22,021 research outputs found
The true redshift distribution of Pre-SWIFT gamma-ray bursts
SWIFT bursts appear to be more distant than previous bursts. We present the
Boer & Gendre relation that link redshift and afterglow luminosities. Taking
advantage of the XMM-Newton, Chandra and BeppoSAX catalogs, and using this
relation, we have investigated the redshift distribution of GRBs. We find that
XMM burst sources with unknown redshift appear to be more distant than those
with a known redshift. We propose that this effect may be due to a selection
effect of pre-SWIFT optical observations.Comment: Proceedings of the "Gamma Ray Bursts in the Swift Era" conference, 6
pages, 5 color figure
Conformal Field Theories: From Old to New
In a short review of recent work, we discuss the general problem of
constructing the actions of new conformal field theories from old conformal
field theories. Such a construction follows when the old conformal field theory
admits new conformal stress tensors in its chiral algebra, and it turns out
that the new conformal field theory is generically a new spin-two gauge theory.
As an example we discuss the new spin-two gauged sigma models which arise in
this fashion from the general conformal non-linear sigma model.Comment: 7 pages, LaTeX, to appear in a memorial issue of Theoretical and
Mathematical Physics in memory of F.A. Lune
Indirect Dark Matter Signals from EGRET and PAMELA compared
Dark Matter annihilation (DMA) may yield an excess of gamma rays and
antimatter particles, like antiprotons and positrons, above the background from
cosmic ray interactions. The excess of diffuse Galactic Gamma Rays from EGRET
shows all the features expected from DMA. The new precise measurements of the
antiproton and positron fractions from PAMELA are compared with the EGRET
excess. It is shown that the charged particles are strongly dependent on the
propagation model used. The usual propagation models with isotropic propagation
models are incompatible with the recently observed convection in our Galaxy.
Convection leads to an order of magnitude uncertainty in the yield of charged
particles from DMA, since even a rather small convection will let drift the
charged particles in the halo to outer space. It is shown that such anisotropic
propagation models including convection prefer a contribution from DMA for the
antiprotons, but the rise in the positron fraction, as observed by PAMELA, is
incompatible with DMA, if compared with the EGRET excess. A rise in the
positron/electron ratio is expected, if the observed rise in the
proton/electron ratio is carefully fitted in a propagation model, although the
rise is slightly larger than expected, so additional local sources may
contribute as well within the limited accuracy of the data.Comment: 10 pages, 4 figures, Contributed paper to the Eighth UCLA Symposium:
Sources and Detection of Dark Matter and Dark Energy in the Univers
The luminosity of GRB afterglows as distance estimator
We investigate the clustering of afterglow light curves observed at X-ray and
optical wavelengths. We have constructed a sample of 61 bursts with known
distance and X-ray afterglow. GRB sources can be divided in three classes,
namely optical and X-ray bright afterglows, optical and X-ray dim one s, and
optically bright -X-ray dim ones. We argue that this clustering is related to
the fireball total energy, the external medium density, the fraction of
fireball energy going in relativistic electrons and magnetic fields. We propose
a method for the estimation of the GRB source redshift based on the observe d
X-ray flux one day after the burst and optical properties. We tested this
method on three recently detected SWIFT GRBs with known redshift, and found it
i n good agreement with the reported distance from optical spectroscopy.Comment: 6 pages, proceeding of the PCHE session at the Journees de la SF2
Unification of the General Non-Linear Sigma Model and the Virasoro Master Equation
The Virasoro master equation describes a large set of conformal field
theories known as the affine-Virasoro constructions, in the operator algebra
(affine Lie algebra) of the WZW model, while the Einstein equations of the
general non-linear sigma model describe another large set of conformal field
theories. This talk summarizes recent work which unifies these two sets of
conformal field theories, together with a presumable large class of new
conformal field theories. The basic idea is to consider spin-two operators of
the form in the background of a general
sigma model. The requirement that these operators satisfy the Virasoro algebra
leads to a set of equations called the unified Einstein-Virasoro master
equation, in which the spin-two spacetime field couples to the usual
spacetime fields of the sigma model. The one-loop form of this unified system
