Unconventional critical activated scaling of two-dimensional quantum spin-glasses

We study the critical behavior of two-dimensional short-range quantum spin glasses by numerical simulations. Using a parallel tempering algorithm, we calculate the Binder cumulant for the Ising spin glass in a transverse magnetic field with two different short-range bond distributions, the bimodal and the Gaussian ones. Through an exhaustive finite-size scaling analysis, we show that the universality class does not depend on the exact form of the bond distribution but, most important, that the quantum critical behavior is governed by an infinite randomness fixed point.Comment: 6 pages, 6 figure

Electromagnetic fields and transport coefficients in a hot pion gas

We present recent results on finite temperature electromagnetic form factors and the electrical conductivity in a pion gas. The standard Chiral Perturbation Theory power counting needs to be modified for transport coefficients. We pay special attention to unitarity and to possible applications for dilepton and photon production.Comment: 4pp, 2 figures, talk given at "Strong and Electroweak Matter 2006", BNL, May 200

On the kinematic evolution of young local associations and the Sco-Cen complex

Context: Over the last decade, several groups of young (mainly low-mass) stars have been discovered in the solar neighbourhood (closer than ~100 pc), thanks to cross-correlation between X-ray, optical spectroscopy and kinematic data. These young local associations -- including an important fraction whose members are Hipparcos stars -- offer insights into the star formation process in low-density environments, shed light on the substellar domain, and could have played an important role in the recent history of the local interstellar medium. Aims: To study the kinematic evolution of young local associations and their relation to other young stellar groups and structures in the local interstellar medium, thus casting new light on recent star formation processes in the solar neighbourhood. Methods: We compiled the data published in the literature for young local associations. Using a realistic Galactic potential we integrated the orbits for these associations and the Sco-Cen complex back in time. Results: Combining these data with the spatial structure of the Local Bubble and the spiral structure of the Galaxy, we propose a recent history of star formation in the solar neighbourhood. We suggest that both the Sco-Cen complex and young local associations originated as a result of the impact of the inner spiral arm shock wave against a giant molecular cloud. The core of the giant molecular cloud formed the Sco-Cen complex, and some small cloudlets in a halo around the giant molecular cloud formed young local associations several million years later. We also propose a supernova in young local associations a few million years ago as the most likely candidate to have reheated the Local Bubble to its present temperature.Comment: 27 pages, 13 figures, 14 tables. Accepted for publication in Astronomy & Astrophysic

Transport coefficients of a massive pion gas

We review or main results concerning the transport coefficients of a light meson gas, in particular we focus on the case of a massive pion gas. Leading order results according to the chiral power-counting are presented for the DC electrical conductivity, thermal conductivity, shear viscosity, and bulk viscosity. We also comment on the possible correlation between the bulk viscosity and the trace anomaly in QCD, as well as the relation between unitarity and a minimum of the quotient $\eta/s$ near the phase transition.Comment: Talk given at the 5th International Conference on Quarks and Nuclear Physics (QNP09), Beijing, September 21-26, 200

Chiral symmetry and mesons in hot and dense matter: recent developments

We review recent results on properties of the meson gas relevant for Heavy Ion Collision and Nuclear Matter experiments, within the framework of chiral lagrangians. In particular, we describe the temperature and density evolution of the $\sigma$ and $\rho$ poles and its connection with chiral symmetry restoration, as well as the chemical nonequilibrated phase and transport coefficients.Comment: Proceedings of the "Chiral10 International Workshop on Chiral Symmetry in Hadrons and Nuclei", Valencia, Spain, 21-24 june 2010. 9 pages, 5 figures. AIP Proceedings styl

Interpolation of bilinear operators and compactness

The behavior of bilinear operators acting on interpolation of Banach spaces for the $\rho$ method in relation to the compactness is analyzed. Similar results of Lions-Peetre, Hayakawa and Person's compactness theorems are obtained for the bilinear case and the $\rho$ method.Comment: This work was published at "Nonlinear Analysis: Theory, Methods and Applications, Volume 73, Issue 2, 2010, Pages 526-537". Since there are some gaps in the original proof of Theorem 4.3, Here we give a new proof. For this, we change the Lemma 4.