1,265 research outputs found

### Orbifold-induced $\mu$ term and electroweak symmetry breaking

It is known that a Higgs $\mu$ term can be naturally generated through the
K\"ahler potential in orbifold string models in which one of the three
compactified complex planes has order two. In this class of models explicit
expressions for both the $\mu$ parameter and the soft SUSY-breaking parameters
can be obtained under the assumption that the goldstino is an arbitrary linear
combination of the fermionic partners of the dilaton $S$ and all the moduli
$T_i,U_i$. We apply this picture to the MSSM and explore the consistency of the
obtained boundary conditions with radiative gauge symmetry breaking. We find
that consistency with the measured value of the top-quark mass can only be
achieved if the goldstino has a negligible dilatino component and relevant
components along the $T_3,U_3$ moduli associated to the order-two complex
plane.Comment: 9 pages, LaTeX fil

### Radiative corrections to the decay H==>hh in the Minimal Supersymmetric Standard Model

We set up a suitable renormalization programme for the one-loop computation
of the decay rate Gamma(H==>hh) in the Minimal Supersymmetric extension of the
Standard Model. We then perform an explicit diagrammatic calculation, including
the full contributions from top, bottom, stop and sbottom loops. We find that,
for tan(beta) close to 1, and m_H greater than or approximately equal to 2 m_t,
the results can significantly differ from those previously obtained in the
effective potential approach. However, the latter method remains a good
approximation in the region of parameter space which is most relevant for H
searches at large hadron colliders.Comment: 11 A4-pages, 3 figures not included, CERN-TH.6603/9

### Soft supersymmetry-breaking terms from supergravity and superstring models

We review the origin of soft supersymmetry-breaking terms in N=1 supergravity
models of particle physics. We first consider general formulae for those terms
in general models with a hidden sector breaking supersymmetry at an
intermediate energy scale. The results for some simple models are given. We
then consider the results obtained in some simple superstring models in which
particular assumptions about the origin of supersymmetry breaking are made.
These are models in which the seed of supersymmetry breaking is assumed to be
originated in the dilaton/moduli sector of the theory.Comment: 24 pages, to appear in the book `Perspectives on Supersymmetry',
World Scientific, Editor G. Kane; some comments and references adde

### Three-loop corrections to the lightest Higgs scalar boson mass in supersymmetry

I evaluate the largest three-loop corrections to the mass of the lightest
Higgs scalar boson in the Minimal Supersymmetric Standard Model in a
mass-independent renormalization scheme, using effective field theory and
renormalization group methods. The contributions found here are those that
depend only on strong and Yukawa interactions and on the leading and
next-to-leading logarithms of the ratio of a typical superpartner mass scale to
the top quark mass. The approximation assumes that all superpartners and the
other Higgs bosons can be treated as much heavier than the top quark, but does
not assume their degeneracy. I also discuss the consistent addition of the
three-loop corrections to a complete two-loop calculation.Comment: 9 page

### Bottom-Up Reconstruction Scenarios for (un)constrained MSSM Parameters at the LHC

We consider some specific inverse problem or "bottom-up" reconstruction
strategies at the LHC for both general and constrained MSSM parameters,
starting from a plausibly limited set of sparticle identification and mass
measurements, using mainly gluino/squark cascade decays, plus eventually the
lightest Higgs boson mass. For the three naturally separated sectors of:
gaugino/Higgsino, squark/slepton, and Higgs parameters, we examine different
step-by-step algorithms based on rather simple, entirely analytical, inverted
relations between masses and basic MSSM parameters. This includes also
reasonably good approximations of some of the relevant radiative correction
calculations. We distinguish the constraints obtained for a general MSSM from
those obtained with universality assumptions in the three different sectors.
Our results are compared at different stages with the determination from more
standard "top-down" fit of models to data, and finally combined into a global
determination of all the relevant parameters. Our approach gives complementary
information to more conventional analysis, and is not restricted to the
specific LHC measurement specificities. In addition, the bottom-up
renormalization group evolution of general MSSM parameters, being an important
ingredient in this framework, is illustrated as a new publicly available option
of the MSSM spectrum calculation code "SuSpect".Comment: 52 pages, 22 figures. Slight reorganization of sections, a few more
results for the neutralino sector, one appendix added on neutralino sector
calculation details. Version to appear in Phys. Rev.

