2,390 research outputs found
Electroweak and Flavor Physics in Extensions of the Standard Model with Large Extra Dimensions
We study the implications of extra dimensions of size on
electroweak and flavor physics due to the presence of Kaluza-Klein excitations
of the SM gauge-bosons. We consider several scenarios with the SM fermions
either living in the bulk or being localized at different points of an extra
dimension. Global fits to electroweak observables provide lower bounds on 1/R,
which are generically in the 2-5 TeV range. We find, however, certain models
where the fit to electroweak observables is better than in the SM, because of
an improvement in the prediction to the weak charge Q_W. We also consider the
case of softly-broken supersymmetric theories and we find new non-decoupling
effects that put new constraints on 1/R. If quarks of different families live
in different points of the extra dimension, we find that the Kaluza-Klein modes
of the SM gluons generate (at tree level) dangerous flavor and CP-violating
interactions. The lower bounds on 1/R can increase in this case up to 5000 TeV,
disfavoring these scenarios in the context of TeV-strings.Comment: 21 pages, 3 figures, Late
A New Gauge Mediation Theory
We propose a class of models with gauge mediation of supersymmetry breaking,
inspired by simple brane constructions, where R-symmetry is very weakly broken.
The gauge sector has an extended N=2 supersymmetry and the two electroweak
Higgses form an N=2 hypermultiplet, while quarks and leptons remain in N=1
chiral multiplets. Supersymmetry is broken via the D-term expectation value of
a secluded U(1) and it is transmitted to the Standard Model via gauge
interactions of messengers in N=2 hypermultiplets: gauginos thus receive Dirac
masses. The model has several distinct experimental signatures with respect to
ordinary models of gauge or gravity mediation realizations of the Minimal
Supersymmetric Standard Model (MSSM). First, it predicts extra states as a
third chargino that can be observed at collider experiments. Second, the
absence of a D-flat direction in the Higgs sector implies a lightest Higgs
behaving exactly as the Standard Model one and thus a reduction of the `little'
fine-tuning in the low tan(beta) region. This breaking of supersymmetry can be
easily implemented in string theory modelsComment: 23 pages, 3 figures, uses axodraw.sty. v2: a mistake in the radiative
generation of the scalar masses is corrected. The main conclusions are
unchange
Indirect Effect of Supersymmetric Triplets in Stop Decays
We study an extension of the minimal supersymmetric standard model with a
zero hypercharge triplet, and the effect that such a particle has on stop
decays. This model has the capability of predicting a 125.5 GeV Higgs even in
the presence of light stops and it can modify the diphoton rate by means of the
extra charged fermion triplet coupled to the Higgs. Working in the limit where
the scalar triplet decouples, and with small values of mA, we find that the
fermion triplet can greatly affect the branching ratios of the stops, even in
the absence of a direct stop-triplet coupling. We compare the triplet extension
with the MSSM and discuss how the additional fields affect the search for stop
pair production.Comment: pdfLateX, 16 pages, 7 figures, 2 tables, Typos, minor changes.
Version published in JHE
Inflation from IIB Superstrings with Fluxes
We study the conditions needed to have an early epoch of inflationary
expansion with a potential coming from IIB superstring theory with fluxes
involving two moduli fields. The phenomenology of this potential is different
from the usual hybrid inflation scenario and we analize the possibility that
the system of field equations undergo a period of inflation in three different
regimes with the dynamics modified by a Randall-Sundrum II term in the
Friedmann equation. We find that the system can produce inflation and due to
the modification of the dynamics, a period of accelerated contraction can
follow or preceed this inflationary stage depending on the sign of one of the
parameters of the potential. We discuss on the viability of this model in a
cosmological context.Comment: 10 pages, 6 figure
Triviality and vacuum stability bounds in the three-loop neutrino mass model
We study theoretical constraints on the parameter space under the conditions
from vacuum stability and triviality in the three-loop radiative seesaw model
with TeV-scale right-handed neutrinos which are odd under the parity. In
this model, some of the neutrino Yukawa coupling constants can be of the order
of one. Requirement of strongly first order phase transition for successful
electroweak baryogenes is also prefers order-one coupling constants in the
scalar sector. Hence, it is important to clarify whether this model satisfies
those theoretical conditions up to a given cutoff scale. It is found that the
model can be consistent up to the scale above 10 TeV in the parameter region
where the neutrino data, the lepton flavor violation data, the thermal relic
abundance of dark matter as well as the requirement from the strongly first
order phase transition are satisfied.Comment: 22 pages, 14 figure
Brans-Dicke-type theories and avoidance of the cosmological singularity
We tudy flat Friedmann-Robertson-Walker cosmology in Brans-Dicke-type
theories of gravitation with minimal coupling between the scalar field and the
matter fields in the Einstein frame (general relativity with an extra scalar
field) for arbitrary values of the Brans-Dicke parameter . It is
shown that the cosmological singularity occuring in the Einstein frame
formulation of this theory is removed in the Jordan frame in the range
. This result is interpreted in the ligth of a
viewpoint (first presented in reference gr-qc/9905071) asserting that both
Jordan frame and Einstein frame formulations of general relativity are
physically equivalent. The implications of the obtained result for string
theory are outlined.Comment: 9 pages, LaTeX, no figures. Improved version accepted for publication
in PR
Analisis Financiero de la Fundacion Integral Campesina (Finca-Costa Rica)
This paper attempts a financial evaluation of Finca-Costa Rica. This private development organization has experienced substantial growth since 1985. Operation losses, in real terms, its subsidy dependence, and the rate of decapitalization have significantly declined as the organization has expanded its operations. Although the general trend of most indicators is positive, Finca is not yet institutionally viable and financially self-sufficient. Despite some weaknesses originating from past mistakes, Finca has acquired enough strength and faces good opportunities to achieve institutional viability in a reasonable period of time. The achievement of this objective is contingent upon the adoption of appropriate financial policies
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