7,222 research outputs found
The improved nuclear parton distributions
In this paper we propose an improvement of the EKS nuclear parton
distributions for the small x region of high energy processes, where the
perturbative high parton density effects cannot be disregarded. We analyze the
behavior of the ratios and and verify that at small x
they are strongly modified when compared to the EKS predictions. The
implications of our results for the heavy ion collisions in RHIC and LHC are
discussed.Comment: 16 pages, 2 figure
Chiral fermion mass and dispersion relations at finite temperature in the presence of hypermagnetic fields
We study the modifications to the real part of the thermal self-energy for
chiral fermions in the presence of a constant external hypermagnetic field. We
compute the dispersion relation for fermions occupying a given Landau level to
first order in g'^2, g^2 and g_phi^2 and to all orders in g'B, where g' and g
are the U(1)_Y and SU(2)_L couplings of the standard model, respectively, g_phi
is the fermion Yukawa coupling, and B is the hypermagnetic field strength. We
show that in the limit where the temperature is large compared to sqrt{g'B},
left- and right-handed modes acquire finite and different B-dependent masses
due to the chiral nature of their coupling with the external field. Given the
current bounds on the strength of primordial magnetic fields, we argue that the
above is the relevant scenario to study the effects of magnetic fields on the
propagation of fermions prior and during the electroweak phase transition.Comment: 11 pages 4 figures, published versio
Pion dispersion relation at finite density and temperature
We study the behavior of the pion dispersion relation in a pion medium at
finite density and temperature. We introduce a pion chemical potential to
describe the finite pion number density and argue that such description is
valid during the hadronic phase of a relativistic heavy-ion collision between
chemical and thermal freeze-out. We make use of an effective Lagrangian that
explicitly respects chiral symmetry through the enforcement of the chiral Ward
identities. The pion dispersion relation is computed through the computation of
the pion self-energy in a non-perturbative fashion by giving an approximate
solution to the Schwinger-Dyson equation for this self-energy. The dispersion
relation is described in terms of a density and temperature dependent mass and
an index of refraction which is also temperature, density as well as momentum
dependent. The index of refraction is larger than unity for all values of the
momentum for finite and . We conclude by exploring some of the
possible consequences for the propagation of pions through the boundary between
the medium and vacuum.Comment: 7 pages, 5 figures, 3 new references, published versio
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