137 research outputs found
Nonperturbative infrared effects for light scalar fields in de Sitter space
We study the phi^4 scalar field theory in de Sitter space using the 2PI
effective action formalism. This formalism enables us to investigate the
nonperturbative quantum effects. We use the mean field and gap equations and
calculate the physical mass and effective potential. We find that
nonperturbative infrared effects on de Sitter space produce a curvature-induced
mass and work to restore the broken Z_2 symmetry.Comment: 14 pages, 3 figures, section 2 revised, discussion in section 4
changed, results not change
Hydrodynamic Models for Heavy-Ion Collisions, and beyond
A generic property of a first-order phase transition in equilibrium, and in
the limit of large entropy per unit of conserved charge, is the smallness of
the isentropic speed of sound in the ``mixed phase''. A specific prediction is
that this should lead to a non-isotropic momentum distribution of nucleons in
the reaction plane (for energies around 40 AGeV in our model calculation). On
the other hand, we show that from present effective theories for low-energy QCD
one does not expect the thermal transition rate between various states of the
effective potential to be much larger than the expansion rate, questioning the
applicability of the idealized Maxwell/Gibbs construction. Experimental data
could soon provide essential information on the dynamics of the phase
transition.Comment: 10 Pages, 4 Figures. Presented at 241st WE-Heraeus Seminar: Symposium
on Fundamental Issues in Elementary Matter: In Honor and Memory of Michael
Danos, Bad Honnef, Germany, 25-29 Sep 200
Bose-Einstein condensation and chiral phase transition in linear sigma model
With the linear sigma model, we have studied Bose-Einstein condensation and
the chiral phase transition in the chiral limit for an interacting pion system.
A phase diagram including these two phenomena is presented. It is found
that the phase plane has been divided into three areas: the Bose-Einstein
condensation area, the chiral symmetry broken phase area and the chiral
symmetry restored phase area. Bose-Einstein condensation can happen either from
the chiral symmetry broken phase or from the restored phase. We show that the
onset of the chiral phase transition is restricted in the area where there is
no Bose-Einstein condensation.Comment: 13 pages, 7 figure
Influence of the U(1)_A Anomaly on the QCD Phase Transition
The SU(3)_{r} \times SU(3)_{\ell} linear sigma model is used to study the
chiral symmetry restoring phase transition of QCD at nonzero temperature. The
line of second order phase transitions separating the first order and smooth
crossover regions is located in the plane of the strange and nonstrange quark
masses. It is found that if the U(1)_{A} symmetry is explicitly broken by the
U(1)_{A} anomaly then there is a smooth crossover to the chirally symmetric
phase for physical values of the quark masses. If the U(1)_{A} anomaly is
absent, then there is a phase transition provided that the \sigma meson mass is
at least 600 MeV. In both cases, the region of first order phase transitions in
the quark mass plane is enlarged as the mass of the \sigma meson is increased.Comment: 5 pages, 3 figures, Revtex, discussion extended and references added.
To appear in PR
Topological String Defect Formation During the Chiral Phase Transition
We extend and generalize the seminal work of Brandenberger, Huang and Zhang
on the formation of strings during chiral phase transitions(berger) and discuss
the formation of abelian and non-abelian topological strings during such
transitions in the early Universe and in the high energy heavy-ion collisions.
