585 research outputs found

### M-Phenomenology

Recent developments involving strongly coupled superstrings are discussed
from a phenomenological point of view. In particular, strongly coupled
$E_8\times E'_8$ is described as an appropriate long-wavelength limit of
M-theory, and some generic phenomenological implications are analyzed,
including a long sought downward shift of the string unification scale and a
novel way to break supersymmetry. A specific scenario is presented that leads
to a rather light, and thus presently experimentally testable, sparticle
spectrum.Comment: 22 pages, 2 figure

### A supergravity explanation of the CDF $ee\gamma\gamma$ event

We present a unified no-scale supergravity model with a light gravitino that
can naturally explain the observed $ee\gamma\gamma$ event at CDF via
right-handed selectron pair-production. The full spectrum of our model can be
described in terms of a single parameter and can be distinguished from
alternative proposals in the literature. Ongoing and future runs at LEP 2
should be able to probe the full allowed parameter space via acoplanar diphoton
events from $e^+e^-\to\chi^0_1\chi^0_1$ production.Comment: 10 pages, LaTeX, 4 figures (included

### Closing the Universe by relaxing the cosmological constant

We propose a string-inspired model which correlates several aspects of
particle physics and cosmology. Inspired by the flat directions and the absence
of adjoint Higgs representations found in typical string models, we consider a
no-scale $SU(5)\times U(1)$ supergravity model. This model entails well
determined low-energy phenomenology, such as the value of the neutralino dark
matter relic abundance and a negative contribution to the vacuum energy. A
positive contribution to the vacuum energy is also typically present in string
theory as a consequence of the running of the fundamental constants towards
their fixed point values. If these two contributions cancel appropriately, one
may end up with a vacuum energy which brings many cosmological observations
into better agreement with theoretical expectations. The present abundance of
neutralinos would then be fixed. We delineate the regions of parameter space
allowed in this scenario, and study the ensuing predictions for the sparticle
and Higgs-boson masses in this model.Comment: 5 pages, 2 figures (included), Latex, CTP-TAMU-06/9

### The Electroweak Phase Transition in Minimal Supergravity Models

We have explored the electroweak phase transition in minimal supergravity
models by extending previous analysis of the one-loop Higgs potential to
include finite temperature effects. Minimal supergravity is characterized by
two higgs doublets at the electroweak scale, gauge coupling unification, and
universal soft-SUSY breaking at the unification scale. We have searched for the
allowed parameter space that avoids washout of baryon number via unsuppressed
anomalous Electroweak sphaleron processes after the phase transition. This
requirement imposes strong constraints on the Higgs sector. With respect to
weak scale baryogenesis, we find that the generic MSSM is {\it not}
phenomenologically acceptable, and show that the additional experimental and
consistency constraints of minimal supergravity restricts the mass of the
lightest CP-even Higgs even further to m_h\lsim 32\GeV (at one loop), also in
conflict with experiment. Thus, if supergravity is to allow for baryogenesis
via any other mechanism above the weak scale, it {\it must} also provide for
B-L production (or some other `accidentally' conserved quantity) above the
electroweak scale. Finally, we suggest that the no-scale flipped $SU(5)$
supergravity model can naturally and economically provide a source of B-L
violation and realistically account for the observed ratio $n_B/n_\gamma\sim
10^{-10}$.Comment: 14 pages (not including two postscript figures available upon
request

### No-scale supergravity confronts LEP diphoton events

We examine the possibility that some anomalous acoplanar diphoton events
observed at LEP may be consistent with the predictions of our previously
proposed one-parameter no-scale supergravity model with a light gravitino, via
the process e^+e^- -> chi chi -> gamma gamma+E_miss. We find that one such
event may indeed be consistent with the model predictions for m_chi \approx
(60-70) GeV. This region of parameter space is also consistent with the
selectron and chargino interpretations of the CDF ee gamma gamma + E_T,miss
event.Comment: 9 pages, LaTeX, 4 figures (included). Updated to include full LEP161
dat

### Some Physical Aspects of Liouville String Dynamics

We discuss some physical aspects of our Liouville approach to non-critical
strings, including the emergence of a microscopic arrow of time, effective
field theories as classical ``pointer'' states in theory space, $CPT$ violation
and the possible apparent non-conservation of angular momentum. We also review
the application of a phenomenological parametrization of this formalism to the
neutral kaon system.Comment: CERN-TH.7269/94, 37 pages, 2 figures (not included), latex. Direct
inquiries to: [email protected]

### $R_b$ in supergravity models

We compute the supersymmetric contribution to
$R_{b}\equiv \Gamma (Z\to b{\bar b})/\Gamma (Z\to {\rm hadrons})$ in a
variety of supergravity models. We find R^{\rm susy}_b\lsim0.0004, which does
not shift significantly the Standard Model prediction
($R^{\rm SM}_b=0.2162$ for m_t=160\GeV). An improvement in experimental
precision by a factor of four would be required to be sensitive to such an
effect.Comment: 5 pages, LaTeX, 1 figure (included)

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