Suchergebnisse

Presented at the XXVII International Conference of Theoretical Physics, "Matter to the Deepest", Ustron, Poland, september 15-21, 2003. ; In supersymmetric (SUSY) models the misalignment between fermion and sfermion families introduces unsuppressed flavour-changing processes. Even if the mass parameters are chosen to give no flavour violation, family dependent radiative corrections make this adjustment not stable. In par- ticular, due to the observed large neutrino mixings and potentially large neutrino Yukawa couplings, sizable lepton flavour violation (LFV) is ex- pected. After introducing the basic concepts, the framework and the main assumptions, we report on a recent study of rare leptonic decays in a class of SUSY–GUT models with three quasi-degenerate neutrinos. We show that LFV effects are likely visible in forthcoming experiments. ; This work has been supported by the Spanish CICYT, the Junta de Andalucía and the European Union under contracts FPA2000-1558, FQM 101, and HPRN-CT-2000-00149, respectively.

We would like to thank Mar Bastero, Adrian Carmona, Mikael R. Chala, Miguel Escud-ero, Javier Olmedo, Jose Santiago and Samuel Witte for discussions. This work was par-tially supported by the Spanish Ministry of Science, Innovation and Universities (PID2019-107844GB-C21/AEI/10.13039/501100011033) and by the Junta de Andalucia (FQM 101, SOMM17/6104/UGR, P18-FR-1962, P18-FR-5057) . ; We propose a singlet majoron model that defines an inverse seesaw mechanism in the v sector. The majoron phi has a mass m(phi) approximate to 0.5 eV and a coupling to the tau lepton similar to the one to neutrinos. In the early universe it is initially in thermal equilibrium, then it decouples at T approximate to 500 GeV and contributes with just Delta N-eff = 0.026 during BBN. At T = 26 keV (final stages of BBN) a primordial magnetic field induces resonant gamma phi oscillations that transfer 6% of the photon energy into majorons, implying Delta N-eff = 0.55 and a 4.7% increase in the baryon to photon ratio. At T approximate to m(phi) the majoron enters in thermal contact with the heaviest neutrino and it finally decays into v (v) over bar pairs near recombination, setting Delta N-eff = 0.85. The boost in the expansion rate at later times may relax the Hubble tension (we obtain H-0 = (71.4 +/- 0.5) km/s/Mpc), while the processes v (v) over bar phi suppress the free streaming of these particles and make the model consistent with large scale structure observations. Its lifetime and the fact that it decays into neutrinos instead of photons lets this axion-like majoron avoid the strong bounds that affect other axion-like particles of similar mass and coupling to photons. ; Spanish Government PID2019-107844GB-C21/AEI/10.13039/501100011033 ; Junta de Andalucia FQM 101 SOMM17/6104/UGR P18-FR-1962 P18-FR-5057

Presented at the XIX International Conference on Theoretical Physics "Particle Physics and Astrophysics in the Standard Model and Beyond", Bystra, Poland, september 19-26, 1995. ; This is a short review of present and future limits on new neutral gauge bosons, in particular on hadrophilic or leptophobic Z's recently proposed to interpret the observed fluctuations of Γc,b at LEP. Light gauge bosons coupled to lepton number differences or to baryon number are also examples of the model dependence of these bounds. The mixing between the U(1) factors plays an important role in the phenomenology of these extended electroweak models. Future improvements based on the analysis of precise electroweak data are emphasized. ; This work has been partially supported by CICYT under contract AEN96-1672 by the Junta de Andalucía, and by the European Union under contract CHRX-CT92-0004.