arXiv subjects
Publications and source records attributed to A. M. Teixeira.
Here we review the main results of LFV in the semileptonic tau decays $τ\to μPP$ ($PP = π^+ π^-, π^0 π^0, K^+ K^-, K^0 \bar{K}^0$), $τ\to μP$ ($P = π, η, η^{\prime}$), and $τ\to μV$ ($V = ρ, ϕ$) as well as in $μ-e$ conversion in nuclei within SUSY-seesaw scenarios, and compare our predictions with the present experimental bounds
We investigate various classes of Gauge Mediated Supersymmetry Breaking models and show that the Next-to-Minimal Supersymmetric Standard Model can solve the mu-problem in a phenomenologically acceptable way. These models include scenarios with singlet tadpole terms, which are phenomenologically viable, e.g., in the presence of a small Yukawa coupling <~ 10^{-5}. Scenarios with suppressed trilinear A-terms at the messenger scale lead naturally to light CP-odd scalars, which play the rôle of pseudo R-axions. A wide range of parameters of such models satisfies LEP constraints, with CP-even Higgs scalars below 114 GeV decaying dominantly into a pair of CP-odd scalars.
Report of the Working Group on Higgs Bosons for the Workshop, ``Physics at TeV Colliders'', Les Houches, France, 11-29 June, 2007.
We consider the fully constrained version of the next-to-minimal supersymmetric extension of the standard model (cNMSSM) in which a singlet Higgs superfield is added to the two doublets that are present in the minimal extension (MSSM). Assuming universal boundary conditions at a high scale for the soft supersymmetry-breaking gaugino, sfermion and Higgs mass parameters as well as for the trilinear interactions, we find that the model is more constrained than the celebrated minimal supergravity model. The phenomenologically viable region in the parameter space of the cNMSSM corresponds to a small value for the universal scalar mass m_0: in this case, one single input parameter is sufficient to describe the phenomenology of the model once the available constraints from collider data and cosmology are imposed. We present the particle spectrum of this very predictive model and discuss how it can be distinguished from the MSSM.
This chapter of the report of the ``Flavour in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavour phenomena in the charged lepton sector and in flavour-conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavour structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the Standard Model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.
In this paper we study $μ-e$ conversion in nuclei within the context of the Constrained Minimal Supersymmetric Standard Model, enlarged by three right handed neutrinos and their supersymmetric partners, and where the neutrino masses are generated via a seesaw mechanism. Two different scenarios with either universal or non-universal soft supersymmetry breaking Higgs masses at the gauge coupling unification scale are considered. In the first part we present a complete one-loop computation of the conversion rate for this process that includes the photon-, $Z$-boson, and Higgs-boson penguins, as well as box diagrams, and compare their size in the two considered scenarios. Then, in these two scenarios we analyse the relevance of the various parameters on the conversion rates, particularly emphasising the role played by the heavy neutrino masses, $\tan β$, and especially $θ_{13}$. In the case of hierachical heavy neutrinos, an extremely high sensitivity of the rates to $θ_{13}$ is indeed found. The last part of this work is devoted to the study of the interesting loss of correlation between the $μ-e$ conversion and $μ\to e γ$ rates that occurs in the non-universal scenario. In the case of large $\tan β$ and light $H^0$ Higgs boson an enhanced ratio of the $μ-e$ to $μ\to e γ$ rates, with respect to the universal case is found, and this could be tested with the future experimental sensitivities.
We address the constraints on the SUSY seesaw parameters arising from Lepton Flavour Violation observables. Working in the Constrained Minimal Supersymmetric Standard Model extended by three right-handed (s)neutrinos, we study the predictions for the branching ratios of $l_j \to l_i γ$ and $l_j \to 3 l_i$ channels. We impose compatibility with neutrino data, electric dipole moment bounds, and further require a successful baryon asymmetry of the Universe (via thermal leptogenesis). We emphasise the interesting interplay between $θ_{13}$ and the LFV muon decays, pointing out the hints on the SUSY seesaw parameters that can arise from measurements of $θ_{13}$ and LFV branching ratios. This is a brief summary of the work of Ref. \cite{Antusch:2006vw}.
