13 research outputs found
Asymmetry in the decay
We consider the asymmetry in the decay
assuming that a Vector Meson Dominance approach for the
transition gives the dominant contribution. Since in this long-distance
approximation the decay is due to a single quark transition , the angular distribution asymmetry is given by the single positive
asymmetry parameter .
We also discuss the asymmetry in , which is
expected to be between -0.2 and 0.3.Comment: 16 pages,no figures,Late
Baryogenesis and Degenerate Neutrinos
We bring the theoretical issue of whether two important cosmological demands,
baryon asymmetry and degenerate neutrinos as hot dark matter, can be compatible
in the context of the seesaw mechanism. To realize leptogenesis with almost
degenerate Majorana neutrinos without severe fine-tuning of parameters, we
propose the hybrid seesaw mechanism with a heavy Higgs triplet and right-handed
neutrinos. Constructing a minimal hybrid seesaw model with SO(3) flavor
symmetry for the neutrino sector, we show that the mass splittings for the
atmospheric and solar neutrino oscillations which are consistent with the
requirements for leptogenesis can naturally arise.Comment: 13 pages with one figure using axodraw.st
SO(10) grand unification model for degenerate neutrino masses
We propose an SO(10) scheme where \neu masses can simultaneously explain the solar and atmospheric neutrino deficits, together with a hot dark matter component. In our scheme the Îœe, ΜΌ, and ÎœÏ are approximately degenerate with a mass of about 2 eV, which can lead to an observable neutrinoless double beta decay rate. The model is based on a realization of the seesaw mechanism in which the main contribution to the light \neu masses is universal, due to a suitable SU(2) horizontal symmetry, while the splittings between \ne and \nm explain the solar \neu deficit and that between \nm and \nt explain the atmospheric \neu anomaly
Supernova Bounds on Majoron-emitting decays of light neutrinos
Neutrino masses arising from the spontaneous violation of ungauged
lepton-number are accompanied by a physical Goldstone boson, generically called
Majoron. In the high-density supernova medium the effects of Majoron-emitting
neutrino decays are important even if they are suppressed in vacuo by small
neutrino masses and/or small off-diagonal couplings. We reconsider the
influence of these decays on the neutrino signal of supernovae in the light of
recent Super-Kamiokande data on solar and atmospheric neutrinos. We find that
majoron-neutrino coupling constants in the range 3\times 10^{-7}\lsim g\lsim
2\times 10^{-5} or g \gsim 3 \times 10^{-4} are excluded by the observation
of SN1987A. Then we discuss the potential of Superkamiokande and the Sudbury
Neutrino Observatory to detect majoron neutrino interactions in the case of a
future galactic supernova. We find that these experiments could probe majoron
neutrino interactions with improved sensitivity.Comment: 28 pages, 5 figure
Neutrino Physics at the Turn of the Millenium
Recent solar & atmospheric nu-data strongly indicate need for physics beyond
the Standard Model. I review the ways of reconciling them in terms of 3-nu
oscillations. Though not implied by data, bi-maximal nu-mixing models emerge as
a possibility. SUSY with broken R-parity provides an attractive way to
incorporate it, opening the possibility of testing nu-anomalies at high- energy
colliders such as the LHC or at the upcoming long-baseline or nu- factory
experiments. Reconciling, in addition, the LSND hint requires a fourth, light
sterile neutrino, nus. The simplest are the most symmetric scenarios, in which
2 of the 4 neutrinos are maximally-mixed and lie at the LSND scale, while the
others are at the solar scale. The lightness of nus, the nearly maximal
atmospheric mixing, and the solar/atmospheric splittings all follow naturally
from the assumed lepton-number symmetry and its breaking. These basic schemes
can be distinguished at neutral-current-sensitive solar & atmospheric neutrino
experiments such as SNO. However underground experiments have not yet proven
neutrino masses, as there are many alternatives. For example flavour changing
interactions can play an important role in the explanation of solar and
contained atmospheric data and could be tested e.g through \mu \to e + \gamma,
\mu-e conversion in nuclei, unaccompanied by neutrino-less double beta decay.
