http://arxiv.org/abs/1108.0320
**Unruh effect without entanglement**
Carlo Rovelli, Matteo Smerlak

(Submitted on 1 Aug 2011)

We estimate the transition rates of a uniformly accelerated Unruh-DeWitt detector coupled to a quantum field with reflecting conditions on a boundary plane (a "mirror"). We find that these are essentially indistinguishable from the usual Unruh rates, viz. that the Unruh effect persists in the presence of the mirror. This shows that the Unruh effect is not merely a consequence of the entanglement between left and right Rindler quanta in the Minkowski vacuum. Since in this setup the state of the field in the Rindler wedge is pure, we argue furthermore that the relevant entropy in the Unruh effect cannot be the von Neumann entanglement entropy. We suggest, in alternative, that it is the Shannon entropy associated with Heisenberg uncertainty.

5 pages

http://arxiv.org/abs/1108.0369
**Twistor Networks and Covariant Twisted Geometries**
Etera R. Livine, Simone Speziale, Johannes Tambornino

(Submitted on 1 Aug 2011)

We study the symplectic reduction of the phase space of two twistors to the cotangent bundle of the Lorentz group. We provide expressions for the Lorentz generators and group elements in terms of the spinors defining the twistors. We use this to define twistor networks as a graph carrying the phase space of two twistors on each edge. We also introduce simple twistor networks, which provide a classical version of the simple projected spin networks living on the boundary Hilbert space of EPRL/FK spin foam models. Finally, we give an expression for the Haar measure in terms of spinors.

18 pages

http://arxiv.org/abs/1108.0005
**Quantum memory of the Universe**
Jakub Mielczarek, Wlodzimierz Piechocki

(Submitted on 29 Jul 2011)

We present results concerning propagation of the Gaussian state across the cosmological quantum bounce. The reduced phase space quantization of loop quantum cosmology is applied to the Friedman-Robertson-Walker universe with a free massless scalar field. The dispersion of observables are studied in the context of the Heisenberg uncertainty principle. We show that the bounce transition is the least quantum part of the evolution. We give an interpretation of this surprising result in terms of entropy. We examine the conservation of semiclassicality across the quantum bounce. The cosmic amnesia may occur or not depending on parameters of the quantum state. We show that this issue can be studied observationally. The preliminary estimations based on astronomical data support the Universe without cosmic forgetfulness.

4 pages,4 figures

http://arxiv.org/abs/1108.0079
**Gravitational wave generation in loop quantum cosmology**
Paulo M. Sá, Alfredo B. Henriques

(Submitted on 30 Jul 2011)

We calculate the full spectrum, as observed today, of the cosmological gravitational waves generated within a model based on loop quantum cosmology. It is assumed that the universe, after the transition to the classical regime, undergoes a period of inflation driven by a scalar field with a chaotic-type potential. Our analysis shows that, for certain conditions, loop quantum effects leave a clear signature on the spectrum, namely, an over-production of low-frequency gravitational waves. One of the aims of our work is to show that loop quantum cosmology models can be tested and that, more generally, pre-inflationary physical processes, contrary to what is usually assumed, leave their imprint in those spectra and can also be tested.

7 pages, 8 figures,

http://arxiv.org/abs/1108.0116
**Anisotropic Structures and Wormholes with Loop Quantum Gravity Holonomy Corrections**
Andrew DeBenedictis

(Submitted on 30 Jul 2011)

Anisotropic spherically symmetric systems are studied in the connection and densitized triad variables used in loop quantum gravity. The material source is an anisotropic fluid, which is arguably the most commonly used source term in anisotropic studies within general relativity. The gravitational+anisotropic fluid constraints are derived and analyzed and then quantum gravity inspired holonomy replacements are performed. The quantum properties of the fluid are dictated by the modified constraint equations. Particular attention is paid to wormhole throats, as they provide a simplistic model of the structures thought to be ubiquitous in the quantum gravity space-time foam at high energy scales. In comparison to the purely classical theory, the quantum corrections act to increase the energy density of the fluid, which indicates that they may lessen the energy condition violation present in the classical theory. Related to this, in principle it would be possible to have scenarios where the classical solution yields everywhere negative (with a zero at the throat) fluid energy density but the corresponding quantum corrected theory possesses only small regions of negative energy density or even everywhere non-negative energy density.

19 pages, 6 figures