26 research outputs found
Rainbow's Stars
In recent years, a growing interest on the equilibrium of compact
astrophysical objects like white dwarf and neutron stars has been manifested.
In particular, various modifications due to Planck scale energy effects have
been considered. In this paper we analyze the modification induced by Gravity's
Rainbow on the equilibrium configurations described by the
Tolman-Oppenheimer-Volkoff (TOV) equation. Our purpose is to explore the
possibility that the Rainbow Planck-scale deformation of space-time could
support the existence of different compact stars.Comment: 18 page
Group velocity in noncommutative spacetime
The realization that forthcoming experimental studies, such as the ones
planned for the GLAST space telescope, will be sensitive to Planck-scale
deviations from Lorentz symmetry has increased interest in noncommutative
spacetimes in which this type of effects is expected. We focus here on
-Minkowski spacetime, a much-studied example of Lie-algebra
noncommutative spacetime, but our analysis appears to be applicable to a more
general class of noncommutative spacetimes. A technical controversy which has
significant implications for experimental testability is the one concerning the
-Minkowski relation between group velocity and momentum. A large
majority of studies adopted the relation , where is the
-Minkowski dispersion relation, but recently some authors advocated
alternative formulas. While in these previous studies the relation between
group velocity and momentum was introduced through ad hoc formulas, we rely on
a direct analysis of wave propagation in -Minkowski. Our results lead
conclusively to the relation . We also show that the previous
proposals of alternative velocity/momentum relations implicitly relied on an
inconsistent implementation of functional calculus on -Minkowski and/or
on an inconsistent description of spacetime translations.Comment: 13 pages, LaTe
Modified Dispersion Relations lead to a finite Zero Point Gravitational Energy
We compute the Zero Point Energy in a spherically symmetric background
distorted at high energy as predicted by \textit{Gravity's Rainbow}. In this
context we setup a Sturm-Liouville problem with the cosmological constant
considered as the associated eigenvalue. The eigenvalue equation is a
reformulation of the Wheeler-DeWitt equation. With the help of a canonical
decomposition, we find that the relevant contribution to one loop is given by
the graviton quantum fluctuations around the given background. By means of a
variational approach based on gaussian trial functionals, we find that the
ordinary divergences can here be handled by an appropriate choice of the
rainbow's functions, in contrast to what happens in other conventional
approaches. A final discussion on the connection of our result with the
observed cosmological constant is also reported.Comment: LaTex 16 pages, 6 figure
Particle propagation and effective space-time in Gravity's Rainbow
Basing on the results obtained in a our previous study on Gravity's Rainbow,
we determine the quantum corrections to the space-time metric for the
Schwarzschild and the de Sitter background, respectively. We analyze how
quantum fluctuations alter these metrics inducing modifications on the
propagation of test particles. Significantly enough we find that quantum
corrections can become relevant not only for particles approaching the Planck
energy but, due to the one loop contribution, even for low-energy particles as
far as Planckian length scales are considered. We briefly compare our results
with others obtained in similar studies and with the recent experimental OPERA
announcement of superluminal neutrino propagation.Comment: RevTeX 4, 11 page
Black-hole thermodynamics with modified dispersion relations and generalized uncertainty principles
In several approaches to the quantum-gravity problem evidence has emerged of the validity of a âGUPâ (a Generalized position-momentum Uncertainty Principle) and/or a âMDRâ (a modification of the energy-momentum dispersion relation), but very little is known about the implications of GUPs and MDRs for black-hole thermodynamics, another key topic for quantum-gravity research. We investigate an apparent link, already suggested in an earlier exploratory study involving two of us, between the possibility of a GUP and/or a MDR and the possibility of a log term in the area-entropy black-hole formula. We then obtain, from that same perspective, a modified relation between the mass of a black hole and its temperature, and we examine the validity of the âGeneralized Second Law of black-hole thermodynamicsâ in theories with a GUP and/or a MDR. After an analysis of GUP- and MDR-modifications of the black-body radiation spectrum, we conclude the study with a description of the black-hole evaporation process
Gravity in quantum spacetime
The literature on quantum-gravity-inspired scenarios for the quantization of
spacetime has so far focused on particle-physics-like studies. This is partly
justified by the present limitations of our understanding of quantum-gravity
theories, but we here argue that valuable insight can be gained through
semi-heuristic analyses of the implications for gravitational phenomena of some
results obtained in the quantum-spacetime literature. In particular, we show
that the types of description of particle propagation that emerged in certain
quantum-spacetime frameworks have striking implications for gravitational
collapse and for the behaviour of gravity at large distances.Comment: This essay received honorable mention in the Gravity Research
Foundation 2010 Awards for Essays on Gravitatio