String theory
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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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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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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Quantum tunneling in flux compactifications
Delia Schwartz-Perlov is a postdoc at Tufts U. working with Alex Vilenkin. Her interests include quantum field theory, string theory, general relativity and cosmology. Dmitry.
I am very happy to find myself writing a blog about a recent paper written by Jose Juan Blanco-Pillado, Alex Vilenkin and myself, and titled “Quantum tunneling in flux compactifications“. In this paper we studied bubble nucleation rates in a 6-dimensional Einstein-Maxwell theory. The two extra dimensions are compactified into a 2-sphere, and their radius is stabilized by a magnetic flux through that sphere. We picked this toy model because it is simple enough to allow a quantitative analysis, yet it also includes some of the essential features of string theory compactifications (a related paper by Sean Carroll, Matthew Johnson and Lisa Randall was posted on the same day as ours!).
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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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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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Witten interviewed by Ira Flatow on Big Ideas: video of the day
.. and a very clear introduction into string and M-theory for dummies
381. M2 branes and Chern-Simons theories
John Davey is a PhD student of Amihay Hanany at Physics Department of Imperial College, London. Dmitry.
Recently Chern-Simons theories have attracted much attention as they are thought to describe the world volume theory of the elusive M2 brane. In this short article I will attempt to outline some of the recent developments in this field and describe how brane tilings can be used to find and investigate a large class of these theories.
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339. Twistors: getting more formal
After discussing (or rather musing about) generalities related to twistor formalism, let me now get a bit more formal – I hope it will finally help you to understand what I was talking about in the previous posts 
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337. Twistors and non-linear differential equations. Curved spacetime
Let my continue our micro-discussion of twistors. Last time I explained how using the language of twistors allows to express solutions of the linear differential equations (massless free fields propagating in the flat spacetime) in a different way – not too deep to really call it a result.
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335. What is twistor
Good Saturday evening, True Geeks!
Since everybody currently seems to be a bit crazy about twistors – see for example, the Witten’s paper “Perturbative gauge theory as a string theory in twistor space” and the buzz it started – I decided that the time has come for me to learn what it is and write minireview post about it.
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324. Video of the day: nice visualizations of elementary particles
Happy early Saturday, science geeks! Here is a little gift for you which will hopefully help you to sleep better (that’s what I am going to do now ) – nice visualizations of elementary particles It is not like they have anything to do with reality, but I liked the idea very much. The set includes: W-boson, some leptons, up quark, gluons and even graviton! All explanations are given by Dr. Manhattan himself.
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