242 research outputs found
A covariant approach to general field space metric in multi-field inflation
We present a covariant formalism for general multi-field system which enables
us to obtain higher order action of cosmological perturbations easily and
systematically. The effects of the field space geometry, described by the
Riemann curvature tensor of the field space, are naturally incorporated. We
explicitly calculate up to the cubic order action which is necessary to
estimate non-Gaussianity and present those geometric terms which have not yet
known before.Comment: (v1) 18 pages, 1 figure; (v2) references added, typos corrected, to
appear in Journal of Cosmology and Astroparticle Physics; (v3) typos in (54),
(62) and (64) correcte
Axionic dark energy and a composite QCD axion
We discuss the idea that the model-independent (MI) axion of string theory is
the source of quintessential dark energy. The scenario is completed with a
composite QCD axion from hidden sector squark condensation that could serve as
dark matter candidate. The mechanism relies on the fact that the hidden sector
anomaly contribution to the composite axion is much smaller than the QCD
anomaly term. This intuitively surprising scenario is based on the fact that
below the hidden sector scale there are many light hidden sector
quarks. Simply, by counting engineering dimensions the hidden sector instanton
potential can be made negligible compared to the QCD anomaly term.Comment: 9 pages, 7 figure
Towards 5D Grand Unification without SUSY Flavor Problem
We consider the renormalization group approach to the SUSY flavor problem in
the supersymmetric SU(5) model with one extra dimension. In higher dimensional
SUSY gauge theories, it has been recently shown that power corrections due to
the Kaluza-Klein states of gauge fields run the soft masses generated at the
orbifold fixed point to flavor conserving values in the infra-red limit. In
models with GUT breaking at the brane where the GUT scale can be larger than
the compactification scale, we show that the addition of a bulk Higgs
multiplet, which is necessary for the successful unification, is compatible
with the flavor universality achieved at the compactification scale.Comment: JHEP style file of 35 pages with 3 figures, Version to appear in JHE
Collider and Dark Matter Phenomenology of Models with Mirage Unification
We examine supersymmetric models with mixed modulus-anomaly mediated SUSY
breaking (MM-AMSB) soft terms which get comparable contributions to SUSY
breaking from moduli-mediation and anomaly-mediation. The apparent (mirage)
unification of soft SUSY breaking terms at Q=mu_mir not associated with any
physical threshold is the hallmark of this scenario. The MM-AMSB structure of
soft terms arises in models of string compactification with fluxes, where the
addition of an anti-brane leads to an uplifting potential and a de Sitter
universe, as first constructed by Kachru {\it et al.}. The phenomenology mainly
depends on the relative strength of moduli- and anomaly-mediated SUSY breaking
contributions, and on the Higgs and matter field modular weights, which are
determined by the location of these fields in the extra dimensions. We
delineate the allowed parameter space for a low and high value of tan(beta),
for a wide range of modular weight choices. We calculate the neutralino relic
density and display the WMAP-allowed regions. We show the reach of the CERN LHC
and of the International Linear Collider. We discuss aspects of MM-AMSB models
for Tevatron, LHC and ILC searches, muon g-2 and b->s \gamma branching
fraction. We also calculate direct and indirect dark matter detection rates,
and show that almost all WMAP-allowed models should be accessible to a
ton-scale noble gas detector. Finally, we comment on the potential of colliders
to measure the mirage unification scale and modular weights in the difficult
case where mu_mir>>M_GUT.Comment: 34 pages plus 42 EPS figures; version with high resolution figures is
at http://www.hep.fsu.edu/~bae
Bulk Gauge Fields in Warped Space and Localized Supersymmetry Breaking
We consider five dimensional supersymmetric warped scenarios in which the
Standard Model quark and lepton fields are localized on the ultraviolet brane,
while the Standard Model gauge fields propagate in the bulk. Supersymmetry is
assumed to be broken on the infrared brane. The relative sizes of supersymmetry
breaking effects are found to depend on the hierarchy between the infrared
scale and the weak scale. If the infrared scale is much larger than the weak
scale the leading supersymmetry breaking effect on the visible brane is given
by gaugino mediation. The gaugino masses at the weak scale are proportional to
the square of the corresponding gauge coupling, while the dominant contribution
to the scalar masses arises from logarithmically enhanced radiative effects
involving the gaugino mass that are cutoff at the infrared scale. While the LSP
is the gravitino, the NLSP which is the stau is stable on collider time scales.
