6,257 research outputs found
A Minimal Superstring Standard Model II: A Phenomenological Study
Recently, we demonstrated the existence of heterotic--string solutions in
which the observable sector effective field theory just below the string scale
reduces to that of the MSSM, with the standard observable gauge group being
just SU(3)_C x SU(2)_L x U(1)_Y and the SU(3)_C x SU(2)_L x U(1)_Y-charged
spectrum of the observable sector consisting solely of the MSSM spectrum.
Associated with this model is a set of distinct flat directions of vacuum
expectation values (VEVs) of non-Abelian singlet fields that all produce solely
the MSSM spectrum. In this paper, we study the effective superpotential induced
by these choices of flat directions. We investigate whether sufficient degrees
of freedom exist in these singlet flat directions to satisfy various
phenomenological constraints imposed by the observed Standard Model data. For
each flat direction, the effective superpotential is given to sixth order. The
variations in the singlet and hidden sector low energy spectrums are analyzed.
We then determine the mass matrices (to all finite orders) for the three
generations of MSSM quarks and leptons. Possible Higgs mu-terms are
investigated. We conclude by considering generalizations of our flat directions
involving VEVs of non-Abelian fields.Comment: 41 pages. Standard Late
NAHE-based string models with SU(4) X SU(2) X U(1) SO(10) Subgroup
The orbifold GUT doublet-triplet splitting mechanism was discussed in 1994 in
the framework of the NAHE-based free fermionic models in which the SO(10) GUT
symmetry is broken to SO(6) X SO(4), SU(3) X SU(2) X U(1)^2, or SU(3) X U(1) X
SU(2)^2. In this paper we study NAHE-based free fermionic models in which the
SO(10) symmetry is broken at the string level to SU(4) X SU(2) X U(1). In
addition to the doublet-triplet splitting this case also has the advantage of
inducing the doublet-doublet splitting already at the string level. We
demonstrate, however, that NAHE-based models with SU(4) X SU(2) X U(1) SO(10)
subgroup are not viable. We show that, similarly to the LRS models, and in
contrast to the FSU5, PS and SLM models, the SU421 case gives rise to models
without an anomalous U(1) symmetry, and discuss the different cases in terms of
their N=4 origins.Comment: 25 pages. Standard Latex. Revised version to appear in NP
Child protection, domestic violence and parental substance misuse : family experiences and effective practice : executive summary
This book draws on a wide range of evidence to explore the facts about the relationship between substance misuse and domestic violence and their effect on children, and examines the response of children's services when there are concerns about the safety and welfare of children.
It reveals the vulnerability of these children and the extent to which domestic violence, parental alcohol or parental drug misuse impact on children's health and development, affect the adults' capacity to undertake key parenting tasks, and influence the response of wider family and the community. It includes parents' own voices and allows them to explain what help they feel would best support families in similar situations. The authors explore the extent to which current local authority plans, procedures, joint protocols and training support information sharing and collaborative working. Emphasising the importance of an holistic inter-agency approach to assessment, planning and service provision, the authors draw from the findings implications for policy and practice in both children and adult services
Stable Superstring Relics and Ultrahigh Energy Cosmic Rays
One of the most intriguing experimental results of recent years is the
observation of Ultrahigh Energy Cosmic Rays (UHECRs) above the GZK cutoff.
Plausible candidates for the UHECR primaries are the decay products of a
meta--stable matter state with mass of order O(10^{12-15 GeV}), which
simultaneously is a good cold dark matter candidate. We study possible
meta-stable matter states that arise from Wilson line breaking of GUT
symmetries in semi-realistic heterotic string models. In the models that we
study the exotic matter states can be classified according to patterns of
SO(10) symmetry breaking. We show that cryptons, which are states that carry
fractional electric charge , and are confined by a hidden gauge group
cannot produce viable dark matter. This is due to the fact that, in addition to
the lightest neutral bound state, cryptons give rise to meta-stable charged
bound states. However, these states may still account for the UHECR events. We
argue that the uniton, which is an exotic Standard Model quark but carries
``fractional'' U(1)_{Z'} charge, as well as the singleton, which is a Standard
Model singlet with ``fractional'' U(1)_{Z'} charge do provide viable dark
matter candidates and can at the same time explain the observed UHECR events.Comment: 24 pages. 5 figure
Phenomenology of Non-Abelian Flat Directions in a Minimal Superstring Standard Model
Recently, we presented the first non-Abelian flat directions that produce
from a heterotic string model solely the three-generation MSSM states as the
massless spectrum in the observable sector of the low energy effective field
theory. In this paper we continue to develop the systematic techniques for the
analysis of nonrenormalizable superpotential terms and non-Abelian flat
direction in realistic string models. Some of our non-Abelian directions were
F-flat to all finite orders in the superpotential. We study for the same string
model the varying phenomenologies resulting from a large set of such all-order
flat directions. We focus on the quark, charged lepton, and Higgs doublet mass
matrices resulting for our phenomenologically superior non-Abelian flat
direction. We review and apply a string-related method for generating large
mass hierarchies between MSSM generations, first discussed in string-derived
flipped SU(5) models, when all generational mass terms are of renormalizable or
very low non-renormalizable order
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