arXiv subjects

J. W. F. Valle

Publications and source records attributed to J. W. F. Valle.

At least 181 records · Page 10Linked to original sources

arXiv2002

Probing neutrino properties with charged scalar lepton decays

Supersymmetry with bilinear R-parity violation provides a predictive framework for neutrino masses and mixings in agreement with current neutrino oscillation data. The model leads to striking signals at future colliders through the R-parity violating decays of the lightest supersymmetric particle. Here we study charged scalar lepton decays and demonstrate that if the scalar tau is the LSP (i) it will decay within the detector, despite the smallness of the neutrino masses, (ii) the relative ratio of branching ratios Br({tilde tau}_1 --> e sum nu_i)/ Br({tilde tau}_1 --> mu sum nu_i) is predicted from the measured solar neutrino angle, and (iii) scalar muon and scalar electron decays will allow to test the consistency of the model. Thus, bilinear R-parity breaking SUSY will be testable at future colliders also in the case where the LSP is not the neutralino.

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arXiv2002

Probing supernova physics with neutrino oscillations

We point out that solar neutrino oscillations with large mixing angle as evidenced in current solar neutrino data have a strong impact on strategies for diagnosing collapse-driven supernova (SN) through neutrino observations. Such oscillations induce a significant deformation of the energy spectra of neutrinos, thereby allowing us to obtain otherwise inaccessible features of SN neutrino spectra. We demonstrate that one can determine temperatures and luminosities of non-electron flavor neutrinos by observing bar{nu}_{e} from galactic SN in massive water Cherenkov detectors by the charged current reactions on protons.

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arXiv2002

Neutrinos in Supersymmetry without R-Parity

We show how Bilinear R-Parity violation within the Minimal Supersymmetric Standard Model can solve the atmospheric and solar neutrino problems by generating naturally small and hierarchical neutrino masses, together with neutrino mixing angles consistent with experiments. The relation between collider and neutrino physics is emphasized.

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arXiv2002

Underlying A_4 Symmetry for the Neutrino Mass Matrix and the Quark Mixing Matrix

The discrete non-Abelian symmetry $A_4$, valid at some high-energy scale, naturally leads to degenerate neutrino masses, without spoiling the hierarchy of charged-lepton masses. Realistic neutrino mass splittings and mixing angles (one of which is necessarily maximal and the other large) are then induced radiatively in the context of softly broken supersymmetry. The quark mixing matrix is also calculable in a similar way. The mixing parameter $U_{e3}$ is predicted to be imaginary, leading to maximal CP violation in neutrino oscillations. Neutrinoless double beta decay and $τ\to μγ$ should be in the experimentally accessible range.

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arXiv2002

SN1987A and the Status of Oscillation Solutions to the Solar Neutrino Problem (including an appendix discussing the NC and day/night data from SNO)

We study neutrino oscillations and the level-crossing probability PLZ in power-law potential profiles A(r)\propto r^n. We give local and global adiabaticity conditions valid for all mixing angles theta and discuss different representations for PLZ. For the 1/r^3 profile typical of supernova envelopes we compare our analytical to numerical results and to earlier approximations used in the literature. We then perform a combined likelihood analysis of the observed SN1987A neutrino signal and of the latest solar neutrino data, including the recent SNO CC measurement. We find that, unless all relevant supernova parameters (released binding energy, \barν_e and \barν_{μ,τ} temperatures) are near their lowest values found in simulations, the status of large mixing type solutions deteriorates considerably compared to fits using only solar data. This is sufficient to rule out the vacuum-type solutions for most reasonable choices of astrophysics parameters. The LOW solution may still be acceptable, but becomes worse than the SMA-MSW solution which may, in some cases, be the best combined solution. On the other hand the LMA-MSW solution can easily survive as the best overall solution, although its size is generally reduced when compared to fits to the solar data only.