We systematically investigate constraints on the parameters of the supersymmetric type-I seesaw mechanism from the requirement of successful thermal leptogenesis in the presence of upper bounds on the reheat temperature $T_\mathrm{RH}$ of the early Universe. To this end, we solve the flavour-dependent Boltzmann equations in the MSSM, extended to include reheating. With conservative bounds on $T_\mathrm{RH}$, leading to mildly constrained scenarios for thermal leptogenesis, compatibility with observation can be obtained for extensive new regions of the parameter space, due to flavour-dependent effects. On the other hand, focusing on (normal) hierarchical light and heavy neutrinos, the hypothesis that there is no CP violation associated with the right-handed neutrino sector, and that leptogenesis exclusively arises from the CP-violating phases of the $U_\text{MNS}$ matrix, is only marginally consistent. Taking into account stricter bounds on $T_\mathrm{RH}$ further suggests that (additional) sources of CP violation must arise from the right-handed neutrino sector, further implying stronger constraints for the right-handed neutrino parameters.
The viability of the lightest neutralino as a dark matter candidate in the Next-to-Minimal Supersymmetric Standard Model is analysed. We carry out a thorough analysis of the parameter space, taking into account accelerator constraints as well as bounds on low-energy observables, such as the muon anomalous magnetic moment and rare $K$ and $B$ meson decays. The neutralino relic density is also evaluated and consistency with present bounds imposed. Finally, the neutralino direct detection cross section is calculated in the allowed regions of the parameter space and compared to the sensitivities of present and projected dark matter experiments. Regions of the parameter space are found where experimental constraints are fulfilled, the lightest neutralino has the correct relic abundance and its detection cross section is within the reach of dark matter detectors. This is possible in the presence of very light singlet-like Higgses and when the neutralino is either light enough so that some annihilation channels are kinematically forbidden, or has a large singlino component.
We study the impact of neutrino masses and mixings on LFV processes within the context of the supersymmetric seesaw scenario, where the CMSSM is extended by three right-handed (s)neutrinos. A hierarchical spectrum is considered for both heavy and light neutrinos. We systematically analyse the interesting relation between the leptonic mixing angle $θ_{13}$ and LFV muon and tau decays, namely $l_j \to l_i γ$ and $l_j \to 3 l_i$, and discuss the interplay with the other relevant parameters. We require compatibility with low energy neutrino data, bounds on both LFV decays and charged lepton electric dipole moments, and impose a successful baryogenesis via thermal leptogenesis. Particular emphasis is given to the implications that a future $θ_{13}$ measurement can have on our knowledge of the heavy neutrino sector.
In these proceedings we present the results for lepton flavour violating tau and muon decays within the SUSY seesaw scenario. Specifically, we consider the Constrained Minimal Supersymmetric Standard Model extended by three right handed neutrinos, $ν_{R_i}$ and their corresponding SUSY partners, ${\tilde ν}_{R_i}$, ($i=1,2,3$), and use the seesaw mechanism for neutrino mass generation. We include the predictions for the branching ratios of two types of lepton flavour violating channels, $l_j \to ł_i γ$ and $l_j \to 3 l_i$, and compare them with the present bounds and future experimental sensitivities. We first analyse the dependence of the branching ratios with the most relevant SUSY seesaw parameters, and we then focus on the particular sensitivity to $θ_{13}$, which we find specially interesting on the light of its potential future measurement. We further study the constraints from the requirement of successfully producing the baryon asymmetry of the Universe via thermal leptogenesis, which is another appealing feature of the SUSY seesaw scenario. We conclude with the impact that a potential measurement of $θ_{13}$ can have on lepton flavour violating physics. This is a very short summary of the works in Refs. \cite{Arganda:2005ji} and \cite{Antusch:2006vw} to which we refer the reader for more details.
We discuss the phenomenological viability of string multi-Higgs doublet models, namely a scenario of heterotic $Z_3$ orbifolds with two Wilson lines, which naturally predicts three supersymmetric families of matter and Higgs fields. We study the orbifold parameter space, and discuss the compatibility of the predicted Yukawa couplings with current experimental data. We address the implications of tree-level flavour changing neutral processes in constraining the Higgs sector of the model, finding that viable scenarios can be obtained for a reasonably light Higgs spectrum. We also take into account the tree-level contributions to indirect CP violation, showing that the experimental value of $ε_K$ can be accommodated in the present framework.
