David Garcia

Effective Lagrangian for the t̄bH+ interaction in the MSSM and charged Higgs phenomenology

Abstract In the framework of a 2HDM effective Lagrangian for the MSSM, we analyse important phenomenological aspects associated with quantum soft SUSY-breaking effects that modify the relation between the bottom mass and the bottom Yukawa coupling. We derive a resummation of the dominant supersymmetric corrections for large values of tan β to all orders in perturbation theory. With the help of the operator product expansion we also perform the resummation of the leading and next-to-leading logarithms of the standard QCD corrections. We use these resummation procedures to compute the radiative corrections to the t→b H + , H + →t b decay rates. In the large tan β regime, we derive simple formulae embodying all the dominant contributions to these decay rates and we compute the corresponding branching ratios. We show, as an example, the effect of these new results on determining the region of the M H + – tan β plane excluded by the Tevatron searches for a supersymmetric charged Higgs boson in top quark decays, as a function of the MSSM parameter space.

b→sγ and supersymmetry with large tanβ

Abstract We discuss the constraints on the supersymmetric parameter space from the decay mode b → sγ for large values of tan β . We improve the theoretical prediction for the decay rate by summing very large radiative corrections to all orders in perturbation theory. This extends the validity of the perturbative calculation to the large tan β regime. This resummation of terms of order α s n tan n +1 β is based on a recently proposed effective Lagrangian for the Yukawa interaction of bottom quarks. Moreover, we identify an additional source of tan β -enhanced terms, which are of order α s tan β and involve the charged Higgs boson, and analyse their behaviour in higher orders of perturbation theory. After correcting the current expressions for this rare decay branching ratio at next-to-leading order, we obtain that, contrary to recent claims, the measured branching ratio of b → sγ constrains the supersymmetric parameter space in a relevant way, even if tan β is large.

b ---> s gamma and supersymmetry with large tan Beta

Abstract We discuss the constraints on the supersymmetric parameter space from the decay mode b → sγ for large values of tan β . We improve the theoretical prediction for the decay rate by summing very large radiative corrections to all orders in perturbation theory. This extends the validity of the perturbative calculation to the large tan β regime. This resummation of terms of order α s n tan n +1 β is based on a recently proposed effective Lagrangian for the Yukawa interaction of bottom quarks. Moreover, we identify an additional source of tan β -enhanced terms, which are of order α s tan β and involve the charged Higgs boson, and analyse their behaviour in higher orders of perturbation theory. After correcting the current expressions for this rare decay branching ratio at next-to-leading order, we obtain that, contrary to recent claims, the measured branching ratio of b → sγ constrains the supersymmetric parameter space in a relevant way, even if tan β is large.

Prospects for heavy supersymmetric charged Higgs boson searches at hadron colliders

We investigate the production of a heavy charged Higgs boson at hadron colliders within the context of the MSSM. A detailed study is performed for all important production modes and basic background processes for the tb signature. In our analysis we include effects of initial and final state showering, hadronization, and principal detector effects. For the signal production rate we include the leading SUSY quantum effects at high tan βmt/mb. Based on the obtained efficiencies for the signal and background we estimate the discovery and exclusion mass limits of the charged Higgs boson at high values of tan β. At the upgraded Tevatron the discovery of a heavy charged Higgs boson (MH±200 GeV) is impossible for the tree-level cross-section values. However, if QCD and SUSY effects happen to reinforce mutually, there are indeed regions of the MSSM parameter space which could provide 3σ evidence and, at best, 5σ charged Higgs boson discovery at the Tevatron for masses MH±300 GeV and MH±250 GeV, respectively, even assuming squark and gluino masses in the (500−1000) GeV range. On the other hand, at the LHC one can discover a H± as heavy as 1 TeV at the canonical confidence level of 5σ; or else exclude its existence at 95% C.L. up to masses ~ 1.5 TeV. Again the presence of SUSY quantum effects can be very important here as they may shift the LHC limits by a few hundred GeV.

FULL ONE-LOOP SUPERSYMMETRIC QUANTUM EFFECTS ON Mw

We present a detailed numerical analysis of a fully-fledged computation of one-loop supersymmetric quantum effects on the mass of the weak gauge boson W± in the standard on-shell renormalization scheme based on the input parameters (GF, α, MZ). The importance of the process-dependent contributions as compared to the universal effects is assessed. The final numerical results show that in large regions of parameter space the potential radiative shifts could be within the level of precision expected at LEP II, depending on the model considered. A comparison is made with other renormalization frameworks.

b {yields} s{gamma} and supersymmetry with large tan{beta}.

Abstract We discuss the constraints on the supersymmetric parameter space from the decay mode b → sγ for large values of tan β . We improve the theoretical prediction for the decay rate by summing very large radiative corrections to all orders in perturbation theory. This extends the validity of the perturbative calculation to the large tan β regime. This resummation of terms of order α s n tan n +1 β is based on a recently proposed effective Lagrangian for the Yukawa interaction of bottom quarks. Moreover, we identify an additional source of tan β -enhanced terms, which are of order α s tan β and involve the charged Higgs boson, and analyse their behaviour in higher orders of perturbation theory. After correcting the current expressions for this rare decay branching ratio at next-to-leading order, we obtain that, contrary to recent claims, the measured branching ratio of b → sγ constrains the supersymmetric parameter space in a relevant way, even if tan β is large.