Condensed Matter

Other interesting things in ArXiv (12 Jun 2009)

Posted by Dmitry

June 15, 2009

Wayne Hu. Acceleration from modified gravity: lessons from worked examples. The main question Wayne Hu discusses in this minireview is “How can we distinguish dark energy from modified gravity theories if the former and the latter provide the same predictions for cosmological dynamics?” He is particularly focused on DGP and f(R) models. His answer is the presence of anisotropic stress for modified gravity models which is coupled directly to lensing potential – if we are able to measure this effect, we will be able to discriminate between IR modified gravity and dark energy. Another idea is to study behavior of theories in non-linear regimes, for example, by means of N-body simulation, and compare it to LSS.

On Moore-Read states

Posted by Raoul Santachiara

May 12, 2009

Raoul Santachiara is a stuff member at Laboratoire de Physique Theorique et Modeles Statistiques, Universite de Paris-Sud. His interests include statistical and mathematical physics, critical phenomena, disordered systems and entanglement properties of many-body systems. Dmitry.

383. Puzzling kinetics of Bose-Enstein condensation

Posted by Dmitry

May 1, 2009

Just finished reading a really review “Magnon BEC and spin superfluidity” by Yu. Bunkov and G. Volovik, which left me with quite a bit of material to think about… Probably the thing that stroke me most after digesting the review is how poorly I (or in truth – it’s better to say “we”) actually understand the kinetics of Bose-Einstein condensation. But before I’ll try to explain why I think so, let me briefly describe the setup discussed by the authors.

377. Temporal and spatial dependence of quantum entanglement

Posted by Shih-Yuin Lin

April 28, 2009

Shih-Yuin Lin is a professor at Physics Division, National Center for Theoretical Sciences, Taiwan. Dmitry.

In textbooks, quantum entanglement are often introduced to readers with the simplest case: in an isolated system with two parties or subsystems, if a quantum states can be factorized into a product of the quantum states for each subsystem,

366. Some interesting recent papers in Arxiv

Posted by Dmitry

April 23, 2009

Just wanted to acknowledge their existence, although I’ll not be really able to review them due to the lack of time…

1. Quantum field theory

1.1. “Non-Abelian Duality and Confinement in N=2 Supersymmetric QCD” by Michail Shifman and Alesha Yung. The authors study transitions from weak to strong coupling in N = 2 SQCD that happen when you change parameters of the theory – that is, the coefficient $\xi$ in front of Fayet?Iliopoulos term and quark mass differences. Here the authors are interested in the case N<N_f<2N and study phases of the theory at different values of $\xi$ .

342. Thermal equilibrium in special relativity

Posted by David Cubero

April 8, 2009

David Cubero is professor at the Department of Applied Physics of the University of Sevilla. Dmitry.

Special relativity, despite being more than a hundred years old, still shows an intriguing capacity to surprise us in very fundamental issues, such as thermal equililbrium. In this post, we will review a recent controversy about the proper velocity distribution of dilute gases at thermal equilibrium.

329. Human Activity in the Web

Posted by Filippo Radicchi

March 30, 2009

Filippo Radicchi is a research scientist in Complex Systems Lagrange Lab, ISI Foundation, Turin. He is interested in non-equilibrium diagrammatic methods, RG group analysis of complex networks and community detection. Dmitry.

323. Fractional quantum Hall effect in some multicomponent systems

Posted by Zlatko Papic

March 27, 2009

Zlatko Papic is a PhD student at LPS, Universite Paris-Sud, France (his advisors are Mark Goerbig and Nicolas Regnault) and SCL, Institute of Physics, Serbia (where his thesis advisor is Milica Milovanovic). His main interests include quantum Hall systems. Dmitry.

314. FDT-violation in colloidal glasses under shear

Posted by Matthias Krueger

March 19, 2009

Matthias Krueger is a PhD student of Matthias Fuchs (U. of Konstanz). His interests include soft condense matter (that’s what this post will be about) and mesoscopic physics. Dmitry.

It is a pleasure for me to follow Dmitry’s invitation and to write a post about the paper which Matthias Fuchs and I have recently written (arXiv:0903.0558). We investigated the extension of the well known fluctuation dissipation theorem (FDT) to the nonequilibrium situation of dense (glassy) Brownian particles under shear.