We conduct a general discussion of supersymmetric models with three families in the Higgs sector. We analyse the scalar potential, and investigate the minima conditions, deriving the mass matrices for the scalar, pseudoscalar and charged states. Depending on the Yukawa couplings and the Higgs spectrum, the model might allow the occurrence of potentially dangerous flavour changing neutral currents at the tree-level. We compute model-independent contributions for several observables, and as an example we apply this general analysis to a specific model of quark-Higgs interactions, discussing how compatibility with current experimental data constrains the Higgs sector.
We analyse the phenomenological viability of heterotic $Z_3$ orbifold models with two Wilson lines, which naturally predict three families of matter and Higgs fields. We study the orbifold parameter space, and discuss the compatibility of the predicted Yukawa couplings with current experimental data, thus evaluating the viability of the orbifold configurations. We address the implications of tree-level flavour changing neutral processes in constraining the Higgs sector of the model, finding that viable scenarios can be obtained for a fairly light Higgs spectrum.
We analyse the direct detection of neutralino dark matter in the framework of the Next-to-Minimal Supersymmetric Standard Model. After performing a detailed analysis of the parameter space, taking into account all the available constraints from LEPII, we compute the neutralino-nucleon cross section, and compare the results with the sensitivity of detectors. We find that sizable values for the detection cross section, within the reach of dark matter detectors, are attainable in this framework. For example, neutralino-proton cross sections compatible with the sensitivity of present experiments can be obtained due to the exchange of very light Higgses with $m_{h_1^0}\lsim 70$ GeV. Such Higgses have a significant singlet composition, thus escaping detection and being in agreement with accelerator data. The lightest neutralino in these cases exhibits a large singlino-Higgsino composition, and a mass in the range $50\lsim m_{\tildeχ_1^0}\lsim 100$ GeV.
We discuss selectron pair production in e- e- scattering. These processes can only occur via t-channel neutralino exchange, provided that the neutralinos are Majorana fermions. We concentrate on the processes e- e- -> e^~_L e^~_L,e^~_R e^~_R -> e- X^~_1^0 e- X^~_2^0 -> e- X^~_1^0 e- X^~_1^0 f f, in which a complete determination of the final state momenta is possible without using the selectron masses as input. The experimental reconstruction of the selectron masses in this decay channel provides clear evidence of the Majorana character of the neutralinos, which is confirmed by the analysis of the electron energy spectrum.
We analyse the CP problem in the context of a supersymmetric extension of the standard model with universal strength of Yukawa couplings. A salient feature of these models is that the CP phases are constrained to be very small by the hierarchy of the quark masses, and the pattern of CKM mixing angles. This leads to a small amount of CP violation from the usual KM mechanism and a significant contribution from supersymmetry is required. Due to the large generation mixing in some of the supersymmetric interactions, the electric dipole moments impose severe constraints on the parameter space, forcing the trilinear couplings to be factorizable in matrix form. We find that the LL mass insertions give the dominant gluino contribution to saturate epsilon_K. The chargino contributions to epsilon'/epsilon are significant and can accommodate the experimental results. In this framework, the standard model gives a negligible contribution to the CP asymmetry in B-meson decay, a_{J/ψK_s}. However, due to supersymmetric contributions to B_d-\bar{B}_d mixing, the recent large value of a_{J/ψK_s} can be accommodated.
We analyse the CP problem in the context of a supersymmetric extension of the standard model with universal strength of Yukawa couplings. In these models we find a small amount of CP violation from the usual CKM mechanism and therefore a significant contribution from supersymmetry is required. The electric dipole moments impose severe constraints on the parameter space, forcing the trilinear couplings to be factorizable in matrix form. We find that the LL mass insertions give the dominant gluino contribution to saturate epsilon_K, while chargino contributions to epsilon'/epsilon are compatible with the experimental results. Due to significant supersymmetric contributions to B_d-\bar{B}_d mixing, the recent large value of a_{J/ψK_S} can be accommodated.