Supersymmetric Flavor Models Research Articles

Controlled flavor violation in the MSSM from a unified \u0394(27) flavor symmetry

We study the phenomenology of a unified supersymmetric theory with a flavor symmetry Δ(27). The model accommodates quark and lepton masses, mixing angles and CP phases. In this model, the Dirac and Majorana mass matrices have a unified texture zero structure in the (1, 1) entry that leads to the Gatto-Sartori-Tonin relation between the Cabibbo angle and ratios of the masses in the quark sectors, and to a natural departure from zero of the θ13ℓ angle in the lepton sector. We derive the flavor structures of the trilinears and soft mass matrices, and show their general non-universality. This causes large flavor violating effects. As a consequence, the parameter space for this model is constrained, allowing it to be (dis)proven by flavor violation searches in the next decade. Although the results are model specific, we compare them to previous studies to show similar flavor effects (and associated constraints) are expected in general in supersymmetric flavor models, and may be used to distinguish them.

Predictivity of models with spontaneously broken non-Abelian discrete flavor symmetries

In a class of supersymmetric flavor models predictions are based on residual symmetries of some subsectors of the theory such as those of the charged leptons and neutrinos. However, the vacuum expectation values of the so-called flavon fields generally modify the Kähler potential of the setting, thus changing the predictions. We derive simple analytic formulae that allow us to understand the impact of these corrections on the predictions for the masses and mixing parameters. Furthermore, we discuss the effects on the vacuum alignment and on flavor changing neutral currents. Our results can also be applied to non-supersymmetric flavor models.

Pseudosmooth tribrid inflation

We explore a new class of supersymmetric models of inflation where the inflaton is realised as a combination of a Higgs field and (gauge non-singlet) matter fields, using a ``tribrid'' structure of the superpotential. Inflation is associated with a phase transition around GUT scale energies. The inflationary trajectory already preselects the later vacuum after inflation, which has the advantage of automatically avoiding the production of dangerous topological defects at the end of inflation. While at first sight the models look similar to smooth inflation, they feature a waterfall and are therefore only pseudosmooth. The new class of models offers novel possibilities for realising inflation in close contact with particle physics, for instance with supersymmetric GUTs or with supersymmetric flavour models based on family symmetries.

Footprints of SUSY GUTs in flavour physics

Supersymmetric (SUSY) Grand Unified theories (GUTs) generally predict FCNC and CP violating processes to occur both in the leptonic and hadronic sectors. Assuming an underlying SU(5) group plus right-handed neutrinos (RN), we perform an extensive study of FCNC and CP violation, analyzing the correlations between leptonic and hadronic processes like μ → eγ and \( {K^0} - {\bar{K}^0} \) mixing, τ → μγ and b → s transitions such as B d → ϕK s and \( B_s^0 - \bar{B}_s^0 \) mixing. Moreover, we examine the impact of the considered scenario on the UT analyses, monitoring the low energy consequences implied by possible solutions to the various tensions in the present UT analyses. We compare the phenomenological implications of this NP scenario with the ones of supersymmetric flavour models finding a few striking differences that could allow to distinguish these different NP models.

Exotic particles below the TeV from low scale flavour theories

A flavour gauge theory is observable only if the symmetry is broken at relatively low energies. The intrinsic parity-violation of the fermion representations in a flavour theory describing quark, lepton and higgsino masses and mixings generically requires anomaly cancellation by new fermions. Benchmark supersymmetric flavour models are built and studied to argue that: i) the flavour symmetry breaking should be about three orders of magnitude above the higgsino mass, enough also to efficiently suppress FCNC and CP violations coming from higher-dimensional operators; ii) new fermions with exotic decays into lighter particles are typically required at scales of the order of the higgsino mass.

