Light Unstable Sterile Neutrino

The three massless active (doublet) neutrinos may mix with two heavy and one \underline {light} sterile (singlet) neutrinos so that the induced masses and mixings among the former are able to explain the present data on atmospheric and solar neutrino oscillations. If the LSND result is also to be explained, one active neutrino mass eigenstate must mix with the light sterile neutrino. A specific model is proposed with the spontaneous and soft explicit breaking of a new global $U(1)_S$ symmetry so that a sterile neutrino will decay into an active antineutrino and a nearly massless pseudo-Majoron.Comment: Discussion and references adde

Massive Neutrinos and Lepton Mixing in Unified Theories

The recent GUT (x SUSY) models which can predict the neutrino properties are reviewed.Comment: 8 pages, Talk presented at the XVI International Workshop on Weak Interactions and Neutrinos, Capri, 199

Ketamine: A Review of Clinical Pharmacokinetics and Pharmacodynamics in Anesthesia and Pain Therapy

Ketamine is a phencyclidine derivative, which functions primarily as an antagonist of the N-methyl-d-aspartate receptor. It has no affinity for gamma-aminobutyric acid receptors in the central nervous system. Ketamine shows a chiral structure consisting of two optical isomers. It undergoes oxidative metabolism, mainly to norketamine by cytochrome P450 (CYP) 3A and CYP2B6 enzymes. The use of S-ketamine is increasing worldwide, since the S(+)-enantiomer has been postulated to be a four times more potent anesthetic and analgesic than the R(-)-enantiomer and approximately two times more effective than the racemic mixture of ketamine. Because of extensive first-pass metabolism, oral bioavailability is poor and ketamine is vulnerable to pharmacokinetic drug interactions. Sublingual and nasal formulations of ketamine are being developed, and especially nasal administration produces rapid maximum plasma ketamine concentrations with relatively high bioavailability. Ketamine produces hemodynamically stable anesthesia via central sympathetic stimulation without affecting respiratory function. Animal studies have shown that ketamine has neuroprotective properties, and there is no evidence of elevated intracranial pressure after ketamine dosing in humans. Low-dose perioperative ketamine may reduce opioid consumption and chronic postsurgical pain after specific surgical procedures. However, long-term analgesic effects of ketamine in chronic pain patients have not been demonstrated. Besides analgesic properties, ketamine has rapid-acting antidepressant effects, which may be useful in treating therapy-resistant depressive patients. Well-known psychotomimetic and cognitive adverse effects restrict the clinical usefulness of ketamine, even though fewer psychomimetic adverse effects have been reported with S-ketamine in comparison with the racemate. Safety issues in long-term use are yet to be resolved

L_e + L_\mu - L_\tau - L_s Symmetry and a Mixed 2+2 Scenario for Neutrino Oscillations

Recent results from SuperKamiokande and SNO experiments have set severe constraints on possible mixings of a light sterile neutrino, \nu_s, with the three active species required for a simultaneous explanation of the solar, atmospheric and LSND neutrino oscillation data. A consistent scheme has emerged from a global analysis of the data wherein two of the neutrinos are nearly degenerate with a mass of order 1 eV, that mix significantly with the two lighter states. We present realizations of such a mixed 2+2 oscillation scenario based on L_e + L_\mu - L_\tau - L_s symmetry (L_i stands for the ith lepton number). Breaking of of this lepton number symmetry by a small mass term for \nu_s leads to the required large mixings for both the atmospheric and the solar neutrino oscillations. Sum rules for the neutrino oscillation parameters are derived within this scheme, and are shown to be consistent with present data. These models predict U_{e3} = 0.02-0.03, which can serve as a test of this idea. We also present gauge models based on mirror extensions of the Standard Model that naturally lead to a light sterile neutrino with the required mixing pattern.Comment: 13 pages, RevTe

The Interplay between Neutrinos and Charged Leptons in the Minimal SU(3)_LxU(1)_N Gauge Model

