9,584 research outputs found
Electroweak Baryogenesis in the Minimal Supersymmetric Standard Model
I describe work done in collaboration with M. Joyce and K. Kainulainen on (1)
the strength of the electroweak phase transition in the MSSM and (2) the
mechanism for producing the baryon asymmetry during the phase transition. In
the former we compare the effective potential and dimensional reduction methods
for describing the phase transition and search the parameter space of the MSSM
for those values where it is strong enough. In the latter we give a systematic
computation of the baryon asymmetry due the CP-violating force acting on
charginos in the vicinity of the bubble wall. We find that a light right-handed
stop, a light Higgs boson, and a large phase in the mu parameter, are the main
necessary ingredients for producing the baryon asymmetry.Comment: 5 pages, Latex; Talk given at the Eotvos Conference in Science,
Strong and Electroweak Matter '97, Eger, Hungary, 21-25 May 1997; and at the
19th Annual MRST (Montreal-Rochester-Syracuse-Toronto) High-energy Theory
Meeting, Syracuse, New York, 12-13 May 199
Interactive Video: One Monitor or Two?
Interactive video is a rapidly growing technologywhich holds great promise for teachingforeign language and culture. Multimediacontextualization of the language and simulationsof typical cultural situations are powerfultools for language teachers and learners. Interactivevideo is often delivered with alternateworkstation designs: one with a single monitorto present simultaneous video and text, and onewith different monitors for video and computertext and graphics. This study investigates thepossibility that the workstation configurationsmight have a differential impact on studentperformance on a test of Spanish culture. Studentsin second semester college Spanish classesstudied five interactive video Spanish culturesimulations during the semester. Some studentsused a single monitor workstation and others adual monitor design. They were given pre- andpost-tests on Spanish culture and the resultswere analyzed for significant differences. Additionalfactors influencing workstation design(e.g., hardware and software costs, user friendliness)are also discussed
Tachyon Defect Formation and Reheating in Brane-Antibrane Inflation
We study analytically the dynamical formation of lower dimensional branes at
the endpoint of brane-antibrane inflation through the condensation of
topological defects of the tachyon field which describes the instability of the
initial state. We then use this information to quantify the efficiency of the
reheating which is due to the coupling of time dependent tachyon background to
massless gauge fields which will be localized on the final state branes. We
improve upon previous estimates indicating that this can be an efficient
reheating mechanism for observers on the brane.Comment: 9 pages. Talk given at the 26th annual
Montreal-Rochester-Syracuse-Toronto Conference on High-Energy Physics: MRST
200
On -filtrations of Weyl modules
This paper considers Weyl modules for a simple, simply connected algebraic
group over an algebraically closed field of positive characteristic
. The main result proves, if (where is the Coxeter
number) and if the Lusztig character formula holds for all (irreducible modules
with) regular restricted highest weights, then any Weyl module
has a -filtration, namely, a filtration with
sections of the form
, where is
restricted and is arbitrary dominant. In case the highest weight
of the Weyl module is -regular, the
-filtration is compatible with the -radical series of the module. The
problem of showing that Weyl modules have -filtrations was first
proposed as a worthwhile ("w\"unschenswert") problem in Jantzen's 1980 Crelle
paper.Comment: Latest version corrects minor mistakes in previous versions. A
reference is made to Williamson's recent arXiv posting, providing some
relevant discussion in a footnote. [Comments on earlier versions: Previous v.
1 with minor errors and statements corrected. Improved organization. Should
replace v. 2 which is an older version (even older than v.1) and was
mistakenly posted.
Supergravity Inspired Warped Compactifications and Effective Cosmological Constants
We propose a supergravity inspired derivation of a Randall-Sundrum's type
action as an effective description of the dynamics of a brane coupled to the
bulk through gravity only. The cosmological constants in the bulk and on the
brane appear at the classical level when solving the equations of motion
describing the bosonic sector of supergravities in ten and eleven dimensions
coupled to the brane. They are related to physical quantities like the brane
electric charge and thus inherit some of their physical properties. The most
appealing property is their quantization: in d_\perp extra dimensions,
Lambda_brane goes like N and Lambda_bulk like N^{2/(2-d_perp)}. This dynamical
origin also explains the apparent fine-tuning required in the Randall-Sundrum
scenario. In our approach, the cosmological constants are derived parameters
and cannot be chosen arbitrarily; instead they are determined by the underlying
Lagrangian. Some of the branes we construct that support cosmological constant
in the bulk have supersymmetric properties: D3-branes of type IIB superstring
theory provide an explicit example.Comment: 17 pages, LaTeX, 1 figure. v2: references added and a comment about
D-8 brane of massive IIA sugra included v3: improved argument on the
effective cosmological constants quantization and clarified discussion on the
supersymmetric issue of the solutions constructed. Final version to appear in
NP
Supersymmetric Electroweak Baryogenesis in the WKB approximation
We calculate the baryon asymmetry generated at the electroweak phase
transition in the minimal supersymmetric standard model, treating the particles
in a WKB approximation in the bubble wall background. A set of diffusion
equations for the particle species relevant to baryon generation, including
source terms arising from the CP violation associated with the complex phase
of the parameter, are derived from Boltzmann equations, and
solved. The conclusion is that must be \gsim 0.1 to generate a
baryon asymmetry consistent with nucleosynthesis. We compare our results to
several other recent computations of the effect, arguing that some are
overestimates.Comment: 12 pages, 1 figure, corrected some criticisms of hep-ph/9702409; to
appear in Phys. Lett.
Method and apparatus for optically monitoring the angular position of a rotating mirror
An optical system monitors the angular position of a rotating scanning mirror to indicate the effective start and end of each scan. At a certain angular position, a ray of energy transmitted to the mirror is reflected a plurality of times between the reflectors associated with the optical system and the line on the mirror parallel to the axis, and then to a detector to sense that angular position. A single optical system may be arranged to sense a plurality of different angular positions for each revolution of the mirror
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