arXiv subjects

P. I. Krastev

Publications and source records attributed to P. I. Krastev.

At least 19 recordsLinked to original sources

arXiv2001

Global Analysis with SNO: Toward the Solution of the Solar Neutrino Problem

We perform a global analysis of the latest solar neutrino data including the SNO result on the CC-event rate. This result further favors the LMA solution of the solar neutrino problem. The best fit values of parameters we find are: Δm^2 = (4.8 - 5.0)10^{-5} eV^2, tan^2 θ= 0.35 - 0.38, f_B = 1.08 - 1.12, and f_{hep} = 1 - 4. With respect to this best fit the LOW solution is accepted at 90% C.L.. The Vacuum oscillation solution with Δm^2 = 1.4 10^{-10} eV^2, gives good fit of the data provided that the boron neutrino flux is substantially smaller than the SSM flux (f_B \sim 0.5). The SMA solution is accepted only at 3σlevel. We find that vacuum oscillations to sterile neutrino, VAC(sterile), with f_B \sim 0.5 also give rather good global fit of the data. All other sterile solutions are strongly disfavored. We check the quality of the fit by constructing the pull-off diagrams of observables. Predictions for the day-night asymmetry, spectrum distortion and NC/CC ratio at SNO are calculated. In the best fit points of the global solutions we find: A_{DN}^{CC} \approx (7 - 8)% for LMA, \sim 3% for LOW, and (2 - 3)% for SMA. It will be difficult to see the distortion of the spectrum expected for LMA as well as LOW solutions. However, future SNO spectral data can significantly affect the VAC and SMA solutions. We also calculate expectations for the BOREXINO rate.

hep-ph↗

arXiv2000

Status of the solution to the solar neutrino problem based on non-standard neutrino interactions

We analyze the current status of the solution to the solar neutrino problem based both on: a) non-standard flavor changing neutrino interactions (FCNI) and b) non-universal flavor diagonal neutrino interactions (FDNI). We find that FCNI and FDNI with matter in the sun as well as in the earth provide a good fit not only to the total rate measured by all solar neutrino experiments but also to the day-night and seasonal variations of the event rate, as well as the recoil electron energy spectrum measured by the SuperKamiokande collaboration. This solution does not require massive neutrinos and neutrino mixing in vacuum. Stringent experimental constraints on FCNI from bounds on lepton flavor violating decays and on FDNI from limits on lepton universality violation rule out $ν_e \to ν_μ$ transitions induced by New Physics as a solution to the solar neutrino problem. However, a solution involving $ν_e \to ν_τ$ transitions is viable and could be tested independently by the upcoming $B$-factories if flavor violating tau decays would be observed at a rate close to the present upper bounds.

hep-ph↗

arXiv1999

Is Large Mixing Angle MSW the Solution of the Solar Neutrino Problems?

Recent results on solar neutrinos provide hints that the LMA MSW solution could be correct. We perform accurate calculations for potential `smoking-gun' effects of the LMA solution in the SuperKamiokande solar neutrino experiment, including: (1) an almost constant reduction of the standard recoil electron energy spectrum (with a weak, < 10%, relative increase below 6.5 MeV); (2) an integrated difference in day-night rates (2% to 14%); (3) an approximately constant zenith-angle dependence of the nighttime event rate; (4) a new test for the difference in the shape of the equally-normalized day-night energy spectra (~ 1%); and (5) annual variations of the signal due to the regeneration effect (~ 6 times smaller than the integrated day-night effect). We also establish a relation between the integrated day-night asymmetry and the seasonal asymmetry due to LMA regeneration. As a cautionary example, we simulate the effect of an absolute energy calibration error on the shape (distortion) of the recoil energy spectrum. We compare LMA predictions with SuperKamiokande data and discuss the possibilities for distinguishing experimentally between LMA and vacuum oscillations.

hep-ph↗

arXiv1999

Global Analysis of Solar Neutrino Data

The data from all solar neutrino experiments presented at the Neutrino 98 conference has been analyzed and a brief summary of the status of the two most popular neutrino solutions of the solar neutrino problem, the MSW mechanism and vacuum oscillations, is presented here. The inclusion of the recoil-electron data and of the zenith angle distribution of events in the SuperKamiokande detector, together with the routine analysis of the rates, into a global $χ^2$ fit impose stringent constraints on these neutrino oscillation scenarios.

hep-ph↗

arXiv1999

Atmospheric neutrino observations and flavor changing interactions

Flavor changing (FC) neutrino-matter interactions can account for the zenith-angle dependent deficit of atmospheric neutrinos observed in the SuperKamiokande experiment, without directly invoking neither neutrino mass, nor mixing. We find that FC $ν_μ$-matter interactions provide a good fit to the observed zenith angle distributions, comparable in quality to the neutrino oscillation hypothesis. The required FC interactions arise naturally in many attractive extensions of the Standard Model.

hep-ph↗

arXiv1998

Where do we stand with solar neutrino oscillations?

