Paride Paradisi

Anatomy and phenomenology of FCNC and CPV effects in SUSY theories

Abstract We perform an extensive study of FCNC and CP Violation within Supersymmetric (SUSY) theories with particular emphasis put on processes governed by b → s transitions and of their correlations with processes governed by b → d transitions, s → d transitions, D 0 – D ¯ 0 oscillations, lepton flavour violating decays, electric dipole moments and ( g − 2 ) μ . We first perform a comprehensive model-independent analysis of Δ F = 2 observables and we emphasize the usefulness of the R b – γ plane in exhibiting transparently various tensions in the present UT analyses. Secondly, we consider a number of SUSY models: the general MSSM, a flavour-blind MSSM, the MSSM with Minimal Flavour Violation as well as SUSY flavour models based on Abelian and non-Abelian flavour symmetries that show representative flavour structures in the soft SUSY breaking terms. We show how the characteristic patterns of correlations among the considered flavour observables allow to distinguish between these different SUSY scenarios. Of particular importance are the correlations between the CP asymmetry S ψ ϕ and B s → μ + μ − , between the anomalies in S ϕ K S and S ψ ϕ , between S ϕ K S and d e , between S ψ ϕ and ( g − 2 ) μ and also those involving lepton flavour violating decays. In our analysis, the presence of right-handed currents and of the double Higgs penguin contributions to B s mixing plays a very important role. We propose a “DNA-Flavour Test” of NP models including Supersymmetry, the Littlest Higgs model with T-parity and the Randall–Sundrum model with custodial protection, with the aim of showing a tool to distinguish between these NP scenarios, once additional data on flavour-changing processes become available. As a byproduct, we present the SM prediction for BR ( B + → τ + ν ) = ( 0.80 ± 0.12 ) × 10 − 4 that follows solely from an analytical formula for this branching ratio in terms of Δ M s , d and S ψ K S asymmetry and which does not involve V u b and F B uncertainties.

Predictions for supersymmetric particle masses using indirect experimental and cosmological constraints

In view of the imminent start of the LHC experimental programme, we use the available indirect experimental and cosmological information to estimate the likely range of parameters of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), using a Markov-chain Monte Carlo (MCMC) technique to sample the parameter space. The 95% confidence-level area in the (m0, m1/2) plane of the CMSSM lies largely within the region that could be explored with 1 fb−1 of integrated luminosity at 14 TeV, and much of the 68% confidence-level area lies within the region that could be explored with 50 pb−1 of integrated luminosity at 10 TeV. A same-sign dilepton signal could well be visible in most of the 68% confidence-level area with 1 fb−1 of integrated luminosity at 14 TeV. We discuss the sensitivities of the preferred ranges to variations in the most relevant indirect experimental and cosmological constraints and also to deviations from the universality of the supersymmetry-breaking contributions to the masses of the Higgs bosons.

Soft SUSY breaking grand unification: Leptons vs quarks on the flavor playground

Abstract We systematically analyze the correlations between the various leptonic and hadronic flavor violating processes arising in SUSY Grand Unified Theories. Using the GUT-symmetric relations between the soft SUSY breaking parameters, we assess the impact of hadronic and leptonic flavor observables on the SUSY sources of flavor violation.

Flavor effects on the electric dipole moments in supersymmetric theories: A beyond leading order analysis

The Standard Model predictions for the hadronic and leptonic electric dipole moments (EDMs) are well far from the present experimental resolutions, thus, the EDMs represent very clean probes of New Physics effects. Especially, within supersymmetric frameworks with flavor-violating soft terms large and potentially visible effects to the EDMs are typically expected. In this work, we systematically evaluate the predictions for the EDMs at the beyond-leading-order (BLO). In fact, we show that BLO contributions to the EDMs dominate over the leading-order (LO) effects in large regions of the supersymmetric parameter space. Hence, their inclusion in the evaluation of the EDMs is unavoidable. As an example, we show the relevance of BLO effects to the EDMs for a SUSY SU(5) model with right-handed neutrinos.

EDMs vs. CPV in Bs,d mixing in two Higgs doublet models with MFV

Abstract We analyze the correlations between electric dipole moments (EDMs) of the neutron and heavy atoms and CP violation in B s , d mixing in two Higgs doublet models respecting the Minimal Flavour Violation hypothesis, with flavour-blind CP-violating (CPV) phases. In particular, we consider the case of flavour-blind CPV phases from (i) the Yukawa interactions and (ii) the Higgs potential. We show that in both cases the upper bounds on the above EDMs do not forbid sizable non-standard CPV effects in B s mixing. However, if a large CPV phase in B s mixing will be confirmed, this will imply EDMs very close to their present experimental bounds, within the reach of the next generation of experiments, as well as BR ( B s , d → μ + μ − ) typically largely enhanced over its SM expectation. The two flavour-blind CPV mechanisms can be distinguished through the correlation between S ψ K S and S ψ ϕ that is strikingly different if only one of them is relevant. Which of these two CPV mechanisms dominates depends on the precise values of S ψ ϕ and S ψ K S , as well as on the CKM phase (as determined by tree-level processes). Current data seems to show a mild preference for a hybrid scenario where both these mechanisms are at work.