297. Exact gravity dual of a gapless superconductor

Posted by George Koutsoumbas

March 8, 2009

This is a guest post by George Koutsoumbas from the National Technical University of Athens. Dmitry.

I would like to thank Dmitry for the invitation to write a blog entry on my recent work with E.Papantonopoulos and G. Siopsis entitled “Exact Gravity Dual of a Gapless Superconductor”, arXiv:0902.0733 [hep-th].

292. Universal properties of the U(1) current at deconfined quantum critical points

Posted by Flavio Nogueira

March 3, 2009

This is a guest post by Flavio Nogueira from the U. of Berlin. Dmitry.

Before I start talking my recent preprint [http://arxiv.org/abs/0902.0364], let me thank Dmitry for inviting me to write this contribution in his blog.

289. Patterned structures from a binary mixture of particles

Posted by Carlos Mendoza

March 1, 2009

This is a guest blog post by Carlos Mendoza from Instituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico.

Let me start by thanking Dmitry for the invitation to write a guest blog entry about my recent paper arXiv:0901.4153. This has been done in collaboration with Erasmo Batta and has been accepted for publication in EPL.

285. Dephasing and diffusion of quantum particles

Posted by Ariel Amir

February 25, 2009

This is a guest post by Ariel Amir from the Weizmann Institute of Science. Dmitry.

I was kindly asked by Dmitry to describe a recent work, where diffusion emerges from the decoherence in a noisy environment. This work was done together with Y. Lahini (an experimentalist) and H. Perets (an astrophysicist), and can be found on condmat (arXiv:0902.0890). Let me start by describing what a tight-binding model (for those of you outside Condensed Matter). This will be a convenient tool for us to understand decoherence, and other interesting physics such as ‘motional narrowing’.

282. Communication among communities

Posted by Massimo Ostilli

February 22, 2009

This is a guest blog post by Massimo Ostilli from the Center of Statistical Mechanics and Complexity (INFM, Roma). Dmitry.

In recent times, in the network science, the problem of detecting the community structure of a given network (a random graph), has attracted more attention. The general idea behind the concept of community structure comes from the observation that, in many situations, real data show an intrinsic partition of the vertices of the graph into groups, called communities, such that between any two communities there is a number of bonds that is relatively small if compared with the number of bonds present in each community. The partition(s) can be used to build a higher-level meta-network where the meta-nodes are now the communities (cells, proteins, groups of people, tec…) and play important roles in unveiling the functional organization inside the network. Given an hypothetical community structure, one of the most important issue is to understand whether or not the communities exchange information and to what extent, and, more in general, what are their correlations. In a recent work, we have emphasized that such a problem cannot be faced through an analysis that takes into account only the network topology (that is, the detailed description of nodes and bonds) that, by its definition, neglects any kind of correlation among the nodes. Nodes, in fact, are the sites where some physical or abstract status manifests as a result of the status of the other nodes. The most elementary example is the case in which at any node there is a dichotomy variable taking values ON and OFF. This happens – for example – in an network in which individuals, in somehow equivalent, are asked to say YES or NO to some politic proposal. The fact that the individuals know, in part, the opinion of the others, makes the answer of each individual partly conditioned by the others, especially, but not only, by those that are near (neighbors) in the social space. Physicists immediately understand that – within the equilibrium statistical mechanics – such a system can be cast by defining a suitable disordered Ising model. In this approach, the temperature can be seen as a parameter describing the freedom of the vertices to assume a state independently of the state of the other vertices, while the Ising couplings $J_{i,j}^{(l,k)}$ between two vertices and belonging to the -th and -th community, respectively, as a tendency of the vertices to be positively or negatively correlated, according to the amplitude and to the sign of $J_{i,j}^{(l,k)}$ . At least in principle, if a Gibbs-Boltzmann $\exp(-\beta H)$ distribution with some Hamiltonian has been assumed, one can obtain $\beta J_{i,j}^{(l,k)}$ from the data of the given graph by isolating the two vertices i,j from all vertices of the graph other then them, and by measuring the correlation function of the obtained isolated dimer.