We determine the neutrino parameters for MSW and vacuum oscillations (active and sterile neutrinos) that are allowed by the separate, and collective, imposition of the constraints from total event rates in the chlorine, GALLEX, SAGE, and SuperKamiokande experiments (504 days), the SuperKamiokande electron energy spectrum, and the SuperKamiokande zenith-angle dependence. The small mixing angle MSW solution is acceptable at the 7% C.L. (8% for sterile nu's) and the vacuum solution is acceptable at the 6% C.L. . The best-fit global MSW solution for active neutrinos is: Delta m^2 = 5 x 10^-6 eV^2, sin^2 (2 theta) = 5.5 x 10^{-3} (and for sterile neutrinos: Delta m^2 = 4 x 10^-6 eV^2, sin^2 (2 theta) = 7 x 10^-3). For vacuum oscillations, the best-fit solution is: Delta m^2 = 6.5 x 10^-11 eV^2, sin^2 (2 theta) = 0.75 . An arbitrary combination of undistorted (no oscillations) pp, 7Be, 8B, and CNO neutrino fluxes is inconsistent with the combined data sets at the 3.5 sigma C.L., independent of astrophysical considerations. We use improved calculations of solar model fluxes, neutrino absorption cross sections and energy spectra, and a detailed evaluation of regeneration effects.

hep-ph↗

arXiv1997

Does the Sun Appear Brighter at Night in Neutrinos?

We calculate accurately the number of solar neutrino events expected as a function of solar zenith angle, with and without neutrino oscillations, for detectors at the locations of Super-Kamiokande, SNO, and the Gran Sasso National Laboratory. Using different earth models to estimate geophysical uncertainties, and different solar models to estimate solar uncertainties, we evaluate distortions predicted by the MSW effect in the zenith angle distributions of solar neutrino events. The distortions are caused by oscillations and by $ν-e$ interactions in the earth that regenerate $ν_e$ from $ν_μ$ or $ν_τ$. We show that the first two moments of the zenith-angle distribution are more sensitive to the small mixing angle MSW solution than the conventionally studied day-night asymmetry. We present iso-sigma contours that illustrate the potential of Super-Kamiokande, SNO, BOREXINO, ICARUS and HERON/HELLAZ for detecting the earth regeneration effect at their actual locations (and at the equator). MSW solutions favored by the four pioneering solar neutrino experiments predict characteristic distortions for Super-Kamiokande, SNO, BOREXINO, and ICARUS that range from being unmeasurably small to $> 5σ$ (stat) after only a few years of observations.

hep-ph↗

arXiv1997

Comments on Neutrino Tests of Special Relativity

We point out that the assumption of Lorentz noninvariance examined recently by Coleman and Glashow leads to neutrino flavor oscillations which are phenomenologically equivalent to those obtained by assuming the neutrinos violate the principle of equivalence. We then comment on the limits on Lorentz noninvariance which can be derived from solar, atmospheric, and accelerator neutrino experiments.

hep-ph↗

arXiv1997

FCNC Solutions to the Solar Neutrino Problem

We present the status of FCNC solutions to the solar neutrino problem. Our analysis shows that the FCNC solutions with massless neutrinos provide a good fit to the latest solar neutrino data. Predictions for future experiments are formulated which will permit further tests of these solutions.

hep-ph↗

arXiv1996

Constraints on Energy Independent Solutions of the Solar Neutrino Problem

We analyze the latest published solar neutrino data assuming an arbitrary neutrino oscillation/conversion mechanism suppresses the electron neutrino flux from the Sun independent of energy. For oscillations/transitions into active (sterile) neutrinos such mechanisms are ruled out at 99.96 (99.9997) % C.L. assuming the standard solar model by Bahcall and Pinnsoneault '95 correctly predicts all solar neutrino fluxes within their estimated uncertainties. Even if one allows for $^8{\rm B}$ and $^7{\rm Be}$ solar neutrino fluxes that are vastly different from the ones in contemporary standard solar models these mechanisms are strongly disfavored by the data.

hep-ph↗

arXiv1996

Neutrino Oscillations and Moments of Electron Spectra

We show that the effects of neutrino oscillations on 8B solar neutrinos are described well by the first two moments (the average and the variance) of the energy distribution of scattered or recoil electrons. For the SuperKamiokande and the Sudbury Neutrino Observatory experiments, the differences between the moments calculated with oscillations and the standard, no-oscillation moments are greater than 3 standard deviations for a significant fraction of the neutrino mass-mixing (Delta m^2, sin^2 2 theta) parameter space.

nucl-ex↗

arXiv1996

How Large Is the $^7{Be}$ Neutrino Flux from the Sun ?

On the basis of present solar neutrino observations and relaxing the constraints from solar models it is possible that most (or nearly all) of the flux of electron neutrinos detected comes from electron capture in $^7{Be}$. These solutions arise from neutrino oscillations in which $ν_e$ $-$ $ν_τ$ mixing suppresses high energy $ν_e$ and $ν_e - ν_μ$ mixing suppresses low energy $ν_e$ as qualitatively suggested from some SO(10) grand unified models. The importance of future observations is emphasized.

hep-ph↗

arXiv1996

Time-Variations of Solar Neutrino Signals

The most popular solutions of the solar neutrino problem which assume massive neutrinos predict varying with time signals in the solar neutrino detectors. The variations represent a distinctive feature of these solutions and do not depend on the theoretically predicted total flux of neutrinos from the Sun. The sensitivity of SuperKamiokande and SNO to day-night variations due to regeneration in the Earth is estimated.

hep-ph↗

arXiv1996

What Can Be Learned by Measuring the Fluxes of the 7-Be and the pep Solar Neutrino Lines?

