A new view on vacuum stability in the MSSM

A consistent theoretical description of physics at high energies requires an assessment of vacuum stability in either the Standard Model or any extension of it. Especially supersymmetric extensions allow for several vacua and the choice of the desired electroweak one gives strong constraints on the parameter space. As the general parameter space in the Minimal Supersymmetric Standard Model is huge, any severe constraint on it unrelated to direct phenomenological observations enhances the predictability of the model. We perform an updated analysis of possible charge and color breaking minima without relying on fixed directions in field space that minimize certain terms in the potential (known as "D-flat" directions). Concerning the cosmological stability of false vacua, we argue that there are always directions in configuration space which lead to very short-lived vacua and therefore such exclusions are strict. In addition to existing strong constraints on the parameter space, we find even stronger constraints extending the field space compared to previous analyses and combine those constraints with predictions for the light CP-even Higgs mass in the Minimal Supersymmetric Standard Model. Low masses for supersymmetric partners are excluded from vacuum stability in combination with the 125 GeV Higgs and the allowed parameter space opens at a few TeV.Comment: 32 pages, 10 figures; v3: typos corrected, matches version to be published in JHE

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

Yukawa coupling quantum corrections to the self couplings of the lightest MSSM Higgs boson

A detailed analysis of the top-quark/squark quantum corrections to the lightest CP-even Higgs boson (h^0) self-couplings is presented in the MSSM. By considering the leading one-loop Yukawa-coupling contributions of O(m_t^4), we discuss the decoupling behaviour of these corrections when the top-squarks are heavy compared to the electroweak scale. As shown analytically and numerically, the large corrections can almost completely be absorbed into the h^0-boson mass. Our conclusion is that the h^0 self-couplings remain similar to the coupling of the SM Higgs boson for a heavy top-squark sector.Comment: LaTeX, 19 pages, 3 figures included. A few minor changes and references adde

Decoupling behaviour of O(m_t^4) corrections to the h^0 self-couplings

The decoupling behaviour of the leading one-loop Yukawa-coupling contributions of O(m_t^4) to the lightest MSSM Higgs boson self-couplings, when the top-squarks are heavy as compared to the electroweak scale, are discussed. As shown analytically and numerically, the large corrections can almost completely be absorbed into the h^0-boson mass and therefore, the h^0 self-couplings remain similar to the coupling of the SM Higgs boson for a heavy top-squark sector.Comment: LaTeX, 5 pages, 3 figures included; typos corrected. Uses npb.sty. Talk given by S.P. at the RADCOR 2002/Loops and Legs in Quantum Field Theory 2002, September 8 to 13, Kloster Banz, German

Higgs-Boson Production in Association with Heavy Quarks

Associated production of a Higgs boson with a heavy, i.e. top or bottom, quark-anti-quark pair provide observation channels for Higgs bosons at the LHC which can be used to measure the respective Yukawa couplings. For the light supersymmetric Higgs boson we present SUSY-QCD corrections at the one-loop level, which constitute a significant contribution to the cross section.Comment: 4 pages, 1 table; to appear in Proceedings of SUSY06, the 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions, UC Irvine, California, 12-17 June 200

Two-loop corrections to the ρ\rho parameter in Two-Higgs-Doublet Models

Models with two scalar doublets are among the simplest extensions of the Standard Model which fulfill the relation $\rho = 1$ at lowest order for the $\rho$ parameter as favored by experimental data for electroweak observables allowing only small deviations from unity. Such small deviations $\Delta\rho$ originate exclusively from quantum effects with special sensitivity to mass splittings between different isospin components of fermions and scalars. In this paper the dominant two-loop electroweak corrections to $\Delta\rho$ are calculated in the $CP$-conserving THDM, resulting from the top-Yukawa coupling and the self-couplings of the Higgs bosons in the gauge-less limit. The on-shell renormalization scheme is applied. With the assumption that one of the $CP$-even neutral scalars represents the scalar boson observed by the LHC experiments, with standard properties, the two-loop non-standard contributions in $\Delta\rho$ can be separated from the standard ones. These contributions are of particular interest since they increase with mass splittings between non-standard Higgs bosons and can be additionally enhanced by $\tan\beta$ and $\lambda_5$, an additional free coefficient of the Higgs potential, and can thus modify the one-loop result substantially. Numerical results are given for the dependence on the various non-standard parameters, and the influence on the calculation of electroweak precision observables is discussed.Comment: 23 pages, 17 figures, extended results section, version accepted for publication in EPJ-

Production of Neutral Higgs + Jet at the LHC in the SM and the MSSM

The cross section prediction for the production of the lightest neutral Higgs boson in association with a high-p_T hadronic jet is presented in the framework of the minimal supersymmetric standard model (MSSM) and compared to the SM case. Prospects for the CERN Large Hadron Collider (LHC) are discussed.Comment: 4 pages, To appear in the Proceedings of SUSY 2003, held at the University of Arizona, Tucson, AZ, 5-10 June 200

Two-loop top-Yukawa-coupling corrections to the Higgs boson masses in the complex MSSM

Results for the leading two-loop corrections of $\mathcal{O}{\left(\alpha_t^2\right)}$ from the Yukawa sector to the Higgs-boson masses of the MSSM with complex parameters are presented. The corresponding self-energies and their renormalization have been obtained in a Feynman-diagrammatic approach. A numerical analysis of the new contributions is performed for the mass of the lightest Higgs boson, supplemented by the full one-loop result and the $\mathcal{O}{\left(\alpha_t \alpha_s\right)}$ terms including complex phases. In the limit of the real MSSM a previous result is confirmed.Comment: 13 pages, 7 figure