Master Mason
269. Hamiltonian formulation of tetrad gravity: three dimensional case
This is a guest blog post by Natalia Kiriushcheva and Sergei Kuzmin from the U. of Western Ontario. Dmitry.
Thank you, Dmitry, for the invitation to write a guest post about our recent work co-authored with Alexei Frolov and Sergei Kuzmin: “Hamiltonian formulation of tetrad gravity: three dimensional case”, arXiv: 0902.0856 [gr-qc]. We are curious about your interest in this paper because our result ought to be of interest primary to LQG practitioners rather than to people working in strings, unless, of course, there are some connections or points, unknown to us, where “loops meet strings”. Maybe, if our article can spark a discussion, someone will explain this interest. So, why did we consider the Hamiltonian formulation of tetrad gravity and what did we find so far?
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249. The fate of unstable gauge flux compactifications
This is a guest post by Ivonne Zavala from the Bethe Center for Theoretical Physics (Bonn). Dmitry.
Let me start by thanking Dmitry for the invitation to write a guest blog entry about my recent paper arXiv:0812.3902. This has been done in collaboration with Cliff Burgess and Susha Parameswaran, and it is about possible end points where unstable monopole configurations can decay to.
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234. Continuing dS/CFT. Why it is so hard to prove?
I continue today the discussion of dS/CFT correspondence started a week ago.
As you probably remember, I finished last time pointing out the discrepancy between non-perturbative and perturbative values of the dimension of the dS Hilbert space. Namely, since the entropy of dS space is finite, the dimension of of the Hilbert space is finite as well since
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223. Starting dS/CFT: Hilbert space
Since I was recently thinking of the dS/CFT correspondence, I find it natural to also start discussing facts and hypotheses related to dS/CFT and other gauge theory – gravity dualities on the blog. In what follows, we will mostly discuss 4-dimensional gauge theories.
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206. A conference on black holes at PI
A very interesting conference organized by Rob Meyers, Herman Verlinde and Jaume Gomis takes place currently in PI. The topic of the conference is related to information loss in black holes and unitarity of quantum gravity in general (the one that I tried to discuss so unsuccessfully on the blog in December – I am a kind of being better prepared now 
).
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203. Quantum Hall effect. One open question
I cannot finish discussing quantum Hall effect without explaining why, after all those years of study, Laughlin wavefunction and composite fermions, it still remains interesting for a condensed matter theorist.
The reason is existence of the state with 
, the only state with even denominator of the filling factor
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198. Fractional quantum Hall effect – a few words about theory
Finally, after going through the integer quantum Hall effect, we are a kind of ready to discuss one of the biggest puzzles in condensed matter theory: the fractional quantum Hall effect.
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195. Integer quantum Hall effect – plateaus in Hall resistivity
This post is my attempt to give an answer to tg’s question: Ok, we a kind of proved that the Hall resistivity is quantized in the integer quantum Hall effect, but how to explain plateaus in the Hall resistivity 
and deep minima in diagonal resistivity 
as shown on the Fig.
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156. Again about condensed matter applications of AdS-CFT
Peter Horava has recently released a somewhat mysterious paper about non-relativistic Yang-Mills theories. Since I was unable to understand why one should be ultimately interested to consider such exotic beasts (that is, non-relativistic YM theories), I decided to postpone the reading until understanding will eventually appear due to background work of my brain
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145. Quantum and thermal decay in de Sitter space
Yesterday there was an interesting talk at Perimeter Institute – Adam Brown from Columbia University has discussed vacuum decay in de Sitter space. The title in the announcement immediately caught me, since I expected that Adam was actually going to discuss instability of de Sitter space, the subject I am currently working on. Then I have realized that Adam probably is to talk about his recent paper with Eric Weinberg, well, not decay of de Sitter space but still – very interesting.
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143. The structure of correlation functions in single-field inflation
This is a guest post by Sarah Shandera from the University of Columbia. Dmitry.
Dmitry has asked me to write a post about my recent paper, arXiv:0812.0818, about correlation functions in single field inflation. The motivation behind this work is the potential of very near-future data (from the Planck satellite and large scale structure surveys) to more significantly test the Gaussianity of primordial fluctuations. In standard single-field slow-roll models, the flatness (and smoothness) of the potential guarantees that the primordial fluctuations are Gaussian to a part in 
. Current observational bounds only require the primordial fluctuations to be Gaussian to a part in 
or 
– still pretty Gaussian, but leaving a surprising amount of room for some interesting physics. Measurements of non-Gaussianity would be a very useful tool for understanding the fundamental picture of inflation, because they probe interactions of the inflaton, and because observations can distinguish between wide classes of models. There are many different statistics that can be used to test Gaussianity. Clearly the 
-point functions are one class of possibilities, but there are also measures like Minkowski functionals or galaxy cluster number counts that depend on an integrated contribution from a series of correlation functions. Often, this series can be simply truncated to depend on a few lower-order moments (for example, when the non-Gaussianity comes from the non-linear gravitational evolution), and this truncation looks suggestively like a perturbative series for the fundamental interactions.
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142. Chaotic inflation on the landscape?
By a chance, do you remember the paper by Nemanja Kaloper and Lorenzo Sorbo that we have recently discussed? There, the authors were modeling quintessence by axion-like fields that dynamically mix with 4-form fields. The mixing introduced mass terms for the axions approximately preserving the shift symmetry. (By the way, I was surprised to see how many people are looking for “Caloper Sorbo quintessence” in Google – it seems that the topic is going to become hot soon.)
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133. Multi-Field Inflation on the Landscape
This is the guest blog post by my friend Thorsten Battefeld from Princeton. Dmitry.
Dmitry asked me to write a guest post about a recent paper written by Diana and myself on “Multi-field Inflation on the Landscape” (a followup to “Staggered Multi-Field Inflation”) where we ask a simple question: assuming that inflaton is driven by many (say of the order of 
) scalar fields, what are the observable consequences of fields decaying or stabilizing one after the other during inflation?
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127. Ashtekar at Perimeter Institute
Abhay Ashtekar has recently visited the Perimeter Institute and gave a couple of talks – about loop quantum gravity of course, since he is one of the major players in the LQG field (considered to be its inventor). I think, both of the talks are worth watching (or at least scanning through his transparencies available as PDF file at PIRSA) for a person who wants to understand what LQG is about. If you do not have an intention to watch them , I shall explain you what both of them are about.
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119. Fun with energy gap for QCD Born-Oppenheimer Hamiltonian
Let us try to solve the Exercise 2 in this post about the Wilson loop. Since we, scientists, are all lazy (as you are!), that’s what I would like to do: I will give three different solutions of the exercise with three different answers 
Then, if you are interested to learn the subject (and you probably are, becase the subject is quark confinement, right?), you can choose a solution you like most (I will even introduce a poll ) and kindly explain in comments why do you think that two other solutions are wrong The goal of the experiment is to show how applicable is the democracy approach (as advocated by Lee Smolin ) to science.
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