162 research outputs found
Atmospheric Neutrino Problem in Maximally-Mixed Three Generations of Neutrinos
Motivated by the indication that both the atmospheric and the solar neutrino
puzzles may simultaneously be solved by (vacuum as well as matter-induced
resonant) oscillations of two generations of neutrinos with large mixing, we
have analyzed the data on the atmospheric and solar neutrinos assuming that all
{\it three} neutrinos are maximally mixed. It is shown that the values of obtained from the two-generation analyses are still valid even in
the three-generation scheme, i.e. the two puzzles can be solved simultaneously
if for the atmospheric
neutrinos and for solar
neutrinos in the maximally mixed three-generation scheme.Comment: Revtex file, 11 pages + 3 figures (included). The postscript file of
text and figures is available at
ftp://toxd01.to.infn.it/pub/giunti/1994/dftt-54-94/dftt-54-94.ps.
Neutrino Masses in Flipped SU(5)
We analyse the fermion masses and mixings in the flipped SU(5) model. The
fermion mass matrices are evolved from the GUT scale down to by solving
the renormalization group equations for the Yukawa couplings. The constraints
imposed by the charged fermion data are then utilised to make predictions about
the neutrino properties . It is found that the {\it generalized } see-saw
mechanism which occurs naturally in this model can provide {\it i})a solution
to the solar neutrino problem via the MSW mechanism and {\it ii})a sufficiently
large mass to contribute as a hot dark matter component as
indicated by the recent COBE data.Comment: (14 Pages,No figures,TEX,IOA-290/92 preprint
General Relativistic Mean Field Theory for Rotating Nuclei
We formulate a general relativistic mean field theory for rotating nuclei
starting from the special relativistic model Lagrangian. The
tetrad formalism is adopted to generalize the model to the accelerated frame.Comment: 13 pages, REVTeX, no figures, submitted to Phys. Rev. Lett., the word
`curved' is replaced by `non-inertial' or `accelerated' in several places to
clarify the physical situation interested, some references are added, more
detail discussions are given with omitting some redundant sentence
Additional Nucleon Current Contributions to Neutrinoless Double Beta Decay
We have examined the importance of momentum dependent induced nucleon
currents such as weak-magnetism and pseudoscalar couplings to the amplitude of
neutrinoless double beta decay in the mechanisms of light and heavy Majorana
neutrino as well as in that of Majoron emission. Such effects are expected to
occur in all nuclear models in the direction of reducing the light neutrino
matrix elements by about 30%. To test this we have performed a calculation of
the nuclear matrix elements of the experimentally interesting nuclei A = 76,
82, 96, 100, 116, 128, 130, 136 and 150 within the pn-RQRPA. We have found that
indeed such corrections vary somewhat from nucleus to nucleus, but in all cases
they are greater than 25 percent. In the case of heavy neutrino the effect is
much larger (a factor of 3). Combining out results with the best presently
available experimental limits on the half-life of the neutrinoless double beta
decay we have extracted new limits on the effective neutrino mass (light and
heavy) and the effective Majoron coupling constant.Comment: 31 pages, RevTex, 3 Postscript figures, submitted to Phys. Rev.
