136 research outputs found
Entropy of Self-Gravitating Systems from Holst's Lagrangian
We shall prove here that conservation laws from Holst's Lagrangian, often
used in LQG, do not agree with the corresponding conservation laws in standard
GR. Nevertheless, these differences vanish on-shell, i.e. along solutions, so
that they eventually define the same classical conserved quantities.
Accordingly, they define in particular the same entropy of solutions, and the
standard law S=A/4 is reproduced for systems described by Holst's Lagragian.
This provides the classical support to the computation usually done in LQG for
the entropy of black holes which is in turn used to fix the Barbero-Immirzi
parameter.Comment: 4 pages, no figures; just acknowledgments change
Extended Loop Quantum Gravity
We discuss constraint structure of extended theories of gravitation (also
known as f(R) theories) in the vacuum selfdual formulation introduced in ref.
[1].Comment: 7 pages, few typos correcte
ADM Pseudotensors, Conserved Quantities and Covariant Conservation Laws in General Relativity
The ADM formalism is reviewed and techniques for decomposing generic
components of metric, connection and curvature are obtained. These techniques
will turn out to be enough to decompose not only Einstein equations but also
covariant conservation laws. Then a number of independent sets of hypotheses
that are sufficient (though non-necessary) to obtain standard ADM quantities
(and Hamiltonian) from covariant conservation laws are considered. This
determines explicitely the range in which standard techniques are equivalent to
covariant conserved quantities. The Schwarzschild metric in different
coordinates is then considered, showing how the standard ADM quantities fail
dramatically in non-Cartesian coordinates or even worse when asymptotically
flatness is not manifest; while, in view of their covariance, covariant
conservation laws give the correct result in all cases.Comment: 40 page
Conformal Gravity as a Gauge Natural Theory
We shall review conformal gravity as a gauge natural theory and discuss the
consequences of Weyl covariance on the definition of physical states.Comment: 7 pages, Workshop Variational principles and conservation laws in
General Relativity, Torino, June 24-25, 2015in memory of Mauro Francavigli
Generally Covariant vs. Gauge Structure for Conformal Field Theories
We introduce the natural lift of spacetime diffeomorphisms for conformal
gravity and discuss the physical equivalence between the natural and gauge
natural structure of the theory. Accordingly, we argue that conformal
transformations must be introduced as gauge transformations (affecting fields
but not spacetime point) and then discuss special structures implied by the
splitting of the conformal group.Comment: 11 pages, comments are welcom
Remarks on the Entropy of Non-Stationary Black Holes
The definition of entropy obtained for stationary black holes is extended in
this paper to the case of non-stationary black holes. Entropy is defined as a
macroscopical thermodynamical quantity which satisfies the first principle of
thermodynamics. In the non-stationary case a volume term appears since the
solution does not admit a Killing vector
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