Paolo Cea

Università degli Studi di Bari Aldo Moro, Bari, Apulia, Italy

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Publications (166)433.29 Total impact

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    ABSTRACT: The chromoelectric field generated by a static quark-antiquark pair, with its peculiar tube-like shape, can be nicely described, at zero temperature, within the dual superconductor scenario for the QCD confining vacuum. In this work we investigate, by lattice Monte Carlo simulations of the SU(3) pure gauge theory, the fate of chromoelectric flux tubes across the deconfinement transition. We find that, as the temperature is increased towards and above the deconfinement temperature $T_c$, the amplitude of the field inside the flux tube gets smaller, while the shape of the flux tube does not vary appreciably across deconfinement. This scenario with flux-tube "evaporation" above $T_c$ has no correspondence in ordinary (type-II) superconductivity, where instead the transition to the phase with normal conductivity is characterized by a divergent fattening of flux tubes as the transition temperature is approached from below. We present also some evidence about the existence of flux-tube structures in the magnetic sector of the theory in the deconfined phase.
    Preview · Article · Nov 2015
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    ABSTRACT: 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.
    No preview · Article · Oct 2015
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    ABSTRACT: 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.
    Preview · Article · Oct 2015
  • Paolo Cea · Leonardo Cosmai
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    ABSTRACT: 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.
    No preview · Article · Sep 2015 · Journal of High Energy Physics
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    ABSTRACT: We determine the continuum limit of the curvature of the pseudocritical line of QCD with $n_f$=2+1 staggered fermions at nonzero temperature and quark density. We perform Monte Carlo simulations at imaginary baryon chemical potentials, adopting the HISQ/tree action discretization, as implemented in the code by the MILC collaboration. Couplings are adjusted so as to move on a line of constant physics, as determined in Ref.~\cite{Bazavov:2011nk}, with the strange quark mass $m_s$ fixed at its physical value and a light-to-strange mass ratio $m_l/m_s=1/20$. The chemical potential is set at the same value for the three quark species, $\mu_l=\mu_s\equiv \mu$. We get a reliable extrapolation to the continuum using the results on lattices with temporal size up to $L_t=12$. Our continuum value for the curvature $\kappa$ at zero baryon density, $\kappa=0.020(4)$, is compared with recent lattice results and with experimental determinations of the freeze-out curve.
    No preview · Article · Aug 2015
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    ABSTRACT: 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}.
    Preview · Article · Oct 2014
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    ABSTRACT: 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.
    Preview · Article · Apr 2014 · Physical Review D
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    ABSTRACT: 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, $\mu_l=\mu_s\equiv \mu$. 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 $\kappa$ of the critical line at $\mu = 0$, which indicate $\kappa=0.018(4)$, and compare them with previous lattice determinations by alternative methods and with experimental determinations of the freeze-out curve.
    Preview · Article · Mar 2014 · Physical Review D
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    Paolo Cea
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    ABSTRACT: Recent Planck data confirm that the cosmic microwave background displays the quadrupole power suppression together with large scale anomalies. Progressing from previous results, we propose that the slightly anisotropic ellipsoidal universe may account for these anomalies. We solve at large scales the Boltzmann equation for the photon distribution functions by taking into account both the effects of the inflation produced primordial scalar perturbations and the anisotropy of the geometry in the ellipsoidal universe. We show that the low quadrupole temperature correlations allows us to fix the eccentricity at decoupling, $e_{\rm dec} \, = \, ( 0.86 \, \pm \, 0.14) \, 10^{-2}$, and to constraint the direction of the symmetry axis. We find that the anisotropy of the geometry of the universe contributes only to the large scale temperature anisotropies without affecting the higher multipoles of the angular power spectrum. Moreover, we show that the ellipsoidal geometry of the universe induces sizable polarization signal at large scales without invoking the reionization scenario. We explicitly evaluate the quadrupole TE and EE correlations. We find an average large scale polarization $\Delta T_{pol} \, = \, (1.20 \, \pm \, 0.38) \; \mu K $. We point out that great care is needed in the experimental determination of the large-scale polarization correlations since the average temperature polarization could be misinterpreted as foreground emission leading, thereby, to a considerable underestimate of the cosmic microwave background polarization signal.
    Preview · Article · Jan 2014 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: 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.
    Preview · Article · Oct 2013
