44 research outputs found
New CP Violation in Neutrino Oscillations
Measurements of CP--violating observables in neutrino oscillation experiments
have been studied in the literature as a way to determine the CP--violating
phase in the mixing matrix for leptons. Here we show that such observables also
probe new neutrino interactions in the production or detection processes.
Genuine CP violation and fake CP violation due to matter effects are sensitive
to the imaginary and real parts of new couplings. The dependence of the CP
asymmetry on source--detector distance is different from the standard one and,
in particular, enhanced at short distances. We estimate that future neutrino
factories will be able to probe in this way new interactions that are up to
four orders of magnitude weaker than the weak interactions. We discuss the
possible implications for models of new physics.Comment: ReVTeX, 28 pages, 7 figues. v2: Modifications in section VIII to
reflect the fact that some of the couplings that were discussed in this
section are irrelevant to our analysis (as pointed out in hep-ph/0112329);
Added a discussion in section IX of the relevance of other future experiments
that will search for lepton flavor violatio
A neutrino mass matrix with seesaw mechanism and two-loop mass splitting
We propose a model which uses the seesaw mechanism and the lepton number
to achieve the neutrino mass spectrum and , together with a lepton mixing matrix with .
In this way, we accommodate atmospheric neutrino oscillations. A small mass
splitting is generated by breaking spontaneously and using
Babu's two-loop mechanism. This allows us to incorporate ``just so''
solar-neutrino oscillations with maximal mixing into the model. The resulting
mass matrix has three parameters only, since breaking leads
exclusively to a non-zero matrix element.Comment: 8 pages, Late
Phenomenology of Maximal and Near-Maximal Lepton Mixing
We study the phenomenological consequences of maximal and near-maximal mixing
of the electron neutrino with other (=tau and/or muon) neutrinos. We
describe the deviations from maximal mixing in terms of a parameter
and quantify the present experimental
status for . We find that the global analysis of solar neutrino
data allows maximal mixing with confidence level better than 99% for
eV^2\lsim\Delta m^2\lsim2\times10^{-7} eV. In the mass ranges \Delta
m^2\gsim 1.5\times10^{-5} eV and eV^2\lsim\Delta
m^2\lsim2\times10^{-7} eV the full interval is allowed
within 4(99.995 % CL). We suggest ways to measure in future
experiments. The observable that is most sensitive to is the rate
[NC]/[CC] in combination with the Day-Night asymmetry in the SNO detector. With
theoretical and statistical uncertainties, the expected accuracy after 5 years
is . We also discuss the effects of maximal and
near-maximal -mixing in atmospheric neutrinos, supernova neutrinos, and
neutrinoless double beta decay.Comment: 49 pages Latex file using RevTeX. 16 postscript figures included. (
Fig.2 and Fig.4 bitmapped for compression,better resolution at
http://ific.uv.es/~pppac/). Improved presentation: some statements included
and labels added in figures. Some misprint corrected. Final version to appear
in Phys. Rev D. Report no: IFIC/00-40, IASSNS-HEP-00-5
The Little Review on Leptogenesis
This is a brief review on the scenario of baryogenesis through leptogenesis.
Leptogenesis is an appealing scenario that may relate the observed baryon
asymmetry in the Universe to the low-energy neutrino data. In this review talk,
particular emphasis is put on recent developments on the field, such as the
flavourdynamics of leptogenesis and resonant leptogenesis near the electroweak
phase transition. It is illustrated how these recent developments enable the
modelling of phenomenologically predictive scenarios that can directly be
tested at the LHC and indirectly in low-energy experiments of lepton-number and
lepton-flavour violation.Comment: 15 pages, based on a plenary presentation given at the DISCRETE'08
Symposium, 11-16 December 2008, Valencia, Spai
SIGNATURES OF CP-VIOLATION IN THE PRESENCE OF MULTIPLE B-PAIR PRODUCTION AT HADRON COLLIDER
We calculate the production of 2 b-quark pairs in hadron collisions. Sources
of multiple pairs are multiple interactions and higher order perturbative QCD
mechanisms. We subsequently investigate the competing effects of multiple
b-pair production on measurements of CP-violation: i) the increase in event
rate with multiple b-pair cross sections which may reach values of order 1 barn
in the presence of multiple interactions and ii) the dilution of versus
tagging efficiency because of the presence of events with 4
-mesons. The impact of multiple -meson production is small unless the
cross section for producing a single pair exceeds 1~mb. We show that even for
larger values of the cross section the competing effects i) and ii) roughly
compensate so that there is no loss in the precision with which CP-violating
CKM angles can be determined.Comment: 14 pages, Latex file using ReVTeX. 7 figures. To Appear in Phys Rev
On Quantum Effects in Soft Leptogenesis
It has been recently shown that quantum Boltzman equations may be relevant
for leptogenesis. Quantum effects, which lead to a time-dependent CP asymmetry,
have been shown to be particularly important for resonant leptogenesis when the
asymmetry is generated by the decay of two nearly degenerate states. In this
work we investigate the impact of the use of quantum Boltzman equations in the
framework ``soft leptogenesis'' in which supersymmetry soft-breaking terms give
a small mass splitting between the CP-even and CP-odd right-handed sneutrino
states of a single generation and provide the CP-violating phase to generate
the lepton asymmetry.Comment: 15 pages, 4 figures. Replacement to match published versio
Minimal models with light sterile neutrinos
We study the constraints imposed by neutrino oscillation experiments on the
minimal extensions of the Standard Model (SM) with gauge singlet fermions
("right-handed neutrinos"), that can account for neutrino masses. We consider
the most general coupling to SM fields of the new fields, in particular those
that break lepton number and we do not assume any a priori hierarchy in the
mass parameters. We proceed to analyze these models starting from the lowest
level of complexity, defined by the number of extra fermionic degrees of
freedom. The simplest choice that has enough free parameters in principle (i.e.
