81 research outputs found
Towards Realistic String Vacua From Branes At Singularities
We report on progress towards constructing string models incorporating both
realistic D-brane matter content and moduli stabilisation with dynamical
low-scale supersymmetry breaking. The general framework is that of local
D-brane models embedded into the LARGE volume approach to moduli stabilisation.
We review quiver theories on del Pezzo () singularities including
both D3 and D7 branes. We provide supersymmetric examples with three
quark/lepton families and the gauge symmetries of the Standard, Left-Right
Symmetric, Pati-Salam and Trinification models, without unwanted chiral
exotics. We describe how the singularity structure leads to family symmetries
governing the Yukawa couplings which may give mass hierarchies among the
different generations. We outline how these models can be embedded into compact
Calabi-Yau compactifications with LARGE volume moduli stabilisation, and state
the minimal conditions for this to be possible. We study the general structure
of soft supersymmetry breaking. At the singularity all leading order
contributions to the soft terms (both gravity- and anomaly-mediation) vanish.
We enumerate subleading contributions and estimate their magnitude. We also
describe model-independent physical implications of this scenario. These
include the masses of anomalous and non-anomalous U(1)'s and the generic
existence of a new hyperweak force under which leptons and/or quarks could be
charged. We propose that such a gauge boson could be responsible for the ghost
muon anomaly recently found at the Tevatron's CDF detector.Comment: 40 pages, 10 figure
SUSY Breaking in Local String/F-Theory Models
We investigate bulk moduli stabilisation and supersymmetry breaking in local
string/F-theory models where the Standard Model is supported on a del Pezzo
surface or singularity. Computing the gravity mediated soft terms on the
Standard Model brane induced by bulk supersymmetry breaking in the LARGE volume
scenario, we explicitly find suppressions by M_s/M_P ~ V^{-1/2} compared to
M_{3/2}. This gives rise to several phenomenological scenarios, depending on
the strength of perturbative corrections to the effective action and the source
of de Sitter lifting, in which the soft terms are suppressed by at least
M_P/V^{3/2} and may be as small as M_P/V^2. Since the gravitino mass is of
order M_{3/2} ~ M_P/V, for TeV soft terms all these scenarios give a very heavy
gravitino (M_{3/2} >= 10^8 GeV) and generically the lightest moduli field is
also heavy enough (m >= 10 TeV) to avoid the cosmological moduli problem. For
TeV soft terms, these scenarios predict a minimal value of the volume to be V ~
10^{6-7} in string units, which would give a unification scale of order M_{GUT}
~ M_s V^{1/6} ~ 10^{16} GeV. The strong suppression of gravity mediated soft
terms could also possibly allow a scenario of dominant gauge mediation in the
visible sector but with a very heavy gravitino M_{3/2} > 1 TeV
Neutralino Dark Matter in BMSSM Effective Theory
We study thermal neutralino dark matter in an effective field theory
extension of the MSSM, called "Beyond the MSSM" (BMSSM) in Dine, Seiberg and
Thomas (2007). In this class of effective field theories, the field content of
the MSSM is unchanged, but the little hierarchy problem is alleviated by
allowing small corrections to the Higgs/higgsino part of the Lagrangian. We
perform parameter scans and compute the dark matter relic density. The light
Higgsino LSP scenario is modified the most; we find new regions of parameter
space compared to the standard MSSM. This involves interesting interplay
between the WMAP dark matter bounds and the LEP chargino bound. We also find
some changes for gaugino LSPs, partly due to annihilation through a Higgs
resonance, and partly due to coannihilation with light stops in models that are
ruled in by the new effective terms.Comment: 37 pages + appendi
String theoretic QCD axion with stabilized saxion and the pattern of supersymmetry breaking
String theoretic axion is a prime candidate for the QCD axion solving the
strong CP problem. For a successful realization of the QCD axion in string
theory, one needs to stabilize moduli including the scalar partner (saxion) of
the QCD axion, while keeping the QCD axion unfixed until the low energy QCD
instanton effects are turned on. We note that a simple generalization of KKLT
moduli stabilization provides such set-up realizing the axion solution to the
strong CP problem. Although some details of moduli stabilization are different
from the original KKLT scenario, this set-up leads to the mirage mediation
pattern of soft SUSY breaking terms as in the KKLT case, preserving flavor and
CP as a consequence of approximate scaling and axionic shift symmetries. The
set-up also gives an interesting pattern of moduli masses which might avoid the
cosmological moduli, gravitino and axion problems.Comment: JHEP style, 21 pages, 3 figures; typos correcte
The Gaugino Code
