8,138 research outputs found
XMM-Newton observation of the double pulsar system J0737-3039
We report on a 50 ksec XMM-Newton observation of the double pulsar system
J0737-3039 performed on April 2004. We present results of the spectral analysis
of these data combined with the much shorter Chandra pointing performed on
January 2004. Black body emission with effective temperature of
0.20^{+0.02}_{-0.02} keV (90% confidence level) and emission radius
75^{+30}_{-9} m for a distance of 0.5 kpc (implying a 0.5-10 keV luminosity
\~6x10^{29} erg/s) is a viable interpretation, calling for a stream of
particles accelerated in the magnetosphere of PSR J0737-3039A and depositing
their kinetic energy in the magnetic polar cap of PSR J0737-3039A or of the
companion PSR J0737-3039B. A single power-law emission model implies a very
steep photon index Gamma=4.2^{+2.1}_{-1.2} and a suspiciously high hydrogen
column density, whereas a photon index Gamma=2 does not provide an adequate
description of the XMM-Newton and Chandra data. A two component model (a black
body plus a power-law with Gamma=2) is statistically acceptable, but the
additional power-law component is not required by the data.Comment: Accepted for publication on ApJ
Lepton Flavour Violation in a Left-Right Symmetric Model
We consider in this paper a Left-Right symmetric gauge model in which a
global lepton-number-like symmetry is introduced and broken spontaneously at a
scale that could be as low as 10^4 GeV or so. The corresponding physical
Nambu-Goldstone boson, which we call majoron and denote J, can have tree-level
flavour-violating couplings to the charged fermions, leading to sizeable
majoron-emitting lepton-flavour-violating weak decays. We consider explicitly a
leptonic variant of the model and show that the branching ratios for \mu ->
e+J, \tau -> e + J and \tau -> \mu + J decays can be large enough to fall
within the sensitivities of future \mu and \tau factories. On the other hand
the left-right gauge symmetry breaking scale may be as low as few TeV.Comment: LaTeX, 16 pages, 3 PS figures, uses JHEP.cls, published versio
Pairing and polarization in systems with retarded interactions
In a system where a boson (e.g, a phonon) of finite frequency is
coupled to electrons, two phenomena occur as the coupling is increased:
electron pairing and polarization of the boson field. Within a path integral
formalism and a Dynamical Mean-Field approach, we introduce {\it ad hoc}
distribution function which allow us to pinpoint the two effects. When
is smaller than the bandwidth , pairing and polarization occur
for fairly similar couplings for all considered temperatures. When , the two phenomena tend to coincide only for , but are no
longer tied for low temperatures so that a state of paired particles without
finite polarization is stabilized.Comment: 4 pages, 2 figure
Direct calculation of the critical Casimir force in a binary fluid
We show that critical Casimir effects can be accessed through direct
simulation of a model binary fluid passing through the demixing transition. We
work in the semi grand canonical ensemble, in slab geometry, in which the
Casimir force appears as the excess of the generalized pressure,
. The excesses of the perpendicular pressure, , and of
, are individually of much larger amplitude. A critical pressure
anisotropy is observed between forces parallel and perpendicular to the
confinement direction, which collapses onto a universal scaling function
closely related to that of the critical Casimir force
Quantum scalar field in D-dimensional static black hole space-times
An Euclidean approach for investigating quantum aspects of a scalar field
living on a class of D-dimensional static black hole space-times, including the
extremal ones, is reviewed. The method makes use of a near horizon
approximation of the metric and -function formalism for evaluating the
partition function and the expectation value of the field fluctuations
. After a review of the non-extreme black hole case, the extreme
one is considered in some details. In this case, there is no conical
singularity, but the finite imaginary time compactification introduces a cusp
singularity. It is found that the -function regularized partition
function can be defined, and the quantum fluctuations are finite on the
horizon, as soon as the cusp singularity is absent, and the corresponding
temperature is T=0.Comment: 9 pages, LaTe
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