1,732 research outputs found
CP Violation from 5-dimensional QED
It has been shown that QED in (1+4)-dimensional space-time, with the fifth
dimension compactified on a circle, leads to CP violation (CPV). Depending on
fermionic boundary conditions, CPV may be either explicit (through the
Scherk--Schwarz mechanism), or spontaneous (via the Hosotani mechanism). The
fifth component of the gauge field acquires (at the one-loop level) a non-zero
vacuum expectation value. In the presence of two fermionic fields, this leads
to spontaneous CPV in the case of CP-symmetric boundary conditions.
Phenomenological consequences are illustrated by a calculation of the electric
dipole moment for the fermionic zero-modes.Comment: 11 pages, 2 figure
Kaluza-Klein States versus Winding States: Can Both Be Above the String Scale?
When closed strings propagate in extra compactified dimensions, a rich
spectrum of Kaluza-Klein states and winding states emerges. Since the masses of
Kaluza-Klein states and winding states play a reciprocal role, it is often
believed that either the lightest Kaluza-Klein states or the lightest winding
states must be at or below the string scale. In this paper, we demonstrate that
this conclusion is no longer true for compactifications with non-trivial shape
moduli. Specifically, we demonstrate that toroidal compactifications exist for
which all Kaluza-Klein states as well as all winding states are heavier than
the string scale. This observation could have important phenomenological
implications for theories with reduced string scales, suggesting that it is
possible to cross the string scale without detecting any states associated with
spacetime compactification.Comment: 8 pages, LaTeX, no figure
Duality without Supersymmetry: The Case of the SO(16)xSO(16) String
We extend strong/weak coupling duality to string theories without spacetime
supersymmetry, and focus on the case of the unique ten-dimensional,
nonsupersymmetric, tachyon-free heterotic string. We
construct a tachyon-free heterotic string model that interpolates smoothly
between this string and the ten-dimensional supersymmetric heterotic
string, and we construct a dual for this interpolating model. We find that the
perturbative massless states of our dual theories precisely match within a
certain range of the interpolation. Further evidence for this proposed duality
comes from a calculation of the one-loop cosmological constant in both
theories, as well as the presence of a soliton in the dual theory. This is
therefore the first known duality relation between nonsupersymmetric
tachyon-free string theories. Using this duality, we then investigate the
perturbative and nonperturbative stability of the string,
and present a conjecture concerning its ultimate fate.Comment: 15 pages, LaTeX, 3 figure
Dark Matter and Dark Forces from a supersymmetric hidden sector
We show that supersymmetric "Dark Force" models with gravity mediation are
viable. To this end, we analyse a simple string-inspired supersymmetric hidden
sector model that interacts with the visible sector via kinetic mixing of a
light Abelian gauge boson with the hypercharge. We include all induced
interactions with the visible sector such as neutralino mass mixing and the
Higgs portal term. We perform a detailed parameter space scan comparing the
produced dark matter relic abundance and direct detection cross sections to
current experiments.Comment: 40 pages, 11 figures comprising 21 plots. 4Mb total size. v2: figures
and references updated; typos removed; some extra explanations added. Matches
version published in PR
Bulk Fermion Stars with New Dimensions
Many efforts have been devoted to the studies of the phenomenology in
particle physics with extra dimensions. We propose degenerate fermion stars
with extra dimensions and study what features characterized by the size of
extra dimensions should appear in its structure. We find that Kaluza-Klein
excited modes arise for the larger scale of extra dimensions and examine the
conditions on which different layers should be caused in the inside of the
stars. We expound how the extra dimensions affect on physical quantities.Comment: 20 pages, 14 figure
Gauge Coupling Constant Unification With Planck Scale Values Of Moduli
Convergence of the standard model gauge coupling constants to a common value
at around GeV is studied in the context of orbifold theories
where the modular symmetry groups for and moduli are broken to
subgroups of . The values of the moduli required for this
unification of coupling constants are studied for this case and also for the
case where string unification is accompanied by unification to a gauge group
larger then Comment: Tex, 15 pages, minor typos corrected and some references adde
Multicomponent Dark Matter in Supersymmetric Hidden Sector Extensions
Most analyses of dark matter within supersymmetry assume the entire cold dark
matter arising only from weakly interacting neutralinos. We study a new class
of models consisting of hidden sector extensions of the MSSM that
includes several stable particles, both fermionic and bosonic, which can be
interpreted as constituents of dark matter. In one such class of models, dark
matter is made up of both a Majorana dark matter particle, i.e., a neutralino,
and a Dirac fermion with the current relic density of dark matter as given by
WMAP being composed of the relic density of the two species. These models can
explain the PAMELA positron data and are consistent with the anti-proton flux
data, as well as the photon data from FERMI-LAT. Further, it is shown that such
models can also simultaneously produce spin independent cross sections which
can be probed in CDMS-II, XENON-100 and other ongoing dark matter experiments.
The implications of the models at the LHC and at the NLC are also briefly
discussed.Comment: Journal: Physical Review D, Latex 32 pages, 4 eps figure
Phenomenological Constraints on Axion Models of Dynamical Dark Matter
In two recent papers (arXiv:1106.4546, arXiv:1107.0721), we introduced
"dynamical dark matter" (DDM), a new framework for dark-matter physics in which
the requirement of stability is replaced by a delicate balancing between
lifetimes and cosmological abundances across a vast ensemble of individual
dark-matter components whose collective behavior transcends that normally
associated with traditional dark-matter candidates. We also presented an
explicit model involving axions in large extra spacetime dimensions, and
demonstrated that this model has all of the features necessary to constitute a
viable realization of the general DDM framework. In this paper, we complete our
study by performing a general analysis of all phenomenological constraints
which are relevant to this bulk-axion DDM model. Although the analysis in this
paper is primarily aimed at our specific DDM model, many of our findings have
important implications for bulk axion theories in general. Our analysis can
also serve as a prototype for phenomenological studies of theories in which
there exist large numbers of interacting and decaying particles.Comment: 48 pages, LaTeX, 13 figures, 1 tabl
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