Non-Gaussian Geostatistical Modeling using (skew) t Processes

We propose a new model for regression and dependence analysis when addressing spatial data with possibly heavy tails and an asymmetric marginal distribution. We first propose a stationary process with $t$ marginals obtained through scale mixing of a Gaussian process with an inverse square root process with Gamma marginals. We then generalize this construction by considering a skew-Gaussian process, thus obtaining a process with skew-t marginal distributions. For the proposed (skew) $t$ process we study the second-order and geometrical properties and in the $t$ case, we provide analytic expressions for the bivariate distribution. In an extensive simulation study, we investigate the use of the weighted pairwise likelihood as a method of estimation for the $t$ process. Moreover we compare the performance of the optimal linear predictor of the $t$ process versus the optimal Gaussian predictor. Finally, the effectiveness of our methodology is illustrated by analyzing a georeferenced dataset on maximum temperatures in Australi

Finding the Higgs Boson through Supersymmetry

The study of displaced vertices containing two b--jets may provide a double discovery at the Large Hadron Collider (LHC): we show how it may not only reveal evidence for supersymmetry, but also provide a way to uncover the Higgs boson necessary in the formulation of the electroweak theory in a large region of the parameter space. We quantify this explicitly using the simplest minimal supergravity model with bilinear breaking of R-parity, which accounts for the observed pattern of neutrino masses and mixings seen in neutrino oscillation experiments.Comment: 7 pages, 7 figures. Final version to appear at PRD. Discussion and results were enlarge

Probing Neutrino Oscillations in Supersymmetric Models at the Large Hadron Collider

The lightest supersymmetric particle may decay with branching ratios that correlate with neutrino oscillation parameters. In this case the CERN Large Hadron Collider (LHC) has the potential to probe the atmospheric neutrino mixing angle with sensitivity competitive to its low-energy determination by underground experiments. Under realistic detection assumptions, we identify the necessary conditions for the experiments at CERN's LHC to probe the simplest scenario for neutrino masses induced by minimal supergravity with bilinear R parity violation.Comment: 11 pages, 6 figures. To appear in Physical Review

Scanning laser techniques for characterisation of different surface breaking defect geometries

Measurements using a laser scanning system consisting of a pulsed Nd:YAG laser to generate surface ultrasonic waves and an interferometer to detect the surface displacement, are presented for different samples and defect geometries. We show, firstly, details of the interaction of Rayleigh waves in thick samples with machined slots inclined at an angle to the surface normal, or with simple branched geometries, scanning the generation source over the defect (SLLS) or scanning the detection point over the defect (SLD). Secondly, we discuss effects of Lamb waves interacting with V-shaped defects in thin samples. The results from these measurements have shown that the signal enhancement found in the near-field in both cases can be used to position the defect and gain an idea of its geometry, and have shown this to be a suitable fingerprint of the presence of the defect

Invisible Higgs Boson Decays in Spontaneously Broken R-Parity

The Higgs boson may decay mainly to an invisible mode characterized by missing energy, instead of the Standard Model channels. This is a generic feature of many models where neutrino masses arise from the spontaneous breaking of ungauged lepton number at relatively low scales, such as spontaneously broken R-parity models. Taking these models as framework, we reanalyze this striking suggestion in view of the recent data on neutrino oscillations that indicate non-zero neutrino masses. We show that, despite the smallness of neutrino masses, the Higgs boson can decay mainly to the invisible Goldstone boson associated to the spontaneous breaking of lepton number. This requires a gauge singlet superfield coupling to the electroweak doublet Higgses, as in the Next to Minimal Supersymmetric Standard Model (NMSSM) scenario for solving the $\mu$-problem. The search for invisibly decaying Higgs bosons should be taken into account in the planning of future accelerators, such as the Large Hadron Collider and the Next Linear Collider.Comment: 24 pages, 10 figures; typos corrected, published versio

Neutrino Oscillations, Fluctuations and Solar Magneto-gravity Waves

This review has two parts. The first part summarizes the current observational constraints on fluctuations in the solar medium deep within the solar Radiative Zone, and shows how the KamLAND and SNO-salt data combine to make the experimental determination of the neutrino oscillation parameters largely insensitive to prior assumptions about the nature of these oscillations. As part of a search for plausible sources of solar fluctuations to which neutrinos could be sensitive, the second part of the talk summarizes a preliminary analysis of the influence of magnetic fields on helioseismic waves. Using simplifying assumptions which should apply to modes in the solar radiative zone, we find a resonance between Alfven waves and helioseismic g-modes which potentially modifies the solar density profile fairly significantly over comparatively short distance scales, too narrow to be ruled out by present-day analyses of p-wave helioseismic spectra.Comment: Plenary talk presented at AHEP 2003, Valencia, Spain, October 200

Will Jets Identify the Progenitors of Type Ia Supernovae?

We use the fact that a Type Ia supernova has been serendipitously discovered near the jet of the active galaxy 3C 78 to examine the question of whether jets can enhance accretion onto white dwarfs. One interesting outcome of such a jet-induced accretion process is an enhanced rate of novae in the vicinity of jets. We present results of observations of the jet in M87 which appear to have indeed discovered 11 novae in close proximity to the jet. We show that a confirmation of the relation between jets and novae and Type Ia supernovae can finally identify the elusive progenitors of Type Ia supernovae.Comment: 10 pages, 3 figure

A sedimentação carbonífera na Bacia do Buçaco (Centro de Portugal)

Os aspectos gerais das ocorrências do Carbónico continental em Portugal são descritos por Ribeiro et al. (1979), Teixeira & Gonçalves (1980) e Teixeira (1981). A revisão da cronoestratigrafia da flora fóssil destas formações e uma síntese da evolução tectónica de cada uma das bacias podem ser encontradas no volume editado por Sousa & Oliveira em 1983, dedicado ao Carbónico de Portugal. (...

Transient Gamma Ray Spectrometer Measurements of Gamma-Ray Lines from Novae. II. Constraining the Galactic Nova Rate from a Survey of the Southern Sky during 1995-1997

The good energy resolution (3--4 keV FWHM) of the Transient Gamma Ray Spectrometer (TGRS) on board the WIND spacecraft makes it sensitive to Doppler-shifted outbursts of 511 keV electron-positron annihilation radiation, the reason being that the Doppler shift causes the cosmic line to be slightly offset from a strong instrumental background 511 keV line at rest, which is ubiquitous in space environments. Such a cosmic line (blueshifted) is predicted to arise in classical novae due to the annihilation of positrons from $\beta$-decay on a timescale of a few hours in an expanding envelope. A further advantage of TGRS - its broad field of view, containing the entire southern ecliptic hemisphere - has enabled us to make a virtually complete and unbiased 3-year search for classical novae at distances up to ~1 kpc. We present negative results of this search, and estimate its implications for the highly-uncertain Galactic classical nova rate and for future space missions.Comment: 22 pp. + 3 fig