedmann equations derived from the two methods are different, they will reduce to the standard Friedmann equation in the case of small energy density $\rho$.

http://arxiv.org/abs/1001.5147

Casting Loop Quantum Cosmology in the Spin Foam Paradigm

Abhay Ashtekar, Miguel Campiglia, Adam Henderson
(Submitted on 28 Jan 2010)
The goal of spin foam models is to provide a viable path integral formulation of quantum gravity. Because of background independence, their underlying framework has certain novel features that are not shared by path integral formulations of familiar field theories in Minkowski space. As a simple viability test, these features were recently examined through the lens of loop quantum cosmology (LQC). Results of that analysis, reported in a brief communication [1], turned out to provide concrete arguments in support of the spin foam paradigm. We now present detailed proofs of those results. Since the quantum theory of LQC models is well understood, this analysis also serves to shed new light on some long standing issues in the spin foam and group field theory literature. In particular, it suggests an intriguing possibility for addressing the question of why the cosmological constant is positive and small.

 

[MTd2]

http://arxiv.org/abs/1002.0308

Projectable Horava-Lifgarbagez gravity in a nutshell

Silke Weinfurtner, Thomas P. Sotiriou, Matt Visser
(Submitted on 1 Feb 2010)
Approximately one year ago Horava proposed a power-counting renormalizable theory of gravity which abandons local Lorentz invariance. The proposal has been received with growing interest and resulted in various different versions of Horava-Lifgarbagez gravity theories, involving a colourful potpourri of new terminology. In this proceedings contribution we first motivate and briefly overview the various different approaches, clarifying their differences and similarities. We then focus on a model referred to as projectable Horava-Lifgarbagez gravity and summarize the key results regarding its viability.

http://arxiv.org/abs/1002.0260

Black holes and asymptotically safe gravity

Kevin Falls, Daniel F. Litim, Aarti Raghuraman
(Submitted on 1 Feb 2010)
Quantum gravitational corrections to black holes are studied in four and higher dimensions using a renormalisation group improvement of the metric. The quantum effects are worked out in detail for asymptotically safe gravity, where the short distance physics is characterized by a non-trivial fixed point of the gravitational coupling. We find that a weakening of gravity implies a decrease of the event horizon, and the existence of a Planck-size black hole remnant with vanishing temperature and vanishing heat capacity. The absence of curvature singularities is generic and discussed together with the conformal structure and the Penrose diagram of asymptotically safe black holes. The production cross section of mini-black holes in energetic particle collisions, such as those at the Large Hadron Collider, is analysed within low-scale quantum gravity models. Quantum gravity corrections imply that cross sections display a threshold, are suppressed in the Planckian, and reproduce the semi-classical result in the deep trans-Planckian region. Further implications are discussed.

 

[marcus]

http://arxiv.org/abs/1002.0138
Ultraviolet behavior in background independent quantum field theory
Viqar Husain, Andreas Kreienbuehl
8 pages, 5 figures
(Submitted on 31 Jan 2010)
"We describe a background independent quantization of the scalar field that provides an explicit realization of Fock-like states and associated operators in a polymer Hilbert space. The vacuum expectation values of the commutator and anti-commutator of the creation and annihilation operators become energy dependent, and exhibit a surprising transition to fermionic behavior at high energy. Furthermore the approach yields a modified dispersion relation with a leading correction proportional to the momentum cubed. These results suggests a fundamental change in the ultraviolet properties of quantum fields."

Here's an odd one. Chamseddine has been a frequent co-author with Alain Connes on past NGG papers:

http://arxiv.org/abs/1002.0541
Gravity with de Sitter and Unitary Tangent Groups
Ali H. Chamseddine, Viatcheslav Mukhanov
23 pages
(Submitted on 2 Feb 2010)
"Einstein Gravity can be formulated as a gauge theory with the tangent space respecting the Lorentz symmetry. In this paper we show that the dimension of the tangent space can be larger than the dimension of the manifold and by requiring the invariance of the theory with respect to 5d Lorentz group (de Sitter group) Einstein theory is reproduced unambiguously. The other possibility is to have unitary symmetry on a complex tangent space of the same dimension as the manifold. In this case the resultant theory is Einstein-Strauss Hermitian gravity. The tangent group is important for matter couplings. We show that in the de Sitter case the 4 dimensional space time vector and scalar are naturally unified by a hidden symmetry being components of a 5d vector in the tangent space. With a de Sitter tangent group spinors can exist only when they are made complex or taken in doublets in a way similar to N=2 supersymmetry."

