788 research outputs found
Lagrangian Symmetries of Chern-Simons Theories
This paper analyses the Noether symmetries and the corresponding conservation
laws for Chern-Simons Lagrangians in dimension . In particular, we find an
expression for the superpotential of Chern-Simons gravity. As a by-product the
general discussion of superpotentials for 3rd order natural and quasi-natural
theories is also given.Comment: 16 pages in LaTeX, some comments and references added. to appear in
Journal of Physics A: Mathematical and Genera
Covariant Lagrangian Formulation of Chern-Simons and BF Theories
We investigate the covariant formulation of Chern-Simons theories in a
general odd dimension which can be obtained by introducing a vacuum connection
field as a reference. Field equations, Noether currents and superpotentials are
computed so that results are easily compared with the well-known results in
dimension 3. Finally we use this covariant formulation of Chern-Simons theories
to investigate their relation with topological BF theories.Comment: 23 pages, refs. adde
Accelerated Cosmological Models in Ricci squared Gravity
Alternative gravitational theories described by Lagrangians depending on
general functions of the Ricci scalar have been proven to give coherent
theoretical models to describe the experimental evidence of the acceleration of
universe at present time. In this paper we proceed further in this analysis of
cosmological applications of alternative gravitational theories depending on
(other) curvature invariants. We introduce Ricci squared Lagrangians in minimal
interaction with matter (perfect fluid); we find modified Einstein equations
and consequently modified Friedmann equations in the Palatini formalism. It is
striking that both Ricci scalar and Ricci squared theories are described in the
same mathematical framework and both the generalized Einstein equations and
generalized Friedmann equations have the same structure. In the framework of
the cosmological principle, without the introduction of exotic forms of dark
energy, we thus obtain modified equations providing values of w_{eff}<-1 in
accordance with the experimental data. The spacetime bi-metric structure plays
a fundamental role in the physical interpretation of results and gives them a
clear and very rich geometrical interpretation.Comment: New version: 26 pages, 1 figure (now included), Revtex
Universality of Einstein Equations for the Ricci Squared Lagrangians
It has been recently shown that, in the first order (Palatini) formalism,
there is universality of Einstein equations and Komar energy-momentum complex,
in the sense that for a generic nonlinear Lagrangian depending only on the
scalar curvature of a metric and a torsionless connection one always gets
Einstein equations and Komar's expression for the energy-momentum complex. In
this paper a similar analysis (also in the framework of the first order
formalism) is performed for all nonlinear Lagrangians depending on the
(symmetrized) Ricci square invariant. The main result is that the universality
of Einstein equations and Komar energy-momentum complex also extends to this
case (modulo a conformal transformation of the metric).Comment: 21 pages, Late
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