196,458 research outputs found
Tree level gauge mediation
No full textWe propose a new scheme in which supersymmetry breaking is communicated to the MSSM sfermions by GUT gauge interactions at the tree level. The (positive) contribution of MSSM fields to Str(M(2)) is automatically compensated by a (negative) contribution from heavy fields. Sfermion masses are flavour universal, thus solving the supersymmetric flavour problem. In the simplest SO(10) embedding, the ratio of different sfermion masses is predicted and differs from mSugra and other schemes, thus making this framework testable at the LHC. Gaugino masses are generated at the loop level but enhanced by model dependent factors
Flavor and CP violation in Higgs decays
No full textFlavor violating interactions of the Higgs boson are a generic feature of models with extended electroweak symmetry breaking sectors. Here, we investigate CP violation in these interactions, which can arise from interference of tree-level and 1-loop diagrams. We compute the CP asymmetry in flavor violating Higgs decays in an effective field theory with only one Higgs boson and in a general Type-III Two Higgs Doublet Model (2HDM). We find that large (~ O(10%)) asymmetries are possible in the 2HDM if one of the extra Higgs bosons has a mass similar to the Standard Model Higgs. For the poorly constrained decay modes h -> tau mu and h -> tau e, this implies that large lepton charge asymmetries could be detectable at the LHC. We quantify this by comparing the sensitivity of the LHC to existing direct and indirect constraints. Interestingly, detection prospects are best if Higgs mixing is relatively small - a situation that is preferred by the current data. Nevertheless, CP violation in h -> tau mu or h -> tau e will only be observable if nonzero rates for these decay modes are measured very soon
General Aspects of Tree Level Gauge Mediation
No full textTree level gauge mediation (TGM) may be considered as the simplest way to communicate supersymmetry breaking: through the tree level renormalizable exchange of heavy gauge messengers. We study its general structure, in particular the general form of tree level sfermion masses and of one loop, but enhanced, gaugino masses. This allows us to set up general guidelines for model building and to identify the hypotheses underlying the phenomenological predictions. In the context of models based on the "minimal" gauge group SO(10), we show that only two "pure" embeddings of the MSSM fields are possible using representations, each of them leading to specific predictions for the ratios of family universal sfermion masses at the GUT scale, or (in SU(5) notation). These ratios are determined by group factors and are peculiar enough to make this scheme testable at the LHC. We also discuss three possible approaches to the -problem, one of them distinctive of TGM
What is the scale of new physics behind the -flavour anomalies?
No full textMotivated by the recent hints of lepton flavour non-universality in B-meson semi-leptonic decays, we study the constraints of perturbative unitarity on the new physics interpretation of the anomalies in and transitions. Within an effective field theory approach we find that fermion scattering amplitudes saturate the unitarity bound below 9 and 80 TeV, respectively for and transitions. Stronger bounds, up to few TeV, are obtained when the leading effective operators are oriented in the direction of the third generation, as suggested by flavour models. We finally address unitarity constraints on simplified models explaining the anomalies and show that the new physics interpretation is ruled out in a class of perturbative realizations.Motivated by the recent hints of lepton flavour non-universality in -meson semi-leptonic decays, we study the constraints of perturbative unitarity on the new physics interpretation of the anomalies in and transitions. Within an effective field theory approach we find that fermion scattering amplitudes saturate the unitarity bound below 9 TeV and 80 TeV, respectively for and transitions. Stronger bounds, up to few TeV, are obtained when the leading effective operators are oriented in the direction of the third generation, as suggested by flavour models. We finally address unitarity constraints on simplified models explaining the anomalies and show that the new physics interpretation is ruled out in a class of perturbative realizations
Hierarchical Soft Terms and Flavor Physics
No full textWe study the framework of hierarchical soft terms, in which the first two generations of squarks and sleptons are heavier than the rest of the supersymmetric spectrum. This scheme gives distinctive predictions for the pattern of flavor violations, which we compare to the case of nearly degenerate squarks. Experiments in flavor physics have started to probe the most interesting parameter region, especially in transitions, where hierarchical soft terms can predict a phase of mixing much larger than in the Standard Model.We study the framework of hierarchical soft terms, in which the first two generations of squarks and sleptons are heavier than the rest of the supersymmetric spectrum. This scheme gives distinctive predictions for the pattern of flavor violations, which we compare to the case of nearly degenerate squarks. Experiments in flavor physics have started to probe the most interesting parameter region, especially in b ↔ s transitions, where hierarchical soft terms can predict a phase of B s mixing much larger than in the Standard Model.We study the framework of hierarchical soft terms, in which the first two generations of squarks and sleptons are heavier than the rest of the supersymmetric spectrum. This scheme gives distinctive predictions for the pattern of flavor violations, which we compare to the case of nearly degenerate squarks. Experiments in flavor physics have started to probe the most interesting parameter region, especially in transitions, where hierarchical soft terms can predict a phase of mixing much larger than in the Standard Model
