6,452 research outputs found
SN/GRB connection: a statistical approach with BATSE and Asiago Catalogues
Recent observations suggest that some types of GRB are physically connected
with SNe of type Ib/c. However, it has been pointed out by several authors that
some GRBs could be associated also with other types of core-collapse SNe (type
IIdw/IIn). On the basis of a comphrensive statistical study, which has made use
of the BATSE and Asiago catalogues, we have found that: i) the temporal and
spacial distribution of SNe-Ib/c is marginally correlated with that of the
BATSE GRBs; ii) we do not confirm the existence of an association between GRBs
and SNe-IIdw/IIn.Comment: Proceeding of the 4th workshop on Gamma Ray Bursts in the Afterglow
Era, Rome, 2004; 4 page
Relation Liftings on Preorders and Posets
The category Rel(Set) of sets and relations can be described as a category of
spans and as the Kleisli category for the powerset monad. A set-functor can be
lifted to a functor on Rel(Set) iff it preserves weak pullbacks. We show that
these results extend to the enriched setting, if we replace sets by posets or
preorders. Preservation of weak pullbacks becomes preservation of exact lax
squares. As an application we present Moss's coalgebraic over posets
Upper Limit on the Cosmic Gamma-Ray Burst Rate from High Energy Diffuse Neutrino Background
We derive upper limits on the ratio , the ratio of the
rate, , of long-duration Gamma Ray Bursts (GRBs) to the rate,
, of core-collapse supernovae (CCSNe) in the Universe ( being the
cosmological redshift and ), by using the upper limit on the
diffuse TeV--PeV neutrino background given by the AMANDA-II experiment in the
South Pole, under the assumption that GRBs are sources of TeV--PeV neutrinos
produced from decay of charged pions produced in interaction of
protons accelerated to ultrahigh energies at internal shocks within GRB jets.
For the assumed ``concordance model'' of cosmic star formation rate, ,
with , our conservative upper limits are
for , and for , for example. These limits are already
comparable to (and, for already more restrictive than) the
current upper limit on this ratio inferred from other astronomical
considerations, thus providing a useful independent probe of and constraint on
the CCSN-GRB connection. Non-detection of a diffuse TeV--PeV neutrino
background by the up-coming IceCube detector in the South pole after three
years of operation, for example, will bring down the upper limit on
to below few level, while a detection will
confirm the hypothesis of proton acceleration to ultrahigh energies in GRBs and
will potentially also yield the true rate of occurrence of these events in the
Universe.Comment: Two references added, an overall constant numerical factor corrected,
Figures and relevant portions of abstract and main text slightly changed,
main conclusions unchanged, 18 pages Latex with 4 Figures, version accepted
for publication in PR
Measurements of vacuum magnetic birefringence using permanent dipole magnets: the PVLAS experiment
The PVLAS collaboration is presently assembling a new apparatus (at the INFN
section of Ferrara, Italy) to detect vacuum magnetic birefringence (VMB). VMB
is related to the structure of the QED vacuum and is predicted by the
Euler-Heisenberg-Weisskopf effective Lagrangian. It can be detected by
measuring the ellipticity acquired by a linearly polarised light beam
propagating through a strong magnetic field. Using the very same optical
technique it is also possible to search for hypothetical low-mass particles
interacting with two photons, such as axion-like (ALP) or millicharged
particles (MCP). Here we report results of a scaled-down test setup and
describe the new PVLAS apparatus. This latter one is in construction and is
based on a high-sensitivity ellipsometer with a high-finesse Fabry-Perot cavity
() and two 0.8 m long 2.5 T rotating permanent dipole magnets.
Measurements with the test setup have improved by a factor 2 the previous upper
bound on the parameter , which determines the strength of the nonlinear
terms in the QED Lagrangian: T
95% c.l. Furthermore, new laboratory limits have been put on the inverse
coupling constant of ALPs to two photons and confirmation of previous limits on
the fractional charge of millicharged particles is given
The PVLAS experiment: measuring vacuum magnetic birefringence and dichroism with a birefringent Fabry-Perot cavity
Vacuum magnetic birefringence was predicted long time ago and is still
lacking a direct experimental confirmation. Several experimental efforts are
striving to reach this goal, and the sequence of results promises a success in
the next few years. This measurement generally is accompanied by the search for
hypothetical light particles that couple to two photons. The PVLAS experiment
employs a sensitive polarimeter based on a high finesse Fabry-Perot cavity. In
this paper we report on the latest experimental results of this experiment. The
data are analysed taking into account the intrinsic birefringence of the
dielectric mirrors of the cavity. Besides the limit on the vacuum magnetic
birefringence, the measurements also allow the model-independent exclusion of
new regions in the parameter space of axion-like and milli-charged particles.
In particular, these last limits hold also for all types of neutrinos,
resulting in a laboratory limit on their charge
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