Patterns of flavour violation in the presence of a fourth generation of quarks and leptons

We calculate a number of observables related to particle-antiparticle mixing and the branching ratios for the most interesting rare and CP-violating K and B decays in the Standard Model (SM3) extended by a fourth generation of quarks and leptons (SM4). A model-independent parameterisation of these observables in terms of gauge-independent functions is adopted, which is useful for studying the breaking of the universality between K, Bd and Bs systems through non-minimal flavour violating interactions. We calculate first the mass differences Delta M_i in the neutral K and B system, the mixing-induced CP asymmetries S_{psi K_S}, S_{psi phi}, S_{phi K_S}, S_{eta' K_S} and epsilon_K. Subsequently, a detailed analysis of K^+ -> pi^+ nu nu, K_L -> pi^0 nu nu, B_{s,d} -> mu^+ mu^-, B -> X_{s,d} nu nu, K_L -> pi^0 l^+ l^-, B -> X_s gamma and B -> X_{s,d} l^+ l^- is presented, and also epsilon'/epsilon is considered. For some of these observables the departures from SM3 predictions can still be spectacular. We discuss how the new mixing parameters (3 angles, 2 CP phases) can be determined using the flavour observables in question. We identify the different hierarchical structures in the SM4 flavour mixing matrix, allowed by phenomenological and theoretical constraints, and define the corresponding generalised Wolfenstein expansion. Most importantly, we show how the characteristic patterns of correlations among the considered flavour observables allow to distinguish this New Physics scenario from supersymmetric flavour models, the Littlest Higgs model with T-parity and the Randall-Sundrum model with custodial protection.

Constraints on supersymmetric flavour models fromb→sγ

We consider the effects of departures from minimal flavour violations (MFV) in the context of CMSSM-like theories. Second and third generation off-diagonal elements in the Yukawa, sfermion, and trilinear mass matrices are taken to be non-zero at the GUT scale. These are run down together with MSSM parameters to the electroweak scale. We apply constraints from fermion masses and CKM matrix elements to limit the range of the new free parameters of the model. We determine the effect of the departure from MFV on the branching ratio of b->s gamma. We find that only when the expansion parameter in the down-squark sector is relatively large there is a noticeable effect, which tends to relax the lower limit from b->s gamma on the universal gaugino mass. We also find that the expansion parameter associated with the slepton sector needs to be smaller than the corresponding parameter in the down-squark sector in order to be compliant with the bound imposed by the branching ratio of tau-> mu gamma.

Solving the supersymmetricCPproblem with flavor breakingFterms

Supersymmetric flavor models for the radiative generation of fermion masses offer an alternative way to solve the SUSY-$CP$ problem. We assume that the supersymmetric theory is flavor and $CP$ conserving. $CP$ violating phases are associated to the vacuum expectation values of flavor violating SUSY-breaking fields. As a consequence, phases appear at tree level only in the soft supersymmetry-breaking matrices. Using a U(2) flavor model as an example we show that it is possible to generate radiatively the first and second generation of quark masses and mixings as well as the Cabibbo-Kobayashi-Maskawa (CKM) $CP$ phase. The one-loop supersymmetric contributions to electric dipole moments are automatically zero since all the relevant parameters in the Lagrangian are flavor conserving and as a consequence real. The size of the flavor and $CP$ mixing in the SUSY-breaking sector is mostly determined by the fermion mass ratios and CKM elements. We calculate the contributions to $ϵ$, ${ϵ}^{\ensuremath{'}}$ and to the $CP$ asymmetries in the $B$ decays to $\ensuremath{\psi}{K}_{s}$, $\ensuremath{\phi}{K}_{s}$, ${\ensuremath{\eta}}^{\ensuremath{'}}{K}_{s}$ and ${X}_{s}\ensuremath{\gamma}$. We analyze a case study with maximal predictivity in the fermion sector. For this worst case scenario the measurements of $\ensuremath{\Delta}{m}_{K}$, $\ensuremath{\Delta}{m}_{B}$ and $ϵ$ constrain the model requiring extremely heavy squark spectra.