Extended tree-level gauge mediation
No full textTree-level gauge mediation (TGM) is a scenario of SUSY breaking in which the tree-level exchange of heavy (possibly GUT) vector fields generates flavor-universal sfermion masses. In this work we extend this framework to the case of E(6) that is the natural extension of the minimal case studied so far. Despite the number of possible E(6) subgroups containing G(SM) is large (we list all rank 6 subgroups), there are only three different cases corresponding to the number of vector messengers. As a robust prediction we find that sfermion masses are SU(5) invariant at the GUT scale, even if the gauge group does not contain SU(5). If SUSY breaking is mediated purely by the U(1) generator that commutes with SO(10) we obtain universal sfermion masses and thus can derive the CMSSM boundary conditions in a novel scenario
Gravitino dark matter and low-scale baryogenesis
No full textA very simple way to obtain comparable baryon and dark matter densities in the early Universe is through their contemporary production from the out-of-equilibrium decay of a mother particle, if both populations are suppressed by comparably small numbers, i.e., the CP violation in the decay and the branching fraction, respectively. We present a detailed study of this kind of scenario in the context of an R-parity violating realization of the minimal supersymmetric standard model in which the baryon asymmetry and the gravitino dark matter are produced by the decay of a Bino. A quantitative determination, in a realistic particle physics framework, of these two quantities is quite involving, due to the non trivial determination of the abundance of the decaying Bino, as well as due to the impact of wash-out processes and of additional sources both for the baryon asymmetry and the DM relic density. To achieve a quantitative determination of the baryon and dark matter abundances, we have implemented and solved a system of coupled Boltzmann equations for the particle species involved in their generation, including all the relevant processes. In the most simple, but still general, limit, in which the processes determining the abundance and the decay rate of the. © 2015 American Physical Society
Framework for baryonic R-parity violation in grand unified theories
No full textWe investigate the possibility of obtaining sizeable R-parity breaking interactions violating baryon number but not lepton number within supersymmetric grand unified theories. Such a possibility allows to ameliorate the naturalness status of supersymmetry while maintaining successful gauge coupling unification, one of its main phenomenological motivations. We show that this can be achieved without fine-tuning or the need of large representations in simple SO(10) models
Out-of-equilibrium baryogenesis and superweakly interacting massive particle dark matter
No full textThe experimental fact that the energy density in dark matter (DM) and in baryons is of the same order is one of the most puzzling in cosmology. In this work we suggest a new mechanism able to explain this coincidence in the context of out-of-equilibrium baryogenesis with DM production á la SuperWIMP starting from the same initial particle. Two simple implementations of this scenario within supersymmetric models with gravitino DM are discussed. © 2014 American Physical Society
Gauging the accidental symmetries of the standard model, and implications for the flavor anomalies
No full textWe explore the possibility that lepton family numbers and baryon number are such good symmetries of Nature because they are the global remnant of a spontaneously broken gauge symmetry. An almost arbitrary linear combination of these symmetries (together with a component of global hypercharge) can be consistently gauged, if the Standard Model (SM) fermion content is augmented by three chiral SM singlet states. Within this framework of U(1) extensions of the SM one generically expects flavor nonuniversality to emerge in the charged leptons, in such a way that naturally prevents lepton flavor violation, by aligning the mass and weak eigenbases. For quarks, all the SM Yukawa couplings responsible for their observed masses and mixings arise at the renormalizable level. We perform fits to show that models in this class can explain RK(∗) and the other neutral current B anomaly data if we introduce a heavy vectorlike quark to mediate the required quark flavor violation, while simultaneously satisfying other constraints from direct Z′ searches at the LHC, Bs meson mixing, a number of electroweak precision observables, and neutrino trident production. Within this symmetry-motivated framework of models, we find interesting implications for the flavor anomalies; notably, any axial couplings of the Z′ to electrons and muons must be flavor universal, with the flavor universality violation arising solely from the vectorlike couplings. We also comment on the generation of neutrino masses in these models
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