Master Mason
99. Eternal inflation with many light scalar fields
I am going to briefly discuss one result from the recent paper by Peter Adshead, Richard Easther and Eugene Lim.
One subject of the authors’ study is the interplay between stochastic and eternal N-flation. Let us recall what is N-flation (or assisted inflation). Suppose that we have a large number 
of scalar fields with equal potentials 
and relatively large vacuum expectation values. How large? We want to have the ordinary slow roll inflation in this setup. While one needs an expectation value of the inflaton to be superplanckian in single field inflationary models in order for slow roll conditions to hold, expectation values of any one among N scalar fields can be rather small and still the inflationary slow roll regime will not be spoiled. Indeed, we have
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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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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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83. Quintessence on the string theory landscape?
Nemanja Kaloper and Lorenzo Sorbo have recently released a paper explaining how the quintessence can be realized on string theory landscape. What is quintessence and why the question is important?
As we know, currently the energy density in the Universe is dominated (in proportion about 70/30) by dark energy. The latter behaves almost like a cosmological constant. We are not sure yet whether the corresponding effective equation of state 
changes with time, but if it does, there is some large probability that the dark energy is actually a very light scalar or axion field with mass at the level
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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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73. How eukaryotic cells feel direction
Eukaryotic cells present in both plants and animals are cells bounded by membranes and containing nuclei.
Often they contain other organelles such as mitochondria or chloroplasts, but this is not what will interest us at this time – let us focus on membranes.
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67. Weak lensing and modifying gravity
Jochen Weller et al. are trying to constrain the modified gravity theories with weak lensing data combined with baryon acoustic oscillations and supernovae data. Namely, the authors are mostly interested to fit the Dvali-Gabadadze-Porrati model and its modification mDGP (one parametric matching between Lambda CDM and DGP).
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59. Eye on Arxiv: Quantum corrections to eta/s
I decided to turn the de Sitter discussion off for a moment, it would be more appropriate to return to it after the paper is ready anyway Hopefully, it will not take too much time for you to see it in ArXives.
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55. Eternal inflation: stochastic approach 3 (Inflationary perturbations 7)
Last time we have found that dynamics of the inflaton field (more precisely, its expectation value w.r.t. to the distribution among different Hubble patches) is determined by the Langevin equation.
As we know, there are two descriptions of the Brownian motion: in terms of the Langevin equation and in terms of the Fokker-Planck equation describing diffusion of the probability distribution to find a randomly moving particle at given 
in a given moment of time 
. This Fokker-Planck equation has the form
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54. Eternal inflation: stochastic approach 2 (Inflationary perturbations 7)
In the previous post we have started to discuss the regime of eternal inflation realized when classical displacement of the inflaton field becomes comparable with the average amplitude of fluctuations generated at super-Hubble scale. The latter in practice means that the gravitational perturbations become of the same order as the background. How to treat theory in this regime?
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51. Planck 2008: day 4 – Soft wall AdS/QCD
I discuss the soft wall AdS/QCD model introduced by Batell&Gherghetta, where AdS gravity and dilaton behavior providing soft wall cutoff is introduced self-consistently.
39. Schwinger-Keldysh: Quasiclassical Keldysh action (non-equilibrium diagrammatic methods 1)
I discuss quasi-classical approximation for the Schwinger-Keldysh action and show that the quasi-classical evolution is described by the Langevin equation.
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