If however the infrared scale is close to the weak scale then the effects of
hard supersymmetry breaking operators on the scalar masses can become
comparable to those from gaugino mediation. These operators alter the relative
strengths of the couplings of gauge bosons and gauginos to matter, and give
loop contributions to the scalar masses that are also cutoff at the infrared
scale. The gaugino masses, while exhibiting a more complicated dependence on
the corresponding gauge coupling, remain hierarchical and become proportional
to the corresponding gauge coupling in the limit of strong supersymmetry
breaking. The scalar masses are finite and a loop factor smaller than the
gaugino masses. The LSP remains the gravitino.Comment: 36 pages, 2 figure
Implications of Compressed Supersymmetry for Collider and Dark Matter Searches
Martin has proposed a scenario dubbed ``compressed supersymmetry'' (SUSY)
where the MSSM is the effective field theory between energy scales M_{\rm weak}
and M_{\rm GUT}, but with the GUT scale SU(3) gaugino mass M_3<< M_1 or M_2. As
a result, squark and gluino masses are suppressed relative to slepton, chargino
and neutralino masses, leading to a compressed sparticle mass spectrum, and
where the dark matter relic density in the early universe may be dominantly
governed by neutralino annihilation into ttbar pairs via exchange of a light
top squark. We explore the dark matter and collider signals expected from
compressed SUSY for two distinct model lines with differing assumptions about
GUT scale gaugino mass parameters. For dark matter signals, the compressed
squark spectrum leads to an enhancement in direct detection rates compared to
models with unified gaugino masses. Meanwhile, neutralino halo annihilation
rates to gamma rays and anti-matter are also enhanced relative to related
scenarios with unified gaugino masses but, depending on the halo dark matter
distribution, may yet be below the sensitivity of indirect searches underway.
In the case of collider signals, we compare the rates for the potentially
dominant decay modes of the stop_1 which may be expected to be produced in
cascade decay chains at the LHC: \tst_1\to c\tz_1 and \tst_1\to bW\tz_1. We
examine the extent to which multilepton signal rates are reduced when the
two-body decay mode dominates. For the model lines that we examine here, the
multi-lepton signals, though reduced, still remain observable at the LHC.Comment: 22 pages including 24 eps figure
Dynamics of oscillating scalar field in thermal environment
There often appear coherently oscillating scalar fields in particle physics
motivated cosmological scenarios, which may have rich phenomenological
consequences. Scalar fields should somehow interact with background thermal
bath in order to decay into radiation at an appropriate epoch, but introducing
some couplings to the scalar field makes the dynamics complicated. We
investigate in detail the dynamics of a coherently oscillating scalar field,
which has renormalizable couplings to another field interacting with thermal
background. The scalar field dynamics and its resultant abundance are
significantly modified by taking account of following effects : (1) thermal
correction to the effective potential, (2) dissipation effect on the scalar
field in thermal bath, (3) non-perturbative particle production events and (4)
formation of non-topological solitons. There appear many time scales depending
on the scalar mass, amplitude, couplings and the background temperature, which
make the efficiencies of these effects non-trivial.Comment: 45 pages, 6 figures; v2: several typos corrected; v3: minor
corrections and references added; v4: minor corrections to reflect the
published version; v5: minor correction
Collider and Dark Matter Searches in Models with Mixed Modulus-Anomaly Mediated SUSY Breaking
We investigate the phenomenology of supersymmetric models where moduli fields
and the Weyl anomaly make comparable contributions to SUSY breaking effects in
the observable sector of fields. This mixed modulus-anomaly mediated
supersymmetry breaking (MM-AMSB) scenario is inspired by models of string
compactification with fluxes, which have been shown to yield a de Sitter vacuum
(as in the recent construction by Kachru {\it et al}). The phenomenology
depends on the so-called modular weights which, in turn, depend on the location
of various fields in the extra dimensions. We find that the model with zero
modular weights gives mass spectra characterized by very light top squarks
and/or tau sleptons, or where M_1\sim -M_2 so that the bino and wino are
approximately degenerate. The top squark mass can be in the range required by
successful electroweak baryogenesis. The measured relic density of cold dark
matter can be obtained via top squark co-annihilation at low \tan\beta, tau
slepton co-annihilation at large \tan\beta or via bino-wino coannihilation.
Then, we typically find low rates for direct and indirect detection of
neutralino dark matter. However, essentially all the WMAP-allowed parameter
space can be probed by experiments at the CERN LHC, while significant portions
may also be explored at an e^+e^- collider with \sqrt{s}=0.5--1 TeV. We also
investigate a case with non-zero modular weights. In this case,
co-annihilation, A-funnel annihilation and bulk annihilation of neutralinos are
all allowed. Results for future colliders are qualitatively similar, but
prospects for indirect dark matter searches via gamma rays and anti-particles
are somewhat better.Comment: 38 pages including 22 EPS figures; latest version posted to conform
with published versio
- …