Chiral symmetry as well as deconfinement are restored in the core of these
defects. Formation of a dense network of string defects is likely to play an
important role in the dynamics following the chiral phase transition. We
speculate that such a network can give rise to non-azimuthal distribution of
transverse energy in heavy-ion collisions.Comment: 10 pages, 4 figures, minor correction
Dashen's phenomenon in gauge theories with spontaneously broken chiral symmetries
We examine Dashen’s phenomenon in the Leutwyler-Smilga regime of QCD with any number of colors and quarks in either the fundamental or adjoint representations of the gauge group. In this limit, the theories only depend on simple combinations of quark masses, the volume, chiral condensate and vacuum angle. Based upon this observation, we derive simple expressions for the chiral condensate and the topological density and show that they are in fact related. By examining the zeros of the various partition functions, we elucidate the mechanism leading to Dashen’s phenomena in QCD
The K/pi ratio from condensed Polyakov loops
We perform a field-theoretical computation of hadron production in large
systems at the QCD confinement phase transition associated with restoration of
the Z(3) global symmetry. This occurs from the decay of a condensate for the
Polyakov loop. From the effective potential for the Polyakov loop, its mass
just below the confinement temperature T_c is in between the vacuum masses of
the pion and that of the kaon. Therefore, due to phase-space restrictions the
number of produced kaons is roughly an order of magnitude smaller than that of
produced pions, in agreement with recent results from collisions of gold ions
at the BNL-RHIC. From its mass, we estimate that the Polyakov loop condensate
is characterized by a (spatial) correlation scale of 1/m_\ell ~ 1/2 fm. For
systems of deconfined matter of about that size, the free energy may not be
dominated by a condensate for the Polyakov loop, and so the process of
hadronization may be qualitatively different as compared to large systems. In
that vein, experimental data on hadron abundance ratios, for example K/pi, in
high-multiplicity pp events at high energies should be very interesting.Comment: 7 pages, 4 figures; discussion of the two-point function of Polyakov
Loops in small versus large systems adde
11 beta-hydroxysteroid dehydrogenase type 1 regulates glucocorticoid-induced insulin resistance in skeletal muscle
OBJECTIVE: Glucocorticoid excess is characterized by increased adiposity, skeletal myopathy, and insulin resistance, but the precise molecular mechanisms are unknown. Within skeletal muscle, 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) converts cortisone (11-dehydrocorticosterone in rodents) to active cortisol (corticosterone in rodents). We aimed to determine the mechanisms underpinning glucocorticoid-induced insulin resistance in skeletal muscle and indentify how 11beta-HSD1 inhibitors improve insulin sensitivity. \ud
RESEARCH DESIGN AND METHODS: Rodent and human cell cultures, whole-tissue explants, and animal models were used to determine the impact of glucocorticoids and selective 11beta-HSD1 inhibition upon insulin signaling and action. \ud
RESULTS: Dexamethasone decreased insulin-stimulated glucose uptake, decreased IRS1 mRNA and protein expression, and increased inactivating pSer insulin receptor substrate (IRS)-1. 11beta-HSD1 activity and expression were observed in human and rodent myotubes and muscle explants. Activity was predominantly oxo-reductase, generating active glucocorticoid. A1 (selective 11beta-HSD1 inhibitor) abolished enzyme activity and blocked the increase in pSer IRS1 and reduction in total IRS1 protein after treatment with 11DHC but not corticosterone. In C57Bl6/J mice, the selective 11beta-HSD1 inhibitor, A2, decreased fasting blood glucose levels and improved insulin sensitivity. In KK mice treated with A2, skeletal muscle pSer IRS1 decreased and pThr Akt/PKB increased. In addition, A2 decreased both lipogenic and lipolytic gene expression.\ud
CONCLUSIONS: Prereceptor facilitation of glucocorticoid action via 11beta-HSD1 increases pSer IRS1 and may be crucial in mediating insulin resistance in skeletal muscle. Selective 11beta-HSD1 inhibition decreases pSer IRS1, increases pThr Akt/PKB, and decreases lipogenic and lipolytic gene expression that may represent an important mechanism underpinning their insulin-sensitizing action
The O(N) Model at Finite Temperature: Renormalization of the Gap Equations in Hartree and Large-N Approximation
The temperature dependence of the sigma meson and pion masses is studied in
the framework of the O(N) model. The Cornwall-Jackiw-Tomboulis formalism is
applied to derive gap equations for the masses in the Hartree and large-N
approximations. Renormalization of the gap equations is carried out within the
cut-off and counter-term renormalization schemes. A consistent renormalization
of the gap equations within the cut-off scheme is found to be possible only in
the large-N approximation and for a finite value of the cut-off. On the other
hand, the counter-term scheme allows for a consistent renormalization of both
the large-N and Hartree approximations. In these approximations, the meson
masses at a given nonzero temperature depend in general on the choice of the
cut-off or renormalization scale. As an application, we also discuss the
in-medium on-shell decay widths for sigma mesons and pions at rest.Comment: 21 pages, 6 figures, typos corrected and refs. added, accepted in
Journal of Physics
General Structure of Relativistic Vector Condensation
We study relativistic massive vector condensation due to a non zero chemical
potential associated to some of the global conserved charges of the theory. We
show that the phase structure is very rich. More specifically there are three
distinct phases depending on the value of one of the zero chemical potential
vector self interaction terms. We also develop a formalism which enables us to
investigate the vacuum structure and dispersion relations in the spontaneously
broken phase of the theory. We show that in a certain limit of the couplings
and for large chemical potential the theory is not stable. This limit,
interestingly, corresponds to a gauge type limit often employed to economically
describe the ordinary vector mesons self interactions in QCD. We finally
indicate for which physical systems our analysis is relevant.Comment: RevTex4 14 pages,4 figure
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