386 research outputs found
Instantons from Low Energy String Actions
We look for instanton solutions in a class of two scalar field gravity
models, which includes the low energy string action in four dimensions. In
models where the matter field has a potential with a false vacuum, we find that
non-singular instantons exist as long as the Dilaton field found in string
theory has a potential with a minimum, and provide an example of such an
instanton. The class of singular instanton solutions are also examined, and we
find that depending on the parameter values, the volume factor of the Euclidean
region does not always vanish fast enough at the singularity to make the action
finite.Comment: revtex 6 pages with 3 figures. Minor numerical correction mad
Penicillin allergy labels drive perioperative prophylactic antibiotic selection in orthopedic procedures
'Clinical Communications'
[No abstract
Readiness for PENicillin allergy testing: Perception of Allergy Label (PEN-PAL) Survey
Clinical Implications: Patients reporting penicillin allergy believe their allergy to be permanent, would take penicillins if tested negative, but are rarely referred for penicillin testing, leading to differential antibiotic utilization
Derivative expansion and gauge independence of the false vacuum decay rate in various gauges
In theories with radiative symmetry breaking, the calculation of the false
vacuum decay rate requires the inclusion of higher-order terms in the
derivative expansion of the effective action. I show here that, in the case of
covariant gauges, the presence of infrared singularities forbids the consistent
calculation by keeping the lowest-order terms. The situation is remedied,
however, in the case of gauges. Using the Nielsen identities I show
that the final result is gauge independent for generic values of the gauge
parameter that are not anomalously small.Comment: Some comments and references adde
Vortex-Antivortex Pair Production in a First Order Phase Transition
We carry out numerical simulation of a first order phase transition in 2+1
dimensions by randomly nucleating bubbles, and study the formation of global
U(1) vortices. Bubbles grow and coalesce and vortices are formed at junctions
of bubbles via standard Kibble mechanism as well as due to a new mechanism,
recently proposed by us, where defect-antidefect pairs are produced due to
field oscillations. We make a comparative study of the contribution of both of
these mechanisms for vortex production. We find that, for high nucleation rate
of bubbles, vortex-antivortex pairs produced via the new mechanism have
overlapping configurations, and annihilate quickly; so only those vortices
survive till late which are produced via the Kibble mechanism. However, for low
nucleation rates, bubble collisions are energetic enough to lead to many well
separated vortex-antivortex pairs being produced via the new mechanism. For
example, in a simulation involving nucleation of 20 bubbles, a total of 14
non-overlapping vortices and antivortices formed via this new mechanism of pair
creation (6 of them being very well separated), as compared to 6 vortices and
antivortices produced via the Kibble mechanism. Our results show the
possibility that in extremely energetic bubble collisions, such as those in the
inflationary models of the early Universe, this new mechanism may drastically
affect the defect production scenario.Comment: 8 pages, Revtex, 14 figures. Figs.1a,b and 5a,d are included, rest
are availaible on reques
Monopoles, noncommutative gauge theories in the BPS limit and some simple gauge groups
For three conspicuous gauge groups, namely, SU(2), SU(3) and SO(5), and at
first order in the noncommutative parameter matrix h\theta^{\mu\nu}, we
construct smooth monopole --and, some two-monopole-- fields that solve the
noncommutative Yang-Mills-Higgs equations in the BPS limit and that are formal
power series in h\theta^{\mu\nu}. We show that there exist noncommutative BPS
(multi-)monopole field configurations that are formal power series in
h\theta^{\mu\nu} if, and only if, two a priori free parameters of the
Seiberg-Witten map take very specific values. These parameters, that are not
associated to field redefinitions nor to gauge transformations, have thus
values that give rise to sharp physical effects.Comment: 30 pages, no figure
Gauge independence of the bubble nucleation rate in theories with radiative symmetry breaking
In field theories where a metastable false vacuum state arises as a result of
radiative corrections, the calculation of the rate of false vacuum decay by
bubble nucleation depends on the effective potential and the other functions
that appear in the derivative expansion of the effective action. Beginning with
the Nielsen identity, we derive a series of identities that govern the gauge
dependence of these functions. Using these, we show, to leading nontrivial
order, that even though these functions are individually gauge-dependent, one
obtains a gauge-independent result for the bubble nucleation rate. Our formal
arguments are complemented by explicit calculations for scalar electrodynamics
in a class of gauges.Comment: 19 pages, 3 figures in uuencoded fil
Magnetism in Dense Quark Matter
We review the mechanisms via which an external magnetic field can affect the
ground state of cold and dense quark matter. In the absence of a magnetic
field, at asymptotically high densities, cold quark matter is in the
Color-Flavor-Locked (CFL) phase of color superconductivity characterized by
three scales: the superconducting gap, the gluon Meissner mass, and the
baryonic chemical potential. When an applied magnetic field becomes comparable
with each of these scales, new phases and/or condensates may emerge. They
include the magnetic CFL (MCFL) phase that becomes relevant for fields of the
order of the gap scale; the paramagnetic CFL, important when the field is of
the order of the Meissner mass, and a spin-one condensate associated to the
magnetic moment of the Cooper pairs, significant at fields of the order of the
chemical potential. We discuss the equation of state (EoS) of MCFL matter for a
large range of field values and consider possible applications of the magnetic
effects on dense quark matter to the astrophysics of compact stars.Comment: To appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
Long-lived oscillons from asymmetric bubbles
The possibility that extremely long-lived, time-dependent, and localized
field configurations (``oscillons'') arise during the collapse of asymmetrical
bubbles in 2+1 dimensional phi^4 models is investigated. It is found that
oscillons can develop from a large spectrum of elliptically deformed bubbles.
Moreover, we provide numerical evidence that such oscillons are: a) circularly
symmetric; and b) linearly stable against small arbitrary radial and angular
perturbations. The latter is based on a dynamical approach designed to
investigate the stability of nonintegrable time-dependent configurations that
is capable of probing slowly-growing instabilities not seen through the usual
``spectral'' method.Comment: RevTeX 4, 9 pages, 11 figures. Revised version with a new approach to
stability. Accepted to Phys. Rev.
The Path-Integral Approach to the N=2 Linear Sigma Model
In QFT the effective potential is an important tool to study symmetry
breaking phenomena. It is known that, in some theories, the canonical approach
and the path-integral approach yield different effective potentials. In this
paper we investigate this for the Euclidean N=2 linear sigma model. Both the
Green's functions and the effective potential will be computed in three
different ways. The relative merits of the various approaches are discussed.Comment: 2 figure
- …