6,385 research outputs found
Constraints on Sparticle Spectrum in different Supersymmetry Breaking Models
We derive sum rules for the sparticle masses in different models of
supersymmetry breaking. This includes the gravity mediated models (SUGRA
models) as well as models in which supersymmetry breaking terms are induced by
super-Weyl anomaly (AMSB models). These sum rules can help in distinguishing
between these models. In particular we obtain an upper bound on the mass of the
lightest neutralino as a function of the gluino mass in SUGRA and AMSB models.Comment: 3 pages, latex, two figures, macros included. Talk presented at IXth
International Symposium on Particles, Strings and Cosmology(PASCOS'03), TIFR,
MUmbai, India, January 3 - 8, 2003. To appear in the proceeding
Current and future graphics requirements for LaRC and proposed future graphics system
The findings of an investigation to assess the current and future graphics requirements of the LaRC researchers with respect to both hardware and software are presented. A graphics system designed to meet these requirements is proposed
Gravitational Waves from Warped Spacetime
We argue that the RSI model can provide a strong signature in gravitational
waves. This signal is a relic stochastic background generated during the
cosmological phase transition from an AdS-Schwarschild phase to the RS1
geometry that should occur at a temperature in the TeV range. We estimate the
amplitude of the signal in terms of the parameters of the potential stabilizing
the radion and show that over much of the parameter region in which the phase
transition completes, a signal should be detectable at the planned space
interferometer, LISA.Comment: 18 pages, 15 figures; v2: discussion improved, in particular on the
justification of the thick wall approximation. 6 figures added. 4 pi factor
corrected in perturbativity bound. N-dependence displayed. Conclusions
unchanged. JHEP versio
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Results of an aqueous source term model for a radiological risk assessment of the Drigg LLW Site, U.K.
A radionuclide source term model has been developed which simulates the biogeochemical evolution of the Drigg low level waste (LLW) disposal site. The DRINK (DRIgg Near field Kinetic) model provides data regarding radionuclide concentrations in groundwater over a period of 100,000 years, which are used as input to assessment calculations for a groundwater pathway. The DRINK model also provides input to human intrusion and gaseous assessment calculations through simulation of the solid radionuclide inventory. These calculations are being used to support the Drigg post closure safety case. The DRINK model considers the coupled interaction of the effects of fluid flow, microbiology, corrosion, chemical reaction, sorption and radioactive decay. It represents the first direct use of a mechanistic reaction-transport model in risk assessment calculations
Influence of deposition parameters on mechanical properties of sputter-deposited Cr2O3 thin films
Among the oxides, Cr2O3 exhibits the highest hardness value and a low coefficient of friction. These properties make chromium oxide an excellent coating material for tribological applications. Cr2O3 thin films were deposited by radio-frequency reactive magnetron sputtering at substrate temperature in the range 363-593 K. The hardness and elastic modulus of the films were measured by two complementary nanoindentation techniques to investigate the influences of the substrate temperature and the oxygen content in the sputtering gas. While the continuous stiffness data method provides information throughout the whole film thickness, nanoindentation combined with scanning force microscopy of the residual imprints allows visualization of pileup, cracking, and delamination from the substrate. Hardness values up to 32 GPa were obtained for substrate temperatures exceeding 500 K and oxygen contents between 15% and 25% of the total gas pressure. The films, obtained with these deposition conditions, showed good adhesion to silicon substrate
Constraints on Embeddings
We show that the embedding of either a static or a time dependent maximally
3-symmetric brane with non-zero spatial curvature into a non-compactified
bulk does not yield exponential suppression of the geometry away from
the brane. Implications of this result for brane-localized gravity are
discussed.Comment: RevTeX, 9 pages (updated version v2, conclusions unchanged after
extension to the non-static case
D-Terms, Unification, and the Higgs Mass
We study gauge extensions of the MSSM that contain non-decoupling D-terms,
which contribute to the Higgs boson mass. These models naturally maintain gauge
coupling unification and raise the Higgs mass without fine-tuning. Unification
constrains the structure of the gauge extensions, limiting the Higgs mass in
these models to roughly less than 150 GeV. The D-terms contribute to the Higgs
mass only if the extended gauge symmetry is broken at energies of a few TeV,
leading to new heavy gauge bosons in this mass range.Comment: 30+1 pages, 7 figure
Black Holes Radiate Mainly on the Brane
We examine the evaporation of a small black hole on a brane in a world with
large extra dimensions. Since the masses of many Kaluza-Klein modes are much
smaller than the Hawking temperature of the black hole, it has been claimed
that most of the energy is radiated into these modes. We show that this is
incorrect. Most of the energy goes into the modes on the brane. This raises the
possibility of observing Hawking radiation in future high energy colliders if
there are large extra dimensions.Comment: 11 page
No-Go Theorem for Horizon-Shielded Self-Tuning Singularities
We derive a simple no-go theorem relating to self-tuning solutions to the
cosmological constant for observers on a brane, which rely on a singularity in
an extra dimension. The theorem shows that it is impossible to shield the
singularity from the brane by a horizon, unless the positive energy condition
(rho+p >= 0) is violated in the bulk or on the brane. The result holds
regardless of the kinds of fields which are introduced in the bulk or on the
brane, whether Z_2 symmetry is imposed at the brane, or whether higher
derivative terms of the Gauss-Bonnet form are added to the gravitational part
of the action. However, the no-go theorem can be evaded if the three-brane has
spatial curvature. We discuss explicit realizations of such solutions which
have both self-tuning and a horizon shielding the singularity.Comment: 7 pages, 4 figures, revtex; added reference and minor correction
Brane versus shell cosmologies in Einstein and Einstein-Gauss-Bonnet theories
We first illustrate on a simple example how, in existing brane cosmological
models, the connection of a 'bulk' region to its mirror image creates matter on
the 'brane'. Next, we present a cosmological model with no symmetry which
is a spherical symmetric 'shell' separating two metrically different
5-dimensional anti-de Sitter regions. We find that our model becomes
Friedmannian at late times, like present brane models, but that its early time
behaviour is very different: the scale factor grows from a non-zero value at
the big bang singularity. We then show how the Israel matching conditions
across the membrane (that is either a brane or a shell) have to be modified if
more general equations than Einstein's, including a Gauss-Bonnet correction,
hold in the bulk, as is likely to be the case in a low energy limit of string
theory. We find that the membrane can then no longer be treated in the thin
wall approximation. However its microphysics may, in some instances, be simply
hidden in a renormalization of Einstein's constant, in which cases Einstein and
Gauss-Bonnet membranes are identical.Comment: 15 pages, submitted to Phys. Rev.
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