Gauginos might play a crucial role in the search for supersymmetry at the
Large Hadron Collider (LHC). Mass predictions for gauginos are rather robust
and often related to the values of the gauge couplings. We analyse the ratios
of gaugino masses in the LHC energy range for various schemes of supersymmetry
breakdown and mediation. Three distinct mass patterns emerge.Comment: 42 pages, Latex; a discussion of deflected anomaly mediation added,
references adde
Energy Transfer between Throats from a 10d Perspective
Strongly warped regions, also known as throats, are a common feature of the
type IIB string theory landscape. If one of the throats is heated during
cosmological evolution, the energy is subsequently transferred to other throats
or to massless fields in the unwarped bulk of the Calabi-Yau orientifold. This
energy transfer proceeds either by Hawking radiation from the black hole
horizon in the heated throat or, at later times, by the decay of
throat-localized Kaluza-Klein states. In both cases, we calculate in a 10d
setup the energy transfer rate (respectively decay rate) as a function of the
AdS scales of the throats and of their relative distance. Compared to existing
results based on 5d models, we find a significant suppression of the energy
transfer rates if the size of the embedding Calabi-Yau orientifold is much
larger than the AdS radii of the throats. This effect can be partially
compensated by a small distance between the throats. These results are
relevant, e.g., for the analysis of reheating after brane inflation. Our
calculation employs the dual gauge theory picture in which each throat is
described by a strongly coupled 4d gauge theory, the degrees of freedom of
which are localized at a certain position in the compact space.Comment: 25 pages; a comment adde
A Nonlinear Force-Free Magnetic Field Approximation Suitable for Fast Forward-Fitting to Coronal Loops. I. Theory
We derive an analytical approximation of nonlinear force-free magnetic field
solutions (NLFFF) that can efficiently be used for fast forward-fitting to
solar magnetic data, constrained either by observed line-of-sight magnetograms
and stereoscopically triangulated coronal loops, or by 3D vector-magnetograph
data. The derived NLFFF solutions provide the magnetic field components
, , , the force-free parameter
, the electric current density , and are
accurate to second-order (of the nonlinear force-free -parameter). The
explicit expressions of a force-free field can easily be applied to modeling or
forward-fitting of many coronal phenomena.Comment: Solar Physics (in press), 26 pages, 11 figure
Low-Energy Supersymmetry Breaking from String Flux Compactifications: Benchmark Scenarios
Soft supersymmetry breaking terms were recently derived for type IIB string
flux compactifications with all moduli stabilised. Depending on the choice of
the discrete input parameters of the compactification such as fluxes and ranks
of hidden gauge groups, the string scale was found to have any value between
the TeV and GUT scales. We study the phenomenological implications of these
compactifications at low energy. Three realistic scenarios can be identified
depending on whether the Standard Model lies on D3 or D7 branes and on the
value of the string scale. For the MSSM on D7 branes and the string scale
between 10^12 GeV and 10^17 GeV we find that the LSP is a neutralino, while for
lower scales it is the stop. At the GUT scale the results of the fluxed MSSM
are reproduced, but now with all moduli stabilised. For the MSSM on D3 branes
we identify two realistic scenarios. The first one corresponds to an
intermediate string scale version of split supersymmetry. The second is a
stringy mSUGRA scenario. This requires tuning of the flux parameters to obtain
the GUT scale. Phenomenological constraints from dark matter, (g-2)_mu and
BR(b->s gamma) are considered for the three scenarios. We provide benchmark
points with the MSSM spectrum, making the models suitable for a detailed
phenomenological analysis.Comment: 29 pages, 12 figures, reference adde
Type IIA Orientifolds on General Supersymmetric Z_N Orbifolds
We construct Type IIA orientifolds for general supersymmetric Z_N orbifolds.
In particular, we provide the methods to deal with the non-factorisable
six-dimensional tori for the cases Z7, Z8, Z8', Z12 and Z12'. As an application
of these methods we explicitly construct many new orientifold models.Comment: 48 pages, LaTeX, 14 figures, refs. added, closed string spectra
slightly change
Metastable Vacua in Flux Compactifications and Their Phenomenology
In the context of flux compactifications, metastable vacua with a small
positive cosmological constant are obtained by combining a sector where
supersymmetry is broken dynamically with the sector responsible for moduli
stabilization, which is known as the F-uplifting. We analyze this procedure in
a model-independent way and study phenomenological properties of the resulting
vacua.Comment: 21 pages, 19 figures; v2: matches version published in JHE
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