0000000000138784
AUTHOR
José Wagner Furtado Valle
Searching for an invisibly decaying Higgs boson in e+ e-, e gamma and gamma gamma collisions
Higgs bosons can have a substantial ``invisible'' branching ratio in many extensions of the Standard Model, such as models where the Higgs bosons decay predominantly into light or massless weakly interacting Goldstone bosons. In this work, we examine the production mechanisms and backgrounds for invisibly decaying Higgs bosons at the Next Linear e+e− Collider operating in the modes e+e−, eγ, and γγ. We demonstrate that such machine is much more efficient to survey for invisibly decaying Higgs bosons than the Large Hadron Collider at CERN.
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 theoret…
Signatures of spontaneously broken r parity and solar neutrino oscillations
Matter-enhanced neutrino-oscillation parameters can be probed in a variety of conventional experiments in supergravity models where the small neutrino mass arises from spontaneous R-parity violation. A combined analysis of astrophysical and laboratory limits tends to exclude regions of oscillation parameters where the high-energy neutrinos are adiabatically converted. This suggests the possibility of a large reduction in the pp and Be7 neutrino flux even for a mildly reduced B8 neutrino flux, thus stressing the importance of gallium experiments.
Constraints on additional Z' gauge bosons from a precise measurement of the Z mass
We analyze the constraints on the mass and mixing of superstring-inspired E6 Z' neutral gauge boson that follow from the recent precise Z mass measurements and show that they depend very sensitively on the assumed value of the W mass and also, to a lesser extent, on the top-quark mass.
Global neutrino data and recent reactor fluxes: the status of three-flavour oscillation parameters
We present the results of a global neutrino oscillation data analysis within the three-flavour framework. We include latest results from the MINOS long-baseline experiment (including electron neutrino appearance as well as anti-neutrino data), updating all relevant solar (SK II+III), atmospheric (SK I+II+III) and reactor (KamLAND) data. Furthermore, we include a recent re-calculation of the anti-neutrino fluxes emitted from nuclear reactors. These results have important consequences for the analysis of reactor experiments and in particular for the status of the mixing angle θ13. In our recommended default analysis we find from the global fit that the hint for non-zero θ13 remains weak, at 1…
Phenomenological Tests of Supersymmetric A_4 Family Symmetry Model of Neutrino Mass
Recently Babu, Ma and Valle proposed a model of quark and lepton mixing based on $A_4$ symmetry. Within this model the lepton and slepton mixings are intimately related. We perform a numerical study in order to derive the slepton masses and mixings in agreement with present data from neutrino physics. We show that, starting from three-fold degeneracy of the neutrino masses at a high energy scale, a viable low energy neutrino mass matrix can indeed be obtained in agreement with constraints on lepton flavour violating $\mu$ and $\tau$ decays. The resulting slepton spectrum must necessarily include at least one mass below 200 GeV which can be produced at the LHC. The predictions for the absolu…
Ruling out four-neutrino oscillation interpretations of the LSND
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 s…
Enhanced muon-electron conversion in nuclei in the inverse seesaw model
We investigate nuclear mu-e conversion in the framework of an effective Lagrangian arising from the inverse seesaw model of neutrino masses. We consider lepton flavour violation interactions that arise from short range (non-photonic) as well as long range (photonic) contributions. Upper bounds for the LFV parameters characterizing mu-e conversion are derived in the inverse seesaw model Lagrangian using the available limits on the mu-e conversion branching ratio, as well as the expected sensitivities of upcoming experiments. We comment on the relative importance of these two types of contributions and their relationship with the measured solar neutrino mixing angle theta_12 and the dependenc…
Broken R-parity, stop decays, and neutrino physics
We discuss the phenomenology of the lightest stop in models where R-parity is broken by bilinear superpotential terms. In this class of models we consider scenarios where the R-parity breaking two-body decay ~t_1->��^+b competes with the leading three-body decays such as ~t_1->W^+b~��^0_1. We demonstrate that the R-parity violating decay can be sizable and in some parts of the parameter space even the dominant one. Moreover we discuss the expectations for t_1->��^+b and ~t_1->e^+b. The recent results from solar and atmospheric neutrinos suggest that these are as important as the tau bottom mode. The t_1->l^+b decays are of particular interest for hadron colliders, as they may…
Neutrinoless double-beta decay in SU(2) x U(1) theories
It is shown that gauge theories give contributions to neutrinoless double-β decay [(ββ)0ν] which are not covered by the standard parametrizations. While probably small, their existence raises the question of whether the observation of (ββ)0ν implies the existence of a Majorana mass term for the neutrino. For a 'natural' gauge theory we argue that this is indeed the case.
Quark-lepton mass relation in a realistic A(4) extension of the Standard Model
We propose a realistic A(4) extension of the Standard Model involving a particular quark-lepton mass relation, namely that the ratio of the third family mass to the geometric mean of the first and second family masses are equal for down-type quarks and charged leptons. This relation, which is approximately renormalization group invariant, is usually regarded as arising from the Georgi-Jarlskog relations, but in the present model there is no unification group or supersymmetry. In the neutrino sector we propose a simple modification of the so-called Zee-Wolfenstein mass matrix pattern which allows an acceptable reactor angle along with a deviation of the atmospheric and solar angles from thei…
Constraining non-standard interactions in nu(e) - e or anti-nu(e) - e scattering
We present a new analysis of non-universal and flavor changing non-standard neutrino interactions (NSI) in \nu_e e or \bar{\nu}_e e scattering. Our global analysis of these process includes all relevant experiments, such as the most recent MUNU measurement from reactor neutrinos, both in the context of the Standard Model as well as extensions where NSI are present. We also compare our constraints on non-universal and flavor changing NSI with results from previous analyses. We stress the importance of combining neutrino and anti-neutrino data in the resulting constraints on electroweak paramaters, and the important role that future low energy solar neutrino experiments can play in improving …
How sensitive is a neutrino factory to the angle Theta(13)?
We consider the impact of non-standard interactions of neutrinos (NSI) on the determination of neutrino mixing parameters at a neutrino factory using $\pnu{e}\to\pnu{\mu}$ ``golden channels'' for the measurement of $\theta_{13}$. We show how a small residual NSI leads to a drastic loss in sensitivity in $\theta_{13}$, of up to two orders of magnitude. This can be somewhat overcome if two baselines are combined.
Neutrino masses: from fantasy to facts
Theory suggests the existence of neutrino masses, but little more. Facts are coming close to reveal our fantasy: solar and atmospheric neutrino data strongly indicate the need for neutrino conversions, while LSND provides an intriguing hint. The simplest ways to reconcile these data in terms of neutrino oscillations invoke a light sterile neutrino in addition to the three active ones. Out of the four neutrinos, two are maximally-mixed and lie at the LSND scale, while the others are at the solar mass scale. These schemes can be distinguished at neutral-current-sensitive solar & atmospheric neutrino experiments. I discuss the simplest theoretical scenarios, where the lightness of the sterile …