9,942 research outputs found
Quasi-Fixed Points and Charge and Colour Breaking in Low Scale Models
We show that the current LEP2 lower bound upon the minimal supersymmetric
standard model (MSSM) lightest Higgs mass rules out quasi-fixed scenarios for
string scales between 10^6 and 10^{11} GeV unless the heaviest stop mass is
more than 2 TeV. We consider the implications of the low string scale for
charge and colour breaking (CCB) bounds in the MSSM, and demonstrate that CCB
bounds from F and D-flat directions are significantly weakened. For scales less
than 10^{10} GeV these bounds become merely that degenerate scalar mass squared
values are positive at the string scale.Comment: 17 pages, 4 figures. Replacement has added discussion on errors due
to alpha_s(MZ) errors, as well as deviations from the quasi-fixed point. Text
has been clarifie
Cosmology of the Next-to-Minimal Supersymmetric Standard Model
We discuss the domain wall problem in the Next-to-Minimal Supersymmetric
Standard Model, with particular attention to the usual solution of explicit
breaking of the discrete symmetry by non-renormalisable operators. This
``solution'' leads to a contradiction between the requirements of cosmology and
those of avoiding the destabilisation of the hierarchy.Comment: 6 pages LaTeX, needs sprocl.sty (included at end) Talk presented by
P.L. White at Valencia 9
Brane Gases on K3 and Calabi-Yau Manifolds
We initiate the study of Brane Gas Cosmology (BGC) on manifolds with
non-trivial holonomy. Such compactifications are required within the context of
superstring theory in order to make connections with realistic particle
physics. We study the dynamics of brane gases constructed from various string
theories on background spaces having a K3 submanifold. The K3 compactifications
provide a stepping stone for generalising the model to the case of a full
Calabi-Yau three-fold. Duality symmetries are discussed within a cosmological
context. Using a duality, we arrive at an N=2 theory in four-dimensions
compactified on a Calabi-Yau manifold with SU(3) holonomy. We argue that the
Brane Gas model compactified on such spaces maintains the successes of the
trivial toroidal compactification while greatly enhancing its connection to
particle physics. The initial state of the universe is taken to be a small, hot
and dense gas of p-branes near thermal equilibrium. The universe has no initial
singularity and the dynamics of string winding modes allow three spatial
dimensions to grow large, providing a possible solution to the dimensionality
problem of string theory.Comment: 26 pages; Significant revisions: review material truncated;
presentation improve
Evolution and Explosion of Very Massive Primordial Stars
While the modern stellar IMF shows a rapid decline with increasing mass,
theoretical investigations suggest that very massive stars (>100 solar masses)
may have been abundant in the early universe. Other calculations also indicate
that, lacking metals, these same stars reach their late evolutionary stages
without appreciable mass loss. After central helium burning, they encounter the
electron-positron pair instability, collapse, and burn oxygen and silicon
explosively. If sufficient energy is released by the burning, these stars
explode as brilliant supernovae with energies up to 100 times that of an
ordinary core collapse supernova. They also eject up to 50 solar masses of
radioactive Ni56. Stars less massive than 140 solar masses or more massive than
260 solar masses should collapse into black holes instead of exploding, thus
bounding the pair-creation supernovae with regions of stellar mass that are
nucleosynthetically sterile. Pair-instability supernovae might be detectable in
the near infrared out to redshifts of 20 or more and their ashes should leave a
distinctive nucleosynthetic pattern.Comment: 7 pages, including 4 figures; in. proc. MPA/ESO/MPE/USM Joint
Astronomy Conference "Lighthouses of the Universe: The Most Luminous
Celestial Objects and their use for Cosmology
Solitonic supersymmetry restoration
Q-balls are a possible feature of any model with a conserved, global U(1)
symmetry and no massless, charged scalars. It is shown that for a broad class
of models of metastable supersymmetry breaking they are extremely influential
on the vacuum lifetime and make seemingly viable vacua catastrophically short
lived. A net charge asymmetry is not required as there is often a significant
range of parameter space where statistical fluctuations alone are sufficient.
This effect is examined for two supersymmetry breaking scenarios. It is found
that models of minimal gauge mediation (which necessarily have a messenger
number U(1)) undergo a rapid, supersymmetry restoring phase transition unless
the messenger mass is greater than 10^8 GeV. Similarly the ISS model, in the
context of direct mediation, quickly decays unless the perturbative
superpotential coupling is greater than the Standard Model gauge couplings.Comment: 17 pages, 3 figures, minor comments added, accepted for publication
in JHE
Design of the flutter suppression system for DAST ARW-IR
The design of the flutter suppression system for a remotely-piloted research vehicle is described. The modeling of the aeroelastic system, the methodology used to synthesized the control law, the analytical results used to evaluate the control law performance, and ground testing of the flutter suppression system onboard the aircraft are discussed. The major emphasis is on the use of optimal control techniques employed during the synthesis of the control law
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