74,162 research outputs found
Dark matter and neutrino masses in the R-parity violating NMSSM
The R-Parity symmetry Violating (RPV) version of the Next-to-Minimal
Supersymmetric Standard Model (NMSSM) is attractive simultaneously with regard
to the so-called mu-problem and the accommodation of three-flavor neutrino data
at tree level. In this context, we show here that if the Lightest
Supersymmetric Particle (LSP) is the gravitino, it possesses a lifetime larger
than the age of the universe since its RPV induced decay channels are
suppressed by the weak gravitational strength. This conclusion holds if one
considers gravitino masses ~ 10^2 GeV like in supergravity scenarios, and is
robust if the lightest pseudoscalar Higgs field is as light as ~ 10 GeV [as may
occur in the NMSSM]. For these models predicting in particular an RPV
neutrino-photino mixing, the gravitino lifetime exceeds the age of the universe
by two orders of magnitude. However, we find that the gravitino cannot
constitute a viable dark matter candidate since its too large RPV decay widths
would then conflict with the flux data of last indirect detection experiments.
The cases of a sneutrino LSP or a neutralino LSP as well as the more promising
gauge-mediated supersymmetry breaking scenario are also discussed. Both the
one-flavor simplification hypothesis and the realistic scenario of three
neutrino flavors are analyzed. We have modified the NMHDECAY program to extend
the neutralino mass matrix to the present framework.Comment: Latex file, 23 pages, 7 figures. References added and discussion on
the indirect detection modifie
SUSY radiative corrections on mu-tau neutrino refraction including possible R-parity breaking interactions
In this paper we investigate the one-loop radiative corrections to the
neutrino indices of refraction from supersymmetric models. We consider the
Next-to Minimal Supersymmetric extension of the Standard Model (NMSSM) which
happens to be a better supersymmetric candidate than the MSSM for both
theoretical and experimental reasons. We scan the relevant SUSY parameters and
identify regions in the parameter space which yield interesting values for
V_{mu tau}. If R-parity is broken there are significant differences between
MSSM and NMSSM contributions contrary to the R-parity conserved case. Finally,
for a non-zero CP-violating phase, we show analytically that the presence of
V_{mu tau} will explicitly imply CP-violation effects on the supernova electron
(anti-) neutrino fluxes.Comment: 23 pages, 15 figures; v2: typos and 5 figures correcte
Redshift estimate of a gravitational lens from the observed reddening of a multiply imaged quasar
Light rays from a multiply imaged quasar usually sample different path
lengths across the deflector. Extinction in the lensing galaxy may thus lead to
a differential obscuration and reddening between the observed macro-lensed QSO
images. These effects naturally depend on the precise shape of the extinction
law and on the redshift of the lens. By means of numerical Monte-Carlo
simulations, using a least-squares fitting method and assuming an extinction
law similar to that observed in the Galaxy, we show how accurate photometric
observations of multiply imaged quasars obtained in several spectral bands
could lead to the estimate of the lens redshift, irrespective of the visibility
of the deflector. Observational requirements necessary to apply this method to
real cases are thoroughly discussed. If extinction laws turn out to be too
different from galaxy to galaxy, we find out that more promising observations
should consist in getting high signal-to-noise low resolution spectra of at
least three distinct images of a lensed quasar, over a spectral range as wide
as possible, from which it should be straightforward to extract the precise
shape of the redshifted extinction law. Very high signal-to-noise, low spectral
resolution, VLT observations of H1413+117 and MG 0414+0534 should enable one to
derive such a redshifted extinction law.Comment: 7 pages, 11 figures, to appear in Astronomy and Astrophysics (also
available at http://vela.astro.ulg.ac.be/preprint/
Development of a task analysis tool to facilitate user interface design
A good user interface is one that facilitates the user in carrying out his task. Such interfaces are difficult and costly to produce. The most important aspect in producing a good interface is the ability to communicate to the software designers what the user's task is. The Task Analysis Tool is a system for cooperative task analysis and specification of the user interface requirements. This tool is intended to serve as a guide to development of initial prototypes for user feedback
Schelling segregation in an open city: a kinetically constrained Blume-Emery-Griffiths spin-1 system
In the 70's Schelling introduced a multi-agent model to describe the
segregation dynamics that may occur with individuals having only weak
preferences for 'similar' neighbors. Recently variants of this model have been
discussed, in particular, with emphasis on the links with statistical physics
models. Whereas these models consider a fixed number of agents moving on a
lattice, here we present a version allowing for exchanges with an external
reservoir of agents. The density of agents is controlled by a parameter which
can be viewed as measuring the attractiveness of the city-lattice. This model
is directly related to the zero-temperature dynamics of the
Blume-Emery-Griffiths (BEG) spin-1 model, with kinetic constraints. With a
varying vacancy density, the dynamics with agents making deterministic
decisions leads to a new variety of "phases" whose main features are the
characteristics of the interfaces between clusters of agents of different
types. The domains of existence of each type of interface are obtained
analytically as well as numerically. These interfaces may completely isolate
the agents leading to another type of segregation as compared to what is
observed in the original Schelling model, and we discuss its possible
socio-economic correlates.Comment: 10 pages, 7 figures, final version accepted for publication in PR
- …