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J. W. F. Valle

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

At least 163 records · Page 9Linked to original sources
arXiv2003

Status of three-neutrino oscillations after the SNO-salt data

We perform a global analysis of neutrino oscillation data in the framework of three neutrinos, including the recent improved measurement of the neutral current events at SNO. In addition to all current solar neutrino data we take into account the reactor neutrino data from KamLAND and CHOOZ, the atmospheric neutrino data from Super-Kamiokande and MACRO, as well as the first spectral data from the K2K long baseline accelerator experiment. The up-to-date best fit values and allowed ranges of the three-flavour oscillation parameters are determined from these data. Furthermore, we discuss in detail the status of the small parameters alpha = Delta_m^2_Sol / Delta_m^2_Atm and sin^2(theta_13), which fix the possible strength of CP violating effects in neutrino oscillations.

hep-ph↗
arXiv2003

Probing neutrino mass with multilepton production at the Tevatron in the simplest R-parity violation model

We analyze the production of multileptons in the simplest supergravity model with bilinear violation of R parity at the Fermilab Tevatron. Despite the small R-parity violating couplings needed to generate the neutrino masses indicated by current atmospheric neutrino data, the lightest supersymmetric particle is unstable and can decay inside the detector. This leads to a phenomenology quite distinct from that of the R-parity conserving scenario. We quantify by how much the supersymmetric multilepton signals differ from the R-parity conserving expectations, displaying our results in the $m_0 \otimes m_{1/2}$ plane. We show that the presence of bilinear R-parity violating interactions enhances the supersymmetric multilepton signals over most of the parameter space, specially at moderate and large $m_0$.

hep-ph↗
arXiv2003

Reconstructing Neutrino Properties from Collider Experiments in a Higgs Triplet Neutrino Mass Model

We extend the minimal supersymmetric standard model with bilinear R-parity violation to include a pair of Higgs triplet superfields. The neutral components of the Higgs triplets develop small vacuum expectation values (VEVs) quadratic in the bilinear R-parity breaking parameters. In this scheme the atmospheric neutrino mass scale arises from bilinear R-parity breaking while for reasonable values of parameters the solar neutrino mass scale is generated from the small Higgs triplet VEVs. We calculate neutrino masses and mixing angles in this model and show how the model can be tested at future colliders. The branching ratios of the doubly charged triplet decays are related to the solar neutrino angle via a simple formula.

hep-ph↗
arXiv2003

Can four neutrinos explain global oscillation data including LSND and cosmology?

We present an analysis of the global neutrino oscillation data in terms of four-neutrino mass schemes. We find that the strong preference of oscillations into active neutrinos implied by solar+KamLAND as well as atmospheric neutrino data allows to rule out (2+2) mass schemes, whereas (3+1) schemes are strongly disfavoured by short-baseline experiments. In addition, we perform an analysis using recent data from cosmology, including CMB data from WMAP and data from 2dFGRS large scale structure surveys. These data lead to further restrictions of the allowed regions for the (3+1) mass scheme.

hep-ph↗
arXiv2003

Status of a hybrid three-neutrino interpretation of neutrino data

We reanalyze the non-standard interaction (NSI) solutions to the solar neutrino problem in the light of the latest solar, atmospheric and reactor neutrino data. We show that such solutions, although preferred by the solar data and consistent with the oscillation description of the atmospheric neutrino data, are ruled out by the first results of the KamLAND reactor experiment, at more than 3_sigma.

hep-ph↗
arXiv2003

Resonant origin for density fluctuations deep within the Sun: helioseismology and magneto-gravity waves

We analyze helioseismic waves near the solar equator in the presence of magnetic fields deep within the solar radiative zone. We find that reasonable magnetic fields can significantly alter the shapes of the wave profiles for helioseismic g-modes. They can do so because the existence of density gradients allows g-modes to resonantly excite Alfven waves, causing mode energy to be funnelled along magnetic field lines, away from the solar equatorial plane. The resulting wave forms show comparatively sharp spikes in the density profile at radii where these resonances take place. We estimate how big these waves might be in the Sun, and perform a first search for observable consequences. We find the density excursions at the resonances to be too narrow to be ruled out by present-day analyses of p-wave helioseismic spectra, even if their amplitudes were to be larger than a few percent. (In contrast it has been shown in (Burgess et al. 2002) that such density excursions could affect solar neutrino fluxes in an important way.) Because solar p-waves are not strongly influenced by radiative-zone magnetic fields, standard analyses of helioseismic data should not be significantly altered. The influence of the magnetic field on the g-mode frequency spectrum could be used to probe sufficiently large radiative-zone magnetic fields should solar g-modes ever be definitively observed. Our results would have stronger implications if overstable solar g-modes should prove to have very large amplitudes, as has sometimes been argued.

