3,340 research outputs found
The transition temperature of the dilute interacting Bose gas for internal degrees of freedom
We calculate explicitly the variation of the Bose-Einstein
condensation temperature induced by weak repulsive two-body interactions
to leading order in the interaction strength. As shown earlier by general
arguments, is linear in the dimensionless product
to leading order, where is the density and the scattering length. This
result is non-perturbative, and a direct perturbative calculation of the
amplitude is impossible due to infrared divergences familiar from the study of
the superfluid helium lambda transition. Therefore we introduce here another
standard expansion scheme, generalizing the initial model which depends on one
complex field to one depending on real fields, and calculating the
temperature shift at leading order for large . The result is explicit and
finite. The reliability of the result depends on the relevance of the large
expansion to the situation N=2, which can in principle be checked by systematic
higher order calculations. The large result agrees remarkably well with
recent numerical simulations.Comment: 10 pages, Revtex, submitted to Europhysics Letter
Background gauge invariance in the antifield formalism for theories with open gauge algebras
We show that any BRST invariant quantum action with open or closed gauge
algebra has a corresponding local background gauge invariance. If the BRST
symmetry is anomalous, but the anomaly can be removed in the antifield
formalism, then the effective action possesses a local background gauge
invariance. The presence of antifields (BRST sources) is necessary. As an
example we analyze chiral gravity.Comment: 17pp., Latex, mispelling in my name! corrected, no other change
Breakdown of the perturbative renormalization group at certain quantum critical points
It is shown that the presence of multiple time scales at a quantum critical
point can lead to a breakdown of the loop expansion for critical exponents,
since coefficients in the expansion diverge. Consequently, results obtained
from finite-order perturbative renormalization-group treatments may be not be
an approximation in any sense to the true asymptotic critical behavior. This
problem manifests itself as a non-renormalizable field theory, or,
equivalently, as the presence of a dangerous irrelevant variable. The quantum
ferromagnetic transition in disordered metals provides an example.Comment: 4pp, 1 eps fi
Batalin-Vilkovisky Integrals in Finite Dimensions
The Batalin-Vilkovisky method (BV) is the most powerful method to analyze
functional integrals with (infinite-dimensional) gauge symmetries presently
known. It has been invented to fix gauges associated with symmetries that do
not close off-shell. Homological Perturbation Theory is introduced and used to
develop the integration theory behind BV and to describe the BV quantization of
a Lagrangian system with symmetries. Localization (illustrated in terms of
Duistermaat-Heckman localization) as well as anomalous symmetries are discussed
in the framework of BV.Comment: 35 page
String Picture of a Frustrated Quantum Magnet and Dimer Model
We map a geometrically frustrated Ising system with transversal field
generated quantum dynamics to a strongly anisotropic lattice of non-crossing
elastic strings. The combined effect of frustration, quantum and thermal spin
fluctuations is explained in terms of a competition between intrinsic lattice
pinning of strings and topological defects in the lattice. From this picture we
obtain analytic results for correlations and the phase diagram which agree
nicely with recent simulations.Comment: 4 pages, 2 figure
The arctic curve of the domain-wall six-vertex model in its anti-ferroelectric regime
An explicit expression for the spatial curve separating the region of
ferroelectric order (`frozen' zone) from the disordered one (`temperate' zone)
in the six-vertex model with domain wall boundary conditions in its
anti-ferroelectric regime is obtained.Comment: 12 pages, 1 figur
Perturbative analysis of the gradient flow in non-abelian gauge theories
The gradient flow in non-abelian gauge theories on R^4 is defined by a local
diffusion equation that evolves the gauge field as a function of the flow time
in a gauge-covariant manner. Similarly to the case of the Langevin equation,
the correlation functions of the time-dependent field can be expanded in
perturbation theory, the Feynman rules being those of a renormalizable field
theory on R^4 x [0,oo). For any matter multiplet and to all loop orders, we
show that the correlation functions are finite, i.e. do not require additional
renormalization, once the theory in four dimensions is renormalized in the
usual way. The flow thus maps the gauge field to a one-parameter family of
smooth renormalized fields.Comment: Plain TeX source, 28 pages, 14 figures; v2: typos corrected, agrees
with published versio
Localisation and mass generation for non-Abelian gauge fields
It has been suggested recently that in the presence of suitably "warped"
extra dimensions, the low-energy limit of pure gauge field theory may contain
massive elementary vector bosons localised on a "brane", but no elementary
Higgs scalars. We provide non-perturbative evidence in favour of this
conjecture through numerical lattice measurements of the static quark-antiquark
force of pure SU(2) gauge theory in three dimensions, of which one is warped.
We consider also warpings leading to massless localised vector bosons, and
again find evidence supporting the perturbative prediction, even though the
gauge coupling diverges far from the brane in this case.Comment: 27 pages; small clarifications adde
Seiberg-Witten maps and noncommutative Yang-Mills theories for arbitrary gauge groups
Seiberg-Witten maps and a recently proposed construction of noncommutative
Yang-Mills theories (with matter fields) for arbitrary gauge groups are
reformulated so that their existence to all orders is manifest. The ambiguities
of the construction which originate from the freedom in the Seiberg-Witten map
are discussed with regard to the question whether they can lead to inequivalent
models, i.e., models not related by field redefinitions.Comment: 12 pages; references added, minor misprints correcte
The Rapidly Rotating, Hydrogen Deficient, Hot Post-Asymptotic Giant Branch Star ZNG 1 in the Globular Cluster M5
We report observations of the hot post-asymptotic giant branch star ZNG 1 in
the globular cluster M5 (NGC 5904) with the Far Ultraviolet Spectroscopic
Explorer (FUSE). From the resulting spectrum, we derive an effective
temperature T_eff = 44300 +/- 300 K, a surface gravity log g = 4.3 +/- 0.1, a
rotational velocity v sin i = 170 +/- 20 km/s, and a luminosity log (L/L_sun) =
3.52 +/- 0.04. The atmosphere is helium-rich (Y = 0.93), with enhanced carbon
(2.6% by mass), nitrogen (0.51%) and oxygen (0.37%) abundances. The spectrum
shows evidence for a wind with terminal velocity near 1000 km/s and an
expanding shell of carbon- and nitrogen-rich material around the star. The
abundance pattern of ZNG 1 is suggestive of the ``born-again'' scenario,
whereby a star on the white-dwarf cooling curve undergoes a very late shell
flash and returns to the AGB, but the star's rapid rotation is more easily
explained by a previous interaction with a binary companion.Comment: 8 pages, 2 PostScript figures, Latex with emulateapj5. Accepted for
publication in ApJ Letter
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