arXiv subjects
Publications and source records attributed to Jose I. Illana.
The little Higgs model with T-parity, compatible with electroweak precision constraints, introduces new flavor-mixing sources, some of which had been ignored until recently. They are reviewed here, showing that their influence does not only enrich the phenomenology of flavor-changing processes but is also needed to render finite one-loop amplitudes.
The Little Higgs (LH) idea attempts to cure the little amount of fine-tuning necessary to bridge the gap between the Higgs mass (electroweak scale) and the new physics scale suggested by electroweak precision tests (~10 TeV). However, we show that LH models do not survive the confrontation with experimental limits on lepton flavor mixing, assuming the same naturalness arguments that motivate their introduction. Two different LH models are analyzed and several aspects of their one-loop predictions for lepton flavor-changing processes are discussed.
The possibility to observe lepton flavour violating Z decays in the GigaZ option of DESY's TESLA project consistently with present bounds from other processes is analyzed in the context of the minimal supersymmetric standard model. In particular, constraints on the slepton mass matrices from radiative lepton decays are updated and taken into account. Their correlation to the present measurement of the muon anomalous dipole moment is briefly discussed.
The origin and nature of ultrahigh-energy cosmic ray events, above the Greisen-Zatsepin-Kuzmin (GZK) cutoff energy, constitute a long-standing, unsolved mistery. Neutrinos are proposed candidates but their standard interactions with matter are too weak. In the context of a TeV-scale string theory, motivated by possible extra space dimensions, the neutrino-nucleon scattering is examined. Resonant string contributions increase substantially the standard model neutrino-nucleon cross section. Although they seem insufficient to explain the trans-GZK cosmic ray events, their effects might be detected in next experiments.
Recent experimental results suggest that the neutrinos of the Standard Model are massive, though light. Therefore they may mix with each other giving rise to lepton flavour or even lepton number violating processes, depending on whether they are Dirac or Majorana particles. Furthermore, the lightness of the observed neutrinos may be explained by the existence of heavy ones, whose effects on LFV would be very sizeable. We present an analysis of the effect of massive neutrinos on flavour-changing decays of the Z boson into leptons, at the one-loop level, independent of neutrino mass models. Constraints from present experiments are taken into account.
Assuming a light Higgs boson is discovered, its nature may remain unknown in case that no supersymmetric particles are found. The detection and study of heavier Higgs particles is then of great interest. For this purpose the Compton-collider option of a high energy e+e- linear collider is optimal both to produce Higgs bosons and to reveal their CP-parity. Assuming realistic photon luminosities for various configurations of laser and linac polarizations, we study the heavy, neutral MSSM Higgs signals for the most relevant decay modes as well as their corresponding backgrounds. The MSSM H and A Higgs bosons with masses up to a ~80% of the linac c.m.s. energy may be observed and their CP-parity tested for Higgs masses ~450 GeV, at the gamma-gamma mode of a ~1 TeV linear collider.
We point out that the cross-section for the process $e^+ e^- \to e^+ e^- τ^+ τ^-$ at LEP is large enough to allow for a study of the anomalous electromagnetic couplings of the $τ$ lepton. We show that the present bounds on the magnetic dipole moment can be improved and that competitive bounds can be obtained for the electric dipole moment using the data taken from 1992 to 1994. Finally, we briefly discuss the improvements that can be obtained at LEP II.