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arXiv2002

Confusing non-standard neutrino interactions with oscillations at a neutrino factory

Most neutrino mass theories contain non-standard interactions (NSI) of neutrinos which can be either non-universal (NU) or flavor-changing (FC). We study the impact of such interactions on the determination of neutrino mixing parameters at a neutrino factory using the so-called ``golden channels'' \pnu{e}\to\pnuμ for the measurement of θ_{13}. We show that a certain combination of FC interactions in neutrino source and earth matter can give exactly the same signal as oscillations arising due to θ_{13}. This implies that information about θ_{13} can only be obtained if bounds on NSI are available. Taking into account the existing bounds on FC interactions, this leads to a drastic loss in sensitivity in θ_{13}, at least two orders of magnitude. A near detector at a neutrino factory offers the possibility to obtain stringent bounds on some NSI parameters. Such near site detector constitutes an essential ingredient of a neutrino factory and a necessary step towards the determination of θ_{13} and subsequent study of leptonic CP violation.

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arXiv2002

Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data

We present a unified global analysis of neutrino oscillation data within the framework of the four-neutrino mass schemes (3+1) and (2+2). We include all data from solar and atmospheric neutrino experiments, as well as information from short-baseline experiments including LSND. If we combine only solar and atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas short-baseline data in combination with atmospheric data prefers (2+2) models. When combining all data in a global analysis the (3+1) mass scheme gives a slightly better fit than the (2+2) case, though all four-neutrino schemes are presently acceptable. The LSND result disfavors the three-active neutrino scenario with only $Δm^2_{sol}$ and $Δm^2_{atm}$ at 99.9% CL with respect to the four-neutrino best fit model. We perform a detailed analysis of the goodness of fit to identify which sub-set of the data is in disagreement with the best fit solution in a given mass scheme.

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arXiv2002

Neutrino Masses and Mixings in SUSY with Broken R-Parity

The simplest unified extension of the Minimal Supersymmetric Standard Model with bilinear R-Parity violation provides a predictive scheme for neutrino masses which can account for the observed atmospheric and solar neutrino anomalies. Despite the smallness of neutrino masses R-parity violation is observable at present and future high-energy colliders, providing an unambiguous cross-check of the model.

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arXiv2001

A non-resonant dark-side solution to the solar neutrino problem

We re-analyse spin-flavour precession solutions to the solar neutrino problem in the light of the recent SNO CC result as well as the 1258--day Super-Kamiokande data and the upper limit on solar anti-neutrinos. In a self-consistent magneto-hydrodynamics approach the resulting scheme has only 3 effective parameters: $Δm^2$, $μB_\perp$ and the neutrino mixing angle $θ$. We show how a rates-only analysis for fixed $μB_\perp$ slightly favours spin-flavour precession (SFP) solutions over oscillations (OSC). In addition to the resonant solution (RSFP for short), there is a new non-resonant solution (NRSFP) in the ``dark-side''. Both RSFP and NRSFP lead to flat recoil energy spectra in excellent agreement with the latest SuperKamiokande data. We also show that in the presence of a neutrino transition magnetic moment of $10^{-11}$ Bohr magneton, a magnetic field of 80 KGauss eliminates all large mixing solutions other than the so-called LMA solution.

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arXiv2001

Modeling Quintessential Inflation

We develop general criteria to construct unified frameworks for inflation and quintessence which employ a unique scalar field to drive both. By using such a minimal theoretical framework we avoid having to fine-tune couplings and mass-scales. In particular the initial conditions for quintessence are already fixed at the end of the inflationary epoch. We provide concrete realizations of the method which meet all inflationary and quintessence requirements, such as the COBE normalization and the resulting spectral index n = 0.97, which is in excellent agreement with the latest CMB data.

astro-ph↗

arXiv2001

How sensitive is a neutrino factory to the angle $θ_{13}$?

We consider the impact of non-standard interactions of neutrinos (NSI) on the determination of neutrino mixing parameters at a neutrino factory using $\pnu{e}\to\pnuμ$ ``golden channels'' for the measurement of $θ_{13}$. We show how a small residual NSI leads to a drastic loss in sensitivity in $θ_{13}$, of up to two orders of magnitude. This can be somewhat overcome if two baselines are combined.

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arXiv2001

Non-Standard Interactions: Atmospheric versus Neutrino Factory Experiments

We consider the potential of a generic neutrino factory (NUFACT) in probing non-standard neutrino-matter interactions (NSI). We find that the sensitivity to flavour-changing (FC) NSI can be substantially improved with respect to present atmospheric neutrino data, especially at energies higher than approximately 50 GeV, where the effect of the tau mass is small. For example, a 100 GeV NUFACT can probe FC neutrino interactions at the level of few $|ε| < {few} \times 10^{-4}$ at 99 % C.L.