 

[MTd2]

http://arxiv.org/abs/1002.0488

Hidden symmetries for thermodynamics and emergence of relativity

Liu Zhao
(Submitted on 2 Feb 2010)
Verlinde recently proposed an idea about the thermodynamic origin of gravity. Though this is a beautiful idea which may resolve many long standing problems in the theories of gravity, it also raises many other problems. In this article I will comment on some of the problems of Verlinde's proposal with special emphasis on the thermodynamical origin of the principle of relativity. It is found that there is a large group of hidden symmetries of thermodynamics which contains the Poincare group of the spacetime for which space is emergent. This explains the thermodynamic origin of the principle of relativity.

http://arxiv.org/abs/1002.0500

Spin Foam State Sums and Chern-Simons Theory

Aleksandar Mikovic, Joao Faria Martins
(Submitted on 2 Feb 2010)
We review the spin foam state-sum invariants of 3-manifolds, and explain their relationship to manifold invariants coming from the Chern-Simons theory. We also explain the relationship between the known invariants of spin networks by using the Chain-Mail formalism of J. Roberts. This formalism can be understood as a quantum-group regularization of the BF theory path integrals.

 

[MTd2]

http://arxiv.org/abs/1002.0813

Ultraviolet Divergences and Scale-Dependent Gravitational Couplings

Herbert W. Hamber
(Submitted on 3 Feb 2010)
I review the field-theoretic renomalization group approach to quantum gravity, built around the existence of a non-trivial ultraviolet fixed point in four dimensions. I discuss the implications of such a fixed point, found in three largely unrelated non-perturbative approaches, and how it relates to the vacuum state of quantum gravity, and specifically to the running of $G$. One distinctive feature of the new fixed point is the emergence of a second genuinely non-perturbative scale, analogous to the scaling violation parameter in non-abelian gauge theories. I argue that it is natural to identify such a scale with the small observed cosmological constant, which in quantum gravity can arise as a non-perturbative vacuum condensate.

http://arxiv.org/abs/1002.0669

Some Aspects of Holst and Nieh-Yan Terms in General Relativity with Torsion

Kinjal Banerjee
(Submitted on 3 Feb 2010)
We explore the relation of the Holst term with the Nieh-Yan term in terms of metric variables. We show that the Holst term indeed affects the classical equations of motion in the presence of matter with spin. Therefore the correct term to add to the Einstein-Hilbert action such that the equations of motion are not affected is the Nieh-Yan term. We then calculate the torsion charge due to this term in the context of a perfect fluid sphere with torsion and show that it vanishes once a horizon is formed but not otherwise. We also show that adding on torsion to General Relativity the Einstein's equations are no longer holographic in torsion although they continue to be so for the metric.

 

[marcus]

http://arxiv.org/abs/1002.0589
Hilbert Spaces from Path Integrals
Fay Dowker, Steven Johnston, Rafael D. Sorkin
(Submitted on 2 Feb 2010)
"It is shown that a Hilbert space can be constructed for a quantum system starting from a framework in which histories are fundamental. The Decoherence Functional provides the inner product on this 'History Hilbert space'. It is also shown that the History Hilbert space is the standard Hilbert space in the case of non-relativistic quantum mechanics."

 

[atyy]

http://physics.aps.org/articles/v3/7
Liberating anyons from two dimensions
Ady Stern, Michael Levin
The combination of trivial and topological band insulators with a superconductor is bringing anyons—particles that behave neither according to purely Bose nor Fermi statistics—into the three-dimensional world.

http://arxiv.org/abs/0909.4741
Majorana Fermions and Non-Abelian Statistics in Three Dimensions
Jeffrey C.Y. Teo, C.L. Kane
(Submitted on 25 Sep 2009 (v1), last revised 28 Jan 2010 (this version, v2))
We show that three dimensional superconductors, described within a Bogoliubov de Gennes framework can have zero energy bound states associated with pointlike topological defects. The Majorana fermions associated with these modes have non-Abelian exchange statistics, despite the fact that the braid group is trivial in three dimensions. This can occur because the defects are associated with an orientation that can undergo topologically nontrivial rotations. A new feature of three dimensional systems is that there are "braidless" operations in which it is possible to manipulate the groundstate associated with a set of defects without moving or measuring them. To illustrate these effects we analyze specific architectures involving topological insulators and superconductors.

