220 research outputs found
Violation of the Equivalence Principle in the light of the SNO and SK solar neutrino results
The SNO result on charged current deuteron disintegration, the
SuperKamiokande 1258-day data on electron scattering, and other solar neutrino
results are used to revisit the model of neutrino oscillations driven by a
violation of the equivalence principle. We use a chisq minimization technique
to examine oscillation between the nu(e) and another active neutrino, both
massless, and find that within the Standard Solar Model the fit to the SNO and
SuperKamiokande spectra are moderately good while a very good fit is obtained
when the absolute normalizations of the 8B and hep neutrino fluxes are allowed
to vary. The best fit prefers large, but not maximal, mixing, essentially no
hep neutrinos, and a 40% reduction in the 8B neutrino flux. The fit to the
total rates from the different experiments is not encouraging but when the
rates and spectra are considerd together the situation is much improved. We
remark on the expectations of the VEP model for the neutral current
measurements at SNO.Comment: Latex, 11 pages (incl. 1 postscript figure
Search for a Lorentz invariance violation in atmospheric neutrino oscillations using MACRO data
The energy spectrum of neutrino-induced upward-going muons in MACRO was
analysed in terms of special relativity principles violating effects, keeping
standard mass-induced atmospheric neutrino oscillations as the dominant source
of nu_mu nu_tau transitions. The data disfavour these exotic possibilities
even at a sub-dominant level, and stringent 90% C.L. limits are placed on the
Lorentz invariance violation parameters. These limits can also be
re-interpreted as upper bounds on the parameters describing violation of the
Equivalence Principle.Comment: 8 pages, 5 EPS figures, uses article.sty. Invited talk at C2CR 2005,
From Colliders to Cosmic Rays, Prague, Czech Republic, 7-13 September 200
Semileptonic form factors - a model-independent approach
We demonstrate that the B->D(*) l nu form factors can be accurately predicted
given the slope parameter rho^2 of the Isgur-Wise function. Only weak
assumptions, consistent with lattice results, on the wavefunction for the light
degrees of freedom are required to establish this result. We observe that the
QCD and 1/m_Q corrections can be systematically represented by an effective
Isgur-Wise function of shifted slope. This greatly simplifies the analysis of
semileptonic B decay. We also investigate what the available semileptonic data
can tell us about lattice QCD and Heavy Quark Effective Theory. A rigorous
identity relating the form factor slope difference rho_D^2-rho_A1^2 to a
combination of form factor intercepts is found. The identity provides a means
of checking theoretically evaluated intercepts with experiment.Comment: 18 pages, Revtex, 4 postscript figures, uses epsfig.st
Extrinsic CPT Violation in Neutrino Oscillations in Matter
We investigate matter-induced (or extrinsic) CPT violation effects in
neutrino oscillations in matter. Especially, we present approximate analytical
formulas for the CPT-violating probability differences for three flavor
neutrino oscillations in matter with an arbitrary matter density profile. Note
that we assume that the CPT invariance theorem holds, which means that the CPT
violation effects arise entirely because of the presence of matter. As special
cases of matter density profiles, we consider constant and step-function matter
density profiles, which are relevant for neutrino oscillation physics in
accelerator and reactor long baseline experiments as well as neutrino
factories. Finally, the implications of extrinsic CPT violation on neutrino
oscillations in matter for several past, present, and future long baseline
experiments are estimated.Comment: 47 pages, 7 figures, RevTeX4. Final version to be published in Phys.
Rev.
Can a CPT Violating Ether Solve ALL Electron (Anti)Neutrino Puzzles?
Assuming that CPT is violated in the neutrino sector seems to be a viable
alternative to sterile neutrinos when it comes to reconciling the LSND anomaly
with the remainder of the neutrino data. There are different (distinguishable)
ways of incorporating CPT violation into the standard model, including
postulating m different from \bar{m}. Here, I investigate the possibility of
introducing CPT violation via Lorentz-invariance violating effective operators
(``Ether'' potentials) which modify neutrino oscillation patterns like ordinary
matter effects. I argue that, within a simplified two-flavor like oscillation
analysis, one cannot solve the solar neutrino puzzle and LSND anomaly while
still respecting constraints imposed by other neutrino experiments, and comment
on whether significant improvements should be expected from a three-flavor
analysis. If one turns the picture upside down, some of the most severe
constrains on such CPT violating terms can already be obtained from the current
neutrino data, while much more severe constraints can arise from future
neutrino oscillation experiments.Comment: 10 pages, 1 eps figure; version to appear in PRD. Comment added,
mistake corrected, results and conclusions unchange
Tests of CPT Invariance at Neutrino Factories
We investigate possible tests of CPT invariance on the level of event rates
at neutrino factories. We do not assume any specific model but phenomenological
differences in the neutrino-antineutrino masses and mixing angles in a Lorentz
invariance preserving context, such as it could be induced by physics beyond
the Standard Model. We especially focus on the muon neutrino and antineutrino
disappearance channels in order to obtain constraints on the
neutrino-antineutrino mass and mixing angle differences; we found, for example,
that the sensitivity
could be achieved.Comment: 6 pages, 1 figure, RevTeX4. Final version to be published in Phys.