Measurements of the interaction rates of the solar neutrino lines of $^7$Be and $pep$ can be used, independent of solar models, to test whether electron flavor is conserved, to determine survival probabilities of electron-type neutrinos at specific energies, and to test for the existence of sterile neutrinos. We present analytic descriptions of these tests. We also illustrate by numerical simulations, assuming matter-enhanced and vacuum neutrino oscillations, what measurements of solar neutrino lines can teach us about neutrino masses and mixing angles.

astro-ph↗

arXiv1996

On the MSW $ν_e \to ν_s$ transition solution of the solar neutrino problem

We study the stability of the two--neutrino MSW solution of the solar neutrino problem, corresponding to solar $ν_e$ transitions into sterile neutrino, $ν_e \rightarrow ν_s$, with respect to changes of the total fluxes of $^{8}$B and $^{7}$Be neutrinos, $Φ_{\rm B}$ and $Φ_{\rm Be}$. For any value of $Φ_{\rm Be}$ from the interval $0.7Φ^{\rm BP}_{\rm Be}\leq Φ_{\rm Be} \leq 1.3Φ^{\rm BP}_{\rm Be}$ (for $Φ_{\rm Be} = 0.7Φ^{\rm BP}_{\rm Be}$) the $ν_e \rightarrow ν_{s}$ MSW transitions provide at 95\% C.L. a description of the existing solar neutrino data for $0.40~(0.39)~Φ^{\rm BP}_{\rm B} \ltap Φ_{\rm B} \ltap 36~(40)Φ^{\rm BP}_{\rm B}$, $Φ^{\rm BP}_{\rm B}$ and $Φ^{\rm BP}_{\rm Be}$ being the fluxes in the solar model of Bahcall--Pinsonneault from 1992. The corresponding allowed regions of values of the parameters \dm2 and \sn2, characterizing the solar neutrino transitions, are derived. The physical implications of the found MSW $ν_e \rightarrow ν_s$ solutions for the future solar neutrino experiments are considered as well.

hep-ph↗

arXiv1996

How Does the Sun Shine?

Assuming that MSW neutrino oscillations occur and ignoring all solar physics except for the constraint that nuclear fusion produces the solar luminosity, we show that new solar neutrino experiments are required to rule out empirically the hypothesis that the sun shines via the CNO cycle.

astro-ph↗

arXiv1995

How Well Do We (and Will We) Know Solar Neutrino Fluxes and Oscillation Parameters?

Assuming neutrino oscillations occur, the pp electron neutrino flux is uncertain by at least a factor of two, the ${\rm ^8B}$ flux by a factor of five, and the ${\rm ^7Be}$ flux by a factor of forty-five. Calculations of the expected results of future solar neutrino experiments (SuperKamiokande, SNO, BOREXINO, ICARUS, HELLAZ, and HERON) are used to illustrate the extent to which these experiments will restrict the range of the allowed neutrino mixing parameters. We present an improved formulation of the ``luminosity constraint'' and show that at 95\% confidence limit this constraint establishes the best available limits on the rate of creation of pp neutrinos in the solar interior and provides the best upper limit to the ${\rm ^7Be}$ neutrino flux.

hep-ph↗

arXiv1995

On The Vacuum Oscillation Solution of The Solar Neutrino Problem

We study the stability of the two--neutrino vacuum oscillation solution of the solar neutrino problem with respect to changes of the total fluxes of boron and beryllium neutrinos. For any value of $Φ_{\rm Be}$ from the interval $0.7Φ^{\rm BP}_{\rm Be}\leq Φ_{\rm Be} \leq 1.3Φ^{\rm BP}_{\rm Be}$ the solar $ν_e$ oscillations into an active neutrino provide at 95\% C.L. a description of the existing solar neutrino data for $Φ_{\rm B} \cong (0.35 - 3.4) Φ^{\rm BP}_{\rm B}$, $Φ^{\rm BP}_{\rm B}$ and $Φ^{\rm BP}_{\rm Be}$ being the fluxes in the solar model of Bahcall--Pinsonneault from 1992. For $Φ_{\rm Be}\cong (0.7 - 1.3)Φ^{\rm BP}_{\rm Be}$ we find also at 95\% C.L. two new (one new) oscillation solutions for oscillations into active (sterile) neutrinos. The physical implications of the new solutions for the future solar neutrino experiments are discussed. The data rule out at 97\% -- 98\% (99 \%) C.L. the possibility of a universal (neutrino energy independent) suppression of the different components of the solar neutrino flux, resulting from solar $ν_e$ oscillations or transitions into active (sterile) neutrino.

hep-ph↗