581 research outputs found
Baryogenesis after Hyperextended Inflation
We study a baryogenesis mechanism operating in the context of hyperextended
inflation and making use of a coupling between the scalar field and a standard
model global current, such as B or B-L. The method is efficient at temperatures
at which these currents are not conserved due to some higher dimensional
operator. The particle physics and cosmological phenomenology are discussed. We
consider constraints stemming from nucleosynthesis and solar system
experiments.Comment: 7 pages, 1 figure, uses RevTe
Courant-like brackets and loop spaces
We study the algebra of local functionals equipped with a Poisson bracket. We
discuss the underlying algebraic structures related to a version of the
Courant-Dorfman algebra. As a main illustration, we consider the functionals
over the cotangent bundle of the superloop space over a smooth manifold. We
present a number of examples of the Courant-like brackets arising from this
analysis.Comment: 20 pages, the version published in JHE
Virasoro Symmetry of Constrained KP Hierarchies
Additional non-isospectral symmetries are formulated for the constrained
Kadomtsev-Petviashvili (\cKP) integrable hierarchies. The problem of
compatibility of additional symmetries with the underlying constraints is
solved explicitly for the Virasoro part of the additional symmetry through
appropriate modification of the standard additional-symmetry flows for the
general (unconstrained) KP hierarchy. We also discuss the special case of \cKP
--truncated KP hierarchies, obtained as Darboux-B\"{a}cklund orbits of initial
purely differential Lax operators. The latter give rise to Toda-lattice-like
structures relevant for discrete (multi-)matrix models. Our construction
establishes the condition for commutativity of the additional-symmetry flows
with the discrete Darboux-B\"{a}cklund transformations of \cKP hierarchies
leading to a new derivation of the string-equation constraint in matrix models.Comment: LaTeX, 11 pg
The Swift-BAT survey reveals the orbital period of three high-mass X-ray binaries
A growing number of previously hidden Galactic X-ray sources are now detected
with recent surveys performed by the Integral and Swift satellites. Most of
these new sources eluded past surveys due to their large local X-ray extinction
and consequent low soft X-ray flux. The Swift-BAT performs daily monitoring of
the sky in an energy band (15-150 keV) which is only marginally affected by
X-ray extinction, thus allowing for the search of long periodicities in the
light curve and identification of the nature of the X-ray sources. We performed
a period search using the folding technique in the Swift-BAT light curves of
three Integral sources: IGR J05007-7047, IGR J13186-6257 and IGR J17354-3255.
Their periodograms show significant peaks at 30.770.01 d, 19.9940.01
d and 8.4480.002 d, respectively. We estimate the significance of these
features from the chi squared distribution of all the trials, finding a
probability less than 1.5 that the detections occurred due to
chance. We complement our analysis with the study of their broadband X-ray
emission. We identify the periodicities with the orbital periods of the
sources. The periods are typical for the wind accretors X-ray binaries and we
support this identification showing that also their energy spectra are
compatible with an X-ray spectral emission characteristic of high-mass X-ray
binaries. The spectrum of IGR J05007-704 that resides in the Large Magellanic
Cloud, does not show any intrinsic local absorption, whereas the spectra of the
Galactic sources IGR J17354-3255 and IGR J13186-6257 may be affected by a local
absorber. The folded light curve for IGR J13186-6257 suggests a possible Be
companion star.Comment: 10 pages, 14 figures. Accepted for publication in A&
Detection of OH absorption against PSR B1849+00
We have searched for OH absorption against seven pulsars using the Arecibo
telescope. In both OH mainlines (at 1665 and 1667 MHz), deep and narrow
absorption features were detected toward PSR B1849+00. In addition, we have
detected several absorption and emission features against B33.6+0.1, a nearby
supernova remnant (SNR). The most interesting result of this study is that a
pencil-sharp absorption sample against the PSR differs greatly from the
large-angle absorption sample observed against the SNR. If both the PSR and the
SNR probe the same molecular cloud then this finding has important implications
for absorption studies of the molecular medium, as it shows that the statistics
of absorbing OH depends on the size of the background source. We also show that
the OH absorption against the PSR most likely originates from a small (<30
arcsec) and dense (>10^5 cm^-3) molecular clump.Comment: 12 pages, 8 figures. Accepted for publication in Ap
Vertex Operator Superalgebras and Odd Trace Functions