Conversely, a short-lived numu might play a role in the explanation of the
atmospheric data. Finally, in the presence of a nus, a long-lived heavy nutau
could delay the time at which the matter and radiation contributions to the
energy density of the Universe become equal, reducing density fluctuations on
smaller scales, thus saving the standard CDM scenario, while the light nue,
numu and nus would explain the solar & atmospheric data.Comment: Invited talk at 2nd International Conference on Non-Accelerator New
Physics (NANP-99), Dubna, June 28 - July 3, 199
Neutrino masses: From fantasy to facts
Theory suggests the existence of neutrino masses, but little more. Facts are
coming close to reveal our fantasy: solar and atmospheric neutrino data
strongly indicate the need for neutrino conversions, while LSND provides an
intriguing hint. The simplest ways to reconcile these data in terms of neutrino
oscillations invoke a light sterile neutrino in addition to the three active
ones. Out of the four neutrinos, two are maximally-mixed and lie at the LSND
scale, while the others are at the solar mass scale. These schemes can be
distinguished at neutral-current-sensitive solar & atmospheric neutrino
experiments. I discuss the simplest theoretical scenarios, where the lightness
of the sterile neutrino, the nearly maximal atmospheric neutrino mixing, and
the generation of & all follow
naturally from the assumed lepton-number symmetry and its breaking. Although
the most likely interpretation of the present data is in terms of
neutrino-mass-induced oscillations, one still has room for alternative
explanations, such as flavour changing neutrino interactions, with no need for
neutrino mass or mixing. Such flavour violating transitions arise in theories
with strictly massless neutrinos, and may lead to other sizeable flavour
non-conservation effects, such as , conversion in
nuclei, unaccompanied by neutrino-less double beta decay.Comment: 33 pages, latex, 16 figures. Invited Talk at Ioannina Conference,
Symmetries in Intermediate High Energy Physics and its Applications, Oct.
1998, to be published by Springer Tracts in Modern Physics. Festschrift in
Honour of John Vergados' 60th Birthda
Supernova Bounds on Resonant Active-Sterile Neutrino Conversions
We discuss the effects of resonant and ( is a sterile neutrino) conversions in the dense medium of
a supernova. In particular, we assume the sterile neutrino to be in the
hot dark matter few eV mass range. The implications of such a scenario for the
supernova shock re-heating, the detected signal from SN1987A and
for the r-process nucleosynthesis hypothesis are analysed in some detail. The
resulting constraints on mixing and mass difference for the
system are derived. There is also an allowed region in the neutrino parameter
space for which the r-process nucleosynthesis can be enhanced.Comment: Latex file, 27 pages including 10 ps figures, uses psfig.sty. Few
references added, some change in the Acknowledgements and some minor
corrections in the tex
Degenerate and Other Neutrino Mass Scenarios and Dark Matter
I discuss in this talk mainly three topics related with dark matter motivated neutrino mass spectrum and a generic issue of mass pattern, the normal versus the inverted mass hierarchies. In the first part, by describing failure of a nontrivial potential counter example, I argue that the standard 3 mixing scheme with the solar and the atmospheric 's is robust. In the second part, I discuss the almost degenerate neutrino (ADN) scenario as the unique possibility of accommodating dark matter mass neutrinos into the 3 scheme. I review a cosmological bound and then reanalyze the constraints imposed on the ADN scenario with the new data of double beta decay experiment. In the last part, I discuss the 3 flavor transformation in supernova (SN) and point out the possibility that neutrinos from SN may distinguish the normal versus inverted hierarchies of neutrino masses. By analyzing the neutrino data from SN1987A, I argue that the inverted mass hierarchy is disfavored by the data