112 research outputs found
Protecting the Baryon Asymmetry with Thermal Masses
We consider the evolution of baryon number in the early universe under
the influence of rapid sphaleron interactions and show that will remain
nonzero at all times even in the case of . This result arises due to
thermal Yukawa interactions that cause nonidentical dispersion relations
(thermal masses) for different lepton families. We point out the relevance of
our result to the Affleck-Dine type baryogenesis.Comment: 11pp., plain tex, UMN-TH-1248/94, CfPA-TH-94-1
Exotic leptoquarks from superstring derived models
The H1 and ZEUS collaborations have recently reported a significant excess of
events at high in positron-proton collisions. While there exists
insufficient data to conclusively determine the origin of this excess, one
possibility is that it is due to a new leptoquark at mass scale around 200 GeV.
We examine the type of leptoquark states that exist in superstring derived
standard-like models, and show that, while these models may contain the
standard leptoquark states which exist in Grand Unified Theories, they also
generically contain new and exotic leptoquark states with fractional lepton
number, . In contrast to the traditional GUT-type leptoquark states,
the couplings of the exotic leptoquarks to the Standard Model states are
generated after the breaking of . This important feature of the
exotic leptoquark states may result in local discrete symmetries which forbid
some of the undesired leptoquark couplings. We examine these couplings in
several models and study the phenomenological implications. The flavor
symmetries of the superstring models are found to naturally suppress leptoquark
flavor changing processes.Comment: 28 pages. Standard Latex. Final version to appear in Nuclear Physics
B. Minor changes. References adde
Recycling universe
If the effective cosmological constant is non-zero, our observable universe
may enter a stage of exponential expansion. In such case, regions of it may
tunnel back to the false vacuum of an inflaton scalar field, and inflation with
a high expansion rate may resume in those regions. An ``ideal'' eternal
observer would then witness an infinite succession of cycles from false vacuum
to true, and back. Within each cycle, the entire history of a hot universe
would be replayed. If there were several minima of the inflaton potential, our
ideal observer would visit each one of these minima with a frequency which
depends on the shape of the potential. We generalize the formalism of
stochastic inflation to analyze the global structure of the universe when this
`recycling' process is taken into account.Comment: 43 pages, 10 figure
Cosmological constraints on R-parity violation from neutrino decay
If the neutrino mass is non-zero, as hinted by several experiments, then
R-parity-violating supersymmetric Yukawa couplings can drive a heavy neutrino
decay into lighter states. The heavy neutrino may either decay radiatively into
a lighter neutrino, or it may decay into three light neutrinos through a
Z-mediated penguin. For a given mass of the decaying neutrino, we calculate its
lifetime for the various modes, each mode requiring certain pairs of
R-parity-violating couplings be non-zero. We then check whether the calculated
lifetimes fall in zones allowed or excluded by cosmological requirements. For
the latter case, we derive stringent new constraints on the corresponding
products of R-parity-violating couplings for given values of the decaying
neutrino mass.Comment: 13 pages, Latex, uses axodraw.sty; version to appear in Physical
Review
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Automatic Alignment of the Advanced Radiographic Capability for the National Ignition Facility
Leptonic CP Violation in Supersymmetric Standard Model
We point out the possibility of spontaneous and hard CP-violation in the
scalar potential of R-parity broken supersymmetric Standard Model. The
existence of spontaneous CP-violation depends crucially on the R-parity
breaking terms in the superpotential and, in addition, on the choice of the
soft supersymmetry breaking terms. Unlike in theories with R-parity
conservation, it is natural, in the context of the present model, for the
sneutrinos to acquire (complex) vacuum expectation values. In the context of
this model we examine here the global implications, like the strength of the
CP-violating interactions and the neutrino masses.Comment: REVTEX, 15 page
How generic is cosmic string formation in SUSY GUTs
We study cosmic string formation within supersymmetric grand unified
theories. We consider gauge groups having a rank between 4 and 8. We examine
all possible spontaneous symmetry breaking patterns from the GUT down to the
standard model gauge group. Assuming standard hybrid inflation, we select all
the models which can solve the GUT monopole problem, lead to baryogenesis after
inflation and are consistent with proton lifetime measurements. We conclude
that in all acceptable spontaneous symmetry breaking schemes, cosmic string
formation is unavoidable. The strings which form at the end of inflation have a
mass which is proportional to the inflationary scale. Sometimes, a second
network of strings form at a lower scale. Models based on gauge groups which
have rank greater than 6 can lead to more than one inflationary era; they all
end by cosmic string formation.Comment: 31 pages, Latex, submitted to PR
Inflation in Supersymmetric Unified Theories
We construct supersymmetric unified models which automatically lead to a
period of inflation. The models all involve a U(1) symmetry which does not
belong to the MSSM. We consider three different types of models depending on
whether this extra U(1) is the subgroup of a non abelian gauge group, is a U(1)
factor belonging to the visible sector or is a U(1) factor belonging to the
hidden sector. Depending on the structure of the unified theory, on the
spontaneous symmetry breaking pattern and on whether we have global or local
supersymmetry, inflation may be driven by the non-vanishing vacuum expectation
value of a F-term or by that of a D-term. In both scenarios cosmic strings form
at the end of inflation, and they have different properties in each model. Both
inflation and cosmic strings contribute to the CMBR temperature anisotropies.
We show that the strings contribute to the 's up to the level of 75 %.
Hence the contribution from strings to the CMBR and to the density
perturbations in the early Universe which lead to structure formation cannot be
neglected. We also discuss a very interesting class of models which involve a
gauge symmetry.Comment: 22 pages, uses Revte
Non-perturbative renormalization of QCD
In these lectures, we discuss different types of renormalization problems in
QCD and their non-perturbative solution in the framework of the lattice
formulation. In particular the recursive finite size methods to compute the
scale-dependence of renormalized quantities is explained. An important
ingredient in the practical applications is the Schr\"odinger functional. It is
introduced and its renormalization properties are discussed.
Concerning applications, the computation of the running coupling and the
running quark mass are covered in detail and it is shown how the
-parameter and renormalization group invariant quark mass can be
obtained. Further topics are the renormalization of isovector currents and
non-perturbative Symanzik improvement.Comment: 49 pages, lectures at Schladming-9
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