astro-ph↗
arXiv2003

Constraining neutrino oscillation parameters with current solar and atmospheric data

We analyze the impact of recent solar, atmospheric and reactor data in the determination of the neutrino oscillation parameters, taking into account that both the solar nu_e and the atmospheric nu_mu may convert to a mixture of active and sterile neutrinos. We use the most recent global solar neutrino data, including the 1496-day Super-K neutrino data sample, and we investigate in detail the impact of the SNO neutral current, spectral and day/night data by performing also an analysis using only the charged current rate from SNO. The implications of the first 145.1 days of KamLAND data on the determination of the solar neutrino parameters are also discussed in detail. We confirm the clear preference of solar+reactor data for the pure active LMA-MSW solution of the solar neutrino problem, and obtain that the LOW, VAC, SMA and Just-So^2 solutions are disfavored with a Delta_chi^2 = 22, 22, 36, 44, respectively. Furthermore, we find that the global solar data constrains the admixture of a sterile neutrino to be less than 43% at 99% CL. By performing an improved fit of the atmospheric data, we also update the corresponding regions of oscillation parameters. We find that the recent atmospheric Super-K (1489-day) and MACRO data have a strong impact on constraining a sterile component in atmospheric oscillations: if the nu_mu is restricted to the atmospheric mass states only a sterile admixture of 16% is allowed at 99% CL, while a bound of 35% is obtained in the unconstrained case. Pure sterile oscillations are disfavored with a Delta_chi^2 = 34.6 compared to the pure active case.

hep-ph↗
arXiv2003

Solar Neutrino Masses and Mixing from Bilinear R-Parity Broken Supersymmetry: Analytical versus Numerical Results

We give an analytical calculation of solar neutrino masses and mixing at one-loop order within bilinear R-parity breaking supersymmetry, and compare our results to the exact numerical calculation. Our method is based on a systematic perturbative expansion of R-parity violating vertices to leading order. We find in general quite good agreement between approximate and full numerical calculation, but the approximate expressions are much simpler to implement. Our formalism works especially well for the case of the large mixing angle MSW solution (LMA-MSW), now strongly favoured by the recent KamLAND reactor neutrino data.

hep-ph↗
arXiv2003

Large mixing angle oscillations as a probe of the deep solar interior

We re-examine the sensitivity of solar neutrino oscillations to noise in the solar interior using the best current estimates of neutrino properties. Our results show that the measurement of neutrino properties at KamLAND provides new information about fluctuations in the solar environment on scales to which standard helioseismic constraints are largely insensitive. We also show how the determination of neutrino oscillation parameters from a combined fit of KamLAND and solar data depends strongly on the magnitude of solar density fluctuations. We argue that a resonance between helioseismic and Alfven waves might provide a physical mechanism for generating these fluctuations and, if so, neutrino-oscillation measurements could be used to constrain the size of magnetic fields deep within the solar radiative zone.

hep-ph↗
arXiv2003

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.

hep-ph↗
arXiv2003

Combining first KamLAND results with solar neutrino data

We consider the impact of the recent KamLAND data on neutrino oscillations, the first terrestrial neutrino experiment that can probe the solar neutrino anomaly. By combining the first 145.1 days of KamLAND data with the full sample of latest solar neutrino data we find an enhanced rejection against non-LMA oscillations, allowed only at more than 4 sigma with respect to LMA. Furthermore, the new data have a strong impact in narrowing down the allowed range of Delta_m^2 inside the LMA region. In contrast, our global analysis indicates that the new data have little impact on the location of the best fit point. In particular the solar neutrino mixing remains significantly non-maximal (3 sigma).

hep-ph↗
arXiv2003

Neutrino Properties Before and After KamLAND

We review neutrino oscillation physics, including the determination of mass splittings and mixings from current solar, atmospheric, reactor and accelerator neutrino data. A brief discussion is given of cosmological and astrophysical implications. Non-oscillation phenomena such as neutrinoless double beta decay would, if discovered, probe the absolute scale of neutrino mass and also reveal their Majorana nature. Non-oscillation descriptions in terms of spin-flavor precession (SFP) and non-standard neutrino interactions (NSI) currently provide an excellent fit of the solar data. However they are at odds with the first results from the KamLAND experiment which imply that, despite their theoretical interest, non-standard mechanisms can only play a sub-leading role in the solar neutrino anomaly. Accepting the LMA-MSW solution, one can use the current solar neutrino data to place important restrictions on non-standard neutrino properties, such as neutrino magnetic moments. Both solar and atmospheric neutrino data can also be used to place constraints on neutrino instability as well as the more exotic possibility of $CPT$ and Lorentz Violation. Weillustrate the potential of future data from experiments such as KamLAND, Borexino and the upcoming neutrino factories in constraining non-standard neutrino properties.

