Renormalisation effects of neutrino masses and interactions

1. Data and implications. 2. Neutrino threshold effects. 3. Renormalisation of the neutrino mass operator and stability properties of neutrino textures. 4. Neutrino thresholds effects and Yukawa unification. 5. Renormalisation-induced lepton-flavour-violating processes from non-zero neutrino masses. 6. Summary.Comment: 19 pages, 6 figures. Invited talk at the Cracow Epiphany Conference on Neutrinos in Physics and Astrophysics, January 2000. Proceedings to appear in Acta Physica Polonica

Can Neutrinos be Degenerate in Mass?

We reconsider the possibility that the masses of the three light neutrinos of the Standard Model might be almost degenerate and close to the present upper limits from Tritium beta decay and cosmology. In such a scenario, the cancellations required by the latest upper limit on neutrinoless double-beta decay enforce near-maximal mixing that may be compatible only with the vacuum-oscillation scenario for solar neutrinos. We argue that the mixing angles yielded by degenerate neutrino mass-matrix textures are not in general stable under small perturbations. We evaluate within the MSSM the generation-dependent one-loop renormalization of neutrino mass-matrix textures that yielded degenerate masses and large mixing at the tree level. We find that m_{nu_e} > m_{nu_mu} > m_{nu_tau} after renormalization, excluding MSW effects on solar neutrinos. We verify that bimaximal mixing is not stable, and show that the renormalized masses and mixing angles are not compatible with all the experimental constraints, even for tanbeta as low as unity. These results hold whether the neutrino masses are generated by a see-saw mechanism with heavy neutrinos weighing approx. 10^{13} GeV or by non-renormalizable interactions at a scale approx. 10^5 GeV. We also comment on the corresponding renormalization effects in the minimal Standard Model, in which m_{nu_e} < m_{nu_mu} < m_{nu_tau}. Although a solar MSW effect is now possible, the perturbed neutrino masses and mixings are still not compatible with atmospheric- and solar-neutrino data.Comment: 17 pages, 4 figures. Corrections to typos and notation: rephrased and clarified statements on impact of induced deviations from bimaximal mixin

Three-body Supersymmetric Top Decays

We discuss three-body supersymmetric top decays, in schemes both with and without R-parity conservation, assuming that sfermion masses are larger than m_t. We find that MSSM top decays into chargino/neutralino pairs have a strong kinematic suppression in the region of the supersymmetric parameter space consistent with the LEP limits, with a decay width =< 10^{-5} GeV. MSSM top decays into neutralino pairs have less kinematical suppression, but require a flavour-changing vertex, and are likely to have a smaller rate. On the other hand, R-violating decays to single charginos, neutralinos and conventional fermions can be larger for values of the R-violating couplings still permitted by other upper limits. The cascade decays of the charginos and neutralinos may lead to spectacular signals with explicit lepton-number violation, such as like-sign lepton events.Comment: CERN-TH/2000-60, 13 pages, LaTex, 10 figure

Inflation with non-canonical scalar fields revisited

We revisit inflation with non-canonical scalar fields by applying deformed-steepness exponential potentials. We show that the resulting scenario can lead to inflationary observables, and in particular to scalar spectral index and tensor-to-scalar ratio, in remarkable agreement with observations. Additionally, a significant advantage of the scenario is that the required parameter values, such as the non-canonicality exponent and scale, as well as the potential exponent and scale, do not need to acquire unnatural values and hence can accept a theoretical justification. Hence, we obtain a significant improvement with respect to alternative schemes, and we present distinct correlations between the model parameters that better fit the data, which can be tested in future probes. This combination of observational efficiency and theoretical justification makes the scenario at hand a good candidate for the description of inflation.Comment: 15 pages, 6 figures, 2 table

Confronting SUSY GUT With Dark Matter, Sparticle Spectroscopy and Muon (g − 2)

We explore the implications of LHC and cold dark matter searches for supersymmetric particle mass spectra in two different grand unified models with left-right symmetry, SO(10) and SU(4)c × SU(2)L × SU(2)R (4-2-2). We identify characteristic differences between the two scenarios, which imply distinct correlations between experimental measurements and the particular structure of the GUT group. The gauge structure of 4-2-2 enhances significantly the allowed parameter space as compared to SO(10), giving rise to a variety of coannihilation scenarios compatible with the LHC data, LSP dark matter and the ongoing muon g-2 experiment

Manifestations of R-Parity Violation in Ultrahigh-Energy Neutrino Interactions

Supersymmetric couplings that do not respect R-parity can induce significant changes in the interaction rates of ultrahigh-energy neutrinos through the direct-channel production of superpartner resonances, and can provide new sources of extremely energetic tau-leptons. We analyze the possible observable consequences of R-parity violating transitions in large-volume neutrino telescopes

Primordial black holes and gravitational waves from non-canonical inflation

Primordial black holes (PBHs) can generically form in inflationary setups through the collapse of enhanced cosmological perturbations, providing us access to the early Universe through their associated observational signatures. In the current work we propose a new mechanism of PBH production within non-canonical inflation, using a class of steep-deformed inflationary potentials compatible with natural values for the non-canonical exponents. In particular, by requiring significant PBH production we extract constraints on the non-canonical exponents. Additionally, we find that our scenario can lead to the formation of asteroid-mass PBHs, which can account for the totality of the dark matter, as well as to production of solar-mass PBHs within the LIGO/VIRGO detection band. Finally, we find that the enhanced cosmological perturbations which collapse to form PBHs can produce a stochastic gravitational-wave (GW) background induced by second-order gravitational interactions. Very interestingly, we obtain a GW signal detectable by future GW experiments, in particular by SKA, LISA and BBO.Comment: 17 pages without appendices (23 in total), 7 figure

Violation of Time-Reversal Invariance and CPLEAR Measurements

Motivated by the recent CPLEAR measurement on the time-reversal non-invariance, we review the situation concerning the experimental measurements of charge conjugation, parity violation and time reversibility, in systems with non-Hermitean Hamiltonians. This includes in particular neutral meson systems, like K0-barK0, D0-barD0 and B0-barB0. We discuss the formalism that describes particle-antiparticle mixing and time evolution of states, paying particular emphasis to the orthogonality conditions of incoming and outgoing states. As a result, we confirm that the CPLEAR experiment makes a direct measurement of violation of time-reversal without any assumption of unitarity and CPT-violation. The asymmetry which signifies T-violation, is found to be independent of time and decay processes.Comment: 12 pages, LATEX file, no figure

Scale of Leptogenesis

We study the scale at which one can generate the lepton asymmetry of the universe which could then get converted to a baryon asymmetry during the electroweak phase transition. We consider the possibility that the Yukawa couplings are small but sufficiently large to generate enough lepton asymmetry. This forbids the possibility of the $(B-L)$ breaking scale being the electroweak scale.Comment: 13 pages, 7 figures, plain Late