In the minimal SU(3)_LxU(1)_N gauge model with a global L_e-L_mu-L_tau (=L') symmetry and a discrete Z_4 symmetry, it is found that the interplay between neutrinos and charged leptons contained in triplets of \psi^i=(\nu^i_L, \ell^i_L, \ell^{ci}_L) (i=1,2,3) naturally leads to the large mixing angle (LMA) MSW solution. The model includes two (anti)sextet Higgs scalars, S^(0) with L'=0 and S^(+) with L'=2, which, respectively, couple to \psi^1\psi^{2,3} for the electron mass and masses of atmospheric neutrinos and to \psi^{2,3}\psi^{2,3} for the \mu- and \tau-masses and one-loop radiative neutrino masses relevant to solar neutrinos. This mechanism is realized by utilizing an additional residual discrete symmetry supplied by explicitly broken L', which guarantees the absence of tree-level neutrino mass terms of the \psi^{2,3}\psi^{2,3}-type. Pure rotation effects due to the diagonalization of neutrino and charged-lepton mass matrices are estimated to yield \Delta m^2_\odot/\Delta m^2_{atm} \leq (m_e/m_\mu)^{3/2}=O(10^{-4}) but the radiative effects supersede the rotation effects to yield \Delta m^2_\odot/\Delta m^2_{atm}=O(10^{-2}) as the LMA solution.Comment: 16 pages, RevTeX, including 2 figures with typos and misprints corrected and with modifications in sections II-B and V, accepted by Nuclear Physics

Four species neutrino oscillations at ν\nu-Factory: sensitivity and CP-violation

The prospects of measuring the leptonic angles and CP-odd phases at a {\em neutrino factory} are discussed in the scenario of three active plus one sterile neutrino. We consider the \nu_\mu \raw \nu_e LSND signal. Its associated large mass difference leads to observable neutrino oscillations at short ($\sim 1$ km) baseline experiments. Sensitivities to the leptonic angles down to $10^{-3}$ can be easily achieved with a 1 Ton detector. Longer baseline experiments ($\sim 100$ km) with a 1 Kton detector can provide very clean tests of CP-violation especially through tau lepton detection.Comment: 15 pages, LaTeX2e, 14 eps files, use package epsfi

Neutrino mixing and CP-violation

The prospects of measuring the leptonic angles and CP-odd phases at a neutrino factory are discussed in two scenarios: 1) three active neutrinos as indicated by the present ensemble of atmospheric plus solar data; 2) three active plus one sterile neutrino when the LSND signal is also taken into account. For the latter we develop one and two mass dominance approximations. The appearance of wrong sign muons in long baseline experiments and tau leptons in short baseline ones provides the best tests of CP-violation in scenarios 1) and 2), respectively.Comment: 22 pages, LaTeX2e, 17 eps files, use package epsfi

Models of Light Singlet Fermion and Neutrino Phenomenology

We suggest that a singlet fermion $S$ exists beyond the standard see-saw structure. It mixes with light neutrinos via interactions with the right-handed neutrino components, so that \n_e \to S conversion solves the solar neutrino problem. Supersymmetry endowed with R-symmetry is shown to give a natural framework for existence, mass scale and mixing ($\sin^22\th_{es} \sim (0.1-1.5)\cdot 10^{-2}$) of such a fermion. Models with an approximate horizontal symmetry are constructed, which embed the fermion $S$ and explain simultaneously solar, atmospheric, hot dark matter problems as well as may predict the oscillation \bar{\n}_\m \to \bar{\n}_e in the region of sensitivity of KARMEN and LSND experiments.Comment: 14 pages, latex, no figure

Cornering (3+1) sterile neutrino schemes

Using the most recent atmospheric neutrino data, as well as short-baseline, long-baseline and tritium $\beta$-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.Comment: 14 pages, 4 figures, v3: extended tritium decay analysis, small corrections in Fig. 2 and Eq.(4), version accepted for publication in Phys. Lett.

Naturally light right-handed neutrinos in a 3-3-1 Model

In this work we show that light right-handed neutrinos, with mass in the sub-eV scale, is a natural outcome in a 3-3-1 model. By considering effective dimension five operators, the model predicts three light right-handed neutrinos, weakly mixed with the left-handed ones. We show also that the model is able to explain the LSND experiment and still be in agreement with solar and atmospheric data for neutrino oscillation.Comment: About 5 pages, no-figure