Constraints on diffuse neutrino background from primordial black holes
We calculated the energy spectra and the fluxes of electron neutrino emitted
in the process of evaporation of primordial black holes (PBHs) in the early
universe. It was assumed that PBHs are formed by a blue power-law spectrum of
primordial density fluctuations. We obtained the bounds on the spectral index
of density fluctuations assuming validity of the standard picture of
gravitational collapse and using the available data of several experiments with
atmospheric and solar neutrinos. The comparison of our results with the
previous constraints (which had been obtained using diffuse photon background
data) shows that such bounds are quite sensitive to an assumed form of the
initial PBH mass function.Comment: 18 pages,(with 7 figures
The role of -induced reactions on lead and iron in neutrino detectors
We have calculated cross sections and branching ratios for neutrino induced
reactions on ^{208}Pb and ^{56}Fe for various supernova and
accelerator-relevant neutrino spectra. This was motivated by the facts that
lead and iron will be used on one hand as target materials in future neutrino
detectors, on the other hand have been and are still used as shielding
materials in accelerator-based experiments. In particular we study the
inclusive ^{56}^{56}Co and ^{208}^{208}Bi cross
sections and calculate the neutron energy spectra following the decay of the
daughter nuclei. These reactions give a potential background signal in the
KARMEN and LSND experiment and are discussed as a detection scheme for
supernova neutrinos in the proposed OMNIS and LAND detectors. We also study the
neutron-emission following the neutrino-induced neutral-current excitation of
^{56}Fe and ^{208}Pb.Comment: 23 pages (including 7 figures
Signatures of Supernova Neutrino Oscillations into Extra Dimensions
We consider the mixing of muon and tau neutrinos with sterile fermion fields
propagating in extra dimensions in the context of core collapse supernova
physics, extending the analysis of the electron neutrino case done in a
previous work. We show that the potentially dramatic modifications to the
supernova evolution are prevented by a mechanism of feedback, so that no severe
bounds on the parameters of the extra dimensions need to be imposed.
Nevertheless, the supernova core evolution is significantly modified. We
discuss the consequences on the delayed explosion mechanism and the
compatibility with the SN1987A signal. Then, for the cases of both nu_{mu,tau}
and nu_e mixing with bulk fermions, we analyse the distinctive features of the
signal on Earth.Comment: 16 pages, 7 figures; v2: minor changes, matches published versio
A supernova constraint on bulk majorons
In models with large extra dimensions all gauge singlet fields can in
principle propagate in the extra dimensional space. We have investigated
possible constraints on majoron models of neutrino masses in which the majorons
propagate in extra dimensions. It is found that astrophysical constraints from
supernovae are many orders of magnitude stronger than previous accelerator
bounds. Our findings suggest that unnatural types of the "see-saw" mechanism
for neutrino masses are unlikely to occur in nature, even in the presence of
extra dimensions.Comment: Minor changes, matches the version to appear in PR
Neutrino Interferometry In Curved Spacetime
Gravitational lensing introduces the possibility of multiple (macroscopic)
paths from an astrophysical neutrino source to a detector. Such a multiplicity
of paths can allow for quantum mechanical interference to take place that is
qualitatively different to neutrino oscillations in flat space. After an
illustrative example clarifying some under-appreciated subtleties of the phase
calculation, we derive the form of the quantum mechanical phase for a neutrino
mass eigenstate propagating non-radially through a Schwarzschild metric. We
subsequently determine the form of the interference pattern seen at a detector.
We show that the neutrino signal from a supernova could exhibit the
interference effects we discuss were it lensed by an object in a suitable mass
range. We finally conclude, however, that -- given current neutrino detector
technology -- the probability of such lensing occurring for a
(neutrino-detectable) supernova is tiny in the immediate future.Comment: 25 pages, 1 .eps figure. Updated version -- with simplified notation
-- accepted for publication in Phys.Rev.D. Extra author adde
Lepton Flavor Non-Conservation
In the present work we review the most prominent lepton flavor violating
processes (\mu \ra e\gamma, \mu \ra 3e, conversion,
oscillations etc), in the context of unified gauge theories. Many currently
fashionable extensions of the standard model are considered, such as: {\it i)}
extensions of the fermion sector (right-handed neutrino); {\it ii)} minimal
extensions involving additional Higgs scalars (more than one isodoublets,
singly and doubly charged isosinglets, isotriplets with doubly charged members
etc.); {\it iii)} supersymmetric or superstring inspired unified models
emphasizing the implications of the renormalization group equations in the
leptonic sector. Special attention is given to the experimentaly most
interesting conversion in the presence of nuclei. The relevant
nuclear aspects of the amplitudes are discussed in a number of fashionable
nuclear models. The main features of the relevant experiments are also
discussed, and detailed predictions of the above models are compared to the
present experimental limits.Comment: (IOA-300/93, review article, 83p, 6 epsf figures , available upon
request from [email protected])
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