 

[MTd2]

http://arxiv.org/abs/1002.1062

Temperature and Energy of 4-dimensional Black Holes from Entropic Force

Yu-Xiao Liu, Yong-Qiang Wang, Shao-Wen Wei
(Submitted on 4 Feb 2010)
We investigate the temperature and energy on holographic screens for 4-dimensional black holes with the entropic force idea proposed by Verlinde. We find that the "Unruh-Verlinde temperature" is equal to the Hawking temperature on the event horizon of these black holes. While they are opposite to each other on the Cauchy horizon. The energy on the holographic screen at infinity is $E=M$ for all of those black holes.

http://arxiv.org/abs/1002.0871

Entropic force in the presence of black hole

Yun Soo Myung
(Submitted on 4 Feb 2010)
We derive the entropic force in the presence of the Schwarzschild black hole by using the local equipartition rule and holographic principle. On the other hand, when using the Tolman temperature, one does not arrive at the Newtonian force law.

http://arxiv.org/abs/1002.1035

A note on gravity, entropy, and BF topological field theory

Jerzy Kowalski-Glikman
(Submitted on 4 Feb 2010)
In this note I argue that the expression for entropic force, used as a starting point in Verlinde's derivation of Newton's law, can be deduced from first principles if one assumes that that the microscopic theory behind his construction is the topological $\SO(4,1)$ BF theory coupled to particles.http://arxiv.org/abs/1002.1027

Beyond Special and General Relativity. Neutrinos and Cosmology

Javier Indurain
(Submitted on 4 Feb 2010)
The widely accepted description of the present cosmic acceleration and the neutrino oscillations in terms of a cosmological constant and neutrino masses, respectively, seems conceptually not very satisfactory. From a phenomenological perspective, the possibility that those phenomena are instead the first windows to new physics at very low energies is explored.

 

[MTd2]

http://arxiv.org/abs/1002.1136

Gravity from the entropy of light

Alessandro Pesci
(Submitted on 5 Feb 2010)
The holographic principle, considered in a semiclassical setting, is shown to have direct consequences on physics at a fundamental level. In particular, a certain relation is pointed out to be the expression of holography in basic thermodynamics. It is argued moreover that through this relation holography is recognized to induce gravity if quantum mechanics is given, and an expression for the gravitational lensing is obtained in terms of the entropy per unit wavelength of black-body radiation, or, at a deeper level, in terms of the maximum entropy per unit of associated space to the elementary bit of information.

http://arxiv.org/abs/1002.1136

Notes on Entropy Force in General Spherically Symmetric Spacetimes

Rong-Gen Cai, Li-Ming Cao, Nobuyoshi Ohta
(Submitted on 5 Feb 2010 (v1), last revised 6 Feb 2010 (this version, v2))
In a recent paper [arXiv:1001.0785], Verlinde has shown that the Newton gravity appears as an entropy force. In this paper we show how gravity appears as entropy force in Einstein's equation of gravitational field in a general spherically symmetric spacetime. We mainly focus on the trapping horizon of the spacetime. We find that when matter fields are absent, the change of entropy associated with the trapping horizon indeed can be identified with an entropy force. When matter fields are present, we see that heat flux of matter fields also leads to the change of entropy. Applying arguments made by Verlinde and Smolin, respectively, to the trapping horizon, we find that the entropy force is given by the surface gravity of the horizon. The cases in the untrapped region of the spacetime are also discussed.


This one cites papers of Padmanabhan:

http://arxiv.org/abs/1002.1132

Quantum gravitational corrections to the propagator in spacetimes with constant curvature

Dawood Kothawala, S. Shankaranarayanan, L. Sriramkumar
(Submitted on 5 Feb 2010)
The existence of a minimal and fundamental length scale, say, the Planck length, is a characteristic feature of almost all the models of quantum gravity. The presence of the fundamental length is expected to lead to an improved ultra-violet behavior of the semi-classical propagators. The hypothesis of path integral duality provides a prescription to evaluate the modified propagator of a free, quantum scalar field in a given spacetime, taking into account the existence of the fundamental length in a locally Lorentz invariant manner. We use this prescription to compute the quantum gravitational modifications to the propagators in spacetimes with constant curvature, and show that: (i) the modified propagators are ultra-violet finite, and (ii) the modifications are non-perturbative in the Planck length. We discuss the implications of our results.

 

[MTd2]

http://arxiv.org/abs/1002.1462

Embedding the Bilson-Thompson model in an LQG-like framework

Deepak Vaid
(Submitted on 8 Feb 2010)
We argue that the Quadratic Spinor Lagrangian approach allows us to approach the problem of forming a geometrical condensate of spinorial tetrads in a natural manner. This, along with considerations involving the discrete symmetries of lattice triangulations, lead us to discover that the quasiparticles of such a condensate are tetrahedra with braids attached to its faces and that these braid attachments correspond to the preons in Bilson-Thompson's model of elementary particles. These "spatoms" can then be put together in a tiling to form more complex structures which encode both geometry and matter in a natural manner. We conclude with some speculations on the relation between this picture and the computational universe hypothesis.http://arxiv.org/abs/1002.1434

Interacting holographic dark energy with entropy corrections

Mubasher Jamil, M. Umar Farooq
(Submitted on 7 Feb 2010)
The holographic dark energy (HDE) is considered to be the most promising candidate of dark energy. Its definition is originally motivated from the entropy-area relation which depends on the theory of gravity under consideration. Recently a new definition of HDE is proposed with the help of quantum corrections to the entropy-area relation in the setup of loop quantum cosmology. Using this new definition, we investigate the model of interacting dark energy and derive its effective equation of state. Finally we establish a correspondence between generalized Chaplygin gas and entropy-corrected holographic dark energy.

