10,547 research outputs found
Bootstrapping Newton Gravity
A non-linear equation obtained by adding gravitational self-interaction terms
to the Poisson equation for Newtonian gravity is here employed in order to
analyse a static spherically sym- metric homogeneous compact source of given
proper mass and radius and the outer vacuum. The main feature of this picture
is that, although the freedom of shifting the potential by an ar- bitrary
constant is of course lost, the solutions remain qualitatively very close to
the Newtonian behaviour. We also notice that the negative gravitational
potential energy is smaller than the proper mass for sources with small
compactness, but for sources that should form black holes according to General
Relativity, the gravitational potential energy becomes of the same order of
magnitude of the proper mass, or even larger. Moreover, the pressure overcomes
the energy density for large values of the compactness, but it remains finite
for finite compactness, hence there exists no Buchdahl limit. This classical
description is meant to serve as the starting point for investigating quantum
features of (near) black hole configurations within the corpuscular picture of
gravity in future developments.Comment: 23 pages, 20 plots. New section and appendix about stability and the
pressure clarify comparison with GR. Conclusions rewritten to make
motivations cleare
Symbolic Sequences and Tsallis Entropy
We address this work to investigate symbolic sequences with long-range
correlations by using computational simulation. We analyze sequences with two,
three and four symbols that could be repeated times, with the probability
distribution . For these sequences, we verified that
the usual entropy increases more slowly when the symbols are correlated and the
Tsallis entropy exhibits, for a suitable choice of , a linear behavior. We
also study the chain as a random walk-like process and observe a nonusual
diffusive behavior depending on the values of the parameter .Comment: Published in the Brazilian Journal of Physic
Investigation of the existence of hybrid stars using Nambu-Jona-Lasinio models
We investigate the hadron-quark phase transition inside neutron stars and
obtain mass-radius relations for hybrid stars. The equation of state for the
quark phase using the standard NJL model is too soft leading to an unstable
star and suggesting a modification of the NJL model by introducing a momentum
cutoff dependent on the chemical potential. However, even in this approach, the
instability remains. In order to remedy the instability we suggest the
introduction of a vector coupling in the NJL model, which makes the EoS
stiffer, reducing the instability. We conclude that the possible existence of
quark matter inside the stars require high densities, leading to very compact
stars.Comment: 4 pages, 2 figures; prepared for IV International Workshop on
Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, 4-8 Oct 200
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