Andre de Gouvea

Phenomenological implications of neutrinos in extra dimensions

Abstract Standard Model singlet neutrinos propagating in extra dimensions induce small Dirac neutrino masses. While it seems rather unlikely that their Kaluza–Klein excitations directly participate in the observed neutrino oscillations, their virtual exchange may lead to detectable signatures in future neutrino experiments and in rare charged lepton processes. We show how these effects can be described by specific dimension-six effective operators and discuss their experimental signals.

Split Fermions in Extra Dimensions and CP Violation

We discuss CP violation in the quark sector within a novel approach to the Yukawa puzzle proposed by Arkani-Hamed and Schmaltz, where Yukawa hierarchies result from localising the Standard Model quark field wave-functions, at different positions (in the extra dimensions) in a “fat-brane.” We show that at least two extra dimensions are necessary in order to obtain sufficient CP violation, while reproducing the correct quark mass spectrum and mixing

Lepton flavor violation in supersymmetric models with trilinear R-parity violation

Supersymmetry with R-parity violation (RPV) provides an interesting framework for naturally accommodating small neutrino masses. Within this framework, we discuss the lepton-flavour violating (LFV) processes ! e, ! eee ,a nd ! e conversion in nuclei. We make a detailed study of the observables related to LFV in dierent RPV models, and compare them to the expectations of R-conserving supersymmetry with heavy right-handed neutrinos. We show that the predictions are vastly dierent and uniquely characterise each model, thus providing a powerful framework for experimentally distinguishing between dierent theories of LFV. Besides the obvious possibility of amplied tree-level generation of ! eee and ! e conversion in nuclei, we nd that even in the case where these processes arise at the one-loop level, their rates are comparable to that of ! e ,i n clear contrast to the predictions of R-conserving models. We conclude that in order to distinguish between the dierent models, such a combined study of all the LFV processes is necessary, and that measuring P-odd asymmetries in polarised ! eee can play a decisive role. We also comment on the intriguing possibility of RPV models yielding a large T-odd asymmetry in the decay of polarised ! eee.

Minimalistic Neutrino Mass Model

We consider the simplest model which solves the solar and atmospheric neutrino puzzles, in the sense that it contains the smallest amount of beyond the Standard Model ingredients. The solar neutrino data is accounted for by Planck-mass effects while the atmospheric neutrino anomaly is due to the existence of a single righthanded neutrino at an intermediate mass scale between 10 9 GeV and 10 14 GeV. Even though the neutrino mixing angles are not exactly predicted, they can be naturally large, which agrees well with the current experimental situation. Furthermore, the amount of lepton asymmetry produced in the early universe by the decay of the right-handed neutrino is very predictive and may be enough to explain the current baryon-to-photon ratio if the right-handed neutrinos are produced out of thermal equilibrium. One definitive test for the model is the search for anomalous seasonal effects at Borexino.

The oscillation probability of GeV solar neutrinos of all active species

Abstract I discuss the oscillation probability of O(GeV) neutrinos of all active flavours produced inside the Sun and detected at the Earth. In the GeV energy regime, matter effects are potentially important both for the “1–3” system and the “1–2” system. A numerical scan of the multidimensional three-flavour parameter space is presented. One curiosity is that in the three-flavour oscillation case Pαβ ≠ Pβα for a large portion of the parameter space, even if the MNS matrix is real. Oscillation effects computed here may play a large role in interpreting solar WIMP search data from large neutrino telescopes.

Theoretical aspects of neutrino oscillations

I review some aspects concerning the physics of neutrino mixing and oscillations. I discuss in some detail the physical neutrino oscillations parameter space in the case of two and three family mixing, and briefly describe the current knowledge of neutrino mixing parameters according to the present solar, atmospheric, and reactor neutrino data. I also briefly comment on the possibility of solving the LNSD anomaly together with the solar and atmospheric ones. I conclude by emphasising that even though in five to ten years time a lot will be learnt from the next round of neutrino experiments, a great deal about neutrino masses and neutrino mixing will remain unknown.

Gravitational Wave Bursts from Brane World Neutrino Oscillations During Supernova Collapse

In braneworld-like solutions of the hierarchy problem gravitons and right-handed (sterile) neutrinos are in principle the unique non-standard model fields allowed to propagate into the bulk, thus their coupling is naturally expected. Since active- to-sterile neutrino oscillations can take place during the core bounce of a supernova collapse, then gravitational waves must be produced over the oscillation length through anisotropic neutrino flow. Because the oscillation feeds mass-energy up into (or takes it out of) the target species, the large mass-squared difference between species makes a huge amount of energy to be given off as gravity waves, which is larger than from neutrino convection and cooling, or quadrupole moments of neutron star matter. The strengthness of these bursts would turn them the more sure supernova gravitational- wave signal detectable by interferometers, for distances out to the VIRGO cluster of galaxies.

Determining the flavour content of the low-energy solar neutrino flux

We study the sensitivity of the HELLAZ and Borexino solar neutrino experiments on discriminating the neutrino species e ,e, ; , ; ,a nds using the dierence in the recoil electron kinetic energy spectra in elastic neutrino-electron scattering. We nd that one can observe a non-vanishing ; component in the solar neutrino flux, especially when the e survival probability is low. Also, if the data turn out to be consistent with e

The dark side of the solar neutrino parameter space

; oscillations, a e component can be excluded eectively.