arXiv subjects
Publications and source records attributed to Marco Aurelio Diaz.
Some aspects of bilinear R-Parity violation, the simplest extension of the MSSM which does not conserve R-Parity, are reviewed in comparison with the MSSM. We put special emphasis on the effect of quantum corrections.
The simplest way of studying systematically R-parity violating phenomena is by introducing a bilinear term in the superpotential of the type $ε\hat L\hat H_2$, which violates R-parity and lepton number but keep barion number conserved. In its simplest version, this ``$ε$--model'' is a two parameter extension of the MSSM and a one parameter extension of the MSSM--SUGRA. Here we study the charged Higgs sector of the model, which mixes with the stau sector, and compare it with the charged Higgs sector of the MSSM. We demonstrate that $m_{H^{\pm}}$ can be lower than $m_W$ already at tree level, and calculate the production cross section of pairs of charged Higgs and staus. In this model it is possible the mixed production of a charged Higgs and a stau and its production cross section can be sizable. We finally comment about the new R-parity violating decay modes of the charged scalars.
We review the extraction of fundamental supersymmetric parameters from experimental observables related to the detection of charginos and selectrons at $e^+e^-$ colliders. We consider supergravity models with universal scalar and gaugino masses and radiatively broken electroweak symmetry. Two scenarios are considered: (a) The lightest chargino is light enough to be produced at LEP2, and (b) the right handed selectron is light enough to be produced at LEP2. We show how the validity of supergravity models can be tested even if experimental errors are large. Interesting differences between the spectrum in the two scenarios are pointed out.
We introduce a momentum dependent mixing angle $α(p^2)$ which allow us to diagonalize at any external momentum $p$ the one-loop corrected inverse propagator matrix of two coupled scalar fields while keeping the full momentum dependence in the self energies. We compare this method with more traditional techniques applied to the diagonalization of coupled scalars at the one-loop level. This method is applied to the CP-even Higgs sector of the Minimal Supersymmetric Model, defining the momentum dependent mixing angle $α(p^2)$, and calculating the two CP-even Higgs masses and the mixing angle at these two scales. We compare the results obtained in this way with alternative techniques. We make explicit the relation between $α(p^2)$ and the running mixing angle. We find differences between the mixing angle calculated with our method and the one calculated with more traditional methods, and these differences are relevant for Higgs searches at LEP2.
If the lightest chargino is discovered at LEP2, the measurement of its mass and cross section together with the mass of the lightest neutralino, enables the determination of the parameters that define the theory and the entire supersymmetric and Higgs spectrum. Within this context, we: (i) study the effect of the one--loop tadpoles in the minimization condition of the Higgs potential, by comparing the RGE--improved Higgs potential approximation with the calculation of the minimum including the effect of the one--loop tadpoles, and (ii) compare the prediction of two different supergravity models, namely, the model based on $B=2m_0$ and motivated by the solution of the $μ$--problem, and the minimal supergravity model, based on $A=B+m_0$.
The renormalization of a system of coupled scalars fields is analyzed. By introducing a momentum dependent mixing angle we diagonalize the inverse propagator matrix at any momentum $p^2$. The zeros of the inverse propagator matrix, \ie, the physical masses, are then calculated keeping the full momentum dependence of the self energies. The relation between this method and others previously published is studied. This idea is applied to the one-loop renormalization of the CP-even neutral Higgs sector of the Minimal Supersymmetric Model, considering top and bottom quarks and squarks in the loops. Presented in the Eighth Meeting of the Division of Particles and Fields of the American Physical Society ``DPF'94'', The University of New Mexico, Albuquerque NM, August 2-6, 1994.
Using the new CLEO bound on the branching ratio of the decay mode $b\longrightarrow sγ$ given by $1\times10^{-4}< B(b\longrightarrow sγ)<4\times10^{-4}$ at 95\% c.l., and the experimental bounds on the masses of the lightest chargino, the second lightest neutralino, and the light CP-odd Higgs, we find that a light gluino is incompatible with a class of supergravity models defined by $N=1$ supergravity, with a radiatively broken electroweak symmetry group and universality of scalar and gaugino masses at the unification scale. We also find in this scenario strong constraints on the parameter space due to the new CLEO bounds on $B(b\longrightarrow sγ)$. Presented in the International Workshop ``SUSY-94'', University of Michigan, Ann Arbor MI, May 14-17, 1994.
Minimal $N=1$ supergravity with a radiatively broken electroweak symmetry group is studied in the light gluino scenario. Constraints from the $b\rightarrow sγ$ decay and from the masses of the light CP-even neutral Higgs $m_h$, the lightest chargino $m_{χ^{\pm}_1}$, and the second lightest neutralino $m_{χ^0_2}$ are analyzed. We consider models in which the relation $A=B+m_0$ holds. We plot the allowed region in the $\tanβ-μ$ plane consistent with chargino/neutralino searches, and an upper bound on $\tanβ$ given by 1.82 (1.85) for $μ>0$ ($μ<0$) is found. We analize the consistency of this upper bound with experimental constraints on the lightest Higgs mass. We find that a gluino with a mass of a few GeV is incompatible with this kind of models.
We study the light gluino scenario giving special attention to constraints from the masses of the light CP-even neutral Higgs $m_h$, the lightest chargino $m_{χ^{\pm}_1}$, and the second lightest neutralino $m_{χ^0_2}$, and from the $b\rightarrow sγ$ decay. We find that minimal $N=1$ supergravity, with a radiatively broken electroweak symmetry group and universality of scalar and gaugino masses at the unification scale, is incompatible with the existence of a light gluino.
It is analyzed the branching ratio $B(b\rightarrow sγ)$ in the context of minimal $N=1$ supergravity with radiatively broken electroweak symmetry group. There is a strong dependence on supersymetric parameters, but constraints on the charged Higgs mass in non-supersymmetric models are relaxed, due to large contribution from the chargino/up-type squark sector that interacts destructively with the Standard Model and the charged Higgs contributions. Large suppressions/enhancements of the branching fraction are found for large values of $\tanβ$.
The effect of loops involving charginos with up-type squarks, and gluinos with down-type squarks, on the inclusive decay mode $b\rightarrow sγ$ is studied in the context of minimal $N=1$ Supergravity models with a radiatively broken electroweak symmetry group. It is confirmed that the strong constraints imposed by the CLEO upper bound $B(b\rightarrow sγ)<5.4\times 10^{-4}$ on two-Higgs doublets models are much weaker in supersymmetric theories due to partial cancelations from loops involving charginos and up-type squarks. The dependence of the branching ratio and the supersymmetry masses on the top quark mass is explored.