two mass differences and two angles) to explain the confirmed solar and
atmospheric oscillations corresponds to . This minimal choice is shown
to be excluded by data. The next-to-minimal choice corresponds to . We
perform a systematic study of the full parameter space in the limit of
degenerate Majorana masses by requiring that at least two neutrino mass
differences correspond to those established by solar and atmospheric
oscillations. We identify several types of spectra that can fit long-baseline
reactor and accelerator neutrino oscillation data, but fail in explaining solar
and/or atmospheric data. The only two solutions that survive are the expected
seesaw and quasi-Dirac regions, for which we set lower and upper bounds
respectively on the Majorana mass scale. Solar data from neutral current
measurements provide essential information to constrain the quasi-Dirac region.
The possibility to accommodate the LSND/MiniBoone and reactor anomalies, and
the implications for neutrinoless double-beta decay and tritium beta decay are
briefly discussed.Comment: 32 pages, 15 figures. Misprints and a small error corrected,
references added. Conclusions unchange
Neutrino Masses and Mixing: Evidence and Implications
Measurements of various features of the fluxes of atmospheric and solar
neutrinos have provided evidence for neutrino oscillations and therefore for
neutrino masses and mixing. We review the phenomenology of neutrino
oscillations in vacuum and in matter. We present the existing evidence from
solar and atmospheric neutrinos as well as the results from laboratory
searches, including the final status of the LSND experiment. We describe the
theoretical inputs that are used to interpret the experimental results in terms
of neutrino oscillations. We derive the allowed ranges for the mass and mixing
parameters in three frameworks: First, each set of observations is analyzed
separately in a two-neutrino framework; Second, the data from solar and
atmospheric neutrinos are analyzed in a three active neutrino framework; Third,
the LSND results are added, and the status of accommodating all three signals
in the framework of three active and one sterile light neutrinos is presented.
We review the theoretical implications of these results: the existence of new
physics, the estimate of the scale of this new physics and the lessons for
grand unified theories, for supersymmetric models with R-parity violation, for
models of extra dimensions and singlet fermions in the bulk, and for flavor
models.Comment: Added note on the effects of KamLAND results. Two new figure
Neutrino Unification
Present neutrino data are consistent with neutrino masses arising from a
common seed at some ``neutrino unification'' scale . Such a simple
theoretical ansatz naturally leads to quasi-degenerate neutrinos that could lie
in the electron-volt range with neutrino mass splittings induced by
renormalization effects associated with supersymmetric thresholds. In such a
scheme the leptonic analogue of the Cabibbo angle describing
solar neutrino oscillations is nearly maximal. Its exact value is correlated
with the smallness of . These features agree both with latest
data on the solar neutrino spectra and with the reactor neutrino data. The two
leading mass-eigenstate neutrinos present in \ne form a pseudo-Dirac neutrino,
avoiding conflict with neutrinoless double beta decay.Comment: RevTex format, 2 figures, 4 pages, a few new references, no other
important change, figures unchanged, version to be published in PR
Models of Neutrino Masses and Mixings
We review theoretical ideas, problems and implications of neutrino masses and
mixing angles. We give a general discussion of schemes with three light
neutrinos. Several specific examples are analyzed in some detail, particularly
those that can be embedded into grand unified theories.Comment: 44 pages, 2 figures, version accepted for publication on the Focus
Issue on 'Neutrino Physics' edited by F.Halzen, M.Lindner and A. Suzuki, to
be published in New Journal of Physics