arXiv subjects

A. D'Alessandro

Publications and source records attributed to A. D'Alessandro.

9 recordsLinked to original sources

arXiv2009

Thermal monopoles and selfdual dyons in the Quark-Gluon Plasma

We perform a numerical study of the excess of non-abelian gauge invariant gluonic action around thermal abelian monopoles which populate the deconfined phase of Yang-Mills theories. Our results show that the excess of magnetic action is close to that of the electric one, so that thermal abelian monopoles may be associated with physical objects carrying both electric and magnetic charge, i.e. dyons. Thus, the quark gluon plasma is likely to be populated by selfdual dyons, which may manifest themselves in the heavy-ion collisions via the chiral magnetic effect. Thermodynamically, thermal monopoles provide a negative contribution to the pressure of the system.

hep-ph↗

arXiv2009

On the phase diagram of the Higgs SU(2) model

The Higgs SU(2) model with fixed Higgs length is usually believed to have two different phases at high gauge coupling (β), separated by a line of first order transitions but not distinuguished by any typical symmetry associated with a local order parameter, as first proved by Fradkin and Shenker. We show that in regions of the parameter space where it is usually supposed to be a first order phase transition only a smooth crossover is in fact present.

hep-lat↗

arXiv2008

Magnetic monopoles in high temperature QCD

We study the density and spatial distribution of thermal Abelian monopoles in the deconfined phase of SU(2) pure gauge theory: they display non-trivial interactions with a well defined continuum limit. The Maximal Abelian Gauge (MAG) has been chosen to perform the Abelian projection. Questions related to the choice of the Abelian projection, as well as possible directions for future studies, are discussed.

hep-lat↗

arXiv2007

Dual superconductivity and vacuum properties in Yang--Mills theories

We address, within the dual superconductivity model for color confinement, the question whether the Yang-Mills vacuum behaves as a superconductor of type I or type II. In order to do that we compare, for the theory with gauge group SU(2), the determination of the field penetration depth $λ$ with that of the superconductor correlation length $ξ$. The latter is obtained by measuring the temporal correlator of a disorder parameter developed by the Pisa group to detect dual superconductivity. The comparison places the vacuum close to the border between type I and type II and marginally on the type II side. We also check our results against the study of directly measurable effects such as the interaction between two parallel flux tubes, obtaining consistent indications for a weak repulsive behaviour. Future strategies to improve our investigation are discussed.

hep-lat↗

arXiv2006

Confining properties of 2-color QCD at finite density

We study the confining properties of QCD with two colors across the finite density phase transition. A disorder parameter detecting dual superconductivity of the QCD vacuum is used as a probe for the confinement/deconfinement phase transition.

hep-lat↗

arXiv2005

Dual superconducting properties of the QCD vacuum

A consistent description of the confining QCD vacuum as a dual superconductor requires a determination of fundamental parameters such as the superconductor correlation length $ξ$ and the field penetration depth $λ$, which determine whether the superconductor is of type I or type II. We illustrate preliminary results of a lattice determination of $ξ$ for the case of pure Yang-Mills with two colors, obtained by measuring the temporal correlator of a disorder parameter detecting dual superconductivity.

hep-lat↗

arXiv2005

Solar-like oscillations in the F9 V beta Virginis

This paper presents the analysis of Doppler p-modes of the F9 V star beta Virginis obtained with the spectrograph CORALIE in March 2003. Eleven nights of observations have made it possible to collect 1293 radial velocity measurements with a standard deviation of about 2.2 m s^-1. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 0.7 and 2.4 mHz showing regularity with a large and small spacings of Delta_nu = 72.1 uHz and delta_nu_02 = 6.3 uHz respectively. Thirty-one individual modes have been identified with amplitudes in the range 23 to 46 cm s^-1, i.e. with a signal to noise between 3 and 6.

astro-ph↗

arXiv1999

First Measurement of the He3+He3-->He4+2p Cross Section down to the Lower Edge of the Solar Gamow Peak

We give the LUNA results on the cross section measurement of a key reaction of the proton-proton chain strongly affecting the calculated neutrino luminosity from the Sun: He3+He3-->He4+2p. Due to the cosmic ray suppression provided by the Gran Sasso underground laboratory it has been possible to measure the cross section down to the lower edge of the solar Gamow peak, i.e. as low as 16.5 keV centre of mass energy. The data clearly show the cross section increase due to the electron screening effect but they do not exhibit any evidence for a narrow resonance suggested to explain the observed solar neutrino flux.

nucl-ex↗

arXiv1998

The Cross Section of 3He(3He,2p)4He measured at Solar Energies

We report on the results of the \hethet\ experiment at the underground accelerator facility LUNA (Gran Sasso). For the first time the lowest projectile energies utilized for the cross section measurement correspond to energies below the center of the solar Gamow peak ($E_{\rm 0}$=22 keV). The data provide no evidence for the existence of a hypothetical resonance in the energy range investigated. Although no extrapolation is needed anymore (except for energies at the low-energy tail of the Gamow peak), the data must be corrected for the effects of electron screening, clearly observed the first time for the \hethet\ reaction. The effects are however larger than expected and not understood, leading presently to the largest uncertainty on the quoted $S_{\rm b}(E_{\rm 0})$ value for bare nuclides (=5.40 MeV b).

nucl-ex↗