321 research outputs found
Black hole and de Sitter solutions in a covariant renormalizable field theory of gravity
It is shown that Schwarzschild black hole and de Sitter solutions exist as
exact solutions of a recently proposed relativistic covariant formulation of
(power-counting) renormalizable gravity with a fluid. The formulation without a
fluid is also presented here. The stability of the solutions is studied and
their corresponding entropies are computed, by using the covariant Wald method.
The area law is shown to hold both for the Schwarzschild and for the de Sitter
solutions found, confirming that, for the case, one is dealing with a
minimal modification of GR.Comment: 7 paages, latex fil
Neutrino oscillation phase dynamically induced by f(R)-gravity
The gravitational phase shift of neutrino oscillation can be discussed in the
framework of f(R)-gravity. We show that the shift of quantum mechanical phase
can depend on the given f(R)-theory that we choose. This fact is general and
could constitute a fundamental test to discriminate among the various
alternative relativistic theories of gravity. Estimations of ratio between the
gravitational phase shift and the standard phase are carried out for the
electronic Solar neutrinos.Comment: 4 page
Modified f(R) gravity from scalar-tensor theory and inhomogeneous EoS dark energy
The reconstruction of f(R)-gravity is showed by using an auxiliary scalar
field in the context of cosmological evolution, this development provide a way
of reconstruct the form of the function f (R) for a given evolution of the
Hubble parameter. In analogy, f(R)-gravity may be expressed by a perfect fluid
with an inhomogeneous equation of state that depends on the Hubble parameter
and its derivatives. This mathematical equivalence that may confuse about the
origin of the mechanism that produces the current acceleration, and possibly
the whole evolution of the Hubble parameter, is shown here.Comment: 8 page
Gravitational Waves Astronomy: a cornerstone for gravitational theories
Realizing a gravitational wave (GW) astronomy in next years is a great
challenge for the scientific community. By giving a significant amount of new
information, GWs will be a cornerstone for a better understanding of
gravitational physics. In this paper we re-discuss that the GW astronomy will
permit to solve a captivating issue of gravitation. In fact, it will be the
definitive test for Einstein's general relativity (GR), or, alternatively, a
strong endorsement for extended theories of gravity (ETG).Comment: To appear in Proceedings of the Workshop "Cosmology, the Quantum
Vacuum and Zeta Functions" for the celebration of Emilio Elizalde's sixtieth
birthday, Barcelona, March 8-10, 201
Dark energy in modified Gauss-Bonnet gravity: late-time acceleration and the hierarchy problem
Dark energy cosmology is considered in a modified Gauss-Bonnet (GB) model of
gravity where an arbitrary function of the GB invariant, , is added to
the General Relativity action. We show that such theory is endowed with a quite
rich cosmological structure: it may naturally lead to an effective cosmological
constant, quintessence or phantom cosmic acceleration, with a possible
transition from deceleration to acceleration. It is demonstrated in the paper
that this theory is perfectly viable, since it is compliant with Solar System
constraints. Specific properties of gravity in a de Sitter universe,
such as dS and SdS solutions, their entropy and its explicit one-loop
quantization are studied. The issue of a possible solution of the hierarchy
problem in modified gravities is addressed too.Comment: LaTeX file 20 pages, new subsections are adde
Viscous Fluids and Gauss-Bonnet Modified Gravity
We study effects of cosmic fluids on finite-time future singularities in
modified -gravity, where and are the Ricci scalar and the
Gauss-Bonnet invariant, respectively. We consider the fluid equation of state
in the general form, , and we suppose the existence of a
bulk viscosity. We investigate quintessence region () and phantom
region () and the possibility to change or avoid the singularities
in -gravity. Finally, we study the inclusion of quantum effects in
large curvatures regime.Comment: 14 page
Vacuum energy fluctuations, the induced cosmological constant and cosmological reconstruction in non-minimal modified gravity models
The one-loop effective action for non-minimal scalar modified gravity on de
Sitter background with a constant scalar field is found. The corresponding
induced cosmological constant is evaluated. It is shown that quantum effects in
non-minimal modified gravity may induce an early-time de Sitter universe even
in the situation when such solution does not occur on the classical level.
Classical reconstruction of the theory is presented in such a way that the
resulting theory has a cosmological solution unifying early-time inflation with
late-time acceleration.Comment: Latex file, 14 pages, no figure
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