1,721,051 research outputs found
A new presymplectic geometrical framework for time-dependent Lagrangian systems: the constraint algorithm and the second-order differential equation problem
No full text
A comment on 'The Cauchy problem of f(R) gravity'
No full textA critical comment on [N. Lanahan--Tremblay and V. Faraoni, 2007, Class. Quantum Grav., 24, 5667] is given discussing the well-formulation of the Chauchy problem for f(R)-gravity in metric-affine theories
A new geometrical look at gravity coupled with Yang-Mills fields
No full textA new geometrical framework for tetrad-af ne formulation of gravity, pure or
coupled with Yang–Mills elds, is proposed. After analyzing the geometrical prop-
erties of the new mathematical setting, eld equations are deduced from a varia-
tional principle in the Poincaré–Cartan formalism. A generalized Noether Theorem
is stated and classical relationship between symmetries and conserved quantities are
recovered in the newer scheme. Some explicit examples are given
A vielbein formulation of unified Einstein-Maxwell theory
No full textIn the framework of J-bundles a vielbein formulation of unified Einstein--Maxwell theory is proposed.
In the resulting scheme, field equations matching the gravitational and electromagnetic fields are derived by constraining a 5-dimensional variational principle. No dynamical scalar field in involved
The Cauchy problem for metric-affine f(R)-gravity in presence of perfect-fluid matter
No full textThe Cauchy problem for metric-affine f(R)-gravity à la
Palatini and with torsion, in presence of perfect fluid matter
acting as source, is discussed following the well-known Bruhat
prescriptions for General Relativity. The problem results
well-formulated and well-posed when the perfect-fluid form
of the stress-energy tensor is preserved under conformal
transformations and the set of viable f(R) models is not
empty. The key role of conservation laws in Jordan and in
Einstein frame is also discussed
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