arXiv subjects

Wolfgang Altmannshofer

Publications and source records attributed to Wolfgang Altmannshofer.

98 records · Page 6Linked to original sources

arXiv2009

Probing the MSSM flavor structure with low energy CP violation

We report on an extensive analysis of FCNC and CPV effects in SUSY theories. We present results for Delta F=2 and Delta F=1 processes governed by b --> s transitions both in the low and high tanbeta regime, focussing in particular on S_psi_phi, the phase of Bs mixing. We emphasize that while the MFV framework is not suited to explain potentially large effects in S_psi_phi as indicated by recent data from CDF and D0, models with large right-right mass insertions in the 32 sector provide natural frameworks to account for such effects. Exemplarily we consider two SUSY models based on an abelian and a non-abelian flavor symmetry that show representative flavor structures in the soft SUSY breaking terms and stress that the characteristic correlations among the considered observables allow to distinguish between the different models.

hep-ph↗

arXiv2009

New strategies for New Physics search in B -> K* nu anti-nu, B -> K nu anti-nu and B -> X(s) nu anti-nu decays

The rare decay B -> K* nu anti-nu allows a transparent study of Z penguin and other electroweak penguin effects in New Physics (NP) scenarios in the absence of dipole operator contributions and Higgs (scalar) penguin contributions that are often more important than Z contributions in B -> K* l+l- and B(s) -> l+l- decays. We present a new analysis of B -> K* nu anti-nu with improved form factors and of the decays B -> K nu anti-nu and B -> X(s) nu anti-nu in the SM and in a number of NP scenarios like the general MSSM, general scenarios with modified Z/Z' penguins and in a singlet scalar extension of the SM. We also summarize the results in the Littlest Higgs model with T-parity and a Randall-Sundrum (RS) model with custodial protection of left-handed Z-di-dj couplings. Our SM prediction BR(B -> K* nu anti-nu)=(6.8^+1.0_-1.1) x 10^-6 turns out to be significantly lower than the ones present in the literature. Our improved calculation BR(B -> X(s) nu anti-nu)=(2.7+-0.2) x 10^-5 in the SM avoids the normalization to the BR(B -> X(c) e anti-nu(e)) and, with less than 10% total uncertainty, is the most accurate to date. The results for the SM and NP scenarios can be transparently summarized in a (epsilon,eta) plane with a non-vanishing eta signalling the presence of new right-handed down-quark flavour violating couplings which can be ideally probed by the decays in question. Measuring the three branching ratios and one additional polarization observable in B -> K* nu anti-nu allows to overconstrain the resulting point in the (epsilon,eta) plane with (epsilon,eta)=(1,0) corresponding to the SM. The correlations of these three channels with the rare decays K+ -> pi+ nu anti-nu, KL -> pi0 nu anti-nu, B -> X(s) l+ l- and B(s) -> mu+ mu- offer powerful tests of New Physics with new right-handed couplings and non-MFV interactions.

hep-ph↗

arXiv2008

A Reconsideration of the b -> s gamma Decay in the Minimal Flavor Violating MSSM

We present a MSSM study of the b -> s gamma decay in a Minimal Flavor Violating (MFV) framework, where the form of the soft SUSY breaking terms is determined by the Standard Model Yukawa couplings. In particular, we address the role of gluino contributions, which are set to zero in most studies of the MFV MSSM. Gluino contributions can play an important role in the MFV MSSM whenever mu * tan(beta) is large. In fact, similarly to chargino contributions, gluino contributions are tan(beta) enhanced and can easily dominate charged Higgs contributions for large values of tan(beta). Even though each of the separate contributions to b -> s gamma can be sizeable by itself, surprisingly no absolute lower bound can be placed on any of the relevant SUSY masses, since patterns of partial cancellations among the three competing contributions (Higgs, chargino and gluino) can occur throughout the MSSM parameter space.

hep-ph↗

arXiv2008

SUSY GUTs with Yukawa unification: a go/no-go study using FCNC processes

We address the viability of exact Yukawa unification in the context of general SUSY GUTs with universal soft-breaking sfermion and gaugino mass terms at the GUT scale. We find that this possibility is challenged, unless the squark spectrum is pushed well above the limits allowed by naturalness. This conclusion is assessed through a global fit using electroweak observables and quark flavour-changing neutral current (FCNC) processes. The problem is mostly the impossibility of accommodating simultaneously the bottom mass and the BR(B --> Xs gamma), after the stringent CDF upper bound on the decay Bs --> mu^+ mu^- is taken into account, and under the basic assumption that the b --> s gamma amplitude have like sign with respect to the Standard Model one, as indicated by the B --> Xs l^+ l^- data. With the same strategy, we also consider the possibility of relaxing Yukawa unification to b - tau Yukawa unification. We find that with small departures from the condition tan beta ~= 50, holding when Yukawa unification is exact, the mentioned tension is substantially relieved. We emphasize that in the region where fits are successful the lightest part of the SUSY spectrum is basically fixed by the requirements of b - tau unification and the applied FCNC constraints. As such, it is easily falsifiable once the LHC turns on.

