132 research outputs found
Phase Structure of the 5D Abelian Higgs Model with Anisotropic Couplings
We establish the phase diagram of the five-dimensional anisotropic Abelian
Higgs model by mean field techniques and Monte Carlo simulations. The
anisotropy is encoded in the gauge couplings as well as in the Higgs couplings.
In addition to the usual bulk phases (confining, Coulomb and Higgs) we find
four-dimensional ``layered'' phases (3-branes) at weak gauge coupling, where
the layers may be in either the Coulomb or the Higgs phase, while the
transverse directions are confining.Comment: LaTeX (amssymb.sty and psfig) 21 pages, 17 figure
Finite temperature Z(N) phase transition with Kaluza-Klein gauge fields
If SU(N) gauge fields live in a world with a circular extra dimension,
coupling there only to adjointly charged matter, the system possesses a global
Z(N) symmetry. If the radius is small enough such that dimensional reduction
takes place, this symmetry is spontaneously broken. It turns out that its fate
at high temperatures is not easily decided with straightforward perturbation
theory. Utilising non-perturbative lattice simulations, we demonstrate here
that the symmetry does get restored at a certain temperature T_c, both for a
3+1 and a 4+1 dimensional world (the latter with a finite cutoff). To avoid a
cosmological domain wall problem, such models would thus be allowed only if the
reheating temperature after inflation is below T_c. We also comment on the
robustness of this phenomenon with respect to small modifications of the model.Comment: 18 pages. Revised version, to appear in Nucl.Phys.
Properties of the deconfining phase transition in SU(N) gauge theories
We extend our earlier investigation of the finite temperature deconfinement
transition in SU(N) gauge theories, with the emphasis on what happens as N->oo.
We calculate the latent heat in the continuum limit, and find the expected
quadratic in N behaviour at large N. We confirm that the phase transition,
which is second order for SU(2) and weakly first order for SU(3), becomes
robustly first order for N>3 and strengthens as N increases. As an aside, we
explain why the SU(2) specific heat shows no sign of any peak as T is varied
across what is supposedly a second order phase transition. We calculate the
effective string tension and electric gluon masses at T=Tc confirming the
discontinuous nature of the transition for N>2. We explicitly show that the
large-N `spatial' string tension does not vary with T for T<Tc and that it is
discontinuous at T=Tc. For T>Tc it increases as T-squared to a good
approximation, and the k-string tension ratios closely satisfy Casimir Scaling.
Within very small errors, we find a single Tc at which all the k-strings
deconfine, i.e. a step-by-step breaking of the relevant centre symmetry does
not occur. We calculate the interface tension but are unable to distinguish
between linear or quadratic in N variations, each of which can lead to a
striking but different N=oo deconfinement scenario. We remark on the location
of the bulk phase transition, which bounds the range of our large-N
calculations on the strong coupling side, and within whose hysteresis some of
our larger-N calculations are performed.Comment: 50 pages, 14 figure
Domain walls and perturbation theory in high temperature gauge theory: SU(2) in 2+1 dimensions
We study the detailed properties of Z_2 domain walls in the deconfined high
temperature phase of the d=2+1 SU(2) gauge theory. These walls are studied both
by computer simulations of the lattice theory and by one-loop perturbative
calculations. The latter are carried out both in the continuum and on the
lattice. We find that leading order perturbation theory reproduces the detailed
properties of these domain walls remarkably accurately even at temperatures
where the effective dimensionless expansion parameter, g^2/T, is close to
unity. The quantities studied include the surface tension, the action density
profiles, roughening and the electric screening mass. It is only for the last
quantity that we find an exception to the precocious success of perturbation
theory. All this shows that, despite the presence of infrared divergences at
higher orders, high-T perturbation theory can be an accurate calculational
tool.Comment: 75 pages, LaTeX, 14 figure
Phase of the Wilson Line at High Temperature in the Standard Model
We compute the effective potential for the phase of the Wilson line at high
temperature in the standard model to one loop order. Besides the trivial vacua,
there are metastable states in the direction of hypercharge. Assuming
that the universe starts out in such a metastable state at the Planck scale, it
easily persists to the time of the electroweak phase transition, which then
proceeds by an unusual mechanism. All remnants of the metastable state
evaporate about the time of the phase transition.Comment: 4 pages in ReVTeX plus 1 figure; Columbia Univ. preprint CU-TP-63
Perturbative analysis for Kaplan's lattice chiral fermions
Perturbation theory for lattice fermions with domain wall mass terms is
developed and is applied to investigate the chiral Schwinger model formulated
on the lattice by Kaplan's method. We calculate the effective action for gauge
fields to one loop, and find that it contains a longitudinal component even for
anomaly-free cases. From the effective action we obtain gauge anomalies and
Chern-Simons current without ambiguity. We also show that the current
corresponding to the fermion number has a non-zero divergence and it flows off
the wall into the extra dimension. Similar results are obtained for a proposal
by Shamir, who used a constant mass term with free boundaries instead of domain
walls.Comment: 25 page, 5 PostScript figures, [some changes in the conclusion
A Planck-scale axion and SU(2) Yang-Mills dynamics: Present acceleration and the fate of the photon
From the time of CMB decoupling onwards we investigate cosmological evolution
subject to a strongly interacting SU(2) gauge theory of Yang-Mills scale
eV (masquerading as the factor of the SM at
present). The viability of this postulate is discussed in view of cosmological
and (astro)particle physics bounds. The gauge theory is coupled to a spatially
homogeneous and ultra-light (Planck-scale) axion field. As first pointed out by
Frieman et al., such an axion is a viable candidate for quintessence, i.e.
dynamical dark energy, being associated with today's cosmological acceleration.
A prediction of an upper limit for the duration of the
epoch stretching from the present to the point where the photon starts to be
Meissner massive is obtained: billion years.Comment: v3: consequences of an error in evolution equation for coupling
rectified, only a minimal change in physics results, two refs. adde
Two-color QCD via dimensional reduction
We study the thermodynamics of two-color QCD at high temperature and/or
density using a dimensionally reduced superrenormalizable effective theory,
formulated in terms of a coarse grained Wilson line. In the absence of quarks,
the theory is required to respect the Z(2) center symmetry, while the effects
of quarks of arbitrary masses and chemical potentials are introduced via soft
Z(2) breaking operators. Perturbative matching of the effective theory
parameters to the full theory is carried out explicitly, and it is argued how
the new theory can be used to explore the phase diagram of two-color QCD.Comment: 17 pages, 1 eps figure, jheppub style; v2: minor update, references
added, published versio
Mesonic correlation lengths in high-temperature QCD
We consider spatial correlation lengths \xi for various QCD light quark
bilinears at temperatures above a few hundred MeV. Some of the correlation
lengths (such as that related to baryon density) coincide with what has been
measured earlier on from glueball-like states; others do not couple to
glueballs, and have a well-known perturbative leading-order expression as well
as a computable next-to-leading-order correction. We determine the latter
following analogies with the NRQCD effective theory, used for the study of
heavy quarkonia at zero temperature: we find (for the quenched case) \xi^{-1} =
2 \pi T + 0.1408 g^2 T, and compare with lattice results. One manifestation of
U_A(1) symmetry non-restoration is also pointed out.Comment: 25 pages. v2: small clarifications; published versio
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