 

[marcus]

http://arxiv.org/abs/1002.1844
On Quantum Correlations across the Black Hole Horizon
Ralf Schützhold, William G. Unruh
5 pages, 1 figure
(Submitted on 9 Feb 2010)
"Inspired by the condensed-matter analogues of black holes, we study the quantum correlations across the event horizon reflecting the entanglement between the outgoing particles of the Hawking radiation and their in-falling partners. For a perfectly covariant theory, the total correlation is conserved in time and piles up arbitrary close to the horizon in the past, where it merges into the singularity of the vacuum two-point function at the light cone. After modifying the dispersion relation (i.e., breaking Lorentz invariance) for large k, on the other hand, the light cone is smeared out and the entanglement is not conserved but actually created in a given rate per unit time."http://arxiv.org/abs/1002.1959
A spin foam model for general Lorentzian 4-geometries
Florian Conrady (Perimeter Inst. Theor. Phys.), Jeff Hnybida (Perimeter Inst. Theor. Phys. and Waterloo U.)
26 pages, 1 figure
(Submitted on 9 Feb 2010)
"We derive simplicity constraints for the quantization of general Lorentzian 4-geometries. Our method is based on the correspondence between coherent states and classical bivectors and the minimization of associated uncertainties. For spacelike geometries, this scheme agrees with the master constraint method of the model by Engle, Pereira, Rovelli and Livine (EPRL). When it is applied to general Lorentzian geometries, we obtain new constraints that include the EPRL constraints as a special case. They imply a discrete area spectrum for both spacelike and timelike surfaces. We use these constraints to define a spin foam model for general Lorentzian 4-geometries."

 

[marcus]

http://arxiv.org/abs/1002.2035
Cosmological inflation driven by holonomy corrections of loop quantum cosmology
Dah-Wei Chiou, Kai Liu
7 pages, 2 figures, 1 table
(Submitted on 10 Feb 2010)
"At the level of heuristic effective dynamics, we investigate the cosmological inflation with holonomy corrections of loop quantum cosmology (LQC) in the k=0 Friedmann-Robertson-Walker model with a single inflaton field subject to a simple potential. In the symmetric bouncing scenario of LQC, the condition for occurrence of the quantum bounce naturally and uniquely fixes the initial conditions at the bouncing epoch. Around the quantum bounce, the universe undergoes a short super-inflationary phase, which drives the inflaton field to its potential hill and thus sets the proper initial conditions for the standard slow-roll inflation. Between the super-inflation and the standard inflation, there is a non-inflationary phase, which violates the slow-roll condition. The violation of slow roll is expected to give some suppression on the low angular power spectrum of the cosmic microwave background and different orders of holonomy corrections shall yield different suppressions."

 

[MTd2]

http://arxiv.org/abs/1002.2029

Condensed Geometry

Koustubh Kabe
(Submitted on 10 Feb 2010)
A spin (dependent) system treatment of gravity is adopted akin to the Sen-Ashtekar treatment. Time is reinserted into the space ``fluid'' at the quantum Level. This time - the Lorentzian one- is shown to be a vorticity of a ``fluid particle'' of the space and the effect is integrated over all the fluid particles to incorporate time in quantum gravity. This spacetime is viewed as a fluid of future light cones called the SU(2) dipoles of causality here in the paper.The future light cone structure is soldered internally to the new variables derived in this paper to accommodate a background free physics of quantum strings. The emergence of spacetime is shown to be a first order phase transition and that of separation of gravity from the unified field to be a second order phase transition. For the former case the cosmic time is chosen as the order parameter and for the latter case the angular momentum is chosen as the order parameter. A quantum black hole thus nucleates at transition temperature which is the Planck temperature, $\tau_{pl}$. Then the SU(2) dipoles enable interpretation of this black hole as a gravity gauge SL(2,$\mathbb{C}$) dual of the U(1) gauge ferromagnetic phase. The usual QFT interpretation of this effect is the existence of locally Lorentzian spacetimes.

