Quantum field theory
Test beam for LHCb
Video about LHCb experiment and the recent test of their detector using Super Proton Synchrotron. LHCb experiment is one of six particle detector experiments aimed to measure CP violation in the interaction of b-hadrons (hadron containing b quarks).
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Other interesting things in ArXiv (11 Jun 2009)
Basically, there were so many interesting and useful papers (or at least they were useful for me) – lecture notes, reviews – that it will give me hard time posting reviews of all of them here – since I am lazy, I’ll just try to list some of them.
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Notes on strongly coupled QCD in the continuum
By continuum here we mean using methods different from lattice QCD, which is currently our main instrument for quantitative understanding of QCD physics at strong coupling.
What can we actually do apart from lattice simulations to study properties of QCD in this regime? Not much really. As recent minireview paper by M. Pennington explains, one approach to the problem would be solving Schwinger-Dyson equations at strong coupling.
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This and that in ArXiv on Monday
Due to unbelievable overload of the last days let me simply list the recent papers in ArXiv that I found the most interesting:
1. Quantum information
T. Tilma el al., “Is entanglement a critical resource for quantum metrology?”
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Jim Simons and C.N. Yang interviewed by Bill Zimmerman
… about math (geometry)/physics interplay.
Yang: there are two types of modern math books – the ones which you cannot read beyond the first page and the ones which you cannot read beyond the first sentence. Stinrood is of the latter kind.
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Workshop on tests of gravity in Case Western – day 2 and Arkani-Hamed’s talk
The second day of the Workshop on Tests of Gravity (and here is my blog post about the first day) was mostly devoted to analog models (Bill Unruh, Michael Uhlmann, George Pickett) and models of modified gravity (Nima Arkani-Hamed, Justin Khoury, Stacy McGaugh, Ted Jacobson, Levon Pogosyan and Mark Wyman).
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Real-time gauge/gravity duality
Balt van Rees from the U. of Amsterdam continues the discussion of non-equilibrium AdS/CFT we have started not so long time ago. Since his recent paper with Skenderis was one of the major achievements in the field, I highly recommend going through his post. Dmitry.
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Correlator of Wilson and t’Hooft loops at strong coupling in N=4 SYM theory
Andrew Zayakin works at LMU, Munich and ITEP, Moscow. His interests include non-perturbative physics of QCD, string theory and AdS/CFT correspondence. Dmitry.
This post is about my recent paper with Alexander Gorsky and Alexander Monin about a correlator of a Wilson and a ‘t Hooft loop. Before I proceed, I should explain what these objects are and why they are important to be studied. QCD possesses a consistent description in terms of “dual variables” – charges and monopoles. Reader familiar with the systematics of particle-like solutions in different theories would stop me at this very moment by pointing out there are no monopoles in QCD. True, there are no monopoles in the sense of e.g. Georgi-Glashow model. However, effectively there is such a thing as monopole, which is widely observed on lattice as a non-zero Abelian flux through a closed lattice surface. A lot is known on “thermodynamics” and “phenomenology” of these quasiparticles. They do not exist in the sense of theory spectrum. Still, they are an important tool of describing QCD. The QCD phase transition, which is an element of common lore, can easily be understood in terms of monopoles (Fig.1).
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String theory and the diffusion equation
Gianluca Calcagni is a postdoc at Penn State working in the group of Martin Bojowald. His interests include string theory, string field theory and cosmology. Dmitry.
This post is based on arXiv:0904.3744, in collaboration with Giuseppe Nardelli. Check the links for references and introductory reviews on the subject.
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Vorticity generation in cosmological perturbation theory
Adam Christopherson is a PhD student at Queen Mary, U. of London working with Karim Malik on cosmological perturbation theory. Dmitry.
In this blog post, I will summarize recent work on vorticity generation in cosmological perturbation theory, undertaken by Karim Malik, David Matravers and myself. The main result of the paper this is based on, arxiv:0904.0940, is that at second order in perturbation theory, vorticity generation is sourced by entropy gradients.
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Correcting the initial vacuum state in quantum gravity
Emre Kahya is a postdoc at Koc University, Turkey (he is a former graduate student of Richard Woodard). Dmitry.
Cosmology is becoming the most active area of research in theoretical physics for the last 10 years. We now understand that initial quantum fluctuations are reasons of our existence with in the context of Inflation. This brings the following question: Can we make quantum gravity calculations and expect to test them by some means? Naively one would say no. One reason is the smallness of the coupling constant:
quantum gravity effects have the order of magnitude ![0^{\rm th}{\rm Order} [1+\alpha_1 G + \alpha_2G^2 + ...]](http://www.nonequilibrium.net/latexrender/pictures/99bb619d901560bc9c639f1c44ea6834.gif "0^{\rm th}{\rm Order} [1+\alpha_1 G + \alpha_2G^2 + ...]")
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A bound on the speed of sound from holography?
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This post is authored by Aleksey Cherman (on the left) and Abhinav Nellore (on the right). Aleksey is a graduate student in the nuclear theory group at the University of Maryland, College Park, working with Tom Cohen, and Abhi is a graduate student in Steve Gubser’s group at Princeton. Dmitry. |  |
We all know that sound travels at about 343 m/s in air, and much faster than that in many solids. But just how much faster could sound travel if given the chance? Could there be a medium in which the speed of sound can approach the speed of light? Or might there be some more stringent fundamental bound on the speed of sound?
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The in-in formalism and cosmological perturbations
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This post is written by two great guys Peter Adshead (his photo is on the left) and Eugene Lim (on the right). Peter is a PhD student of Richard Easther at Yale U., while Eugene is Richard’s former postdoc now working at Columbia U. Dmitry. |  |
The discovery of the anisotropies in the cosmic microwave background (CMB) by the COBE satellite in 1992 heralded in a new era of cosmology. Instead of simply studying the gross evolution of the universe (usually termed “background evolution”), cosmologists now study the structure and evolution of the tiny perturbations about this background. The anisotropies observed in the CMB are believed to be the seeds from which all of the structure (stars, galaxies etc.) we observe today eventually grew. These perturbations, detected as an average of over/under-density of 
, are thought to be generated during an early period of accelerated expansion – inflation.
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Fermionic Schwinger-Keldysh propagators from AdS/CFT
Gregory Giecold is a PhD student at CEA, Saclay. Dmitry.
In this post I will describe recent work on fermionic Schwinger-Keldysh propagators from AdS/CFT. For further details and references see ArXiv: 0904.4869.
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(In)visible Z’ and dark matter
Alberto Romagnoni is a postdoc at LPT, Orsay. Dmitry.
In this post I discuss my recent work “(In)visible Z’ and dark matter”, done in collaboration with E. Dudas, Y. Mambrini and S. Pokorski. I think there are two main messages I should stress to summarize our paper. The first one is more interesting for its phenomenological consequences and a possible striking signature for dark matter. The second one is more important from a theoretical point of view, and concerns the so-called “decoupling” theorem.
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