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arXiv2001

Cornering (3+1) sterile neutrino schemes

Using the most recent atmospheric neutrino data, as well as short-baseline, long-baseline and tritium $β$-decay data we show that the joint interpretation of the LSND, solar and atmospheric neutrino anomalies in (3+1) sterile neutrino schemes is severely disfavored, in contrast to the theoretically favored (2+2) schemes.

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arXiv2001

Generalized Bounds on Majoron-neutrino couplings

We discuss limits on neutrino-Majoron couplings both from laboratory experiments as well as from astrophysics. They apply to the simplest class of Majoron models which covers a variety of possibilities where neutrinos acquire mass either via a seesaw-type scheme or via radiative corrections. By adopting a general framework including CP phases we generalize bounds obtained previously. The combination of complementary bounds enables us to obtain a highly non-trivial exclusion region in the parameter space. We find that the future double beta project GENIUS, together with constraints based on supernova energy release arguments, could restrict neutrino-Majoron couplings down to the 10^{-7} level.

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arXiv2001

Status of Neutrino Oscillations

Solar and atmospheric neutrino data require physics beyond the Standard Model of particle physics. The simplest, most generic, but not yet unique, interpretation of the data is in terms of neutrino oscillations. I summarize the results of the latest three-neutrino oscillation global fit of the data, in particular the bounds on the angle $θ_{13}$ probed in reactor experiments. Even though not implied by the data, bi-maximal neutrino mixing emerges as an attractive possibility either in hierarchical or quasi-degenerate neutrino scenarios.

astro-ph↗

arXiv2001

Testing neutrino mixing at future collider experiments

Low energy supersymmetry with bilinear breaking of R-parity leads to a weak-scale seesaw mechanism for the atmospheric neutrino scale and a radiative mechanism for the solar neutrino scale. The model has striking implications for collider searches of supersymmetric particles. Assuming that the lightest SUSY particle is the lightest neutralino we demonstrate that (i) The neutralino decays inside the detector even for tiny neutrino masses. (ii) Measurements of the neutrino mixing angles lead to predictions for the ratios of various neutralino branching ratios implying an independent test of neutrino physics at future colliders, such as the Large Hadron Collider or a Linear Collider.

hep-ph↗

arXiv2001

Neutralino Phenomenology at LEP2 in Supersymmetry with Bilinear Breaking of R-parity

We discuss the phenomenology of the lightest neutralino in models where an effective bilinear term in the superpotential parametrizes the explicit breaking of R-parity. We consider supergravity scenarios where the lightest supersymmetric particle (LSP) is the lightest neutralino and which can be explored at LEP2. We present a detailed study of the LSP decay properties and general features of the corresponding signals expected at LEP2. We also contrast our model with gauge mediated supersymmetry breaking.

hep-ph↗

arXiv2001

Large lepton mixing and supernova 1987A

We reconsider the impact of $\barν_e \leftrightarrow \barν_{μ,τ}$ neutrino oscillations on the observed $\barν_e$ signal of supernova SN 1987A. Performing a maximum-likelihood analysis using as fit parameters the released binding energy $\Eb$ and the average neutrino energy $\Ee$, we find as previous analyses that $\barν_e \leftrightarrow \barν_{μ,τ}$ oscillations with large mixing angles have lower best-fit values for $\Ee$ than small-mixing angle (SMA) oscillations. Moreover, the inferred value of $\Ee$ is already in the SMA case lower than those found in simulations. This apparent conflict has been interpreted as evidence against the large mixing oscillation solutions to the solar neutrino problem. In order to quantify the degree to which the experimental data favour the SMA over the large mixing solutions we use their likelihood ratios as well as a Kolmogorov-Smirnov test. We find within the range of SN parameters predicted by simulations regions in which the LMA-MSW solution is either only marginally disfavoured or favoured compared to the SMA-MSW solution. We conclude therefore that the LMA-MSW solution is not in conflict with the current understanding of SN physics. In contrast, the vacuum oscillation and the LOW solutions to the solar neutrino problem can be excluded at the $4σ$ level for most of the SN parameter ranges found in simulations. Only a marginal region with low values of $\Ee$, $ $ and $\Eb$ is left over, in which these oscillation solutions can be reconciled with the neutrino signal of SN 1987A.

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