 

[MTd2]

http://arxiv.org/abs/1002.2618

Quantum gravity effects on space-time
Martin Bojowald
Comments: 24 pages, 4 figures, plenary talk at The Nineteenth Workshop on General Relativity and Gravitation in Japan (JGRG19) at Rikkyo University, Dec 2009
Subjects: General Relativity and Quantum Cosmology (gr-qc)
General relativity promotes space-time to a physical, dynamical object subject to equations of motion. Quantum gravity, accordingly, must provide a quantum framework for space-time, applicable on the smallest distance scales. Just like generic states in quantum mechanics, quantum space-time structures may be highly counter-intuitive. But if low-energy effects can be extracted, they shed considerable light on the implications to be expected for a dynamical quantum space-time. Loop quantum gravity has provided several such effects, but even in the symmetry-reduced setting of loop quantum cosmology no complete picture of effective space-time geometries describing especially the regime near the big bang has been obtained. The overall situation regarding space-time structures and cosmology is reviewed here, with an emphasis on the role of dynamical states, effective equations, and general covariance.

http://arxiv.org/abs/1002.2454

Entropic Force Law, Emergent Gravity and the Uncertainty Principle

I. V. Vancea, M. A. Santos
(Submitted on 12 Feb 2010)
The entropic formulation of the inertia and the gravity relies on quantum, geometrical and informational arguments. The fact that the results are completely classical is missleading. In this paper we argue that the entropic formulation is a powerfull tool which provides new insights into the quantum nature of the inertia and the gravity. We use the entropic postulate to determine the quantum uncertainty in the law of inertia and in the gravity law in both Newtonian Mechanics and General Relativity. These results are obtained by considering the most general quantum property of the matter represented by the Uncertainty Principle and by postulating an expression for the uncertainty of the entropy such that: i) it is the simplest quantum generalization of the postulate of the variation of the entropy and ii) it reduces to the variation of the entropy in the absence of the uncertainty.

 

[John86]

http://arxiv.org/abs/0907.4335

From Entropic Dynamics to Quantum Theory
Authors: Ariel Caticha
(Submitted on 24 Jul 2009 (v1), last revised 12 Feb 2010 (this version, v3))
Abstract: Non-relativistic quantum theory is derived from information codified into an appropriate statistical model. The basic assumption is that there is an irreducible uncertainty in the location of particles: positions constitute a configuration space and the corresponding probability distributions constitute a statistical manifold. The dynamics follows from a principle of inference, the method of Maximum Entropy. The concept of time is introduced as a convenient way to keep track of change. A welcome feature is that the entropic dynamics notion of time incorporates a natural distinction between past and future. The statistical manifold is assumed to be a dynamical entity: its curved and evolving geometry determines the evolution of the particles which, in their turn, react back and determine the evolution of the geometry. Imposing that the dynamics conserve energy leads to the Schroedinger equation and to a natural explanation of its linearity, its unitarity,
and of the role of complex numbers. The phase of the wave function is explained as a feature of purely statistical origin. There is a quantum analogue to the gravitational equivalence principle.

http://arxiv.org/abs/1002.2593

Probabilistic time
Authors: C. Wetterich
(Submitted on 12 Feb 2010)
Abstract: The concept of time emerges as an ordering structure in a classical statistical ensemble. Local probability distributions $p_\tau(t)$ obtain by integrating out the past and future. A unitary time evolution is described by rotations of the wave function $q_\tau(t)=\pm \sqrt{p_\tau(t)}$. We establish a map to quantum physics and the Schr\"odinger equation. Our discussion of classical statistics is based on two-level observables that take the values one or zero in the states of the statistical ensemble. Then the wave functions can be mapped to elements of Grassmann algebra. Quantum field theories for fermions arise naturally from our formulation of probabilistic time.

 

[MTd2]

http://arxiv.org/abs/1002.2640
One Loop Beta Functions in Topologically Massive Gravity

R. Percacci, E. Sezgin
(Submitted on 15 Feb 2010)
We calculate the running of the three coupling constants in cosmological, topologically massive 3d gravity. We find that \nu, the dimensionless coefficient of the Chern-Simons term, has vanishing beta function. The flow of the cosmological constant and Newton's constant depends on \nu, and for any positive \nu there exist both a trivial and a nontrivial fixed point.http://arxiv.org/abs/1002.2668

Comment on "On the Origin of Gravity and the Laws of Newton" by Erik P. Verlinde

Sheldon Gao
(Submitted on 13 Feb 2010)
We show that Verlinde's idea of gravity as an entropic force is untenable. The main reason is that Verlinde made a mistake in identifying the causal relationship between physical variables when applying the first law of thermodynamics to the interacting process between a holographic screen and a particle. Moreover, it is shown that Verlinde's argument also has some other flaws.

