Absence of the London limit for the first-order phase transition to a color superconductor
We study the effects of gauge-field fluctuations on the free energy density of a homogeneous color superconductor in the color-flavor-locked (CFL) phase. Gluonic fluctuations induce a strong first-order phase transition, in contrast to electronic superconductors where this transition is weakly first order. The critical temperature for this transition is larger than the one corresponding to the diquark pairing instability. The physical reason is that the gluonic Meissner masses suppress long-wavelength fluctuations as compared to the normal conducting phase where gluons are massless, which stabilizes the superconducting phase. In weak coupling, we analytically compute the temperatures associated with the limits of metastability of the normal and superconducting phases, as well as the latent heat associated with the first-order phase transition. We then extrapolate our results to intermediate densities and numerically evaluate the temperature of the fluctuation-induced first-order phase transition, as well as the discontinuity of the diquark condensate at the critical point. We find that the London limit of magnetic interactions is absent in color superconductivity.

title: Effect of gauge-field fluctuations on the phase transition between normal and color-superconducting quark matter
abstract: Type-I color superconductors display a first-order phase transition due to thermal gauge-field fluctuations. We numerically evaluated the critical temperature of the first-order phase transition and the corresponding discontinuity of the diquark condensate at the critical point.

title: Fermion Field on a Random Lattice
abstract: On etudie les modes zeros d'une action fermion sur un reseau aleatoire. On calcule les valeurs propres basses de l'action et on discute leur distribution

title: A neutral two-flavor LOFF color superconductor
abstract: In this Letter we construct analytically a LOFF color superconducting state that is both color and charge neutral using the weak coupling approximation. We demonstrate that this state is free from chromomagnetic instabilities. Its relevance to the realistic quark matter at moderately high baryon density is discussed.

title: Gauge field fluctuations and first-order phase transition in color superconductivity.
abstract: We study the gauge field fluctuations in dense quark matter and determine the temperature of the induced first-order phase transition to the color-superconducting phase in weak coupling. We find that the local approximation of the coupling between the gauge potential and the order parameter, employed in the Ginzburg-Landau theory, has to be modified by restoring the full momentum dependence of the polarization function of gluons in the superconducting phase.

title: Bosonization of lattice fermions.
abstract: For any purely fermionic system on a lattice in arbitrary space dimension we prove that there is a different but well-defined system on the same lattice, consisting of both [ital bona] [ital fide] fermions and bosons with an interaction depending on a parameter [lambda], which characterizes a same-site repulsion between particles. The energy spectrum and the scattering matrix of the former are identical to those in the finite energy sector of the latter, in the limit [lambda][r arrow][infinity] (i.e., hard-core repulsion). This general theorem is applied to a resonance-boson model in a lattice fermion system, whose solution may have relevance to high-[ital T][sub [ital c]] superconductivity.

title: WZW model based on the extended de Sitter group
abstract: We study the WZW model based on the centrally extended 2D de Sitter algebra. We obtain the spacetime metric and its explicitly conformally flat expression. The symmetries of the spacetime are found by identifying the Killing vectors with the group generators. The energy-momentum tensor obtained from the affine-Sugawara construction agrees with that from the more conventional approach. The exact center charge agrees to one-loop order with the one-loop beta function equations. We have also studied the representations of the corresponding enveloping Virasoro algebra.

title: Fermions in a global monopole background
abstract: We study the scattering of fermions in a “global monopole” background metric. This is the four-dimensional analogue of the scattering on a cone in three dimensions. The scattering amplitude is exactly obtained. We then study massless fermion-dyon systems in such a background metric. The density of the S -wave fermion condensate is found to be given by a constant times the flat space value of Callan and Rubakov.

title: Various topics in field theory

title: A neural network clustering algorithm for the ATLAS silicon pixel detector
abstract: A novel technique to identify and split clusters created by multiple charged particles in the ATLAS pixel detector using a set of artificial neural networks is presented. Such merged clusters are a common feature of tracks originating from highly energetic objects, such as jets. Neural networks are trained using Monte Carlo samples produced with a detailed detector simulation. This technique replaces the former clustering approach based on a connected component analysis and charge interpolation. The performance of the neural network splitting technique is quantified using data from proton-proton collisions at the LHC collected by the ATLAS detector in 2011 and from Monte Carlo simulations. This technique reduces the number of clusters shared between tracks in highly energetic jets by up to a factor of three. It also provides more precise position and error estimates of the clusters in both the transverse and longitudinal impact parameter resolution.

title: Measurement of the cross section of high transverse momentum $\it{Z\rightarrow b\bar{b}}$ production in proton--proton collisions at $\sqrt{s}=8 TeV$ with the ATLAS Detector