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    ABSTRACT: We exploit analytic continuation to prolongate to the region of real chemical potentials the (pseudo)critical lines of QCD with two degenerate staggered fermions at nonzero temperature and quark or isospin density obtained in the region of imaginary chemical potentials. We determine the curvatures at zero chemical potential and quantify the deviation between the cases of finite quark and of finite isospin chemical potential. In both circumstances deviations from a quadratic dependence of the pseudocritical lines on the chemical potential are clearly seen. We try different extrapolations and, for the nonzero isospin chemical potential, confront them with the results of direct Monte Carlo simulations. We also find that, as for the finite quark chemical potential, an imaginary isospin chemical potential can strengthen the transition till turning it into strong first order.
    Preview · Article · Oct 2012
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    Paolo Cea
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    ABSTRACT: We comment on the Standard Model Higgs boson evidence from LHC. We propose that the new resonance at 125 GeV could be interpreted as a pseudoscalar meson with quantum number $J^{PC} = 0^{- +}$. We show that this pseudoscalar could mimic the decays of the Standard Model Higgs boson in all channels with the exception of the decay into two leptons that is strongly suppressed due to charge-conjugation invariance.
    Preview · Article · Sep 2012
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    ABSTRACT: 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.
    Preview · Article · Aug 2012 · Physical review D: Particles and fields
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    ABSTRACT: In this paper we investigate Charged Domain Walls (CDW's), topological defects that acquire surface charge density Q induced by fermion states localized on the walls. The presence of an electric and magnetic field on the walls is also discussed. We find a relation in which the value of the surface charge density Q is connected with the existence of such topological defects.
    Full-text · Article · May 2012 · International Journal of Modern Physics D
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    ABSTRACT: We discuss a new mechanism which allows domain walls produced during the primordial electroweak phase transition. We show that the effective surface tension of these domain walls can be made vanishingly small due to a peculiar magnetic condensation induced by fermion zero modes localized on the wall. We find that in the perfect gas approximation the domain wall network behaves like a radiation gas. We consider the recent high-red shift supernova data and we find that the corresponding Hubble diagram is compatible with the presence in the Universe of an ideal gas of ferromagnetic domain walls. We show that our domain wall gas induces a completely negligible contribution to the large-scale anisotropy of the microwave background radiation.
    No preview · Article · May 2012 · International Journal of Modern Physics D
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    ABSTRACT: 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.
    Preview · Article · Apr 2012 · Physical review D: Particles and fields
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    ABSTRACT: We determine the (pseudo)critical lines of QCD with two degenerate staggered fermions at nonzero temperature and quark or isospin density, in the region of imaginary chemical potentials; analytic continuation is then used to prolongate to the region of real chemical potentials. We obtain an accurate determination of the curvatures at zero chemical potential, quantifying the deviation between the case of finite quark and of finite isospin chemical potential. Deviations from a quadratic dependence of the pseudocritical lines on the chemical potential are clearly seen in both cases: we try different extrapolations and, for the case of nonzero isospin chemical potential, confront them with the results of direct Monte Carlo simulations. Finally we find that, as for the finite quark density case, an imaginary isospin chemical potential can strengthen the transition till turning it into strong first order.
    Preview · Article · Feb 2012 · Physical review D: Particles and fields
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    ABSTRACT: We investigate gravitational properties of thin planar wall solutions of the Einstein's equations in the weak field approximation. We find the general metric solutions and discuss the behavior of a particle placed initially at rest to one side of the plane. Moreover we study the case of non-reflection-symmetric solutions.
    Full-text · Article · Jan 2012 · International Journal of Modern Physics D
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    P.cea · L.tedesco
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    ABSTRACT: In this paper we discuss once more the zero mode contribution to the vacuum energy density. We show that a careful treatment of the zero modes leads to the conclusion that domain walls may be ferromagnetic, and could generate a magnetic field of cosmological interest.
    Preview · Article · Jan 2012 · International Journal of Modern Physics D
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    P.cea · L.cosmai · M.consoli
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    ABSTRACT: General arguments related to "triviality" predict that, in the broken phase of (λΦ4)4 theory, the condensate <Φ> rescales by a factor Zφ different from the conventional wave function renormalization factor, Zprop. Using a lattice simulation in the Ising limit, we measure Zφ= m2χ from the physical mass and susceptibility and Zprop from the residue of the shifted-field propagator. We find that the two Z's differ, with the difference increasing rapidly as the continuum limit is approached. Since Zφ affects the relation of <Φ> to the Fermi constant, it can sizably affect the present bounds on the Higgs mass.
    Preview · Article · Nov 2011 · Modern Physics Letters A