hep-ph↗

arXiv2008

Large |Vub|: A challenge for the Minimal Flavour Violating MSSM

Under the assumption of Minimal Flavour Violation (MFV), the Unitarity Triangle (UT) can be determined by using only angle measurements and tree-level observables. In this respect, the most accurate quantities today available are sin 2 beta_{psi Ks}, |Vcb| and |Vub|. Among the latter, |Vub| is at present the quantity suffering from largest systematic uncertainties, given the discrepancy between the inclusive and the exclusive determinations. We show with a numerical fit how sensitively the MFV-UT determination depends on the choice of |Vub|. In addition, we focus on the implications of the inclusive value for |Vub|, which favors two non-SM like solutions in the rhobar - etabar plane. We study in detail the possibility of reproducing such solutions within the MFV MSSM. Our findings indicate that the case for the MFV MSSM is in this respect quite problematic, unless the non-perturbative parameters xi and BK are significantly different from those obtained by lattice methods. As a byproduct, we point out that scenarios with 200 GeV <~ MA <~ 500 GeV and tan beta =~ 50 that predict a significant suppression for Delta Ms in correlation with an enhancement for BR(Bs --> mu^+ mu^-) have to be fine-tuned in order not to violate the new combined bound on the latter decay mode from the CDF and D0 collaborations. Relatively large correlated effects can however still occur for negative values of mu and large values for MA >~ 500 GeV, increasing with increasing tan beta >~ 30.

hep-ph↗

arXiv2007

Challenging SO(10) SUSY GUTs with family symmetries through FCNC processes

We perform a detailed analysis of the SO(10) SUSY GUT model with D3 family symmetry of Dermisek and Raby (DR). The model is specified in terms of 24 parameters and predicts, as a function of them, the whole MSSM set of parameters at low energy scales. Concerning the SM subset of such parameters, the model is able to give a satisfactory description of the quark and lepton masses, of the PMNS matrix and of the CKM matrix. We perform a global fit to the model, including flavour changing neutral current (FCNC) processes Bs --> mu+ mu-, B --> Xs gamma, B --> Xs l+ l- and the B(d,s) - bar B(d,s) mass differences Delta M(d,s) as well as the flavour changing (FC) process B+ --> tau+ nu. These observables provide at present the most sensitive probe of the SUSY mass spectrum and couplings predicted by the model. Our analysis demonstrates that the simultaneous description of the FC observables in question represents a serious challenge for the DR model, unless the masses of the scalars are moved to regions which are problematic from the point of view of naturalness and probably beyond the reach of the LHC. We emphasize that this problem could be a general feature of SUSY GUT models with third generation Yukawa unification and weak-scale minimal flavour violation.

hep-ph↗

arXiv2007

The MFV limit of the MSSM for low tan(beta): meson mixings revisited

We apply the effective field theory definition of Minimal Flavour Violation (MFV) to the MSSM. We explicitly show how, by this definition, the new sources of flavour and CP violation present in the MSSM become functions of the SM Yukawa couplings, and cannot be simply set to zero, as is common wisdom in phenomenological MSSM studies that assume MFV. We apply our approach to the MSSM Delta B = 2 Hamiltonian at low tan(beta). The limit of MFV amounts to a striking increase in the predictivity of the model. In particular, SUSY corrections to meson-antimeson mass differences Delta M(d,s) are always found to be positive with respect to the SM prediction. This feature is due to an interesting interplay between chargino and gluino box diagrams (the dominant contributions) in the different mass regimes one can consider. Finally, we point out that, due to the presence of gluinos, the MFV MSSM does not belong -- even at low tan(beta) -- to the class of models with the so-called `constrained' MFV (CMFV), in which only the SM operator (V-A)x(V-A) contributes to Delta M(d,s). Consequently, for the MSSM and in the general case of MFV, one should not use the Universal Unitarity Triangle (UUT), relevant for CMFV models, but a MFV-UT constructed from beta(psi KS) and |V(ub)| or gamma from tree level decays. In particular, with the measured value of beta(psi KS), MFV implies a testable correlation between |V(ub)| and gamma. With the present high value of |V(ub)|, MFV favours gamma > 80 degrees.

hep-ph↗

arXiv2007

Flavor Changing Neutral Current Processes in a SO(10) SUSY GUT with Family Symmetry

We report on a detailed analysis of a SO(10) SUSY GUT model of Dermisek and Raby (DR) with a D3 family symmetry. The model is completely specified in terms of only 24 parameters and is able to successfully describe both quark and lepton masses and mixings, except for |Vub| that turns out to be too low. However, a global fit shows that flavor changing (FC) processes like Bs --> mu+ mu-, Bs-mixing, B+ --> tau+ nu, B --> Xs gamma and B --> Xs l+ l- pose a serious problem to the DR model. The simultaneous description of these FC processes forces squarks to have masses well above 1 TeV, not appealing on grounds of naturalness and probably beyond the reach of the LHC.

hep-ph↗