Quantum field theory
97. Second week of November on NEQNET
Physics
* Quintessence on the string theory landscape?
I discuss the recent paper by Kaloper and Sorbo explaining how quintessence can be realized on the string theory landscape, as follows from the title. The post also contains small introduction explaining what is quintessence field and why we want so hard to find it on the landscape 
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96. Quintessence with w less than -1
In another very interesting recent paper on quintessence the Italian Team (Creminelli, D’Amico, Norena, Vernizzi – and warmest regards from Helsinki if you read it, Filippo ) is trying to construct an reliable example of QFT that behaves like the quintessence with ?ghost-like? effective equation of state 
.
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94. Quantum scale invariance on the lattice
Arguably, the most interesting paper in archives today is the one by M. Shaposhnikov and I. Tkachev. As the authors state, they have found a scheme leading to a non-perturbative definition of lattice field theories scale invariant on the quantum level. I have so many problems understanding this paper, that I don’t even have a slightest idea where to begin… Since I know Igor personally (and he is an extraordinary guy), this probably just shows that I am pretty bad, but I shall still pose my questions – one of the most attracting blogging Powers is that you can ask dumb questions, isn’t it?
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93. Second order hydrodynamic coefficients in some field theories (like QCD)
By definition, we call an IR mode of a quantum field theory hydrodynamical, if its relaxation time goes to infinity, while its wave length 
. If this mode is hydrodynamical, does it mean that its evolution is determined by one of the equations we study in hydrodynamics – like, say, Euler equation or Navier-Stokes equation?
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89. First week of November on NEQNET
Below is the list of what I wrote on this blog during the first week of November… not bad actually, it looks like with Agata’s birth I have become more productive, not less… Surprising
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88. Belavin and Zamolodchikov on 2D quantum gravity
Both people are among inventors of conformal field theory, string theory and the chapter of field theory that is called “integrable systems” nowadays, so naturally, one cannot help taking an hour of her time and learn what each of them has new to say. But if they are co-authors of the same paper, the probability for me to try studying their paper doubles!
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87. Leptophilic dark matter
Recall the tempest in the physics blogosphere during the last two weeks – I mean, the one due to the CDF anomaly? As Jester at RESONAANCES said, whether we want it or not, it will essentially dominate model building for the next few months, and another confirmation to this statement is the recent paper by Erich Poppitz and Patrick Fox.
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85. Hard thermal loops: what is it?
Suppose that you are a person studying non-equilibrium diagrammatic methods. At some point you realize that in many situations (such as at the time scale of prethermalization in the quark-gluon plasma or soon after the end of preheating) brute-force perturbation theory breaks down, as breaks the description of the dynamics by means of a single kinetic equation (in such case, the whole BBGKY chain of equations is necessary to take into account). In order to describe your strongly coupled plasma and deal with full BBGKY chain, you need to develop some non-perturbative methods, and very soon you figure out that not so many of them are currently on the market.
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81. Edward Witten’s talk on 3D gravity
Fascinating video of Edward Witten’s talk on 3D quantum gravity given at the Princeton Institute for Advanced Study.The picture that goes back to Deser, ‘t Hooft and Jackiw is the following. Since there are no dynamical (propagating) degrees of freedom in 3D gravity, the physics of the latter is completely defined by matter fields. Matter particle creates a conical singularity around it, and, in a sence, the 3D quantum gravity is the theory of scattering of these conical deffects on each other.
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80. Watching worlds collide: bubbles, bubbles, bubbles
Getting tired of malicious attacks by anti-landscapists, Spencer Chang, Matt Kleban and Thomas Levi released a paper about one observable effect on string theory landscape.
As we remember, when people talk about dynamics of eternal inflation on the string theory landscape (see for example my own paper and references therein), they keep in mind the picture of Coleman-de Luccia tunnelings between different vacua on the landscape. These tunnelings happen through bubble nucleation; you can live in the bubble with one vacuum, and then suddenly another bubble near you starts to grow, then another – inside the bubble N2 etc., etc.
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78. A talk on scalar QFT, exact renormalization group and RG fixed points
Oliver Rosten who, as I gather, now works in the U. of Sussex with Daniel Litim, recently gave a talk on exact renormalization group in Perimeter. The main conclusion is that there are non non-trivial RG fixed points for a scalar QFT in D=4 (that is, no fixed points except the gaussian one corresponding to free field theory), and the theory is trivial in the IR.
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76. Chaos in quantum field theory
Clearly, the topic of interplay between confinement and chaos in classical YM got some interest, so let me continue. Contrary to what the title says, I shall not mention “confinement” this time, focusing on “chaos” instead.
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75. Chaos in YM and confinement
I think we are currently having a somewhat fruitful discussion with Marco Frasca on his blog. The question is how relevant is chaotic behavior of classical solutions of Yang-Mills equations of motion for the quantum theory (or, more precisely, for YM at strong coupling).
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74. Nima and CDF anomaly
The post is deleted.
71. More talks: M2 branes and AdS/CFT, correlations of low multipoles in CMB
Here is another couple of recent talk at Perimeter Institute worth if not watching, but at least going through the presentation file:
1. Igor Klebanov from Princeton discusses M2 branes and AdS/CFT correspondence. M2 branes are very hot topic in string theory now (see the review of membrane minirevolution on the Lubos Motl’s blog). Let me remind you that M2 branes are supermembranes in 11-dimensional M-theory, and one naturally wants to get a kind of AdS/CFT considering world volume theory on them. Generally, this should be more complicated than the construction of 
duality, since the M-theory is inherently strongly coupled, while the analysis of the 10-dim. string theory is well under control at least in the regime of weak coupling.
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