[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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}.
[Show abstract][Hide abstract] 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 · 4.64 Impact Factor
[Show abstract][Hide abstract] 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 · 4.64 Impact Factor
[Show abstract][Hide abstract] 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 · 5.11 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 · 1.74 Impact Factor
[Show abstract][Hide abstract] 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 · 1.74 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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 · 1.74 Impact Factor
[Show abstract][Hide abstract] 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 · 1.74 Impact Factor
[Show abstract][Hide abstract] 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 · 1.20 Impact Factor
[Show abstract][Hide abstract] 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 · 1.20 Impact Factor
[Show abstract][Hide abstract] 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 · 1.20 Impact Factor
[Show abstract][Hide abstract] 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 · 1.20 Impact Factor