The decay h0→A0A0h^0 \to A^0A^0: a complete 1-loop calculation in the MSSM

In the minimal supersymmetric standard model the decay $h^0 \to A^0A^0$ of the light neutral scalar $h^0$ is kinematically allowed for low values of $\tan\beta$ when radiative corrections to the neutral Higgs masses are taken into account. The width of this decay mode is revisited on the basis of a complete 1-loop diagrammatic calculation. We give the analytical expressions and numerical results and compare them with the corresponding ones from the simpler and compact approximations of the effective potential method and the renormalization group approach.Comment: 25 pages, LaTex, 10 figures included. Complete ps-file also available via WWW at http://itpaxp1.physik.uni-karlsruhe.de/prep/prep.htm

Improved full one--loop corrections to A^0 -> \sq_1 \sq_2 and \sq_2 -> \sq_1 A^0

We calculate the full electroweak one-loop corrections to the decay of the CP-odd Higgs boson A^0 into scalar quarks in the minimal supersymmetric extension of the Standard Model (MSSM). Due to the complex structure of the electroweak sector a proper renormalization of many parameters in the on-shell renormalization scheme is necessary. For the decay into sbottom quarks, especially for large tanb, the corrections can be very large in the on-shell renormalization scheme, which makes the perturbation series unreliable. We solve this problem by an appropriate definition of the tree-level coupling in terms of running quark masses and running trilinear couplings A_q. We also discuss the decay of heavy scalar quarks into light scalar quarks and A^0. We find that the corrections are significant and therefore cannot be neglected.Comment: 15 pages, 9 figures, Fig. 8 correcte

Supersymmetric one-loop corrections to the process e^+e^- to f fbar

Radiative one-loop corrections to fermion pair production in $e^+e^-$ annihilation are calculated in the Minimal Supersymmetric Standard Model (MSSM). The size of the non-standard corrections is discussed for the process e^+e^- to mu^+mu^- and e^+e^- to hadrons at LEP2 energies and for e^+e^- to t tbar at a high energy e^+e^- collider. The relative difference between the predictions of the MSSM and the Standard Model is typically below 10%.Comment: 48 pages, LaTex. Typos corrected, some comments added, diagram classes changed. Paper accepted by Nucl. Phys.

The sfermion mass spectrum of the MSSM at the one-loop level

The sfermion-mass spectrum of the minimal supersymmetric standard model is investigated at the one-loop level. An on-shell scheme has been specified for renormalization of the basic breaking parameters of the sfermionic sector. Owing to SU(2)-invariance, the soft-breaking mass parameters of the left-chiral scalar fermions of each isospin doublet are identical. Thus, one of the sfermion-masses of each doublet can be expressed in terms of the other masses and receives a mass shift at the one-loop level with respect to the lowest-order value, which can be of $O(10$ GeV). Both strong and electroweak contributions have been calculated for scalar quarks and leptons.Comment: 13 pages, 3 figures, version to appear in Eur. Phys. J.

Gauge dependence and renormalization of tan⁡β\tan\beta in the MSSM

Well-known and newly developed renormalization schemes for $\tan\beta$ are analyzed in view of three desirable properties: gauge independence, process independence, and numerical stability in perturbation theory. Arguments are provided that no scheme can meet all three requirements, and as an illustration, a ``No-Go-Theorem'' for the renormalization of $\tan\beta$ is established. Nevertheless, two particularly attractive schemes emerge. A discussion about which scheme might be the best compromise in practice is given.Comment: 20 pages, improved version that was published in PRD D66 (2002

Higgs decays in the Two Higgs Doublet Model: Large quantum effects in the decoupling regime

We study the Higgs-boson decays h0 -> b \bar{b}, h0 -> \gamma \gamma and h0 -> \gamma Z within the framework of the Two Higgs Doublet Model (THDM) in the context of the decoupling regime, together with tree level unitarity constraints. We show that when the light CP-even Higgs boson of the THDM mimics the Standard-Model Higgs boson, not only the one-loop effects to h0 -> {\gamma \gamma ,\gamma Z} but also the one-loop contribution to h0 -> b \bar{b} can be used to distinguish between THDM and SM. The size of the quantum effects in h0 -> b \bar{b} are of the same order as in h0 -> {\gamma \gamma ,\gamma Z} and can reach 25% in both cases.Comment: LaTeX, 13 pages, 5 figures. Improved text, added references, appendix removed. Version to appear in PL

Scale-independent mixing angles

A radiatively-corrected mixing angle has to be independent of the choice of renormalization scale to be a physical observable. At one-loop in MS-bar, this only occurs for a particular value, p*, of the external momentum in the two-point functions used to define the mixing angle: p*^2=(M1^2+M2^2)/2, where M1, M2 are the physical masses of the two mixed particles. We examine two important applications of this to the Minimal Supersymmetric Standard Model: the mixing angle for a) neutral Higgs bosons and b) stops. We find that this choice of external momentum improves the scale independence (and therefore provides a more reliable determination) of these mixing angles.Comment: 14 pages, 11 ps figures Version to appear in PR