Signals of supersymmetric flavor models inBphysics

If the mechanism of Supersymmetry breaking is not flavour blind, some flavour symmetry is likely to be needed to prevent excessive flavour changing neutral current effects. We discuss two flavour models (based respectively on a U(2) and on a SU(3) horizontal symmetry) providing a good fit to fermion masses and mixings and particularly constraining the supersymmetry soft breaking terms. We show that, while reproducing successfully the Standard Model fit of the unitarity triangle, it is possible to obtain sizable deviations from the Standard Model predictions for three very clean B-physics observables: the time dependent CP asymmetries in $B_d \to J/\psi K^0$ and in $B_s \to J/\psi \phi$ and the $B_s-\bar{B}_s$ mass difference. Our analysis exhibits with two explicit realizations that in supersymmetric theories with a new flavour structure in addition to the Yukawa matrices there exist concrete potentialities for revealing supersymmetry indirectly in theoretically clean $B$-physics observables.

Probing supersymmetric flavor models with ε′/ε

We discuss the supersymmetric contribution to $\epsilon'/\epsilon$ in various supersymmetric flavor models. We find that in alignment models the supersymmetric contribution could be significant while in heavy squark models it is expected to be small. The situation is particularly interesting in models that solve the flavor problems by either of the above mechanisms and the remaining CP problems by means of approximate CP, that is, all CP violating phases are small. In such models, the standard model contributions cannot account for $\epsilon'/\epsilon$ and a failure of the supersymmetric contributions to do so would exclude the model. In models of alignment and approximate CP, the supersymmetric contributions can account for $\epsilon'/\epsilon$ only if both the supersymmetric model parameters and the hadronic parameters assume rather extreme values. Such models are then strongly disfavored by the $\epsilon'/\epsilon$ measurements. Models of heavy squarks and approximate CP are excluded.

Lepton parity in supersymmetric flavor models

We investigate supersymmetric models where neither R-parity nor lepton number nor baryon number is imposed. The full high energy theory has an exact horizontal U(1) symmetry that is spontaneously broken. Quarks and Higgs fields carry integer horizontal charges but leptons carry half integer charges. Consequently, the effective low energy theory has two special features: a U(1) symmetry that is explicitly broken by a small parameter, leading to selection rules, and an exact residual Z_2 symmetry, that is lepton parity. As concerns neutrino parameters, the Z_2 symmetry forbids contributions from R_p-violating couplings and the U(1) symmetry induces the required hierarchy. As concerns baryon number violation, the Z_2 symmetry forbids proton decay and the U(1) symmetry provides sufficient suppression of double nucleon decay and of neutron - antineutron oscillations.

CP-violating lepton asymmetries from B decays and their implication for supersymmetric flavor models

The lepton and dilepton charge asymmetries from B d and B s are predicted to be small in the standard model, whereas new physics could increase their values significantly. In this paper, we explore the use of the lepton asymmetries as a probe of the flavor structure of supersymmetric theories. In particular, we determine the sensitivity to parameters of various models. We find that in many interesting models which attempt to address the supersymmetric flavor problem, the mixing structure is such that it could be possible to detect new physics. The predictions are model dependent; with a measurement in both the B s and B d systems one can hope to constrain the flavor physics model, especially once squarks are detected and their masses measured. Thus, lepton charge asymmetries can be used as an alternative means of searching for new physics and distinguishing among potential solutions to the flavor problem. They are interesting precisely because they are small in the standard model and are therefore necessarily evidence of new physics.

Probing the flavor and CP structure of supersymmetric models with [formula omitted] decays

We study the implications of various supersymmetric models on the rare K +→π +ν ν ̄ and K L→π 0ν ν ̄ decays. Although large effects are possible in generic supersymmetric models, most of the known supersymmetric flavor models lead to negligible effects. Thus, it is likely that one can get information about CKM matrix elements from these decays even in the presence of supersymmetry. Moreover, the possibility of large contributions to K→πν ν ̄ in generic supersymmetry models can be constrained by improved bounds on D− D ̄ mixing. We show that it may be possible to distinguish between different supersymmetric flavor models by combining the information from the K→πν ν ̄ decays with that from B− B ̄ and D− D ̄ mixing.