Paolo Cea

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

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Publications (158)418.35 Total impact

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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}.
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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.
    Physical Review D 04/2014; 89(9). DOI:10.1103/PhysRevD.89.094505 · 4.86 Impact Factor
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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.
    Physical Review D 03/2014; 89(7). DOI:10.1103/PhysRevD.89.074512 · 4.86 Impact Factor
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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.
    Monthly Notices of the Royal Astronomical Society 01/2014; 441(2). DOI:10.1093/mnras/stu687 · 5.23 Impact Factor
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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.
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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.
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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.
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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.
    Physical review D: Particles and fields 08/2012; 86(5). DOI:10.1103/PhysRevD.86.054501 · 4.86 Impact Factor
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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.
    International Journal of Modern Physics D 05/2012; 13(01). DOI:10.1142/S021827180400369X · 1.42 Impact Factor
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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.
    International Journal of Modern Physics D 05/2012; 14(03n04). DOI:10.1142/S021827180500681X · 1.42 Impact Factor
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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.
    Physical review D: Particles and fields 04/2012; 85(9). DOI:10.1103/PhysRevD.85.094505 · 4.86 Impact Factor
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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.
    Physical review D: Particles and fields 02/2012; 85(9). DOI:10.1103/PhysRevD.85.094512 · 4.86 Impact Factor
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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.
    International Journal of Modern Physics D 01/2012; 12(08). DOI:10.1142/S0218271803003773 · 1.42 Impact Factor
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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.
    International Journal of Modern Physics D 01/2012; 12(04). DOI:10.1142/S0218271803003153 · 1.42 Impact Factor
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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.
    Modern Physics Letters A 11/2011; 13(29). DOI:10.1142/S0217732398002515 · 1.34 Impact Factor
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    ABSTRACT: We investigate the scattering of fermions off domain walls at the electroweak phase transition in the presence of a magnetic field. We consider both the bubble wall and the kink domain wall. We derive and solve the Dirac equation for fermions with momentum perpendicular to the walls, and compute the transmission and reflection coefficients. In the case of kink domain wall, we briefly discuss the zero mode solutions localized on the wall. The possible role of the magnetic field for the electroweak baryogenesis is also discussed.
    Modern Physics Letters A 11/2011; 15(28). DOI:10.1142/S0217732300002243 · 1.34 Impact Factor
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    ABSTRACT: The gravitational field produced by a domain wall acts as a medium with spacetime-dependent permittivity ε. Therefore, the fine structure constant α=e2/4πε will be a time-dependent function at fixed position. The most stringent constraint on the time-variation of α comes from the natural reactor Oklo and gives . This limit constrains the tension of a cosmic domain wall to be less than σ ≲ 10-2MeV3, and then represents the most severe limit on the energy density of a cosmic wall stretching our Universe.
    Modern Physics Letters A 11/2011; 22(14). DOI:10.1142/S0217732307023006 · 1.34 Impact Factor
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    ABSTRACT: Using a high-statistics lattice simulation of the Ising limit of (λΦ4)4 theory, we have measured the susceptibility and propagator in the broken phase. We confirm our earlier finding of a discrepancy between the field rescaling implied by the propagator data and that implied by the susceptibility. The discrepancy becomes worse as one goes closer to the continuum limit; thus, it cannot be explained by residual perturbative effects. The data are consistent with an unconventional description of symmetry breaking and "triviality" in which the rescaling factor for the finite-momentum fluctuations tends to unity, but the rescaling factor for the condensate becomes larger and larger as one approaches the continuum limit. In the standard model this changes the interpretation of the Fermi-constant scale and its relation to the Higgs mass.
    Modern Physics Letters A 11/2011; 14(24). DOI:10.1142/S0217732399001760 · 1.34 Impact Factor
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    ABSTRACT: We present preliminary results about the critical line of QCD with two degenerate staggered quarks at nonzero temperature and chemical potential, obtained by the method of analytic continuation. As in our previous studies with different numbers of colors and flavors, we find deviations from a simple quadratic dependence on the chemical potential. We comment on the shape of the critical line at real chemical potential and give an estimate of the curvature of the critical line, both for quark chemical potential and isospin chemical potential.
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    ABSTRACT: 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.