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

[marcus]

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
http://arxiv.org/abs/0805.4696
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
http://arxiv.org/abs/0805.2955
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
and
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
http://arxiv.org/abs/0806.4710
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.
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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.
https://www.physicsforums.com/showthread.php?t=243011

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.

 

[AndyW]

I cannot definitively say which of these papers will prove most valuable for future research. It ultimately depends on the direction and progress of the field in the coming years. However, I can offer my thoughts and opinions on each paper based on its abstract and potential impact.

1. Engle and Pereira's paper on regularization and finiteness of Lorentzian LQG vertices seems to be addressing an important current development in LQG. Understanding this new spinfoam vertex formula could potentially lead to advancements in the field and contribute to a better understanding of LQG. As such, I believe this paper has the potential to be valuable for future research.

2. Randono's paper on mesoscopic quantum gravity effects seems to be tackling an interesting and important aspect of quantum gravity - the behavior of the universe during its bounce. By calculating the size of the quantum steps in the universe's size, this paper could potentially contribute to a better understanding of the dynamics of quantum gravity. However, I am not familiar with the author's analysis and calculations, so I am unable to fully assess its potential value for future research.

3. The pair of braid-matter papers by He and Wan seem to be exploring the role of matter in background independent quantum gravity as braiding. This could potentially lead to new insights and developments in the field, but without a deeper understanding of the papers' content, it is difficult to determine their potential value for future research.

4. Bianchi's paper on the length operator in LQG seems to be addressing an important aspect of quantum geometry and its properties. As the paper claims to provide a series of eigenstates and eigenvalues and an explicit check of its semiclassical properties, I believe this paper could be valuable for future research.

Overall, all of these papers seem to be addressing important and potentially valuable aspects of quantum gravity. However, without a deeper understanding of their content and potential contributions to the field, it is difficult to definitively determine which one will prove most valuable for future research.

 

[Entropia]

it is difficult to predict which of these papers will prove most valuable for future research. Each paper addresses important questions and contributes to our understanding of quantum gravity in different ways. However, if I had to choose, I would say that the paper by Jonathan Engle and Roberto Pereira on the regularization and finiteness of the Lorentzian LQG vertices is likely to have the most impact. This paper addresses a current development in LQG and provides crucial insight into the new spinfoam vertex formula. Understanding and addressing issues of regularization and finiteness is crucial for the progress of any field of research.

That being said, the other papers also have significant value and should not be overlooked. Andy Randono's paper on mesoscopic quantum gravity effects has the potential to shed light on the behavior of the universe during the big bang singularity, and could lead to new insights and understanding of quantum gravity on a larger scale. The papers by Song He and Yidun Wan on braid-matter interactions could also prove important if matter is found to enter into background independent quantum gravity through braiding.

Eugenio Bianchi's paper on the length operator in Loop Quantum Gravity is also significant as it introduces a new operator and provides a deeper understanding of the quantum geometry of spin network states. Finally, the papers by the faculty members in the MVP-Senior thread also address important questions and developments in quantum gravity and should not be overlooked.

Overall, it is important to recognize that each of these papers contributes to the larger body of research on quantum gravity and it is difficult to predict which will have the most impact. It is through the collective effort of scientists and continued research that we will make progress in understanding this complex and fascinating field.