1,507 research outputs found
Mott effect at the chiral phase transition and anomalous J/Psi suppression
We investigate the in-medium modification of the charmonium break-up
processes due to the Mott effect for light (pi) and open-charm (D, D*) mesons
at the chiral/deconfinement phase transition. A model calculation for the
process J/Psi + pi -> D + \bar D* + h.c. is presented which demonstrates that
the Mott effect for the D-mesons leads to a threshold effect in the thermal
averaged break-up cross section. This effect is suggested as an explanation of
the phenomenon of anomalous J/Psi suppression in the CERN NA50 experiment.Comment: 9 pages, 3 figures; final version to appear in Phys. Lett.
Hadronic correlations above the chiral/deconfinement transition
The statistical bootstrap model is critically revised in order to include a
medium-dependent resonance width in it. We show that a thermodynamic model with
a vanishing width below the Hagedorn temperature T_H and a Hagedorn
spectrum-like width above T_H may not only eliminate the divergence of the
thermodynamic functions above T_H, but also gives a satisfactory description
the lattice quantum chromodynamics (QCD) data on the energy density above the
chiral/deconfinement transition as the main result of this contribution. This
model allows to explain the absence of heavy resonance contributions in the fit
of the experimentally measured particle ratios at SPS and RHIC energies.Comment: 9 pages, 2 figures, contribution to proceedings of NAPP 2003,
Dubrovnik, Croatia, 26-31 May, 200
Nonlocality effects on spin-one pairing patterns in two-flavor color superconducting quark matter and compact stars applications
We study the influence of nonlocality in the interaction on two spin one
pairing patterns of two-flavor quark matter: the anisotropic blue color paring
besides the usual two color superconducting matter (2SCb), in which red and
green colors are paired, and the color spin locking phase (CSL). The effect of
nonlocality on the gaps is rather large and the pairings exhibit a strong
dependence on the form factor of the interaction, especially in the low density
region. The application of these small spin-one condensates for compact stars
is analyzed: the early onset of quark matter in the nonlocal models may help to
stabilize hybrid star configurations. While the anisotropic blue quark pairing
does not survive a big asymmetry in flavor space as imposed by the charge
neutrality condition, the CSL phase as a flavor independent pairing can be
realized as neutral matter in compact star cores. However, smooth form factors
and the missmatch between the flavor chemical potential in neutral matter make
the effective gaps of the order of magnitude keV, and a more
systematic analysis is needed to decide whether such small gaps could be
consistent with the cooling phenomenology.Comment: 18 pages, 7 figures, corrected version with revised parameterizatio
Color neutrality effects in the phase diagram of the PNJL model
The phase diagram of a two-flavor Polyakov loop Nambu-Jona-Lasinio model is
analyzed imposing the constraint of color charge neutrality. Main effects of
this constraint are a shrinking of the chiral symmetry breaking (chiSB) domain
in the T-mu plane, a shift of the critical point to lower temperatures and a
coexistence of chiSB and two-flavor superconducting phases. The effects can be
understood in view of the presence of a nonvanishing color chemical potential
mu_8, which is necessary to compensate the color charge density rho_8 induced
by the nonvanishing Polyakov-loop mean field phi_3.Comment: 8 pages, 4 figures, figures added, minor text modification
Particle Production in Strong Time-dependent Fields
In these lecture notes we give an introduction to the kinetic equation
approach to pair production form the vacuum in strong, time-dependent external
fields (dynamical Schwinger process). We first give a derivation of the kinetic
equation with the source term for the case of fermions starting from the Dirac
equation and for bosons from the Klein-Gordon equation. In a second part we
discuss the application of the approach to the situation of external field
pulses as single-sheeted functions of time (like the Sauter-pulse) and as
multi- sheeted functions approximating the situation in the focal point of
counter-propagating laser beams. Special emphasis is on the discussion of the
time evolution of the system that exhibits the characteristics of a
field-induced phase transition for which we discuss the behaviour of the
entropy and particle density of the system. We give an outlook to applications
of the approach in describing particle production in strong fields formed in
particle and nuclear collisions.Comment: 23 pages, 7 figures, Lecture Notes based on arXiv:hep-ph/9809227 and
arxiv:1607.08775; to appear in Proceedings of the Helmholtz International
Summer School on "Quantum Field Theory at the Limits: From Strong Fields to
Heavy Quarks", July 18-30, 2016, Dubna, Russi
Conformal relativity versus Brans-Dicke and superstring theories
Conformal relativity theory which is also known as Hoyle-Narlikar theory has
recently been given some new interest. It is an extended relativity theory
which is invariant with respect to conformal transformations of the metric.
In this paper we show how conformal relativity is related to the Brans-Dicke
theory and to the low-energy-effective superstring theory. We show that
conformal relativity action is equaivalent to a transformed Brans-Dicke action
for Brans-Dicke parameter in contrast to a reduced
(graviton-dilaton) low-energy-effective superstring action which corresponds to
a Brans-Dicke action with Brans-Dicke parameter . In fact,
Brans-Dicke parameter gives a border between a standard scalar
field evolution and a ghost.
We also present basic cosmological solutions of conformal relativity in both
Einstein and string frames. The Eintein limit for flat conformal cosmology
solutions is unique and it is flat Minkowski space. This requires the scalar
field/mass evolution instead of the scale factor evolution in order to explain
cosmological redshift.
It is interesting that like in ekpyrotic/cyclic models, a possible transition
through a singularity in conformal cosmology in the string frame takes place in
the weak coupling regime.Comment: REVTEX4, 12 pages, an improved version, references adde
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