93 research outputs found
Curvature of the chiral pseudo-critical line in QCD: continuum extrapolated results
We determine the curvature of the pseudo-critical line of strong interactions
by means of numerical simulations at imaginary chemical potentials. We consider
stout improved staggered fermions with physical quark masses and the
tree level Symanzik gauge action, and explore four different sets of lattice
spacings, corresponding to , in order to extrapolate results
to the continuum limit. Our final estimate is .Comment: 11 pages, 10 figures, 4 tables. Version to appear in Physical Review
Roberge-Weiss endpoint at the physical point of QCD
We study the phase diagram of QCD in the plane and
investigate the critical point corresponding to the onset of the Roberge-Weiss
transition, which is found for imaginary values of . We make use of
stout improved staggered fermions and of the tree level Symanzik gauge action,
and explore four different sets of lattice spacings, corresponding to , and different spatial sizes, in order to assess the universality
class of the critical point. The continuum extrapolated value of the endpoint
temperature is found to be MeV, i.e. , where is the chiral pseudocritical temperature
at zero chemical potential, while our finite size scaling analysis, performed
on and lattices, provides evidence for a critical point in
the Ising universality class.Comment: 10 pages, 14 eps figures, 2 tables, final version published in
Physical Review
Curvature of the chiral pseudo-critical line in QCD
We determine the curvature of the pseudo-critical line of strong interactions
by means of numerical simulations at imaginary chemical potentials. We consider
stout improved staggered fermions with physical quark masses and the
tree level Symanzik gauge action, and explore two different sets of lattice
spacings, corresponding to temporal extensions and . Both
the renormalized chiral condensate and the renormalized chiral susceptibility
are used to locate the transition. The determinations obtained from the two
quantities are in good agreement, a preliminary continuum extrapolation yields
. We also investigate the impact of a non-zero strange
quark chemical potential and compare our results to previous determinations in
the literature, discussing the possible sources of systematic errors affecting
the various procedures.Comment: 16 pages, 12 figures, 11 tables. Published versio
Anisotropy of the quark-antiquark potential in a magnetic field
We investigate the static -potential for QCD at
the physical point in the presence of a constant and uniform external magnetic
field. The potential is found to be anisotropic and steeper in the directions
transverse to the magnetic field than in the longitudinal one. In particular,
when compared to the standard case with zero background field, the string
tension increases (decreases) in the transverse (longitudinal) direction, while
the absolute value of the Coulomb coupling and the Sommer parameter show an
opposite behavior.Comment: 6 pages, 5 figures, 1 table. Final published versio
Magnetic field effects on the static quark potential at zero and finite temperature
We investigate the static potential at zero and finite temperature
in the presence of a constant and uniform external magnetic field ,
for several values of the lattice spacing and for different orientations with
respect to . As a byproduct, we provide continuum limit extrapolated
results for the string tension, the Coulomb coupling and the Sommer parameter
at and . We confirm the presence in the continuum of a
-induced anisotropy, regarding essentially the string tension, for which it
is of the order of 15\% at and would suggest, if
extrapolated to larger fields, a vanishing string tension along the magnetic
field for GeV. The angular dependence for GeV can be nicely parametrized by the first allowed term in an angular
Fourier expansion, corresponding to a quadrupole deformation. Finally, for , the main effect of the magnetic field is a general suppression of the
string tension, leading to a precocious loss of the confining properties: this
happens even before the appearance of inverse magnetic catalysis in the chiral
condensate, supporting the idea that the influence of the magnetic field on the
confining properties is the leading effect originating the decrease of as
a function of .Comment: 13 pages, 4 tables, 14 figure
Screening masses in strong external magnetic fields
We present results for the (color)magnetic and (color)electric screening
masses of the Quark-Gluon Plasma in the presence of an external magnetic field.
The screening masses are extracted from the correlators of Polyakov loops,
determined by lattice QCD simulations at the physical point. We explore
temperatures in the range and magnetic field intensities up to . We find that both screening masses are increasing
functions of the magnetic field and that the dependence on becomes weaker
for larger temperatures. In the case of the magnetic screening mass a slight
anisotropy is also observable.Comment: 8 pages, 2 tables, 10 eps figures; This version matches the published
on
Axion phenomenology and -dependence from lattice QCD
We investigate the topological properties of QCD with physical
quark masses, both at zero and finite temperature. We adopt stout improved
staggered fermions and explore a range of lattice spacings
fm. At zero temperature we estimate both finite size and finite cut-off
effects, comparing our continuum extrapolated results for the topological
susceptibility with predictions from chiral perturbation theory. At
finite temperature, we explore a region going from up to around , where we provide continuum extrapolated results for the topological
susceptibility and for the fourth moment of the topological charge
distribution. While the latter converges to the dilute instanton gas prediction
the former differs strongly both in the size and in the temperature dependence.
This results in a shift of the axion dark matter window of almost one order of
magnitude with respect to the instanton computation.Comment: 24 pages, 12 figures, 5 tables, final version published in JHE
Recent progress on QCD inputs for axion phenomenology
The properties of the QCD axion are strictly related to the dependence of
strong interactions on the topological parameter theta. We present a
determination of the topological properties of QCD for temperatures up to
around 600 MeV, obtained by lattice QCD simulations with 2+1 flavors and
physical quark masses. Numerical results for the topological susceptibility,
when compared to instanton gas computations, differ both in size and in the
temperature dependence. We discuss the implications of such findings for axion
phenomenology, also in comparison to similar studies in the literature, and the
prospects for future investigations.Comment: Invited talk at XII Quark Confinement, 29 August - 3 September, 2016,
Thessaloniki, Greece, 9 pages, 6 figure
Axion phenomenology and lattice QCD
The properties of the QCD axion can be studied from the dependence of strong interactions on theθ-parameter. We present a study of the moments of the topological charge for temperatures up to around 600 MeV, obtained by lattice QCD simulations with 2+1 flavors at the physical quark masses. Our numerical results for the topological susceptibility, when compared to the instanton gas calculation, differ both in size and in the temperature dependence. We discuss the implications of these results for axion phenomenology, a comparison with other more recent studies and the prospects for future investigations
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