Isabel Campos

Spin-glass transition of the three-dimensional Heisenberg spin glass.

It is shown, by means of Monte Carlo simulation and finite size scaling analysis, that the Heisenberg spin glass undergoes a finite-temperature phase transition in three dimensions. There is a single critical temperature, at which both a spin glass and a chiral glass ordering develop. The Monte Carlo algorithm, adapted from lattice gauge theory simulations, makes it possible to thermalize lattices of size L = 32, larger than in any previous spin-glass simulation in three dimensions. High accuracy is reached thanks to the use of the Marenostrum supercomputer. The large range of system sizes studied allows us to consider scaling corrections.

Global Anomalies in Chiral Gauge Theories on the Lattice

We discuss the issue of global anomalies in chiral gauge theories on the lattice. In Luschers approach, these obstructions make it impossible to define consistently a fermionic measure for the path integral. We show that an SU(2) theory has such a global anomaly if the Weyl fermion is in the fundamental representation. The anomaly in higher representations is also discussed. We finally show that this obstruction is the lattice analogue of the SU(2) anomaly first discovered by Witten.

Phenomenology tools on cloud infrastructures using OpenStack

We present a new environment for computations in particle physics phenomenology employing recent developments in cloud computing. On this environment users can create and manage “virtual” machines on which the phenomenology codes/tools can be deployed easily in an automated way. We analyze the performance of this environment based on “virtual” machines versus the utilization of physical hardware. In this way we provide a qualitative result for the influence of the host operating system on the performance of a representative set of applications for phenomenology calculations.

A STUDY OF THE PHASE TRANSITION IN 4D PURE COMPACT U(1) LGT ON TOROIDAL AND SPHERICAL LATTICES

Abstract We have performed a systematic study of the phase transition in the pure compact U(1) lattice gauge theory in the extended coupling parameter space (β, γ) on toroidal and spherical lattices. The observation of a non-zero latent heat in both topologies for all investigated γ ϵ [+0.2, −0.4], together with an exponent ν eff ∼ 1 d when large enough lattices are considered, lead us to conclude that the phase transition is first order. For negative γ, our results point to an increasingly weak first-order transition as γ is made more negative.

The U(1)-Higgs model: critical behaviour in the confining-Higgs region

Abstract We study numerically the critical properties of the U(1)-Higgs lattice model, with fixed Higgs modulus, in the region of small gauge coupling where the Higgs and confining phases merge. We find evidence for a first-order transition line that ends in a second-order point. By means of a rotation in parameter space we introduce thermodynamic magnitudes and critical exponents in close resemblance with simple models that show analogous critical behaviour. The measured data allow us to fit the critical exponents finding values in agreement with the mean-field prediction. The location of the critical point and the slope of the first-order line are accurately measured.

First order signatures in 4D pure compact U(1) gauge theory with toroidal and spherical topologies

We study the pure compact U(1) gauge theory with the extended Wilson action (�, couplings) by finite size scaling techniques, in lattices ranging from L=6 to L=24 in the region of ≤ 0 with toroidal and spherical topologies. The phase transition presents a double peak structure which survives in the thermodynamical limit in the torus. In the sphere the evidence supports the idea of a weaker, but still first order, phase transition. For < 0 the transition becomes weaker and larger lattices are needed to find its asymptotic behaviour. Along the transient region the behaviour is the typical one of a weak first order transition for both topologies, with a region where 1/d < � < 0.5, which becomes � ≈ 1/4 when larger lattices are used.

Instanton-like contributions to the dynamics of Yang-Mills fields on the twisted torus

Abstract We study SU(2) lattice gauge theory in small volumes and with twist m = (1, 1, 1) . We investigate the presence of the periodic instantons of Q = 1 2 and determine their free energy and their contribution to the splitting of energy flux sectors E( e = (1, 1, 1)) − E( e = (0, 0, 0)) .

Scientific workflow orchestration interoperating HTC and HPC resources

Abstract In this work we describe our developments towards the provision of a unified access method to different types of computing infrastructures at the interoperation level. For that, we have developed a middleware suite which bridges not interoperable middleware stacks used for building distributed computing infrastructures, UNICORE and gLite. Our solution allows to transparently access and operate on HPC and HTC resources from a single interface. Using Kepler as workflow manager, we provide users with the needed integration of codes to create scientific workflows accessing both types of infrastructures.

On the SU(2)-Higgs phase transition

Abstract We investigate the properties of the Confinement-Higgs phase transition in the SU(2)-Higgs model. The system is shown to exhibit a transient behavior up to L = 24 along which, the order of the phase transition cannot be discerned. In order to get a global vision on the problem, we have introduced a second (next-to-nearest neighbors) gauge-Higgs coupling (κ2). On this extended parameter space we find a line of phase transitions becoming increasely weak as the standard case is approached (κ2 = 0). From the global behavior on this parameter space we conclude that the transition is also first order in the standard case.We investigate the properties of the Confinement-Higgs phase transition in the SU(2)-Higgs model. The system is shown to exhibit a transient behavior up to L=24 along which, the order of the phase transition cannot be discerned. In order to get a global vision on the problem, we have introduced a second (next-to-nearest neighbors) gauge-Higgs coupling (k2). On this extended parameter space we find a line of phase transitions becoming increasely weak as the standard case is approached (k2 = 0). From the global behavior on this parameter space we conclude that the transition is also first order in the standard case.

Global anomalies in chiral lattice gauge theory

Abstract As first realized by Witten an SU(2) gauge theory coupled to a single Weyl fermion suffers from a global anomaly. This problem is addressed here in the context of the recent developments on chiral gauge theories on the lattice. We find Wittens anomaly manifests in the impossibility of defining globally a fermion measure that reproduces the proper continuum limit. Moreover, following Wittens original argument, we check numerically the crossing of the lowest eigenvalues of Neubergers operator along a path connecting two gauge fields that differ by a topologically non-trivial gauge transformation.