No Net Charge Separation in Hot QCD in a Magnetic Field

We study the realization of axion electrodynamics in QCD in the presence of a background magnetic field at temperatures high enough for the occurrence of topological charge transitions that are reflected in the presence of a $\theta$-vacuum term in the action. We show that in this system, the Maxwell equations contain two equal and opposite electric currents that are proportional to the time derivative of the axion field $\theta$. One of these currents comes directly from the Abelian chiral anomaly term in the action and can be interpreted as a polarization current due to the magnetoelectricity of the system with CP-broken symmetry. The other current is obtained from the regular tadpole diagrams and can be understood as produced by the medium chiral imbalance and the single spin projection of the quarks in the lowest Landau level. Since the two currents cancel out, the net electric charge separation along the magnetic field, a phenomenon known as the Chiral Magnetic Effect, does not take place in hight-T QCD at least in equilibrium, in sharp contrast with many claims in the literature. We discuss the similarities and differences with Weyl semimetals in a magnetic field.Comment: 17 page

Magnetic Response in Anyon Fluid at High Temperature

The magnetic response of the charged anyon fluid at temperatures lower and larger than the fermion enery gap $\omega_{c}$ is investigated in the self-consistent field approximation. We prove that the anyon system with boundaries exhibits a total Meissner effect at temperatures smaller than the fermion energy gap ($T\ll \omega_{c}$). The London penetration length at $T$ $\sim 200K$ is of the order $\lambda \sim 10^{-5}cm$. At $T\gg \omega_{c}$ a new phase, characterized by an inhomogeneous magnetic penetration, is found. We conclude that the energy gap, $\omega_{c},$ defines a scale that separates two phases: a superconducting phase at $T\ll \omega_{c}$, and a non-superconducting one at $T\gg \omega_{c}$.Comment: 7 pages, Talk presented at SILAFAE'98. April 8-11, 1998, San Juan, Puerto Ric

Novel Topological Effects in Dense QCD in a Magnetic Field

We study the electromagnetic properties of dense QCD in the so-called Magnetic Dual Chiral Density Wave phase. This inhomogeneous phase exhibits a nontrivial topology that comes from the fermion sector due to the asymmetry of the lowest Landau level modes. The nontrivial topology manifests in the electromagnetic effective action via a chiral anomaly term $~\theta F^{\mu\nu}\tilde{F}_{\mu\nu}$, with a dynamic axion field $\theta$ given by the phase of the dual chiral density wave condensate. The coupling of the axion with the electromagnetic field leads to several macroscopic effects that include, among others, an anomalous, nondissipative Hall current, an anomalous electric charge, magnetoelectricity, and the formation of a hybridized propagating mode known as an axion polariton. Connection to topological insulators and Weyls semimetals, as well as possible implications for heavy-ion collisions and neutron stars are all highlighted.Comment: Section 3 completely revised, discussions added, and typos correcte

A search for Galactic transients disguised as gamma-ray bursts

A significant fraction of cosmological gamma-ray bursts (GRBs) are characterised by a fast rise and exponential decay (FRED) temporal structure. This is not a distinctive feature of this class, since it is observed in many Galactic transients and is likely descriptive of a sudden release of energy followed by a diffusion process. Possible evidence has recently been reported by Tello et al. (2012) for a Galactic contamination in the sample of FRED GRBs discovered with Swift. We searched for possible Galactic intruders disguised as FRED GRBs in the Swift catalogue up to September 2014. We selected 181 FRED GRBs (2/3 with unknown redshift) and considered different subsamples. We tested the degree of isotropy through the dipole and the quadrupole moment distributions, both with reference to the Galaxy and in a coordinate-system-independent way, as well as with the two-point angular autocovariance function. In addition, we searched for possible indicators of a Galactic origin among the spectral and temporal properties of individual GRBs. We found marginal (~3 sigma) evidence for an excess of FREDs with unknown redshift towards the Galactic plane compared with what is expected for an isotropic distribution corrected for the non-uniform sky exposure. However, when we account for the observational bias against optical follow-up observations of low-Galactic latitude GRBs, the evidence for anisotropy decreases to ~2 sigma. In addition, we found no statistical evidence for different spectral or temporal properties from the bulk of cosmological GRBs. We found marginal evidence for the presence of a disguised Galactic population among Swift GRBs with unknown redshift. The estimated fraction is f=(19 +- 11)%, with an upper limit of 34% (90% confidence).Comment: 6 pages, 4 figures, accepted by A&

Spinodal instability growth in new stochastic approaches

Are spinodal instabilities the leading mechanism in the fragmentation of a fermionic system? Numerous experimental indications suggest such a scenario and stimulated much effort in giving a suitable description, without being finalised in a dedicated transport model. On the one hand, the bulk character of spinodal behaviour requires an accurate treatment of the one-body dynamics, in presence of mechanical instabilities. On the other hand, pure mean-field implementations do not apply to situations where instabilities, bifurcations and chaos are present. The evolution of instabilities should be treated in a large-amplitude framework requiring fluctuations of Langevin type. We present new stochastic approaches constructed by requiring a thorough description of the mean-field response in presence of instabilities. Their particular relevance is an improved description of the spinodal fragmentation mechanism at the threshold, where the instability growth is frustrated by the mean-field resilience.Comment: Conf. proc. IWM2014-EC, Catania, 6-9 May 201

A practical approach to the global analysis of CLP programs

This paper presents and illustrates with an example a practical approach to the dataflow analysis of programs written in constraint logic programming (CLP) languages using abstract interpretation. It is first argued that, from the framework point of view, it sufnces to propose relatively simple extensions of traditional analysis methods which have already been proved useful and practical and for which efncient fixpoint algorithms have been developed. This is shown by proposing a simple but quite general extensión of Bruynooghe's traditional framework to the analysis of CLP programs. In this extensión constraints are viewed not as "suspended goals" but rather as new information in the store, following the traditional view of CLP. Using this approach, and as an example of its use, a complete, constraint system independent, abstract analysis is presented for approximating definiteness information. The analysis is in fact of quite general applicability. It has been implemented and used in the analysis of CLP(R) and Prolog-III applications. Results from the implementation of this analysis are also presented