Rev.
Probing neutrino non-standard interactions with atmospheric neutrino data
We have reconsidered the atmospheric neutrino anomaly in light of the laetst
data from Super-Kamiokande contained events and from Super-Kamiokande and MACRO
up-going muons. We have reanalysed the proposed solution to the atmospheric
neutrino anomaly in terms of non-standard neutrino-matter interactions (NSI) as
well as the standard nu_mu -> nu_tau oscillations (OSC). Our statistical
analysis shows that a pure NSI mechanism is now ruled out at 99%, while the
standard nu_mu -> nu_tau OSC mechanism provides a quite remarkably good
description of the anomaly. We therefore study an extended mechanism of
neutrino propagation which combines both oscillation and non-standard
neutrino-matter interactions, in order to derive limits on flavour-changing
(FC) and non-universal (NU) neutrino interactions. We obtain that the
off-diagonal flavour-changing neutrino parameter epsilon and the diagonal
non-universality neutrino parameter epsilon' are confined to -0.03 < epsilon <
0.02 and |epsilon'| < 0.05 at 99.73% CL. These limits are model independent and
they are obtained from pure neutrino-physics processes. The stability of the
neutrino oscillation solution to the atmospheric neutrino anomaly against the
presence of non-standard neutrino interactions establishes the robustness of
the near-maximal atmospheric mixing and massive-neutrino hypothesis. The best
agreement with the data is obtained for Delta_m^2 = 2.3*10^{-3} eV^2,
sin^2(2*theta) = 1, epsilon = 6.7*10^{-3} and epsilon' = 1.1*10^{-3}, although
the chi^2 function is quite flat in the epsilon and epsilon' directions for
epsilon, epsilon' -> 0.Comment: 26 pages, LaTeX file using REVTeX4, 1 table and 12 figures included.
Added a revised analysis which takes into account the new 1489-day
Super-Kamiokande and final MACRO data. The bound on NSI parameters is
considerably improve
Short-Baseline Neutrino Oscillations at a Neutrino Factory
Within the framework of three-neutrino and four-neutrino scenarios that can
describe the results of the LSND experiment, we consider the capabilities of
short baseline neutrino oscillation experiments at a neutrino factory. We find
that, when short baseline (L \alt 100 km) neutrino factory measurements are
used together with other accelerator-based oscillation results, the complete
three-neutrino parameter space can best be determined by measuring the rate of
oscillations, and measuring CP violation with either
or oscillations (including the
corresponding antineutrino channels). With measurements of CP violation in both
and it may be possible to
distinguish between the three- and four-neutrino cases.Comment: 16 pages, Revtex (single-spaced), 8 postscript figures, uses epsf.st
Lagrangian evolution of global strings
We establish a method to trace the Lagrangian evolution of extended objects
consisting of a multicomponent scalar field in terms of a numerical calculation
of field equations in three dimensional Eulerian meshes. We apply our method to
the cosmological evolution of global strings and evaluate the energy density,
peculiar velocity, Lorentz factor, formation rate of loops, and emission rate
of Nambu-Goldstone (NG) bosons. We confirm the scaling behavior with a number
of long strings per horizon volume smaller than the case of local strings by a
factor of 10. The strategy and the method established here are
applicable to a variety of fields in physics.Comment: 5 pages, 2 figure
Maximal Neutrino Mixing from a Minimal Flavor Symmetry
We study a number of models, based on a non-Abelian discrete group, that
successfully reproduce the simple and predictive Yukawa textures usually
associated with U(2) theories of flavor. These models allow for solutions to
the solar and atmospheric neutrino problems that do not require altering
successful predictions for the charged fermions or introducing sterile
neutrinos. Although Yukawa matrices are hierarchical in the models we consider,
the mixing between second- and third-generation neutrinos is naturally large.
We first present a quantitative analysis of a minimal model proposed in earlier
work, consisting of a global fit to fermion masses and mixing angles, including
the most important renormalization group effects. We then propose two new
variant models: The first reproduces all important features of the SU(5)xU(2)
unified theory with neither SU(5) nor U(2). The second demonstrates that
discrete subgroups of SU(2) can be used in constructing viable supersymmetric
theories of flavor without scalar universality even though SU(2) by itself
cannot.Comment: 34 pages LaTeX, 1 eps figure, minor revisions and references adde
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