### Low-scale supersymmetry breaking: effective description, electroweak breaking and phenomenology

We consider supersymmetric scenarios in which the scale of SUSY breaking is
low, sqrt{F}=O(TeV). Instead of studying specific models of this type, e.g.
those with extra dimensions and low fundamental scale, we follow a
model-independent approach based on a general effective Lagrangian, in which
the MSSM supermultiplets are effectively coupled to a singlet associated to
SUSY breaking. Our goal is to analyse the interplay bewteen SUSY breaking and
electroweak breaking, generalizing earlier results. The conventional MSSM
picture can be substantially modified, mainly because the Higgs potential
contains additional effective quartic terms and resembles that of
two-Higgs-doublet models, with an additional singlet. Novel opportunities to
achieve electroweak breaking arise, and the electroweak scale may be obtained
in a less fine-tuned way. Also the Higgs spectrum can be strikingly changed,
and the lightest state can be much heavier than in usual supersymmetric
scenarios. Other effects appear in the chargino and neutralino sectors, which
contain the goldstino. Finally, we discuss the role of electroweak breaking in
processes in which two goldstinos could be emitted, such as fermion-antifermion
annihilation and the invisible decay of a Z boson or of neutral Higgs bosons.Comment: LaTeX, 47 pages, 5 figures; typos corrected, to appear in Nucl. Phys.

### F-term inflation in Superstring Theories

A supersymmetric inflationary stage dominated by an $F$-term has the problem
that the flatness of the potential is spoiled by supergravity corrections, that
is the slow-roll parameter $\eta$ gets contributions of order unity. We show
that in $F$-term inflationary models based on strings there is natural way of
obtaining small values of $\eta$. This happens in models of hybrid inflation
based on orbifold constructions, in which a modulus $T$ field is responsible
for the large value of the potential during inflation, and a second field
$\phi$ with appropriate modular weight is responsible for the roll-over. We
illustrate the mechanism with a model in which the inflaton potential is
provided by gaugino condensation, leading to succesful inflation.Comment: 9 pages, LaTe

### Sparticle Spectrum and Dark Matter in M-Theory

The phenomenological implications of the eleven dimensional limit of
$M$-theory (strongly coupled $E_8\times E_8$) are investigated. In particular
we calculate the supersymmetric spectrum subject to constraints of correct
electroweak symmetry breaking and the requirement that the lighest
supersymmetric particle provides the dark matter of the universe. The $B$-soft
term associated with the generation of a $\mu$ term in the superpotential is
calculated and its phenomenology is discussed.Comment: LaTeX file 15 pages,1 figure adde

### FCNCs in supersymmetric multi-Higgs doublet models

We conduct a general discussion of supersymmetric models with three families
in the Higgs sector. We analyse the scalar potential, and investigate the
minima conditions, deriving the mass matrices for the scalar, pseudoscalar and
charged states. Depending on the Yukawa couplings and the Higgs spectrum, the
model might allow the occurrence of potentially dangerous flavour changing
neutral currents at the tree-level. We compute model-independent contributions
for several observables, and as an example we apply this general analysis to a
specific model of quark-Higgs interactions, discussing how compatibility with
current experimental data constrains the Higgs sector.Comment: 30 pages, 9 figures. Comments and references added. Final version
published in Physical Review

### Challenges for MSSM Higgs searches at Hadron Colliders

In this article we analyze the impact of B-physics and Higgs physics at LEP
on standard and non-standard Higgs bosons searches at the Tevatron and the LHC,
within the framework of minimal flavor violating supersymmetric models. The
B-physics constraints we consider come from the experimental measurements of
the rare B-decays b -> s gamma and B_u -> tau nu and the experimental limit on
the B_s -> mu+ mu- branching ratio. We show that these constraints are severe
for large values of the trilinear soft breaking parameter A_t, rendering the
non-standard Higgs searches at hadron colliders less promising. On the contrary
these bounds are relaxed for small values of A_t and large values of the
Higgsino mass parameter mu, enhancing the prospects for the direct detection of
non-standard Higgs bosons at both colliders. We also consider the available
ATLAS and CMS projected sensitivities in the standard model Higgs search
channels, and we discuss the LHC's ability in probing the whole MSSM parameter
space. In addition we also consider the expected Tevatron collider
sensitivities in the standard model Higgs h -> b bbar channel to show that it
may be able to find 3 sigma evidence in the B-physics allowed regions for small
or moderate values of the stop mixing parameter.Comment: 22 pages, 5 figures. Added references and acknowledgements. Submitted
to PR

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