157 research outputs found
Box Compactification and Supersymmetry Breaking
We discuss all possible compactifications on flat three-dimensional smooth
spaces. In particular, various fields are studied on a box with opposite sides
identified, after two of them are rotated by , and their spectra are
obtained. The compactification of a general 7D supersymmetric theory in such a
box is considered and the corresponding four-dimensional theory is studied, in
relation to the boundary conditions chosen. The resulting spectrum, according
to the allowed field boundary conditions, corresponds to partially or
completely broken supersymmmetry. We briefly discuss also the breaking of gauge
symmetries under the proposed box compactification.Comment: 11 pages, 1figure. As it appeared in Phys. Lett.
Localized Gravitons, Gauge Bosons and Chiral Fermions in Smooth Spaces Generated by a Bounce
We study five-dimensional solutions to Einstein equations coupled to a scalar
field. Bounce-type solutions for the scalar field are associated with AdS_5
spaces with smooth warp functions. Gravitons are dynamically localized in this
framework in analogy to the Randall-Sundrum solution whereas, a bulk fermion
gives rise to a single chiral zero mode localized at the bounce. Additional
bulk scalar fields are incorporated in this picture. The dilaton, as a bulk
scalar leads, through its coupling, to localized gauge boson fields, something
that holds also in the case that the bounce system is replaced by a brane.Comment: latex, 14 page
Inflation in no-scale supergravity
Supergravity is known to be equivalent to standard Supergravity
coupled to two chiral supermultiples with a no-scale K\"ahler potential. Within
this framework, that can accomodate vanishing vacuum energy and spontaneous
supersymmetry breaking, we consider modifications of the associated
superpotential and study the resulting models, which, viewed as generalizations
of the Starobinsky model, for a range of the superpotential parameters,
describe viable single-field slow-roll inflation. In all models studied in this
work the tensor to scalar ratio is found to be small, well below the upper
bound established by the very recent PLANCK and BICEP2 data.Comment: 15 pages, 6 figures, references and comments adde
A Self-Tuning Solution of the Cosmological Constant Problem
We discuss the four-dimensional cosmological constant problem in a
five-dimensional setting. A scalar field coupled to the SM forms dynamically a
smooth brane with four-dimensional Poincare invariance, independently of SM
physics. In this respect, our solution may be regarded as a self-tuning
solution, free of any singularities and fine-tuning problems.Comment: latex, 4 pages, some new material adde
Palatini inflation in models with an term
The Starobinsky model, considered in the framework of the Palatini formalism,
in contrast to the metric formulation, does not provide us with a model for
inflation, due to the absence of a propagating scalar degree of freedom that
can play the role of the inflaton. In the present article we study the Palatini
formulation of the Starobinsky model coupled, in general nonminimally, to
scalar fields and analyze its inflationary behavior. We consider scalars,
minimally or nonminimally coupled to the Starobinsky model, such as a quadratic
model, the induced gravity model or the standard Higgs-like inflation model and
analyze the corresponding modifications favorable to inflation. In addition we
examine the case of a classically scale-invariant model driven by the
Coleman-Weinberg mechanism. In the slow-roll approximation, we analyze the
inflationary predictions of these models and compare them to the latest
constraints from the Planck collaboration. In all cases, we find that the
effect of the term is to lower the value of the tensor-to-scalar ratio.Comment: 22 pages, 8 figures, JCAP accepted versio
Rescuing Quartic and Natural Inflation in the Palatini Formalism
When considered in the Palatini formalism, the Starobinsky model does not
provide us with a mechanism for inflation due to the absence of a propagating
scalar degree of freedom. By (non)--minimally coupling scalar fields to the
Starobinsky model in the Palatini formalism we can in principle describe the
inflationary epoch. In this article, we focus on the minimally coupled quartic
and natural inflation models. Both theories are excluded in their simplest
realization since they predict values for the inflationary observables that are
outside the limits set by the Planck data. However, with the addition of the
term and the use of the Palatini formalism, we show that these models can
be rendered viable.Comment: JCAP accepted version, 16 pages, 7 figure
Rare Top-quark Decays to Higgs boson in MSSM
In full one-loop generality and in next-to-leading order in QCD, we study
rare top to Higgs boson flavour changing decay processes with
quarks, in the general MSSM with R-parity conservation. Our primary
goal is to search for enhanced effects on that could be visible
at current and high luminosity LHC running. To this end, we perform an
analytical expansion of the amplitude in terms of flavour changing squark mass
insertions that treats both cases of hierarchical and degenerate squark masses
in a unified way. We identify two enhanced effects allowed by various
constraints: one from holomorphic trilinear soft SUSY breaking terms and/or
right handed up squark mass insertions and another from non-holomorphic
trilinear soft SUSY breaking terms and light Higgs boson masses. Interestingly,
even with flavour violating effects in the, presently
unconstrained, up-squark sector, SUSY effects on come out to be
unobservable at LHC mainly due to leading order cancellations between penguin
and self energy diagrams and the constraints from charge- and colour-breaking
minima (CCB) of the MSSM vacuum. An exception to this conclusion may be effects
arising from non-holomorphic soft SUSY breaking terms in the region where the
CP-odd Higgs mass is smaller than the top-quark mass but this scenario is
disfavoured by recent LHC searches. Our calculations for decay are
made available in SUSY_FLAVOR numerical library.Comment: 32 pages, 6 figures; version accepted for publication in JHEP:
additional comparison with literature added, minor misprints correcte
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