Neutrino Mixing from SUSY breaking

We propose a mechanism to generate the neutrino mixing matrix from supersymmetric threshold corrections. Flavor violating soft breaking terms induce flavor changing self-energies that give a finite renormalization to the mixing matrix. The described threshold corrections get enhanced in case of quasi-degenerate neutrino masses. In this scenario, we adjust potentially arbitrary soft breaking parameters in a way to reproduce the observed neutrino mixing at one loop working with non-minimal flavor violating soft parameters. To incorporate small neutrino masses already at tree-level via a type I seesaw mechanism, we extend the Minimal Supersymmetric Standard Model with singlet Majorana neutrinos. The radiative corrections do not decouple with the scale of Supersymmetry and persist when the spectrum is shifted to higher values. Moreover, the mixing matrix renormalization with flavor-changing self-energies is not restricted to supersymmetric theories and give similar results in any theory with new flavor structures.Comment: 11 pages. Talk given at the Summer School and Workshop on the Standard Model and Beyond 2013; to appear in the Proceedings of the Corfu Summer Institute 2014 "School and Workshops on Elementary Particle Physics and Gravity

Texture zeros and hierarchical masses from flavour (mis)alignment

We introduce an unconventional interpretation of the fermion mass matrix elements. As the full rotational freedom of the gauge-kinetic terms renders a set of infinite bases called weak bases, basis-dependent structures as mass matrices are unphysical. Matrix invariants, on the other hand, provide a set of basis-independent objects which are of more relevance. We employ one of these invariants to give a new parametrization of the mass matrices. By virtue of it, one gains control over its implicit implications on several mass matrix structures. The key element is the trace invariant which resembles the equation of a hypersphere with a radius equal to the Frobenius norm of the mass matrix. With the concepts of alignment or misalignment we can identify texture zeros with certain alignments whereas Froggatt-Nielsen structures in the matrix elements are governed by misalignment. This method allows further insights of traditional approaches to the underlying flavour geometry.Comment: 27 pages; v2 matches version accepted by NPB, discussion on Dirac CP phase for neutrinos adde

Vacuum stability of the effective Higgs potential in the Minimal Supersymmetric Standard Model

The parameters of the Higgs potential of the Minimal Supersymmetric Standard Model (MSSM) receive large radiative corrections which lift the mass of the lightest Higgs boson to the measured value of 126 GeV. Depending on the MSSM parameters, these radiative corrections may also lead to the situation that the local minimum corresponding to the electroweak vacuum state is not the global minimum of the Higgs potential. We analyze the stability of the vacuum for the case of heavy squark masses as favored by current LHC data. To this end we first consider an effective Lagrangian obtained by integrating out the heavy squarks and then study the MSSM one-loop effective potential V_eff, which comprises all higher-dimensional Higgs couplings of the effective Lagrangian. We find that only the second method gives correct results and argue that the criterion of vacuum stability should be included in phenomenological analyses of the allowed MSSM parameter space. Discussing the cases of squark masses of 1 and 2 TeV we show that the criterion of vacuum stability excludes a portion of the MSSM parameter space in which (mu tanbeta) and A_t are large.Comment: minor changes in text and list of references, figures in eps format, matches published version; Erratum added and sent to PR

The electroweak contribution to the top quark forward-backward asymmetry at the Tevatron

The electroweak contributions to the forward-backward asymmetry in the production of top-quark pairs at the Tevatron are evaluated at O(alpha^2) and O(alpha*alphas^2). We perform a detailed analysis of all partonic channels that produce an asymmetry and combine them with the QCD contributions. They provide a non-negligible fraction of the QCD-induced asymmetry with the same overall sign, thus enlarging the Standard Model prediction and diminishing the observed deviation. For the observed mass-dependent forward-backward asymmetry a 3-sigma deviation still remains at an invariant-mass cut of M_(t-tbar) > 450 GeV.Comment: 14 pages, 8 figure

Hadronic production of squark-squark pairs: The electroweak contributions

We compute the electroweak (EW) contributions to squark--squark pair production processes at the LHC within the framework of the Minimal Supersymmetric Standard Model (MSSM). Both tree-level EW contributions, of O(alpha_s alpha + alpha^2), and next-to-leading order (NLO) EW corrections, of O(alpha_s^2 alpha), are calculated. Depending on the flavor and chirality of the produced quarks, many interferences between EW-mediated and QCD-mediated diagrams give non-zero contributions at tree-level and NLO. We discuss the computational techniques and present an extensive numerical analysis for inclusive squark--squark production as well as for subsets and single processes. While the tree-level EW contributions to the integrated cross sections can reach the 20% level, the NLO EW corrections typically lower the LO prediction by a few percent.Comment: 36 pages, 18 figure

Hadronic production of bottom-squark pairs with electroweak contributions

We present the complete computation of the tree-level and the next-to-leading order electroweak contributions to bottom-squark pair production at the LHC. The computation is performed within the minimal supersymmetric extension of the Standard Model. We discuss the numerical impact of these contributions in several supersymmetric scenarios.Comment: 33 pages, v2: preprint numbers correcte

The MSSM prediction for W+/- H-/+ production by gluon fusion

We discuss the associated W+/- H-/+ production in p p collision for the Large Hadron Collider. A complete one-loop calculation of the loop-induced subprocess g g -> W+/- H-/+ is presented in the framework of the Minimal Supersymmetric Standard Model (MSSM), and the possible enhancement of the hadronic cross section is investigated under the constraint from the squark direct-search results and the low-energy precision data. Because of the large destructive interplay in the quark-loop contributions between triangle-type and box-type diagrams, the squark-loop contributions turn out to be comparable with the quark-loop ones. In particular, the hadronic cross section via gluon fusion can be extensively enhanced by squark-pair threshold effects in the box-type diagrams, so that it can be as large as the hadronic cross section via the b b-bar -> W+/- H-/+ subprocess which appears at tree level.Comment: 35 pages, 7 figures, version to appear in Physical Review

Precise Prediction for M_W in the MSSM

We present the currently most accurate evaluation of the W boson mass, M_W, in the Minimal Supersymmetric Standard Model (MSSM). The full complex phase dependence at the one-loop level, all available MSSM two-loop corrections as well as the full Standard Model result have been included. We analyse the impact of the different sectors of the MSSM at the one-loop level with a particular emphasis on the effect of the complex phases. We discuss the prediction for M_W based on all known higher-order contributions in representative MSSM scenarios. Furthermore we obtain an estimate of the remaining theoretical uncertainty from unknown higher-order corrections.Comment: 38 pages, 25 figures. Minor corrections, additional reference

Top quark physics in hadron collisions

The top quark is the heaviest elementary particle observed to date. Its large mass makes the top quark an ideal laboratory to test predictions of perturbation theory concerning heavy quark production at hadron colliders. The top quark is also a powerful probe for new phenomena beyond the Standard Model of particle physics. In addition, the top quark mass is a crucial parameter for scrutinizing the Standard Model in electroweak precision tests and for predicting the mass of the yet unobserved Higgs boson. Ten years after the discovery of the top quark at the Fermilab Tevatron top quark physics has entered an era where detailed measurements of top quark properties are undertaken. In this review article an introduction to the phenomenology of top quark production in hadron collisions is given, the lessons learned in Tevatron Run I are summarized, and first Run II results are discussed. A brief outlook to the possibilities of top quark research a the Large Hadron Collider, currently under construction at CERN, is included.Comment: 84 pages, 32 figures, accepted for publication by Reports on Progress in Physic