573,099 research outputs found
Lineal gravity from planar gravity
We show how to obtain the two-dimensional black hole action by dimensional
reduction of the three-dimensional Einstein action with a non-zero cosmological
constant. Starting from the Chern-Simons formulation of 2+1 gravity, we obtain
the 1+1 dimensional gauge formulation given by Verlinde. Remarkably, the
proposed reduction shares the relevant features of the formulation of Cangemi
and Jackiw, without the need for a central charge in the algebra. We show how
the Lagrange multipliersin these formulations appear naturally as the remnants
of the three dimensional connection associated to symmetries that have been
lostin the dimensional reduction. The proposed dimensional reduction involves a
shift in the three dimensional connection whose effect is to make the length of
the extra dimension infinite.Comment: 13 pages, plain Te
Induced Affine Inflation
Induced gravity, metrical gravity in which gravitational constant arises from
vacuum expectation value of a heavy scalar, is known to suffer from Jordan
frame vs. Einstein frame ambiguity, especially in inflationary dynamics.
Induced gravity in affine geometry, as we show here, leads to an emergent
metric and gravity scale, with no Einstein-Jordan ambiguity. While gravity is
induced by the vacuum expectation value of the scalar field, nonzero vacuum
energy facilitates generation of the metric. Our analysis shows that induced
gravity results in a relatively large tensor-to-scalar ratio in both metrical
and affine gravity setups. However, the fact remains that the induced affine
gravity provides an ambiguity-free framework.Comment: 7 pages, 1 table and 3 figures, matches the published versio
The generalized second law of thermodynamics in generalized gravity theories
We investigate the generalized second law of thermodynamics (GSL) in
generalized theories of gravity. We examine the total entropy evolution with
time including the horizon entropy, the non-equilibrium entropy production, and
the entropy of all matter, field and energy components. We derive a universal
condition to protect the generalized second law and study its validity in
different gravity theories. In Einstein gravity, (even in the phantom-dominated
universe with a Schwarzschild black hole), Lovelock gravity, and braneworld
gravity, we show that the condition to keep the GSL can always be satisfied. In
gravity and scalar-tensor gravity, the condition to protect the GSL can
also hold because the gravity is always attractive and the effective Newton
constant should be approximate constant satisfying the experimental bounds.Comment: 19 pages, no figure, mistakes corrected, references added, to appear
in Class. Quantum Gra
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