565 research outputs found
The Finite Temperature SU(2) Savvidy Model with a Non-trivial Polyakov Loop
We calculate the complete one-loop effective potential for SU(2) gauge bosons
at temperature T as a function of two variables: phi, the angle associated with
a non-trivial Polyakov loop, and H, a constant background chromomagnetic field.
Using techniques broadly applicable to finite temperature field theories, we
develop both low and high temperature expansions. At low temperatures, the real
part of the effective potential V_R indicates a rich phase structure, with a
discontinuous alternation between confined (phi=pi) and deconfined phases
(phi=0). The background field H moves slowly upward from its zero-temperature
value as T increases, in such a way that sqrt(gH)/(pi T) is approximately an
integer. Beyond a certain temperature on the order of sqrt(gH), the deconfined
phase is always preferred. At high temperatures, where asymptotic freedom
applies, the deconfined phase phi=0 is always preferred, and sqrt(gH) is of
order g^2(T)T. The imaginary part of the effective potential is non-zero at the
global minimum of V_R for all temperatures. A non-perturbative magnetic
screening mass of the form M_m = cg^2(T)T with a sufficiently large coefficient
c removes this instability at high temperature, leading to a stable
high-temperature phase with phi=0 and H=0, characteristic of a
weakly-interacting gas of gauge particles. The value of M_m obtained is
comparable with lattice estimates.Comment: 28 pages, 5 eps figures; RevTeX 3 with graphic
Complex periodic potentials with real band spectra
This paper demonstrates that complex PT-symmetric periodic potentials possess
real band spectra. However, there are significant qualitative differences in
the band structure for these potentials when compared with conventional real
periodic potentials. For example, while the potentials V(x)=i\sin^{2N+1}(x),
(N=0, 1, 2, ...), have infinitely many gaps, at the band edges there are
periodic wave functions but no antiperiodic wave functions. Numerical analysis
and higher-order WKB techniques are used to establish these results.Comment: 8 pages, 7 figures, LaTe
Free Energy of an SU(2) Model of (2+1)-dimensional QCD in the Constant Condensate Background
Gluon and quark contributions to the thermodynamic potential (free energy) of
a (2+1)-dimensional QCD model at finite temperature in the background of a
constant homogeneous chromomagnetic field H combined with A_0 condensate are
calculated. The role of the tachyonic mode in the gluon energy spectrum is
discussed. A possibility of the free energy global minimum generation at
nonzero values of H and A_0 condensates is investigated.Comment: LaTeX 2e, 14 pages, 6 eps figures, some miscalculations were
correcte
Universality in Random Walk Models with Birth and Death
Models of random walks are considered in which walkers are born at one
location and die at all other locations with uniform death rate. Steady-state
distributions of random walkers exhibit dimensionally dependent critical
behavior as a function of the birth rate. Exact analytical results for a
hyperspherical lattice yield a second-order phase transition with a nontrivial
critical exponent for all positive dimensions . Numerical studies
of hypercubic and fractal lattices indicate that these exact results are
universal. Implications for the adsorption transition of polymers at curved
interfaces are discussed.Comment: 11 pages, revtex, 2 postscript figure
Effects of mesonic correlations in the QCD phase transition
The finite temperature phase transition of strongly interacting matter is
studied within a nonlocal chiral quark model of the NJL type coupled to a
Polyakov loop. In contrast to previous investigations which were restricted to
the mean-field approximation, mesonic correlations are included by evaluating
the quark-antiquark ring sum. For physical pion masses, we find that the pions
dominate the pressure below the phase transition, whereas above T_c the
pressure is well described by the mean-field approximation result. For large
pion masses, as realized in lattice simulations, the meson effects are
suppressed.Comment: 11 pages, 4 figures; version accepted for publication in Yad. Fiz.,
text extended, 1 figure adde
Structure, Time Propagation and Dissipative Terms for Resonances
For odd anharmonic oscillators, it is well known that complex scaling can be
used to determine resonance energy eigenvalues and the corresponding
eigenvectors in complex rotated space. We briefly review and discuss various
methods for the numerical determination of such eigenvalues, and also discuss
the connection to the case of purely imaginary coupling, which is PT-symmetric.
