Fellow Craft
122. Where are quarks in the Wilson loop?
An anonymous reader from Spain asks in comments to my “Wilson loop – physical introduction” post:
Why do you interpret a mathematical expresion that displays a gluon field (Amu) as a qqbar loop? Where are the q fields? Why they don’t appear in the Wilson loop but you still interpret they’re there? And where did the gluon go?
I think, these questions are such that the answer to them deserves a separate post, so thanks a lot for asking!
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121. On interaction between coherent condensate and turbulent flow in two dimensions
It looks like I did not review new nice papers in ArXiv for so long time 
While I have no idea what is the reason for this particular fact, I tell you that the ultimate reason for similar facts was always my tremendous laziness. What could a man do with such an evil? The only sane manly way seems to constantly try to overcome your disadvantages 
So, let me try.
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120. Talk in Munich. Regularizing inflaton correlation functions
Let me get again back from confinement to eternal inflation , or more precisely, to the infrared behavior of correlation functions of a self-interacting massless scalar field on de Sitter background. In what follows, I will consider the case 
(a QFT in fixed dS spacetime).
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117. Recent lattice QCD simulations – how good is QCD in the infrared?
A very interesting paper on lattice QCD spectroscopy by the European collaboration (DESY, Marceille, Wuppertal, Julich) is published in the recent issue of Science.The authors were able to reproduce the mass scales of light hadrons which coincide with measured ones up to 1% precision (take a look at the Table 1 in the paper). It means that a) QCD does describe the low energy physics perfectly, i.e., we don’t need corrections to the QCD Lagrangian at energies lower than the scale of 
and b) lattice QCD has reached the stage of development when all systematic error effects are under control. No more, no less.
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115. Talk in Munich. Leading logs
Last time I have claimed that the leading IR divergences in the loop expansion for the inflaton pair correlation function in 
theory contribute in the form of expansion
.
Let me now show how these divergences appear. First of all, let us forget about the interaction term and show that the correlation function 
for the free field 
on dS background diverges in the IR.
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112. Talk in Munich. Other two interesting infrared scales
As Instanton figured out in comments to the previous post, the scale 
is related to the self-reproduction scale. How to show this? Well, recall that the classical displacement of the inflaton field during one efolding is
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111. Talk in Munich. One interesting infrared scale in inflationary cosmology
I am back to Helsinki, was not this visit really short? :-)
For those of you how were unable to come to the Sommerfeld Center in Munich to hear my talk and for those of you who were there but did not understand it ? I decided to put the outline of my talk on the blog.
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110. Introducing doubt in Bayesian statistics 1
This is a guest post by my old friend Pascal Vaudrevange, who was a student of Lev Kofman when we were together in CITA, and is now a postdoc at Case Western University working with Glenn Starkman. Dmitry.
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108. How stringy is QCD string?
I am in Munich now, so please forgive me for being a bit quiet
As I’ve explained in this small introduction into criteria of confinement, breaking of the chromoelectric tube (string) connecting heavy quark and antiquark happens through the production of a pair of light quark and antiquark in the strong chromoelectric field. The physics behind this is the following. Suppose we are trying to pull the heavy quark and antiquark from each other. As was explained in this post, the energy of the string grows (almost) linearly as
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106. Criteria for confinement. Wilson loop – getting more technical
Last time we have discussed a bit the behavior of the Wilson loop expected in the confinement and deconfinement phases and have concluded from simple physical considerations that the first one corresponds to the area law, while the second – to the perimeter law. Let us now show directly that the Wilson loop VEV satisfies the area law for a large rectangular contour. This derivation will allow us to get familiar with several interesting features of the Wilson loop variable.
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103. Criteria of confinement. Wilson loop – physical discussion
It is often said that the most physically relevant criterion of confinement is the behaviour of the potential between two fermions: confinement implies the linear growth of potential between two charges with distance. Is it really so? In a gauge theory with fermions in the fundamental representation and the gauge group 
(
corresponds to quantum chromodynamics), the string of chromoelectric field connecting a heavy quark 
and antiquark 
may break down if the distance 
between the fermions becomes sufficiently large. This is due to the production of light quark-antiquark pair in the strong chromoelectric field (I estimate the maximal length of the chromoelectric string in this post.)
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92. A new theory of galaxy formation needed
It is well known that an ordinary galaxy can be described by seven physical parameters: total mass, baryon fraction, age, specific angular momentum, specific heat energy (related to random motion within the galaxy), its radius and concentration. According to the virial theorem, only six of them can be independent. This gives quite a bit of freedom for the model building and a large part of the astrophysical community is quite busy with constructing models of galaxy formation.
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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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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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53. Eternal inflation: stochastic approach 1 (Inflationary perturbations 7)
In this post I start to discuss physics of eternal inflation – regime where superhorizon cosmological perturbations become of the order 1.
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