arXiv subjects

Leonardo Cosmai

Publications and source records attributed to Leonardo Cosmai.

At least 37 records · Page 2Linked to original sources

arXiv2015

N$_f$ = 1 QCD in External Magnetic Fields: Staggered Fermions

We investigate N$_f$ = 1 QCD in external magnetic fields on the lattice. The background field is introduced by means of the so-called Schrodinger functional. We adopt standard staggered fermions with constant bare mass $am = 0.025$ and magnetic fields with constant magnetic flux up to $a^2 e H \simeq 2.3562$. We find that the the deconfinement and chiral symmetry restoration temperatures do not depend on the strength of the applied magnetic field. Our method allow us to easily study the effects of the external magnetic fields on the QCD thermodynamics. We determine the influences of applied magnetic fields to the free energy, pressure, and equation of state of strongly interacting matter.

hep-lat↗

arXiv2015

Anatomy of SU(3) flux tubes at finite temperature

An attempt to adapt the study of color flux tubes to the case of finite temperature has been made. The field is measured both through the correlator of two Polyakov loops, one of which connected to a plaquette, and through a connected correlator of Wilson loop and plaquette in the spatial sublattice. Still the profile of the flux tube resembles the transverse field distribution around an isolated vortex in an ordinary superconductor. The temperature dependence of all the parameters characterizing the flux tube is investigated.

hep-lat↗

arXiv2015

Curvature of the pseudocritical line in (2+1)-flavor QCD with HISQ fermions

We study QCD with (2+1)-HISQ fermions at nonzero temperature and nonzero imaginary baryon chemical potential. Monte Carlo simulations are performed using the MILC code along the line of constant physics with a light to strange mass ratio of $m_l/m_s=1/20$ on lattices up to $48^3 \times 12$ to check for finite cutoff effects. We determine the curvature of the pseudocritical line extrapolated to the continuum limit.

hep-lat↗

arXiv2014

London penetration depth and coherence length of SU(3) vacuum flux tubes

The transverse profile of the chromoelectric field generated by a quark-antiquark pair in the SU(3) vacuum is analysed within the dual superconductor scenario, then the London penetration depth and coherence length are extracted. The color field is determined on the lattice through a connected correlator of two Polyakov loops measured on smeared configurations.

hep-lat↗

arXiv2014

Curvature of the QCD critical line with 2+1 HISQ fermions

We present results on the curvature of the critical line of QCD with 2+1 HISQ fermions at nonzero temperature and quark density obtained by analytic continuation from imaginary chemical potentials. Monte Carlo simulations are performed by means of the MILC code, suitably modified to include a nonzero imaginary baryon chemical potential. We set the chemical potential at the same value for the three quark species and work on the line of constant physics with a light to strange mass ratio of 1/20 as determined in Ref.~\cite{Bazavov:2011nk}.

hep-lat↗

arXiv2014

Flux tubes in the SU(3) vacuum: London penetration depth and coherence length

Within the dual superconductor scenario for the QCD confining vacuum, the chromoelectric field generated by a static $q\overline{q}$ pair can be fitted by a function derived, by dual analogy, from a simple variational model for the magnitude of the normalized order parameter of an isolated Abrikosov vortex. Previous results for the SU(3) vacuum are revisited, but here the transverse chromoelectric field is measured by means of the connected correlator of two Polyakov loops and, in order to reduce noise, the smearing procedure is used instead of cooling. The penetration and coherence lengths of the flux tube are then extracted from the fit and compared with previous results.

hep-lat↗

arXiv2014

On the critical line of 2+1 flavor QCD

We determine the curvature of the (pseudo)critical line of QCD with $n_f$=2+1 staggered fermions at nonzero temperature and quark density, by analytic continuation from imaginary chemical potentials. Monte Carlo simulations are performed adopting the HISQ/tree action discretization, as implemented in the code by the MILC collaboration, suitably modified to include a nonzero imaginary baryon chemical potential. We work on a line of constant physics, as determined in Ref.\cite{Bazavov:2011nk}, adjusting the couplings so as to keep the strange quark mass $m_s$ fixed at its physical value, with a light to strange mass ratio $m_l/m_s=1/20$. In the present investigation we set the chemical potential at the same value for the three quark species, $μ_l=μ_s\equiv μ$. We explore lattices of different spatial extensions, $16^3\times 6$ and $24^3\times 6$, to check for finite size effects, and present results on a $32^3 \times 8$ lattice, to check for finite cut-off effects. We discuss our results for the curvature $κ$ of the critical line at $μ= 0$, which indicate $κ=0.018(4)$, and compare them with previous lattice determinations by alternative methods and with experimental determinations of the freeze-out curve.

