177 research outputs found
Gauge Couplings at High Temperature and the Relic Gravitino Abundance
In higher-dimensional supersymmetric theories gauge couplings of the
effective four-dimensional theory are determined by expectation values of
scalar fields. We find that at temperatures above a critical temperature ,
which depends on the supersymmetry breaking mass scales, gauge couplings
decrease like T^{-\a}, \a > 1. This has important cosmological
consequences. In particular it leads to a relic gravitino density which becomes
independent of the reheating temperature for . For small gravitino
masses, m_{3/2} \ll m_{\gl}, the mass density of stable gravitinos is
essentially determined by the gluino mass. The observed value of cold dark
matter, \O_{\rm CDM}h^2 \sim 0.1, is obtained for gluino masses m_{\gl} =
{\cal O}(1 {\rm TeV}).Comment: 11 pages, 2 figures, comment on supersymmetry breaking mechanisms and
two references adde
The Hilbert basis method for D-flat directions and the superpotential
We discuss, using the Hilbert basis method, how to efficiently construct a
complete basis for D-flat directions in supersymmetric Abelian and non-Abelian
gauge theories. We extend the method to discrete (R and non-R) symmetries. This
facilitates the construction of a basis of all superpotential terms in a theory
with given symmetries.Comment: 11 pages; a related mathematica code can be found at
http://einrichtungen.ph.tum.de/T30e/codes/NonAbelianHilbert
Leptogenesis with Dirac Neutrinos
We describe a "neutrinogenesis" mechanism whereby, in the presence of
right-handed neutrinos with sufficiently small pure Dirac masses,
(B+L)-violating sphaleron processes create the baryon asymmetry of the
Universe, even when B=L=0 initially. It is shown that the resulting neutrino
mass constraints are easily fulfilled by the neutrino masses suggested by
current experiments. We present a simple toy model which uses this mechanism to
produce the observed baryon asymmetry of the Universe. (PostScript Errors
corrected in latest Version).Comment: 4 pages, Latex (using amsmath,feynmp,graphicx), 4 figure
Coping with the extremes : comparative osteology of the tepui-associated toad Oreophrynella and its bearing on the evolution of osteological novelties in the genus
The only study of the osteology of the toad genus Oreophrynella dates back to 1971 and was based on a single species. Here, we use high-resolution X-ray microcomputed tomography to analyse the osteology of all nine described Oreophrynella species, which are compared with representatives of other bufonid lineages. Oreophrynella is unique among bufonids in having opposable digits. Osteological synapomorphies confirmed for the genus are as follows: presence of parietal fontanelles and exposed frontoparietal fontanelle, absence of quadratojugal, five presacral vertebrae, distally enlarged terminal phalanges and urostyle greatly expanded into flanges. Ancestral character reconstruction indicates that arboreal habits in some Oreophrynella species are likely to have evolved after the evolution of opposable digits. Opposable digits, in combination with an extension of the interdigital integument and the relative length/orientation of the digits, are likely to be adaptations to facilitate life on rocky tepui summits and an exaptation to arboreality. Cranial simplification in Oreophrynella, in the form of cranial fontanelles and absence of the quadratojugal, is possibly driven by a reduction of developmental costs, increase in flexibility and reduction of body weight. Cranial simplification combined with the shortening of the vertebral column and the shift towards a partly firmisternal girdle might be adaptations to the peculiar tumbling behaviour displayed by Oreophrynella
Dilaton Destabilization at High Temperature
Many compactifications of higher-dimensional supersymmetric theories have
approximate vacuum degeneracy. The associated moduli fields are stabilized by
non-perturbative effects which break supersymmetry. We show that at finite
temperature the effective potential of the dilaton acquires a negative linear
term. This destabilizes all moduli fields at sufficiently high temperature. We
compute the corresponding critical temperature which is determined by the scale
of supersymmetry breaking, the beta-function associated with gaugino
condensation and the curvature of the K"ahler potential, T_crit ~ (m_3/2
M_P)^(1/2) (3/\beta)^(3/4) (K'')^(-1/4). For realistic models we find T_crit ~
10^11-10^12 GeV, which provides an upper bound on the temperature of the early
universe. In contrast to other cosmological constraints, this upper bound
cannot be circumvented by late-time entropy production.Comment: 19 pages, 9 figure
Renormalization Group Evolution of Dirac Neutrino Masses
There are good reasons why neutrinos could be Majorana particles, but there
exist also a number of very good reasons why neutrinos could have Dirac masses.