hep-ph↗
arXiv2003

CP Phases, LFV, RpV & all that

Most phenomenological analyses of searches for supersymmetric particles have been performed within the MSSM with real SUSY parameters and conserved R-parity and lepton flavour. Here we summarize recent results obtained in the (s)lepton sector when one of the above assumptions is relaxed.

hep-ph↗
arXiv2002

Global analysis of neutrino oscillation data in four-neutrino schemes

We present an analysis of the global neutrino oscillation data in terms of four-neutrino mass schemes. We find that the strong preference of oscillations into active neutrinos implied by the latest solar as well as atmospheric neutrino data allows to rule out (2+2) mass schemes, whereas (3+1) schemes are strongly disfavoured by short-baseline experiments. Our analysis shows that four-neutrino oscillations do not provide a satisfactory description of the global neutrino oscillation data including the LSND result.

hep-ph↗
arXiv2002

Standard and non-standard neutrino properties

I review the interpretation of solar and atmospheric neutrino data in terms neutrino oscillations and describe some ways to account for the required neutrino masses and mixing angles from first principles, both within top-down and bottom-up approaches. I also discuss non-oscillation phenomena such as nu-less double beta which may probe the absolute scale of neutrino mass, and also reveal its Majorana nature. I note that leptonic CP violation induced by ``Majorana'' phases drop from oscillations but play a role in the leptogenesis scenario for the baryon asymmetry of the Universe. Direct tests of leptonic CP violation in oscillation experiments, such as neutrino factories, will be a tough challenge, due to the hierarchical neutrino mass splittings and the smallness of theta13 indicated by reactors. The large solar mixing angle theta12 offers a way to probe otherwise inaccessible features of supernova physics. Finally, I note that in low-scale models of neutrino mass, one may probe all mixing angles, including the atmospheric theta23, at high energy accelerator experiments such as the LHC or NLC. A neat example is supersymmetry with bilinear breaking of R parity, where the LSP decay branching ratios are directly correlated to the neutrino mixing angles. I also discuss non-oscillation solutions to the solar neutrino problem in terms of spin-flavor precession and non-standard neutrino interactions, which will be crucially tested at KamLAND.

hep-ph↗
arXiv2002

Constraining Majorana neutrino electromagnetic properties from the LMA-MSW solution of the solar neutrino problem

In this paper we use solar neutrino data to derive stringent bounds on Majorana neutrino transition moments (TMs). Should such be present, they would contribute to the neutrino--electron scattering cross section and hence alter the signal observed in Super-Kamiokande. Motivated by the growing robustness of the LMA-MSW solution of the solar neutrino problem indicated by recent data, and also by the prospects of its possible confirmation at KamLAND, we assume the validity of this solution, and we constrain neutrino TMs by using the latest global solar neutrino data. We find that all elements of the TM matrix can be bounded at the same time. Furthermore, we show how reactor data play a complementary role to the solar neutrino data, and use the combination of both data sets to improve the current bounds. Performing a simultaneous fit of LMA-MSW oscillation parameters and TMs we find that 6.3 times 10^{-10} mu_B and 2.0 times 10^{-10} mu_B are the 90% C.L. bounds from solar and combined solar + reactor data, respectively. Finally, we perform a simulation of the upcoming Borexino experiment and show that it will improve the bounds from today's data by roughly one order of magnitude.

hep-ph↗
arXiv2002

Ruling out four-neutrino oscillation interpretations of the LSND anomaly?

Prompted by recent solar and atmospheric data, we re-analyze the four-neutrino description of current global neutrino oscillation data, including the LSND evidence for oscillations. The higher degree of rejection for non-active solar and atmospheric oscillation solutions implied by the SNO neutral current result as well as by the latest 1489-day Super-K atmospheric neutrino data allows us to rule out (2+2) oscillation schemes proposed to reconcile LSND with the rest of current neutrino oscillation data. Using an improved goodness of fit (gof) method especially sensitive to the combination of data sets we obtain a gof of only 1.6 times 10^{-6} for (2+2) schemes. Further, we re-evaluate the status of (3+1) oscillations using two different analyses of the LSND data sample. We find that also (3+1) schemes are strongly disfavoured by the data. Depending on the LSND analysis we obtain a gof of 5.6 times 10^{-3} or 7.6 times 10^{-5}. This leads to the conclusion that all four-neutrino descriptions of the LSND anomaly, both in (2+2) as well as (3+1) realizations, are highly disfavoured. Our analysis brings the LSND hint to a more puzzling status.

hep-ph↗