hep-lat↗

arXiv2013

Flux tubes and coherence length in the SU(3) vacuum

An estimate of the London penetration and coherence lengths in the vacuum of the SU(3) pure gauge theory is given downstream an analysis of the transverse profile of the chromoelectric flux tubes. Within ordinary superconductivity, a simple variational model for the magnitude of the normalized order parameter of an isolated vortex produces an analytic expression for magnetic field and supercurrent density. In the picture of SU(3) vacuum as dual superconductor, this expression provides us with the function that fits the chromoelectric field data. The smearing procedure is used in order to reduce noise.

hep-lat↗

arXiv2012

Chromoelectric flux tubes and coherence length in QCD

The transverse profile of the chromoelectric flux tubes in SU(2) and SU(3) pure gauge theories is analyzed by a simple variational ansatz using a strict analogy with ordinary superconductivity. Our method allows to extract the penetration length and the coherence length of the flux tube.

hep-lat↗

arXiv2012

Chiral Symmetry Breaking in Planar QED in External Magnetic Fields

We investigate planar quantum electrodynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. We argue that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak-coupling region. We extrapolate our lattice results to the quantum Hall effect in graphene.

hep-lat↗

arXiv2011

The Higgs boson: from the lattice to LHC

We discuss the triviality and spontaneous symmetry breaking scenario where the Higgs boson without self-interaction coexists with spontaneous symmetry breaking. We argue that non perturbative lattice investigations support this scenario. Moreover, from lattice simulations we predict that the Higgs boson is rather heavy. We estimate the Higgs boson mass $m_H = 754 \pm 20 {\text{(stat)}} \pm 20 {\text{(syst)}} {\text{GeV}}$ and the Higgs total width $Γ(H) \simeq 340 {\text{GeV}}$.

hep-ph↗

arXiv2011

Flux tubes in the SU(3) vacuum

We analyze the distribution of the chromoelectric field generated by a static quark-antiquark pair in the SU(3) vacuum. We find that the transverse profile of the flux tube resembles the dual version of the Abrikosov vortex field distribution and give an estimate of the London penetration length in the confined vacuum.

hep-lat↗

arXiv2011

Lattice Planar QED in external magnetic field

We investigate planar Quantum ElectroDynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. Our preliminary results indicate that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak coupling region. We comment on possible implications to the quantum Hall effect in graphene.

hep-lat↗

arXiv2010

Chromoelectric flux tubes in QCD

We analyze the distribution of the chromoelectric field generated by a static quark-antiquark pair in the SU(3) vacuum and revisit previous results for SU(2). We find that the transverse profile of the flux tube resembles the dual version of the Abrikosov vortex field distribution. We give an estimate of the London penetration length of the chromoelectric field in the confined vacuum. We also speculate on the value of the ratio between the penetration lengths for SU(2) and SU(3) gauge theories.

hep-lat↗

arXiv2010

The phase diagram of QCD with four degenerate quarks

We revisit the determination of the pseudo-critical line of QCD with four degenerate quarks at non-zero temperature and baryon density by the method of analytic continuation. We determine the pseudo-critical couplings at imaginary chemical potentials by high-statistics Monte Carlo simulations and reveal deviations from the simple quadratic dependence on the chemical potential visible in earlier works on the same subject. Finally, we discuss the implications of our findings for the shape of the pseudo-critical line at real chemical potential, comparing different possible extrapolations.

hep-lat↗

arXiv2010

On the analytic continuation of the critical line

We perform a numerical study of the systematic effects involved in the determination of the critical line at real baryon chemical potential by analytic continuation from results obtained at imaginary chemical potentials. We present results obtained in a theory free of the sign problem, three-color QCD with finite isospin chemical potential, and comment on general features which could be relevant also to the continuation of the critical line in real QCD at finite baryon density.

hep-lat↗

arXiv2009

Analytic continuation of the critical line: suggestions for QCD

We perform a numerical study of the systematic effects involved in the determination of the critical line at real baryonic chemical potential by analytic continuation from results obtained at imaginary chemical potentials. We present results obtained in theories free of the sign problem, such as two-color QCD with finite baryonic density and three-color QCD with finite isospin chemical potential, and comment on general features which could be relevant also to the continuation of the critical line in real QCD at finite baryonic density.

hep-lat↗

arXiv2008

The critical line from imaginary to real baryonic chemical potentials in two-color QCD

The method of analytic continuation from imaginary to real chemical potentials $μ$ is one of the few available techniques to study QCD at finite temperature and baryon density. One of its most appealing applications is the determination of the critical line for small $μ$: we perform a direct test of the validity of the method in this case by studying two-color QCD, where the sign problem is absent. The (pseudo)critical line is found to be analytic around $μ^2 = 0$, but a very large precision would be needed at imaginary $μ$ to correctly predict the location of the critical line at real $μ$.

hep-lat↗