A. Tiemblo

Nonlinear gauge realization of spacetime symmetries including translations

We present a general scheme for the nonlinear gauge realizations of spacetime groups on coset spaces of the groups considered. In order to show the relevance of the method for the rigorous treatment of the translations in gravitational gauge theories, we apply it in particular to the affine group. This is an illustration of the family of spacetime symmetries having the form of a semidirect productH ⊗ T, whereH is the stability subgroup andT are the translations. The translational component of the connection behaves like a true tensor underH when coset realizations are involved.

Ordinary matter in non-linear affine gauge theories of gravitation

We present a general framework to include ordinary fermionic matter in the metric--affine gauge theories of gravity. It is based on a non-linear gauge realization of the affine group, with the Lorentz group as the classification subgroup of the matter and gravitational fields.We present a general framework to include ordinary fermionic matter in the metric--affine gauge theories of gravity. It is based on a nonlinear gauge realization of the affine group, with the Lorentz group as the classification subgroup of the matter and gravitational fields.

Gravitational contribution to fermion masses

Abstract.In the context of a non-linear gauge theory of the Poincaré group, we show that covariant derivatives of Dirac fields include a coupling to the translational connections, manifesting itself in the matter action as a universal background mass contribution to fermions.PACS. 04.50. + h, 11.15.-q

Particle contents of higher derivative gravity

The (lower derivative) action, which describes the actual degrees of freedom of a (higher derivative) theory of gravity quadratic in the scalar and Ricci curvatures, is found. Key steps are a Legendre transform and a suitable diagonalization procedure. Some consequences of this insight are outlined.

Husain-Kuchař model: Time variables and nondegenerate metrics

We study the Husain-Kuchayr model by introducing a new action principle similar to the self-dual action used in the Ashtekar variables approach to Quantum Gravity. This new action has several interesting features; among them, the presence of a scalar time variable that allows the definition of geometric observables without adding new degrees of freedom, the appearance of a natural non-degenerate four-metric and the possibility of coupling ordinary matter.

Nonlinear 4D conformal gauge spacetime symmetry

The nonlinear local theory of the 4D conformal spacetime group is presented. Effective theories of gravity quadratic in curvatures may be viewed as nonlinear realizations of this group. We find that in the absence of torsion and under very general assumptions derived from the structure of the algebra, the symmetry takes the form of the simpler Weyl scale invariance and the resulting theory is Einsteins gravity with, generally, a cosmological constant.

Conformal gravity and the bosonic string

We show that the Callan et al. effective equations of motion for the bosonic closed string in a non-trivial background may not be derived only from the bosonic part of theN=1 supergravity action of Manton and Chapline, but also from just a general conformally invariant theory of gravity. In our scheme the invariance under gauge transformations of the antisymmetric tensor field turns out to be a consequence of the metricity condition.

Electromagnetic gauge invariance, hadron interactions and the new particle

SummaryA generalization of the KLZ Lagrangian is developed. The hadronic symmetrySU4×U1 is broken in a gauge-invariant manner and the ψ(3.105) included as the new neutral meson in the 15⊕1 multiplet. With independence of the quantum-number content we obtain

Time evolution in the presence of gravity

\Gamma _{\psi \to e^ + e^ - }