Flavour Changing Neutral Currents and Inverted Sfermion Mass Hierarchy

We study the contraints on non-flavour-blind soft supersymmetry breaking terms coming from flavour and CP violating processes in the presence of hierarchical Yukawa couplings, and quantify how much these constraints are weakened in the regions of the MSSM parameter space characterized by heavy gauginos and multi-TeV sfermion masses, respectively. We also study the inverted sfermion mass hierarchy scenario in the context of D-term supersymmetry breaking, and show that generic hierarchical Yukawa couplings with arbitrary phases require first generation squarks in the few 10 TeV range.Comment: 9 pages, 6 figures. Talk given at the XLth Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Aosta Valley, Italy, 5-12 March 2005. V3: one reference correcte

Leptogenesis in SO(10) models with a left-right symmetric seesaw mechanism

We study leptogenesis in supersymmetric SO(10) models with a left-right symmetric seesaw mechanism, including flavour effects and the contribution of the next-to-lightest right-handed neutrino. Assuming M_D = M_u and hierarchical light neutrino masses, we find that successful leptogenesis is possible for 4 out of the 8 right-handed neutrino mass spectra that are compatible with the observed neutrino data. An accurate description of charged fermion masses appears to be an important ingredient in the analysis.Comment: Submitted for the SUSY07 proceedings, 4 pages, 9 figure

Update on Fermion Mass Models with an Anomalous Horizontal U(1) Symmetry

We reconsider models of fermion masses and mixings based on a gauge anomalous horizontal U(1) symmetry. In the simplest model with a single flavon field and horizontal charges of the same sign for all Standard Model fields, only very few charge assignements are allowed when all experimental data, including neutrino oscillation data, is taken into account. We show that a precise description of the observed fermion masses and mixing angles can easily be obtained by generating sets of the order one parameters left unconstrained by the U(1) symmetry. The corresponding Yukawa matrices show several interesting features which may be important for flavour changing neutral currents and CP violation effects in supersymmetric models.Comment: 23 pages, 8 figure

Diffractive SUSY particle production at the LHC

We give detailed predictions for diffractive SUSY Higgs boson and top squark associated productions at the LHC via the exclusive double pomeron exchange mechanism. We study how the SUSY Higgs cross section and the signal over background ratio are enhanced as a function of tangent beta in different regimes. The prospects are particularly promising in the ``anti-decoupling'' regime, which we study in detail. We also give the prospects for a precise measurement of the top squark mass using the threshold scan of central diffractive associated top squark events at the LHC.Comment: 14 pages, 6 fig

Flavor effects in leptogenesis

Flavor effects can have a significant impact on the final estimate of the lepton (and therefore baryon) asymmetry in scenarios of leptogenesis. It is therefore necessary to account fully for this flavor dynamics in the relevant transport equations that describe the production (and washout) of the asymmetry. Doing so can both open up and restrict viable regions of parameter space relative to the predictions of more approximate calculations. In this review, we identify the regimes in which flavor effects can be relevant and illustrate their impact in a number of phenomenological models. These include type I and type II seesaw embeddings, and low-scale resonant scenarios. In addition, we provide an overview of the semi-classical and field-theoretic methods that have been developed to capture flavor effects in a consistent way

On non-universal Goldstino couplings to matter

Using the constrained superfields formalism to describe the interactions of a light goldstino to matter fields in supersymmetric models, we identify generalised, higher-order holomorphic superfield constraints that project out the superpartners and capture the non-universal couplings of the goldstino to matter fields. These arise from microscopic theories in which heavy superpartners masses are of the order of the supersymmetry breaking scale (\sqrt f). In the decoupling limit of infinite superpartners masses, these constraints reduce to the familiar, lower-order universal constraints discussed recently, that describe the universal goldstino-matter fields couplings, suppressed by inverse powers of \sqrt f. We initiate the study of the couplings of the Standard Model (SM) fields to goldstino in the constrained superfields formalism.Comment: 28 pages; one comment adde

Charged lepton contributions to the solar neutrino mixing and theta_13

A charged lepton contribution to the solar neutrino mixing induces a contribution to theta_13, barring cancellations/correlations, which is independent of the model building options in the neutrino sector. We illustrate two robust arguments for that contribution to be within the expected sensitivity of high intensity neutrino beam experiments. We find that the case in which the neutrino sector gives rise to a maximal solar angle (the natural situation if the hierarchy is inverse) leads to a theta_13 close to or exceeding the experimental bound depending on the precise values of theta_12, theta_23, an unknown phase and possible additional contributions. We finally discuss the possibility that the solar angle originates predominantly in the charged lepton sector. We find that the construction of a model of this sort is more complicated. We comment on a recent example of natural model of this type.Comment: 10 pages, 1 figur

A New Parametrization of the Seesaw Mechanism and Applications in Supersymmetric Models

We present a new parametrization of the minimal seesaw model, expressing the heavy-singlet neutrino Dirac Yukawa couplings $(Y_\nu)_{ij}$ and Majorana masses $M_{N_i}$ in terms of effective light-neutrino observables and an auxiliary Hermitian matrix $H.$ In the minimal supersymmetric version of the seesaw model, the latter can be related directly to other low-energy observables, including processes that violate charged lepton flavour and CP. This parametrization enables one to respect the stringent constraints on muon-number violation while studying the possible ranges for other observables by scanning over the allowed parameter space of the model. Conversely, if any of the lepton-flavour-violating process is observed, this measurement can be used directly to constrain $(Y_\nu)_{ij}$ and $M_{N_i}.$ As applications, we study flavour-violating $\tau$ decays and the electric dipole moments of leptons in the minimal supersymmetric seesaw model.Comment: Important references adde

Fair scans of the seesaw. Consequences for predictions on LFV processes

Usual analyses based on scans of the seesaw parameter-space can be biassed since they do not cover in a fair way the complete parameter-space. More precisely, we show that in the common "R-parametrization", many acceptable R-matrices, compatible with the perturbativity of Yukawa couplings, are normally disregarded from the beginning, which produces biasses in the results. We give a straightforward procedure to scan the space of complex R-matrices in a complete way, giving a very simple rule to incorporate the perturbativity requirement as a condition for the entries of the R-matrix, something not considered before. As a relevant application of this, we show that the extended believe that BR(mu --> e, gamma) in supersymmetric seesaw models depends strongly on the value of theta_13 is an "optical effect" produced by such biassed scans, and does not hold after a careful analytical and numerical study. When the complete scan is done, BR(mu --> e, gamma) gets very insensitive to theta_13. Moreover, the values of the branching ratio are typically larger than those quoted in the literature, due to the large number of acceptable points in the parameter-space which were not considered before. Including (unflavoured) leptogenesis does not introduce any further dependence on theta_13, although decreases the typical value of BR(mu --> e, gamma).Comment: 22 pages, 5 figure