We begin by reviewing Zhu's theorem on modular invariance of trace functions
associated to a vertex operator algebra, as well as a generalisation by the
author to vertex operator superalgebras. This generalisation involves objects
that we call `odd trace functions'. We examine the case of the N=1
superconformal algebra. In particular we compute an odd trace function in two
different ways, and thereby obtain a new representation theoretic
interpretation of a well known classical identity due to Jacobi concerning the
Dedekind eta function.Comment: 13 pages, 0 figures. To appear in Conference Proceedings `Advances in
Lie Superalgebras
Lagrange Anchor for Bargmann-Wigner equations
A Poincare invariant Lagrange anchor is found for the non-Lagrangian
relativistic wave equations of Bargmann and Wigner describing free massless
fields of spin s > 1/2 in four-dimensional Minkowski space. By making use of
this Lagrange anchor, we assign a symmetry to each conservation law.Comment: A contribution to Proceedings of the XXXI Workshop on the Geometric
Methods in Physic
On the apparent absence of broad iron lines in Seyfert galaxies
We present an analysis of XMM-Newton observations of eleven Seyfert galaxies
that appear to be missing a broad iron K alpha line. These objects represent a
challenge to the established paradigm for active galactic nuclei, where a
relatively cold accretion disc feeds the central black hole. In that paradigm,
X-ray illumination of the accretion disc should lead to continuum and
fluorescence emission from iron which is broadened and shifted by relativistic
effects close the hole. We extend the work of Nandra et al. (2007), who found
no evidence for such a component in an earlier analysis of these objects, by
testing a variety of more complex relativistic reflection models. Specifically,
we consider the possibility that the disc is highly ionised, and/or that the
the reflection is heavily blurred by strong relativistic effects in a Kerr
geometry. We find that in 8/11 of the observations with no apparent broad iron
line, the fit is significantly improved when an ionised or strongly blurred
reflector is included, and that all 11 observations allow for such a component.
The disc inclinations are found generally to be around 60 degrees, which when
combined with a steep emissivity profile results in strong relativistic
blurring of the reflection, rendering the K alpha line difficult to distinguish
from the underlying continuum. Nevertheless, relativistic reflection does
appear to be present, and the strength of the smeared reflection is similar to
that expected from a flat disc illuminated by a point source. Such blurred
reflection and the associated steep radial emissivity profiles are consistent
with the gravitational light bending of the continuum photons close to the
black hole.Comment: 9 pages, 2 figures. Accepted for publication in MNRA
Multiple shifts and fractional integration in the us and uk unemployment rates
This paper analyses the long-run behaviour of the US and UK unemployment rates by testing for possibly fractional orders of integration and multiple shifts using a sample of over 100 annual observations. The results show that the orders of integration are higher than 0 in both series, which implies long memory. If we assume that the underlying disturbances are white noise, the values are higher than 0.5, i.e., nonstationary. However, if the disturbances are autocorrelated, the orders of integration are in the interval (0, 0.5), implying stationarity and mean-reverting behaviour. Moreover, when multiple shifts are taken into account, unemployment is more persistent in the US than in the UK, implying the need for stronger policy action in the former to bring unemployment back to its original level
Obscuring clouds playing hide-and-seek in the Active Nucleus H0557-385
This paper reports on two XMM-Newton observations of the Seyfert 1 Galaxy
H0557-385 obtained in 2006, which show the source at an historical low flux
state, more than a factor of 10 lower than a previous XMM-Newton look in 2002.
The low flux spectrum presents a strong Fe Kalpha line associated to a Compton
reflection continuum. An additional spectral line around 6.6 keV is required to
fit Kalpha emission from Fe XXV. The spectral curvature below 6 keV implies
obscuration by neutral gas with a column density of 8*10^{23}cm^{-2} partially
covering the primary emission, which still contributes for a few percent of the
soft X-ray emission. Absorption by ionised material on the line of sight is
required to fit the deep trough below 1 keV. The comparison of the two spectral
states shows that the flux transition is to be ascribed entirely to intervening
line-of-sight clouds with high column density.Comment: 5 pages, accepted for publication on MNRAS Letter
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