47,590 research outputs found
A Layman's guide to SUSY GUTs
The determination of the most straightforward evidence for the existence of
the Superworld requires a guide for non-experts (especially experimental
physicists) for them to make their own judgement on the value of such
predictions. For this purpose we review the most basic results of Super-Grand
unification in a simple and clear way. We focus the attention on two specific
models and their predictions. These two models represent an example of a direct
comparison between a traditional unified-theory and a string-inspired approach
to the solution of the many open problems of the Standard Model. We emphasize
that viable models must satisfy {\em all} available experimental constraints
and be as simple as theoretically possible. The two well defined supergravity
models, and , can be described in terms of only a few
parameters (five and three respectively) instead of the more than twenty needed
in the MSSM model, \ie, the Minimal Supersymmetric extension of the Standard
Model. A case of special interest is the strict no-scale
supergravity where all predictions depend on only one parameter (plus the
top-quark mass). A general consequence of these analyses is that supersymmetric
particles can be at the verge of discovery, lurking around the corner at
present and near future facilities. This review should help anyone distinguish
between well motivated predictions and predictions based on arbitrary choices
of parameters in undefined models.Comment: 25 pages, Latex, 11 figures (not included), CERN-TH.7077/93,
CTP-TAMU-65/93. A complete ps file (1.31MB) with embedded figures is
available by request from [email protected]
A sharp vanishing theorem for line bundles on K3 or Enriques surfaces
Let be a line bundle on a K3 or Enriques surface. We give a vanishing
theorem for that, unlike most vanishing theorems, gives necessary and
sufficient geometrical conditions for the vanishing. This result is essential
in our study of Brill-Noether theory of curves on Enriques surfaces (reference
[KL1]) and of Enriques-Fano threefolds (reference [KLM]).Comment: 4 pages, latex. Minor corrections. To appear on Proc. Amer. Math. So
Gravitational cooling of self-gravitating Bose-Condensates
Equilibrium configurations for a self-gravitating scalar field with
self-interaction are constructed. The corresponding Schr\"odinger-Poisson (SP)
system is solved using finite differences assuming spherical symmetry. It is
shown that equilibrium configurations of the SP system are late-time attractor
solutions for initially quite arbitrary density profiles, which relax and
virialize through the emission of scalar field bursts; a process dubbed
gravitational cooling. Among other potential applications, these results
indicate that scalar field dark matter models (in its different flavors)
tolerate the introduction of a self-interaction term in the SP equations. This
study can be useful in exploring models in which dark matter in galaxies is not
point-like.Comment: 10 aastex pages, 12 eps figures. Accepted for publication in Ap
Subvarieties of generic hypersurfaces in any variety
Let W be a projective variety of dimension n+1, L a free line bundle on W, X
in a hypersurface of degree d which is generic among those given by
sums of monomials from , and let be a generically finite map
from a smooth m-fold Y. We suppose that f is r-filling, i.e. upon deforming X
in , f deforms in a family such that the corresponding deformations
of dominate . Under these hypotheses we give a lower bound for the
dimension of a certain linear system on the Cartesian product having
certain vanishing order on a diagonal locus as well as on a double point locus.
This yields as one application a lower bound on the dimension of the linear
system |K_{Y} - (d - n + m)f^*L - f^*K_{W}| which generalizes results of Ein
and Xu (and in weaker form, Voisin). As another perhaps more surprising
application, we conclude a lower bound on the number of quadrics containing
certain projective images of Y.Comment: We made some improvements in the introduction and definitions. In an
effort to clarify the arguments we separated the 1-filling case from the
r-filling case and we gave a more detailed proof of the key lemma. The
article will appear in the Math. Proc. Cambridge Philos. So
SUSY signals at HERA in the no-scale flipped SU(5) supergravity model
Sparticle production and detection at HERA are studied within the recently
proposed no-scale flipped supergravity model. Among the various
reaction channels that could lead to sparticle production at HERA, only the
following are within its limit of sensitivity in this model: , where are the
two lightest neutralinos and is the lightest chargino. We study the
elastic and deep-inelastic contributions to the cross sections using the
Weizs\"acker-Williams approximation. We find that the most promising
supersymmetric production channel is right-handed selectron ()
plus first neutralino (), with one hard electron and missing energy
signature. The channel leads to comparable rates but also
allows jet final states. A right-handedly polarized electron beam at HERA would
shut off the latter channel and allow preferentially the former one. With an
integrated luminosity of {\cal L}=100\ipb, HERA can extend the present LEPI
lower bounds on by
\approx25\GeV, while {\cal L}=1000\ipb will make HERA competitive with
LEPII. We also show that the Leading Proton Spectrometer (LPS) at HERA is an
excellent supersymmetry detector which can provide indirect information about
the sparticle masses by measuring the leading proton longitudinal momentum
distribution.Comment: 11 pages, 8 figures (available upon request as uuencoded file or
separate ps files), tex (harvmac) CTP-TAMU-15/93, CERN/LAA/93-1
New Precision Electroweak Tests of SU(5) x U(1) Supergravity
We explore the one-loop electroweak radiative corrections in supergravity via explicit calculation of vacuum-polarization and
vertex-correction contributions to the and
parameters. Experimentally, these parameters are obtained from a global fit to
the set of observables , and . We
include -dependent effects, which induce a large systematic negative shift
on for light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). The
(non-oblique) supersymmetric vertex corrections to \Zbb, which define the
parameter, show a significant positive shift for light chargino
masses, which for can be nearly compensated by a negative
shift from the charged Higgs contribution. We conclude that at the 90\%CL, for
m_t\lsim160\GeV the present experimental values of and
do not constrain in any way supergravity in
both no-scale and dilaton scenarios. On the other hand, for m_t\gsim160\GeV
the constraints on the parameter space become increasingly stricter. We
demonstrate this trend with a study of the m_t=170\GeV case, where only a
small region of parameter space, with \tan\beta\gsim4, remains allowed and
corresponds to light chargino masses (m_{\chi^\pm_1}\lsim70\GeV). Thus
supergravity combined with high-precision LEP data would
suggest the presence of light charginos if the top quark is not detected at the
Tevatron.Comment: LaTeX, 11 Pages+4 Figures(not included), the figures available upon
request as an uuencoded file(0.4MB) or 4 PS files from [email protected],
CERN-TH.7078/93, CTP-TAMU-68/93, ACT-24/9
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