 

[MTd2]

http://arxiv.org/abs/1002.3041

A relation between the Barbero-Immirzi parameter and the standard model

Bogusław Broda, Michał Szanecki
(Submitted on 16 Feb 2010)
It has been shown that Sakharov's induced, from the fields entering the standard model, Barbero-Immirzi parameter assumes, in the framework of euclidean formalism, the UV cutoff-independent value, 1/9. The calculus uses the Schwinger's proper-time formalism, the Seeley-DeWitt heat-kernel expansion, and it is akin to the derivation of the ABJ chiral anomaly in space-time with torsion

 

[marcus]

Strong presentation by Livine (video)
http://pirsa.org/10020027/
The U(N) structure of Loop Quantum Gravity
Etera Livine
Abstract: It has recently uncovered that the intertwiner space for LQG carries a natural representation of the U(N) unitary group. I will describe this U(N) action in details and show how it can be used to compute the LQG black hole entropy, to define coherent intertwiner states and to reformulate the LQG dynamics in new terms.
Date: 16/02/2010

The seminar talk is based on work with Laurent Freidel and others. There seem to be some landmark results. The talk makes the papers easier to understand and I'm finding it well worth watching.

In case of interest, here for reference is a 2009 paper with Freidel related to this talk:
http://arxiv.org/abs/0911.3553
The Fine Structure of SU(2) Intertwiners from U(N) Representations
Laurent Freidel, Etera R. Livine
21 pages
(Submitted on 18 Nov 2009)
"In this work we study the Hilbert space space of N-valent SU(2) intertwiners with fixed total spin, which can be identified, at the classical level, with a space of convex polyhedra with N face and fixed total boundary area. We show that this Hilbert space provides, quite remarkably, an irreducible representation of the U(N) group. This gives us therefore a precise identification of U(N) as a group of area preserving diffeomorphism of polyhedral spheres. We use this results to get new closed formulae for the black hole entropy in loop quantum gravity."

 

[marcus]

Livine gives good seminar talks. He's fast, clear, well-organized. He motivates the stuff he's talking about. So I'm including this review of spinfoams video just as if it were an arxiv paper.

http://pirsa.org/10020079/
A review of Spinfoams and Group Field Theory
Etera Livine
Abstract: We will review the definitions of spin foam models for quantum gravity and the recent advances in this field, such as the "graviton propagator", the definition of coherent states of geometry and the derivation of non-commutative field theories as describing the effective dynamics of matter coupled to quantum gravity. I will insist on the role of group field theories as providing a non-perturbative definition of spinfoams and their intricate relation with non-commutative geometry and matrix models.
Date: 17/02/2010 - 2:00 pm

http://arxiv.org/abs/1002.3298
CDT meets Horava-Lifgarbagez gravity
J. Ambjorn, A. Gorlich, S. Jordan, J. Jurkiewicz, R. Loll
14 pages, 3 figures
(Submitted on 17 Feb 2010)
"The theory of causal dynamical triangulations (CDT) attempts to define a non-perturbative theory of quantum gravity as a sum over space-time geometries. One of the assumptions in the CDT framework is the existence of a global time foliation. The same assumption is central in the quantum gravity theory recently formulated by Horava. We show that the phase diagram of CDT is surprising similar to the generic Lifgarbagez phase diagram appealed to by Horava. We argue that CDT might provide a unifying non-perturbative framework for anisotropic as well as isotropic theories of quantum gravity."

If anyone wants to look up an interesting paper that formed part of the basis of Livine's pirsa talk, here's one:

http://arxiv.org/abs/0903.3475
4d Deformed Special Relativity from Group Field Theories
Florian Girelli, Etera R. Livine, Daniele Oriti
23 pages; Physical Review D 81:024015, 2010
(Submitted on 20 Mar 2009)
"We derive a scalar field theory of the deformed special relativity type, living on non-commutative kappa-Minkowski spacetime and with a kappa-deformed Poincare symmetry, from the SO(4,1) group field theory defining the transition amplitudes for topological BF-theory in 4 space-time dimensions. This is done at a non-perturbative level of the spin foam formalism working directly with the group field theory (GFT). We show that matter fields emerge from the fundamental model as perturbations around a specific phase of the GFT, corresponding to a solution of the fundamental equations of motion, and that the non-commutative field theory governs their effective dynamics."