Moreover, we show that a suitable generalization of the complex scaling method
leads to an algorithm for the time propagation of wave packets in potentials
which give rise to unstable resonances. This leads to a certain unification of
the structure and the dynamics. Our time propagation results agree with known
quantum dynamics solvers and allow for a natural incorporation of structural
perturbations (e.g., due to dissipative processes) into the quantum dynamics.Comment: 14 pages; LaTeX; minor change
Reproductive Factors and Serum Uric Acid Levels in Females from the General Population: The KORA F4 Study
Hyperuricemia is associated with an increased risk of metabolic and cardiovascular diseases. There are pronounced sex differences in the levels of uric acid. It is largely unknown whether or not reproductive parameters which induce hormonal changes are responsible for this. We examined if there are associations between reproductive parameters and uric acid levels in a female population-based sample.
In this cross-sectional analysis, data of 1530 women aged 32 to 81 years participating in the KORA F4 study, conducted between 2006 and 2008 in Southern Germany were used. Reproductive parameters were obtained by standardized interviews. Uric acid levels were tested by the uricase method. The whole study sample and stratified in pre- and postmenopausal women was analyzed.
Menopausal status and earlier age at menarche were associated with higher serum uric acid levels (age-adjusted: p-values 0.003, <0.001 respectively; after multivariable adjustment, including BMI: p-values 0.002, 0.036). A history of oral contraceptive use showed an association with uric acid levels only after multivariable adjustment (p-value 0.009). Hot flushes showed an association with uric acid levels only after age-adjustment (p-value 0.038), but lost significance after adding other confounders. Other reproductive factors, including parity, current or ever use of hormone replacement therapy, current use of oral contraceptives, hysterectomy, bilateral oophorectomy, or depressive mood related to menopausal transition were not associated with uric acid levels.
Postmenopausal status, earlier age at menarche and a history of oral contraceptive use were independently associated with higher serum uric acid concentrations in women from the general population. Further studies, especially longitudinal population-based studies investigating the relationship of female reproductive parameters with uric acid levels are necessary to confirm our findings
Trace Anomaly and Quasi-Particles in Finite Temperature SU(N) Gauge Theory
We consider deconfined matter in SU(N) gauge theory as an ideal gas of
transversely polarized quasi-particle modes having a temperature-dependent mass
m(T). Just above the transition temperature, the mass is assumed to be
determined by the critical behavior of the energy density and the screening
length in the medium. At high temperature, it becomes proportional to T as the
only remaining scale. The resulting (trace anomaly based) interaction measure
Delta=(e - 3P)/T^4 and energy density are found to agree well with finite
temperature SU(3) lattice calculations.Comment: 13 pages, 13 figures; references added for version
Continuity, Deconfinement, and (Super) Yang-Mills Theory
We study the phase diagram of SU(2) Yang-Mills theory with one adjoint Weyl
fermion on R^3xS^1 as a function of the fermion mass m and the compactification
scale L. This theory reduces to thermal pure gauge theory as m->infinity and to
circle-compactified (non-thermal) supersymmetric gluodynamics in the limit
m->0. In the m-L plane, there is a line of center symmetry changing phase
transitions. In the limit m->infinity, this transition takes place at
L_c=1/T_c, where T_c is the critical temperature of the deconfinement
transition in pure Yang-Mills theory. We show that near m=0, the critical
compactification scale L_c can be computed using semi-classical methods and
that the transition is of second order. This suggests that the deconfining
phase transition in pure Yang-Mills theory is continuously connected to a
transition that can be studied at weak coupling. The center symmetry changing
phase transition arises from the competition of perturbative contributions and
monopole-instantons that destabilize the center, and topological molecules
(neutral bions) that stabilize the center. The contribution of molecules can be
computed using supersymmetry in the limit m=0, and via the
Bogomolnyi--Zinn-Justin (BZJ) prescription in the non-supersymmetric gauge
theory. Finally, we also give a detailed discussion of an issue that has not
received proper attention in the context of N=1 theories---the non-cancellation
of nonzero-mode determinants around supersymmetric BPS and KK
monopole-instanton backgrounds on R^3xS^1. We explain why the non-cancellation
is required for consistency with holomorphy and supersymmetry and perform an
explicit calculation of the one-loop determinant ratio.Comment: A discussion of the non-cancellation of the nonzero mode determinants
around supersymmetric monopole-instantons in N=1 SYM on R^3xS^1 is added,
including an explicit calculation. The non-cancellation is, in fact, required
by supersymmetry and holomorphy in order for the affine-Toda superpotential
to be reproduced. References have also been adde
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