The latter option deserves more attention and we derive therefore analytic
expressions describing the renormalization group evolution of mixing angles and
of the CP phase for Dirac neutrinos. Radiative corrections to leptonic mixings
are in this case enhanced compared to the quark mixings because the hierarchy
of neutrino masses is milder and because the mixing angles are larger. The
renormalization group effects are compared to the precision of current and
future neutrino experiments. We find that, in the MSSM framework, radiative
corrections of the mixing angles are for large \tan\beta comparable to the
precision of future experiments.Comment: 19 pages, 5 figures; error in eq. 8 corrected, references adde
Flux Compactifications: Stability and Implications for Cosmology
We study the dynamics of the size of an extra-dimensional manifold stabilised
by fluxes. Inspecting the potential for the 4D field associated with this size
(the radion), we obtain the conditions under which it can be stabilised and
show that stable compactifications on hyperbolic manifolds necessarily have a
negative four-dimensional cosmological constant, in contradiction with
experimental observations. Assuming compactification on a positively curved
(spherical) manifold we find that the radion has a mass of the order of the
compactification scale, M_c, and Planck suppressed couplings. We also show that
the model becomes unstable and the extra dimensions decompactify when the
four-dimensional curvature is higher than a maximum value. This in particular
sets an upper bound on the scale of inflation in these models: V_max \sim M_c^2
M_P^2, independently of whether the radion or other field is responsible for
inflation. We comment on other possible contributions to the radion potential
as well as finite temperature effects and their impact on the bounds obtained.Comment: 16 pages, 1 figure, LaTeX; v2: typos fixed and references adde
Neutralino Dark Matter in Mirage Mediation
We study the phenomenology of neutralino dark matter (DM) in mirage mediation
scenario of supersymmetry breaking which results from the moduli stabilization
in some string/brane models. Depending upon the model parameters, especially
the anomaly to modulus mediation ratio determined by the moduli stabilization
mechanism, the nature of the lightest supersymmetric particle (LSP) changes
from Bino-like neutralino to Higgsino-like one via Bino-Higgsino mixing region.
For the Bino-like LSP, the standard thermal production mechanism can give a
right amount of relic DM density through the stop/stau-neutralino
coannihilation or the pseudo-scalar Higgs resonance process. We also examine
the prospect of direct and indirect DM detection in various parameter regions
of mirage mediation. Neutralino DM in galactic halo might be detected by near
future direct detection experiments in the case of Bino-Higgsino mixed LSP. The
gamma ray flux from Galactic Center might be detectable also if the DM density
profile takes a cuspy shape.Comment: One reference adde
Gravitino Dark Matter and Cosmological Constraints
The gravitino is a promising candidate for cold dark matter. We study
cosmological constraints on scenarios in which the gravitino is the lightest
supersymmetric particle and a charged slepton the next-to-lightest
supersymmetric particle (NLSP). We obtain new results for the hadronic
nucleosynthesis bounds by computing the 4-body decay of the NLSP slepton into
the gravitino, the associated lepton, and a quark-antiquark pair. The bounds
from the observed dark matter density are refined by taking into account
gravitinos from both late NLSP decays and thermal scattering in the early
Universe. We examine the present free-streaming velocity of gravitino dark
matter and the limits from observations and simulations of cosmic structures.
Assuming that the NLSP sleptons freeze out with a thermal abundance before
their decay, we derive new bounds on the slepton and gravitino masses. The
implications of the constraints for cosmology and collider phenomenology are
discussed and the potential insights from future experiments are outlined. We
propose a set of benchmark scenarios with gravitino dark matter and long-lived
charged NLSP sleptons and describe prospects for the Large Hadron Collider and
the International Linear Collider.Comment: 51 pages, 20 figures, revised version matches published version
(results unchanged, JHEP style used, figures replaced with new high-quality
figures, typos corrected, references added
Extended Smoothed Boundary Method for Solving Partial Differential Equations with General Boundary Conditions on Complex Boundaries
In this article, we describe an approach for solving partial differential
equations with general boundary conditions imposed on arbitrarily shaped
boundaries. A continuous function, the domain parameter, is used to modify the
original differential equations such that the equations are solved in the
region where a domain parameter takes a specified value while boundary
conditions are imposed on the region where the value of the domain parameter
varies smoothly across a short distance. The mathematical derivations are
straightforward and generically applicable to a wide variety of partial
differential equations. To demonstrate the general applicability of the
approach, we provide four examples herein: (1) the diffusion equation with both
Neumann and Dirichlet boundary conditions; (2) the diffusion equation with both
surface diffusion and reaction; (3) the mechanical equilibrium equation; and
(4) the equation for phase transformation with the presence of additional
boundaries. The solutions for several of these cases are validated against
corresponding analytical and semi-analytical solutions. The potential of the
approach is demonstrated with five applications: surface-reaction-diffusion
kinetics with a complex geometry, Kirkendall-effect-induced deformation,
thermal stress in a complex geometry, phase transformations affected by
substrate surfaces, and a self-propelled droplet.Comment: This document is the revised version of arXiv:0912.1288v
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