Another window on what Girelli Livine Oriti are doing is this talk by Girelli at the July 2009 Planck Scale conference:
http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php?plik=http://panoramix.ift.uni.wroc.pl/~planckscale/video/Day4/4-2.flv&tytul=4.2%20Girelli
The talk was written up in this paper:
http://arxiv.org/abs/0910.3107
Field theories with homogenous momentum space
Florian Girelli, Etera R. Livine
9 pages, To appear in the Proceedings of the XXV Max Born Symposium, "The Planck Scale", Wroclaw, Poland, July 2009
(Submitted on 16 Oct 2009)
"We discuss the construction of a scalar field theory with momentum space given by a coset. By introducing a generalized Fourier transform, we show how the dual scalar field theory actually lives in Snyder's space-time. As a side-product we identify a star product realization of Snyder's non-commutative space, but also the deformation of the Poincare symmetries necessary to have these symmetries realized in Snyder's space-time. A key feature of the construction is that the star product is non-associative."

There was also this recent followup paper. again by Girelli Livine:
http://arxiv.org/abs/1001.2919
A Deformed Poincare Invariance for Group Field Theories
Florian Girelli, Etera R. Livine
11 pages
(Submitted on 17 Jan 2010)
"In the context of quantum gravity, group field theories are field theories that generate spinfoam amplitudes as Feynman diagrams. They can be understood as generalizations of the matrix models used for 2d quantum gravity. In particular Boulatov's theory reproduces the amplitudes of the Ponzano-Regge spinfoam model for 3d quantum gravity. Motivated by recent works on field theories on non-commutative flat spaces, we show that Boulatov's theory (and its colored version) is actually invariant under a global deformed Poincare symmetry. This allows to define a notion of flat/excited geometry states when considering scalar perturbations around classical solutions of the group field equations of motion. As a side-result, our analysis seems to point out that the notion of braiding of group field theories should be a key feature to study further in this context."

The way I see it, the 17 February PIRSA video talk by Livine is the main window on an area of research that is especially interesting and proceeding rapidly. I have listed a few of the papers describing what went into the 17 February talk. Also there is the Planck Scale video talk by Girelli---I just watched this 25 minute talk and the lively question period following it.

 

[MTd2]

http://arxiv.org/abs/1002.3298

CDT meets Horava-Lifgarbagez gravity

J. Ambjorn, A. Gorlich, S. Jordan, J. Jurkiewicz, R. Loll
(Submitted on 17 Feb 2010)
The theory of causal dynamical triangulations (CDT) attempts to define a non-perturbative theory of quantum gravity as a sum over space-time geometries. One of the assumptions in the CDT framework is the existence of a global time foliation. The same assumption is central in the quantum gravity theory recently formulated by Ho\v{r}ava. We show that the phase diagram of CDT is surprising similar to the generic Lifgarbagez phase diagram appealed to by Ho\v rava. We argue that CDT might provide a unifying non-perturbative framework for anisotropic as well as isotropic theories of quantum gravity.

 

[marcus]

http://arxiv.org/abs/1002.3488
The Cosmological Parameters 2010
Ofer Lahav, Andrew R Liddle
25 pages. Article for The Review of Particle Physics 2010 (aka the Particle Data Book), on-line version at http://pdg.lbl.gov/. This article supersedes arXiv:astro-ph/0601168 and arXiv:astro-ph/0406681
(Submitted on 18 Feb 2010)

"This is a review article for The Review of Particle Physics 2010 (aka the Particle Data Book). It forms a compact review of knowledge of the cosmological parameters at the beginning of 2010. Topics included are Parametrizing the Universe; Extensions to the standard model; Probes; Bringing observations together; Outlook for the future."

 

[MTd2]

http://arxiv.org/abs/1002.3592

Linearized Group Field Theory and Power Counting Theorems

Joseph Ben Geloun, Thomas Krajewski, Jacques Magnen, Vincent Rivasseau
(Submitted on 18 Feb 2010)
We introduce a linearized version of group field theory. It can be viewed either as a group field theory over the additive group of a vector space or as an asymptotic expansion of any group field theory around the unit group element. We prove exact power counting theorems for any graph of such models. For linearized colored models the power counting of any amplitude is further computed in term of the homology of the graph. An exact power counting theorem is also established for a particular class of graphs of the nonlinearized models, which satisfy a planarity condition. Examples and connections with previous results are discussed.

