881 research outputs found
Individual GRB sensitivity of a cubic-kilometer deep-sea neutrino telescope KM3NeT
Gamma-ray bursts (GRB) are powerful and highly variable sources of gamma rays
that indicate the existence of cosmic particle accelerators. Under the
assumption of hadronic acceleration in the jet, the expected neutrino energy
spectrum is derived according to the intrinsic fireball model parameters and to
the observed electromagnetic data of GRBs measured with ground-based and
satellite observations. Using the performance characteristics of a
cubic-kilometre scale neutrino detector placed in the Mediterranean Sea, the
number of events is calculated individually for all the GRBs having a known
redshift below the horizon of this detector. The good angular resolution of
this detector and the narrow time windows around the GRB detection time allow
suppression of almost all the atmospheric neutrino background. From the SWIFT
GRB catalogue, we have derived the mean characteristics of a burst in order to
be detected as an individual point source by a cubic-kilometre detector.Comment: 4 pages proceeding for the Very Large Volume Neutrino Telescopes
VLVNT 0
Mapping Self-Organized Criticality onto Criticality
We present a general conceptual framework for self-organized criticality
(SOC), based on the recognition that it is nothing but the expression,
''unfolded'' in a suitable parameter space, of an underlying {\em unstable}
dynamical critical point. More precisely, SOC is shown to result from the
tuning of the {\em order parameter} to a vanishingly small, but {\em positive}
value, thus ensuring that the corresponding control parameter lies exactly at
its critical value for the underlying transition. This clarifies the role and
nature of the {\em very slow driving rate} common to all systems exhibiting
SOC. This mechanism is shown to apply to models of sandpiles, earthquakes,
depinning, fractal growth and forest-fires, which have been proposed as
examples of SOC.Comment: 17 pages tota
Five-dimensional Superfield Supergravity
We present a projective superspace formulation for matter-coupled simple
supergravity in five dimensions. Our starting point is the superspace
realization for the minimal supergravity multiplet proposed by Howe in 1981. We
introduce various off-shell supermultiplets (i.e. hypermultiplets, tensor and
vector multiplets) that describe matter fields coupled to supergravity. A
projective-invariant action principle is given, and specific dynamical systems
are constructed including supersymmetric nonlinear sigma-models. We believe
that this approach can be extended to other supergravity theories with eight
supercharges in space-time dimensions, including the important case
of 4D N=2 supergravity.Comment: 18 pages, LaTeX; v2: comments added; v3: minor changes, references
added; v4: comments, reference added, version to appear in PL
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