Orbifold-induced μ\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

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

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