264 research outputs found
Exploring the SO(32) Heterotic String
We give a complete classification of Z_N orbifold compactification of the
heterotic SO(32) string theory and show its potential for realistic model
building. The appearance of spinor representations of SO(2n) groups is analyzed
in detail. We conclude that the heterotic SO(32) string constitutes an
interesting part of the string landscape both in view of model constructions
and the question of heterotic-type I duality.Comment: 21 pages, 5 figure
Supersymmetry Breakdown at a Hidden Wall
We consider hidden sector supersymmetry breakdown in the strongly coupled
heterotic theory of Ho\v{r}ava and Witten. Using effective
field theory methods in four dimensions, we can show that gravitational
interactions induce soft breaking terms in the observable sector that are of
order of the gravitiono mass. We apply these methods to the mechanism of
gaugino condensation at the hidden wall. Although the situation is very similar
to the weakly coupled case, there is a decisive difference concerning the
observable sector gaugino mass; with desirable phenomenological as well as
cosmological consequences.Comment: 29 pages, latex, no figures, To appear in Nuclear Physics B. Minor
change
Heterotic orbifold models on Lie lattice with discrete torsion
We provide a new class of Z_N x Z_M heterotic orbifolds on non-factorisable
tori, whose boundary conditions are defined by Lie lattices. Generally, point
groups of these orbifolds are generated by Weyl reflections and outer
automorphisms of the lattices. We classify abelian orbifolds with and without
discrete torsion. Then we find that some of these models have smaller Euler
numbers than those of models on factorisable tori T^2 x T^2 x T^2. There is a
possibility that these orbifolds provide smaller generation numbers of N=1
chiral matter fields than factorisable models.Comment: 24 pages, 5 figures; v2: a few errors on tables are corrected, typos
corrected, version to appear in JHE
Possible astrophysical signatures of heavy stable neutral relics in supergravity models
We consider heavy stable neutral particles in the context of supergravity and
show that a gravitationally suppressed inflaton decay can produce such
particles in cosmologically interesting abundances within a wide mass range
. In gravity-mediated
supersymmetry breaking models, a heavy particle can decay into its superpartner
and a photon-photino pair or a gravitino. Such decays only change the identity
of a possible dark matter candidate. However, for , astrophysical bounds from gamma-ray background and
photodissociation of light elements can be more stringent than the overclosure
bound, thus ruling out the particle as a dark matter candidate.Comment: 12 page
Supergravity Inflation Free from Harmful Relics
We present a realistic supergravity inflation model which is free from the
overproduction of potentially dangerous relics in cosmology, namely moduli and
gravitinos which can lead to the inconsistencies with the predictions of baryon
asymmetry and nucleosynthesis. The radiative correction turns out to play a
crucial role in our analysis which raises the mass of supersymmetry breaking
field to intermediate scale. We pay a particular attention to the non-thermal
production of gravitinos using the non-minimal Kahler potential we obtained
from loop correction. This non-thermal gravitino production however is
diminished because of the relatively small scale of inflaton mass and small
amplitudes of hidden sector fields.Comment: 10 pages, revtex, 1 eps figure, references added, conclusion section
expande
Z_2 x Z_2 Heterotic Orbifold Models of Non Factorisable Six Dimensional Toroidal Manifolds
We discuss heterotic strings on Z_2 x Z_2 orbifolds of non factorisable
six-tori. Although the number of fixed tori is reduced as compared to the
factorisable case, Wilson lines are still needed for the construction of three
generation models. An essential new feature is the straightforward appearance
of three generation models with one generation per twisted sector. We
illustrate our general arguments for the occurrence of that property by an
explicit example. Our findings give further support for the conjecture that
four dimensional heterotic strings formulated at the free fermionic point are
related to Z_2 x Z_2 orbifolds.Comment: 33 pages, LaTeX; discussion of modular invariance added in section
four; added references; to be published in JHE
Higher-dimensional perturbations of the vacuum energy density
The vacuum energy density arising from the broken supersymmetry of the
(standard-model) fields living on a brane cannot be fully "off-loaded" to the
bulk: even assuming the existence of an effective "self-tuning" mechanism, a
small fraction of the transferred energy "bunces back" to the brane, as a
backreaction of the supersymmetry breaking gravitationally transmitted to the
bulk. In that case the SUSY scale of the brane has to be bounded, to guarantee
the consistency of such a residual energy density with current large-scale
phenomonological constraints. This effect is illustrated by computing the
zero-point energies of the tower of (higher-dimensional) massive states
associated to tensor metric fluctuations on a brane embedded in a warped bulk
geometry, and it is shown to be independent of the number of compact or
non-compact extra dimensions.Comment: 10 pages, no figures, to appear in JHE
Spontaneous localization of bulk matter fields
We study models compactified on S^1/Z_2 with bulk and brane matter fields
charged under U(1) gauge symmetry. We calculate the FI-terms and show by
minimizing the resulting potential that supersymmetry or gauge symmetry is
spontaneously broken if the sum of the charges does not vanish. Even if this
sum vanishes, there could be an instability as a consequence of localized
FI-terms. This leads to a spontaneous localization of charged bulk fields on
respective branes.Comment: 11 pages, LaTeX, 1 figur
Implications of non-universality of soft terms in supersymmetric grand unified theories
Most discussions of supersymmetric grand unified theories assume universality
of the soft supersymmetry breaking terms at the grand scale. We point out that
the behaviour of these theories might change significantly in the presence of
non--universal soft terms. Particularly in SO(10)--like models with a large
value of tan we observe a decisive change of predictions, allowing the
presence of relatively light gauginos as well as small supersymmetric
corrections to the b--quark mass. Some results remain rather stable, including
the -- correlation. Models with small tan seem to be less
affected by non--universality which mainly leads to the new possibility of
small (i.e. the squark and slepton soft mass parameter), excluded in
the universal case.Comment: 15 pages (Latex) plus 5 figures (uuencoded postscript file). TUM-HEP
201/9
Cosmological Constant and Soft Terms in Supergravity
Some of the soft SUSY breaking parameters in hidden sector supergravity model
depend on the expectation value of the hidden sector scalar potential, ,
whose tree level value is equal to the tree level cosmological constant. The
current practice of calculating soft parameters assumes that $=0$. Quantum
correction to the cosmological constant can differ from the correction to
by an amount of order . This implies that, for
the vanishing cosmological constant, the --dependent parts of soft terms
can be sizable, and hence the supergravity phenomenology should be accordingly
modified.Comment: Latex file, 11 pages plus 1 figure (the figure not included), SNUTP
94--1
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