271 research outputs found
Lattice QCD estimate of the decay rate
We compute the hadronic matrix element relevant to the physical radiative
decay by means of lattice QCD. We use the
(maximally) twisted mass QCD action with Nf=2 light dynamical quarks and from
the computations made at four lattice spacings we were able to take the
continuum limit. The value of the mass ratio we
obtain is consistent with the experimental value, and our prediction for the
form factor is , leading to keV, which is much larger than and within reach of modern experiments.Comment: 19 pages, 4 fig
QCD Phase Transition in a Strong Magnetic Background
We investigate the properties of the deconfining/chiral restoring transition
for two flavor QCD in presence of a uniform background magnetic field. We adopt
a standard staggered discretization of the fermion action and a lattice spacing
of the order of 0.3 fm. We explore different values of the bare quark mass,
corresponding to pion masses in the range 200 - 480 MeV, and magnetic fields up
to |e|B ~ 0.75 GeV^2. The deconfinement and chiral symmetry restoration
temperatures remain compatible with each other and rise very slightly (< 2 %
for our largest magnetic field) as a function of the magnetic field. On the
other hand, the transition seems to become sharper as the magnetic field
increases.Comment: 5 pages, 8 figures. References and figures updated. Matches the
published versio
Magnetic susceptibility and equation of state of N_f = 2+1 QCD with physical quark masses
We determine the free energy of strongly interacting matter as a function of
an applied constant and uniform magnetic field. We consider N_f = 2+1 QCD with
physical quark masses, discretized on a lattice by stout improved staggered
fermions and a tree level improved Symanzik pure gauge action, and explore
three different lattice spacings. For magnetic fields of the order of those
produced in non-central heavy ion collisions (eB ~ 0.1 GeV^2) strongly
interacting matter behaves like a medium with a linear response, and is
paramagnetic both above and below the deconfinement transition, with a
susceptibility which steeply rises in the deconfined phase. We compute the
equation of state, showing that the relative increase in the pressure due to
the magnetic field gets larger around the transition, and of the order of 10 %
for eB ~ 0.1 GeV^2.Comment: 11 pages, 10 figures, 3 tables. Final version published in Physical
Review
The order of the Roberge-Weiss endpoint (finite size transition) in QCD
We consider the endpoint of the Roberge-Weiss (RW) first order transition
line present for imaginary baryon chemical potentials. We remark that it
coincides with the finite size transition relevant in the context of large
QCD and study its order in the theory with two degenerate flavors. The RW
endpoint is first order in the limit of large and small quark masses, while it
weakens for intermediate masses where it is likely in the Ising 3d universality
class. Phenomenological implications and further speculations about the QCD
phase diagram are discussed.Comment: 5 pages, 8 figures. Version accepted for publication in Physical
Review D (R
Magnetic Susceptibility of Strongly Interacting Matter across the Deconfinement Transition
We propose a method to determine the total magnetic susceptibility of
strongly interacting matter by lattice QCD simulations, and present first
numerical results for the theory with two light flavors, which suggest a weak
magnetic activity in the confined phase and the emergence of strong
paramagnetism in the deconfined, Quark-Gluon Plasma phase.Comment: 6 pages, 6 figures, 2 tables. Final version published in Physical
Review Letter
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