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MVP-Junior: second quarter papers by QG grad students and postdocs

  1. Jonathan Engle and Roberto Pereira

    0 vote(s)
  2. Andy Randono

    0 vote(s)
  3. Yidun Wan and Song He (two papers)

  4. Eugenio Bianchi

    0 vote(s)
  1. Jul 1, 2008 #1


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    Which of these papers do you think will prove most valuable for future research? For brevity, papers are designated by their authors. So much potentially important QG research appeared during the second quarter (April-June 2008) that for simplicity I split the list in two. The following are papers authored by PhD students and postdocs which appeared during the second quarter of 2008.
    Descriptive comment (or quote from the abstract) is in parentheses.

    1. Jonathan Engle, Roberto Pereira
    Regularization and finiteness of the Lorentzian LQG vertices
    (This paper contributes to understanding the new spinfoam vertex formula, an important current development in LQG.)

    2. Andy Randono
    A Mesoscopic Quantum Gravity Effect
    (When the universe is doing its bounce----which in QG replaces the big bang singularity--- the scalefactor, indicating the universe size, decreases and then increases in ripples, according to Randono's analysis. He finds that the size comes down in quasi-discrete quantum steps, and then increases again in little steps. See figure 2---the picture makes it clear. Randono calculates the size of the steps, which, although small, turns out to be many orders of magnitude larger than planck scale. A bit like finding the energy levels in the hydrogen atom.)

    3. The pair of braid-matter papers posted this quarter by Song He and Yidun Wan
    http://arxiv.org/abs/0805.0453 and http://arxiv.org/abs/0805.1265
    Conserved Quantities and the Algebra of Braid Excitations in Quantum Gravity
    C, P, and T of Braid Excitations in Quantum Gravity
    (If matter enters into background independent quantum gravity as braiding, these papers could be important.)

    4. Eugenio Bianchi
    The length operator in Loop Quantum Gravity
    ("The dual picture of quantum geometry provided by a spin network state is discussed. From this perspective, we introduce a new operator in Loop Quantum Gravity - the length operator. We describe its quantum geometrical meaning and derive some of its properties. In particular we show that the operator has a discrete spectrum and is diagonalized by appropriate superpositions of spin network states. A series of eigenstates and eigenvalues is presented and an explicit check of its semiclassical properties is discussed.")

    Questions and discussion about these papers would be welcome. I'm very interested in how people come to conclusions about which research is likely to prove important in the future. Five papers is already a lot. It's requested that we concentrate discussion here on these papers in this thread and not bring in links to other papers.

    Five other papers, potentially important ones which appeared in the same time-frame (second quarter 2008) and where one or more of the authors was faculty, will be discussed and rated in a different thread: "MVP-Senior" poll.

    The papers considered in that poll are as follows:

    1. Florian Conrady, Laurent Freidel
    Path integral representation of spin foam models of 4d gravity
    "We give a unified description of all recent spin foam models introduced by Engle, Livine, Pereira and Rovelli (ELPR) and by Freidel and Krasnov (FK). We show that the FK models are, for all values of the Immirzi parameter, equivalent to path integrals of a discrete theory and we provide an explicit formula for the associated actions. We discuss the relation between the FK and ELPR models and also study the corresponding boundary states. For general Immirzi parameter, these are given by Alexandrov's and Livine's SO(4) projected states. For 0 <= gamma < 1, the states can be restricted to SU(2) spin networks."

    2. Stephon H.S. Alexander, Gianluca Calcagni
    Superconducting loop quantum gravity and the cosmological constant
    "We argue that the cosmological constant is exponentially suppressed in a candidate ground state of loop quantum gravity as a nonperturbative effect of a holographic Fermi-liquid theory living on a two-dimensional spacetime. Ashtekar connection components, corresponding to degenerate gravitational configurations breaking large gauge invariance and CP symmetry, behave as composite fermions that condense as in Bardeen--Cooper--Schrieffer theory of superconductivity. Cooper pairs admit a description as wormholes on a de Sitter boundary."

    3. Abhay Ashtekar, Edward Wilson-Ewing
    The covariant entropy bound and loop quantum cosmology
    (Proving the important covariant entropy bound in LQG is a major milestone. The original conjecture by Bousso actually fails near the singularity in classic cosmology. LQC supplies what is needed to validate it.)

    4. Laurent Freidel
    Reconstructing AdS/CFT
    "What is AdS/CFT from the point of view of background independent quantum gravity?"

    5. J. Ambjorn, K.N. Anagnostopoulos, R. Loll, I. Pushkina
    Shaken, but not stirred - Potts model coupled to quantum gravity
    "We investigate the critical behaviour of both matter and geometry of the three-state Potts model coupled to two-dimensional Lorentzian quantum gravity in the framework of causal dynamical triangulations. Contrary to what general arguments of the effects of disorder suggest, we find strong numerical evidence that the critical exponents of the matter are not changed under the influence of quantum fluctuations in the geometry, compared to their values on fixed, regular lattices. This lends further support to previous findings that quantum gravity models based on causal dynamical triangulations are in many ways better behaved than their Euclidean counterparts."

    If there are questions or comment about these please contribute them to the MVP-Senior thread.
    Last edited: Jul 1, 2008
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