Low energy probes of CP violation in a flavor blind MSSM

Abstract We analyze the low energy implications of a flavor blind supersymmetric scenario (where the CKM matrix is the only source of flavor violation) in the presence of new CP violating but flavor conserving phases in the soft sector. We find that the best probes of this rather restricted scenario are (i) the electric dipole moments (EDMs) of the electron ( d e ) and the neutron ( d n ) and (ii) flavor changing and CP violating processes in B systems, like the CP asymmetries in b → s γ and B → ϕ ( η ′ ) K S , i.e. A CP ( b → s γ ) and S ϕ ( η ′ ) K S , respectively. The non-standard values for S ϕ ( η ′ ) K S , measured at the B factories, can find a natural explanation within our scenario and this would unambiguously imply (i) positive and often large (non-standard) values for A CP ( b → s γ ) and (ii) a lower bound for the electron and neutron EDMs at the level of d e , n ≳ 10 −28 e cm . Moreover, we predict positive New Physics (NP) contributions to ϵ K which could be welcomed in view of the recently lowered Standard Model value for ϵ K . Interestingly, an explanation for the non-standard values for S ϕ ( η ′ ) K S can also naturally lead to an explanation for the anomaly of the muon anomalous magnetic moment. Finally, we outline the role and the interplay of the direct NP searches at the LHC with the indirect searches performed by low energy flavor physics observables.

Probing new physics through μ − e universality in K → ℓ ν

The recent NA48/2 improvement on R_K=Gamma(K->e nu_e)/Gamma(K->mu nu_mu) emphasizes the role of K_l2 decays in probing the mu-e universality. Supersymmetric (SUSY) extensions of the Standard Model can exhibit mu-e non-universal contributions. Their origin is twofold: those deriving from lepton flavor conserving couplings are subdominant with respect to those arising from lepton flavor violating (LFV) sources. We show that mu-e non-universality in K_l2 is quite effective in constraining relevant regions of SUSY models with LFV (for instance, supergravities with a see-saw mechanism for neutrino masses). A comparison with analogous bounds coming from tau LFV decays proves the relevance of the measurement of R_K to probe LFV in SUSY.

Running minimal flavor violation

Abstract We consider the flavor structure of the minimal supersymmetric standard model (MSSM) in the framework of ‘minimal flavor violation’ (MFV). We show that, if one imposes the MFV structure at some scale, to a good accuracy the MFV decomposition works at all other scales. That is, quantum effects can be described by running coefficients of the MFV decomposition. We find that the coefficients get driven to non-trivial fixed points.

Waiting for μ → eγ from the MEG experiment

The Standard Model (SM) predictions for the lepton flavor-violating (LFV) processes like μ → eγ are well far from any realistic experimental resolution, thus, the appearance of μ → eγ at the running MEG experiment would unambiguously point towards a New Physics (NP) signal. In this article, we discuss the phenomenological implications in case of observation/improved upper bound on μ → eγ at the running MEG experiment for supersymmetric (SUSY) scenarios with a see-saw mechanism accounting for the neutrino masses. We outline the role of related observables to μ → eγ in shedding light on the nature of the SUSY LFV sources providing useful tools i) to reconstruct some fundamental parameters of the neutrino physics and ii) to test whether an underlying SUSY Grand Unified Theory (GUT) is at work. The perspectives for the detection of LFV signals in τ decays are also discussed.The Standard Model (SM) predictions for the lepton flavor-violating (LFV) processes like mu->eg are well far from any realistic experimental resolution, thus, the appearance of m->eg at the running MEG experiment would unambiguously point towards a New Physics (NP) signal. In this article, we discuss the phenomenological implications in case of observation/improved upper bound on m->eg at the running MEG experiment for supersymmetric (SUSY) scenarios with a see-saw mechanism accounting for the neutrino masses. We outline the role of related observables to m->eg in shedding light on the nature of the SUSY LFV sources providing useful tools i) to reconstruct some fundamental parameters of the neutrino physics and ii) to test whether an underlying SUSY Grand Unified Theory (GUT) is at work. The perspectives for the detection of LFV signals in tau decays are also discussed.

Anatomy and phenomenology of the lepton flavor universality in SUSY theories

High precision electroweak tests, such as deviations from the Standard Model expectations of the Lepton Flavor Universality (LFU) breaking in K → lνl (with l = e or μ), represent a powerful tool to test the Standard Model and, hence, to constrain or obtain indirect hints of New Physics beyond it. We explore such a possibility within Supersymmetric theories. Interestingly enough, a process that in itself does not need lepton flavor violation to occur, i.e. the violation of μ−e non-universality in K → lνl, proves to be quite effective in constraining not only relevant regions of SUSY models where lepton flavor is conserved, but even those where specific lepton flavor violating contributions arise. Indeed, a comparison with analogous bounds coming from τ lepton flavor violating decays shows the relevance of the measurement of RKe/μ = Γ(K → eν)/Γ(K → μν) to probe Lepton Flavor Violation in SUSY. We outline the role and the interplay of the direct New Physics searches at the LHC with the indirect searches performed by LFU tests.