 

[marcus]

http://arxiv.org/abs/1002.4278
Entropic Accelerating Universe
Damien A. Easson, Paul H. Frampton, George F. Smoot
10 pages, 1 figure
(Submitted on 23 Feb 2010)
"To accommodate the observed accelerated expansion of the universe, one popular idea is to invoke a driving term in the Friedmann-Lemaître equation of dark energy which must then comprise 70% of the present cosmological energy density. We propose an alternative interpretation which takes into account the temperature intrinsic to the information holographically stored on the screen which is the surface of the universe. Dark energy is thereby obviated and the acceleration is due to an entropic force naturally arising from the information storage on a surface screen. We consider an additional quantitative approach based upon the entropy and surface terms usually neglected in General Relativity and show that this leads to the entropic accelerating universe."

http://arxiv.org/abs/1002.4209
Complete quantum mechanics: an axiomatic formulation of the Montevideo interpretation
Rodolfo Gambini, Luis Pedro Garcia-Pintos, Jorge Pullin
21 pages
(Submitted on 22 Feb 2010)
"We make a first attempt to axiomatically formulate the Montevideo interpretation of quantum mechanics. In this interpretation environmental decoherence is supplemented with loss of coherence due to the use of realistic clocks to measure time to solve the measurement problem. The resulting formulation is framed entirely in terms of quantum objects without having to invoke the existence of measurable classical quantities like the time in ordinary quantum mechanics. The formulation eliminates any privileged role to the measurement process giving an objective definition of when an event occurs in a system."

The next paper is part of Fotini's program. Prémont-Schwarz is a collaborator of hers.
http://arxiv.org/abs/1002.4190
Lieb-Robinson bounds with dependence on interaction strengths
Isabeau Prémont-Schwarz, Jeff Hnybida
19 pages, 1 figure
(Submitted on 22 Feb 2010)
We propose new Lieb-Robinson bounds (bounds on the speed of propagation of information in quantum systems) with an explicit dependence on the interaction strengths of the Hamiltonian. For systems with more than two interactions it is found that the Lieb-Robinson speed is not always algebraic in the interaction strengths. We consider Hamiltonians with any finite number of bounded operators and also a certain class of unbounded operators. We obtain bounds and propagation speeds for quantum systems on lattices and also general graphs possessing a kind of homogeneity and isotropy. One area for which this formalism could be useful is the study of quantum phase transitions which occur when interactions strengths are varied."brief mention:
http://arxiv.org/abs/1002.3877
Higgs for Graviton: Simple and Elegant Solution
Ali H. Chamseddine, Viatcheslav Mukhanov
7 pages

http://arxiv.org/abs/1002.3836
BF gravity with Immirzi parameter and cosmological constant
Merced Montesinos, Mercedes Velazquez
4 pages

 

[MTd2]

http://arxiv.org/abs/1002.4568

Gravity as Quantum Entanglement Force

Jae-Weon Lee, Hyeong-Chan Kim, Jungjai Lee
(Submitted on 24 Feb 2010)
We conjecture that quantum entanglement of matter and vacuum in the universe tend to increase with time, like entropy, and there is an effective force called quantum entanglement force associated with this tendency. It is also suggested that gravity and dark energy are types of the quantum entanglement force, similar to Verlinde's entropic force. If the entanglement entropy of the universe saturates the Bekenstein bound, this gives holographic dark energy with the equation of state consistent with current observational data. This connection between quantum information and gravity gives some new insights on the origin of gravity, dark energy, the holographic principle and arrow of time.

 

[MTd2]

http://arxiv.org/abs/1002.4723

Group field theory in non-commutative metric variables

Aristide Baratin, Daniele Oriti
(Submitted on 25 Feb 2010)
We introduce a dual formulation of group field theories, making them a type of non-commutative field theories. In this formulation, the variables of the field are Lie algebra variables with a clear interpretation in terms of simplicial geometry. For Ooguri-type models, the Feynman amplitudes are simplicial path integrals for BF theories. This formulation suggests ways to impose the simplicity constraints involved in BF formulations of 4d gravity directly at the level of the group field theory action. We illustrate this by giving a new GFT definition of the Barrett-Crane model.

 

[marcus]

http://arxiv.org/abs/1002.4618
Coupling Point-Like Masses to Quantum Gravity with Causal Dynamical Triangulations
Igor Khavkine, Renate Loll, Paul Reska
24 pages, 11 figures
(Submitted on 24 Feb 2010)
"We analyze the possibility of coupling a point-like mass to four-dimensional quantum gravity in the nonperturbative setting of Causal Dynamical Triangulations (CDT). The spatial volume profile of Euclidean Schwarzschild de Sitter space in proper-time form glued to an interior matter solution is derived in the continuum and for small masses, to provide a point of comparison for the classical limit of the matter-coupled CDT model. The volume profile we compute deviates in a characteristic manner from that of the pure-gravity model. As part of the construction, we introduce a particularly simple set of proper-time coordinates on the resulting Euclidean manifold, matching the global time slicing present in CDT. To avoid having to deal with caustics which appear near the source, we excise a tubular neighbourhood around it from the spacetime. We also discuss some of the implementation details for measuring numerically the expectation value of the volume profiles in the framework of CDT when coupled appropriately to the matter source."