is presented, and some of its algebraic and geometric properties are discussed.Comment: 18 pages, Latex. Talk presented by MBH at the NATO Workshop `New
Developments in Quantum Field Theory', June 14-20, 1997, Zakopane, Polan
Unified Einstein-Virasoro Master Equation in the General Non-Linear Sigma Model
The Virasoro master equation (VME) describes the general affine-Virasoro
construction T=L^{ab}J_aJ_b+iD^a \dif J_a in the operator algebra of the WZW
model, where is the inverse inertia tensor and is the
improvement vector. In this paper, we generalize this construction to find the
general (one-loop) Virasoro construction in the operator algebra of the general
non-linear sigma model. The result is a unified Einstein-Virasoro master
equation which couples the spacetime spin-two field to the background
fields of the sigma model. For a particular solution , the unified
system reduces to the canonical stress tensors and conventional Einstein
equations of the sigma model, and the system reduces to the general
affine-Virasoro construction and the VME when the sigma model is taken to be
the WZW action. More generally, the unified system describes a space of
conformal field theories which is presumably much larger than the sum of the
general affine-Virasoro construction and the sigma model with its canonical
stress tensors. We also discuss a number of algebraic and geometrical
properties of the system, including its relation to an unsolved problem in the
theory of -structures on manifolds with torsion.Comment: LaTeX, 55 pages, one postscript figure, uses epsfig.sty. contains a
few minor corrections; version to be published in Int. J. Mod. Phys.
The orbifold-string theories of permutation-type: II. Cycle dynamics and target space-time dimensions
We continue our discussion of the general bosonic prototype of the new
orbifold-string theories of permutation type. Supplementing the extended
physical-state conditions of the previous paper, we construct here the extended
Virasoro generators with cycle central charge
, where is the length of cycle
in twisted sector . We also find an equivalent, reduced formulation
of each physical-state problem at reduced cycle central charge
. These tools are used to begin the study of the target
space-time dimension of cycle in sector , which
is naturally defined as the number of zero modes (momenta) of each cycle. The
general model-dependent formulae derived here will be used extensively in
succeeding papers, but are evaluated in this paper only for the simplest case
of the "pure" permutation orbifolds.Comment: 32 page
The Orbifold-String Theories of Permutation-Type: III. Lorentzian and Euclidean Space-Times in a Large Example
To illustrate the general results of the previous paper, we discuss here a
large concrete example of the orbifold-string theories of permutation-type. For
each of the many subexamples, we focus on evaluation of the \emph{target
space-time dimension} , the \emph{target space-time
signature} and the \emph{target space-time symmetry} of each cycle in each
twisted sector . We find in particular a gratifying \emph{space-time
symmetry enhancement} which naturally matches the space-time symmetry of each
cycle to its space-time dimension. Although the orbifolds of
-permutation-type are naturally Lorentzian, we find that the target
space-times associated to larger permutation groups can be Lorentzian,
Euclidean and even null (\hat{D}_{j}(\sigma)=0), with varying space-time
dimensions, signature and symmetry in a single orbifold.Comment: 36 page
Evidence for a dual population of neutron star mergers from short Gamma-Ray Burst observations
Short duration Gamma-Ray Bursts are thought to originate from the coalescence
of neutron stars in binary systems. They are detected as a brief ( 2s),
intense flash of gamma-ray radiation followed by a weaker, rapidly decreasing
afterglow. They are expected to be detected by Advanced LIGO and Virgo when
their sensitivity will be low enough. In a recent study we identified a
population of short Gamma-Ray Bursts that are intrinsically faint and nearby.
Here we provide evidence in favor of the existence of this new population that
can hardly be reproduced with a model of field neutron star binary
coalescences. We propose that these systems may be produced dynamically in
globular clusters, and may result from the merger of a black hole and a neutron
star. The advanced LIGO and Virgo observation of a high rate of NSBH mergers
compatible with the dynamical formation in globular clusters would be a
confirmation of this hypothesis and would enable for the derivation of the mass
function of black holes inside globular clusters, as well as the luminosity
function of faint short GRBs.Comment: 15 pages, 5 figures, 1 table, submitted to Ap
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