http://arxiv.org/abs/0805.2503
Fundamentals and recent developments in non-perturbative canonical Quantum Gravity
F. Cianfrani, O.M. Lecian, G. Montani
94 pages
(Submitted on 16 May 2008)
"The aim of this review is to provide a detailed account of the physical content emerging from this story of the canonical approach to Quantum Gravity. All the crucial steps in our presentation have a pedagogical character, providing the reader with the necessary tools to become involved in the field. Such a pedagogical aspect is then balanced and completed by subtle discussions on specific topics which we regard as relevant for the physical insight they outline on the treated questions. Our analysis is not aimed at convincing the reader about a pre-constituted point of view, bu instead our principal goal is to review the picture of Canonical Quantum Gravity on the basis of the concrete facts at the ground of its clear successes, but also of its striking shortcomings."
[Giovanni Montani is a senior guy at Rome. 87 papers on arxiv. This pedagogical review of LQG looks like it may prove useful.]
http://arxiv.org/abs/0805.2536
The entropic boundary law in BF theory
Etera R. Livine, Daniel R. Terno
17 pages
(Submitted on 16 May 2008)
"We compute the entropy of a closed bounded region of space for pure 3d Riemannian gravity formulated as a topological BF theory for the gauge group SU(2) and show its holographic behavior. More precisely, we consider a fixed graph embedded in space and study the flat connection spin network state without and with particle-like topological defects. We regularize and compute exactly the entanglement for a bipartite splitting of the graph and show it scales at leading order with the number of vertices on the boundary (or equivalently with the number of loops crossing the boundary). More generally these results apply to BF theory with any compact gauge group in any space-time dimension."
http://arxiv.org/abs/0805.2411
Measuring the Scalar Curvature with Clocks and Photons: Voronoi-Delaunay Lattices in Regge Calculus
Jonathan R. McDonald, Warner A. Miller
7 pages, 2 figures, submitted to Classical and Quantum Gravity
(Submitted on 15 May 2008)
"The Riemann scalar curvature plays a central role in Einstein's geometric theory of gravity. We describe a new geometric construction of this scalar curvature invariant at an event (vertex) in a discrete spacetime geometry. This allows one to constructively measure the scalar curvature using only clocks and photons.
Given recent interest in discrete pre-geometric models of quantum gravity, we believe is it ever so important to reconstruct the curvature scalar with respect to a finite number of communicating observers. This derivation makes use of a new fundamental lattice cell built from elements inherited from both the original simplicial (Delaunay) spacetime and its circumcentric dual (Voronoi) lattice. The orthogonality properties between these two lattices yield an expression for the vertex-based scalar curvature which is strikingly similar to the corresponding hinge-based expression in Regge calculus (deficit angle per unit Voronoi dual area). In particular, we show that the scalar curvature is simply a vertex-based weighted average of deficits per weighted average of dual areas."
http://arxiv.org/abs/0805.2584
Is Physics Asking for a New Kinematics?
R. Aldrovandi, J. G. Pereira
8 pages. Honorable Mention in the Gravity Research Foundation essay contest, 2008
(Submitted on 16 May 2008)
"It is discussed whether some of the consistency problems of present-day physics could be solved by replacing special relativity, whose underlying kinematics is ruled by the Poincare' group, by de Sitter relativity, with underlying kinematics ruled by the de Sitter group. In contrast to ordinary special relativity, which seems to fail at the Planck scale, this new relativity is "universal" in the sense that it holds at all energy scales."
http://arxiv.org/abs/0805.2555
Quantum black-hole information missing in the semiclassical treatment
H. Nikolic
7 pages
(Submitted on 16 May 2008)
"In the semiclassical treatment of gravity, an external observer can measure only the mean (not the exact) mass of the black hole (BH). By contrast, in fully quantum gravity the exact (not only mean) BH mass is measurable by the external observer. This additional information (missing in the semiclassical treatment) available to the external observer significantly helps to understand how information leaks out during the BH evaporation."
[Harvey Nikolic is a PF Beyond regular---Demystifier. Might like to discuss/explain the paper.]
http://arxiv.org/abs/0805.2429
Galactic Neutrino Communication
John G. Learned, Sandip Pakvasa, A. Zee
6 pages, 2 figures
(Submitted on 16 May 2008)
"We examine the possibility to employ neutrinos to communicate within the galaxy. We discuss various issues associated with transmission and reception, and suggest that the resonant neutrino energy near 6.3 PeV may be most appropriate. In one scheme we propose to make Z^o particles in an overtaking e^+ - e^- collider such that the resulting decay neutrinos are near the W^- resonance on electrons in the laboratory. Information is encoded via time structure of the beam. In another scheme we propose to use a 30 PeV pion accelerator to create neutrino or anti-neutrino beams. The latter encodes information via the particle/anti-particle content of the beam, as well as timing. Moreover, the latter beam requires far less power, and can be accomplished with presently foreseeable technology. Such signals from an advanced civilization, should they exist, will be eminently detectable in neutrino detectors now under construction."
