32,129 research outputs found

### On the anomalous mass defect of strange stars in the Field Correlator Method

We investigate general aspects of the mass defects of strange stars in the
context of the Field Correlator Method, without magnetic field. The main
parameters of the model that enter the corresponding nonperturbative equation
of state of the quark gluon plasma are the gluon condensate $G_2$ and the large
distance static $Q{\bar Q}$ potential $V_1$. We calculate mass defects of
stellar configurations in the central density range $11<\log\rho_c<18$. In
general, the mass defects are strongly dependent on the model parameters. For a
large range of values of $G_2$ and $V_1$, we obtain anomalous mass defects with
magnitudes around $10^{53}\,$erg\,, of the same order of the observed energies
of gamma-ray bursts and neutrino emissions in SN1987A, and of the theoretically
predicted energies of the quark-novae explosions.Comment: 24 pages, 6 figure

### Strange stars properties calculated in the framework of the Field Correlator Method

We calculate the strange star properties in the framework of the Field
Correlator Method. We find that for the values of the gluon condensate
$G_2=0.006\;{\rm GeV}^4$ and $G_2=0.0068\;{\rm GeV}^4$, which give a critical
temperature $T_c\sim170\;{\rm MeV}$ at $\mu_c=0$, the sequences of strange
stars are compatible with some of the semi-empirical mass-radius relations and
data obtained from astrophysical observations.Comment: 26 pages, 10 figure

### On the non-negative first-order exponential bilinear time series model

In this paper the bilinear model BL(1,0,1,1) driven by exponential distributed innovations is studied in some detail. Conditions under which the model is strictly stationary as well as some properties of the stationary distribution are discussed. Moreover, parameter estimation is also addressed. (C) 2005 Elsevier B.V. All rights reserved

### Replicated INAR(1) processes

Replicated time series are a particular type of repeated measures, which consist of time-sequences of measurements taken from several subjects (experimental units). We consider independent replications of count time series that are modelled by first-order integer-valued autoregressive processes, INAR(1). In this work, we propose several estimation methods using the classical and the Bayesian approaches and both in time and frequency domains. Furthermore, we study the asymptotic properties of the estimators. The methods are illustrated and their performance is compared in a simulation study. Finally, the methods are applied to a set of observations concerning sunspot data.PRODEP II

### Spacetime: Arena or Reality?

For small values of the mass (in relation to the angular momentum and
electric charge), the Kerr-Newman (KN) solution of Einstein equation reduces to
a naked singularity of circular shape. By considering the Hawking and Ellis
extended interpretation of the KN spacetime, as well as Wheeler's idea of
"charge without charge", the non-trivial topological structure of the extended
KN spatial section is found to represent gravitational states with
half-integral angular momentum. As a consequence, it can be consistently
interpreted as a model for the electron-positron system, in which the concepts
of mass, charge and spin emerge from the spacetime geometry. According to this
model, therefore, instead of a simple arena, spacetime must have a concrete
existence, being responsible -- through its highly non-trivial topological
structures -- for the building blocks of (at least some of) the existing matter
in the universe.Comment: Chapter in the book "Relativity and the Dimensionality of the World",
Springer series "Fundamental Theories of Physics", Vol. 153 (2007). Volume
Editor: Vesselin Petko

### Estimation and forecasting in SUINAR(1) model

This work considers a generalization of the INAR(1) model to the panel data first order Seemingly Unrelated INteger AutoRegressive Poisson model, SUINAR(1). It presents Bayesian and classical methodologies to estimate the parameters of Poisson SUINAR(1) model and to forecast future observations of the process. In particular, prediction intervals for forecasts - classical approach - and HPD prediction intervals - Bayesian approach - are derived. A simulation study is provided to give additional insight into the finite sample behaviour of the parameter estimates and forecasts

### Optimal alarm systems for count processes

In many phenomena described by stochastic processes, the implementation of an alarm system becomes fundamental to predict the occurrence of future events. In this work we develop an alarm system to predict whether a count process will upcross a certain level and give an alarm whenever the upcrossing level is predicted. We consider count models with parameters being functions of covariates of interest and varying on time. This article presents classical and Bayesian methodology for producing optimal alarm systems. Both methodologies are illustrated and their performance compared through a simulation study. The work finishes with an empirical application to a set of data concerning the number of sunspot on the surface of the sun

### Kerr-Newman solution as a Dirac particle

For m^2 < a^2 + q^2, with m, a, and q respectively the source mass, angular
momentum per unit mass, and electric charge, the Kerr--Newman (KN) solution of
Einstein's equation reduces to a naked singularity of circular shape, enclosing
a disk across which the metric components fail to be smooth. By considering the
Hawking and Ellis extended interpretation of the KN spacetime, it is shown
first that, similarly to the electron-positron system, this solution presents
four inequivalent classical states. Next, it is shown that due to the
topological structure of the extended KN spacetime it does admit states with
half-integral angular momentum. This last property is corroborated by the fact
that, under a rotation of the space coordinates, those inequivalent states
transform into themselves only after a 4pi rotation. As a consequence, it
becomes possible to naturally represent them in a Lorentz spinor basis. The
state vector representing the whole KN solution is then constructed, and its
evolution is shown to be governed by the Dirac equation. The KN solution can
thus be consistently interpreted as a model for the electron-positron system,
in which the concepts of mass, charge and spin become connected with the
spacetime geometry. Some phenomenological consequences of the model are
explored.Comment: 19 pages, 6 figures. References added, section 2 enhanced, an
appendix and one figure adde

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