Scalar-tetrad theories of gravity

A general theory of gravitation is constructed using a tetrad and a scalar field. The resulting theory, called a scalar-tetrad theory, does not contain Einstein's or the Brans-Dicke theories as special cases. However, there is a range of scalar-tetrad theories with the same post-Newtonian limit as Einstein's theory. Two particular models are interesting because of their simplicity.     

Covariant canonical formalism for gravity

We continue the previous discussion (A. D'Adda, J. E. Nelson, and T. Regge, Ann. Phys. (N.Y.)165) of the covariant canonical formalism for the group manifold and relate it to the standard canonical vierbein formalism as pioneered by Dirac. The form bracket is related to the Poisson bracket of classical mechanics. We utilise systematically the calculus of differential forms and a compound notation which labels Poincaré multiplets. In this way we obtain a particularly clear and compact expression for the Hamiltonian and the constraints algebra of the vierbein formalism.     

Physical variables in gauge theories

The symplectic method is applied to obtain the physical variables and the physical Hamiltonian in two examples of gauge theories: the electrodynamics in the Coulomb gauge and the two-dimensional bosonic Schwinger model.     

Nonlinear Lagrangian theories of gravity

Gravitational theories derived from an action principle where the Lagrange density is a power of the curvature scalerR ⁿ are investigated. For all values ofn the theories have the correct Newtonian limit and forn = 1 the same weak field solution, which predicts a bending of light of three-quarters of the value predicted by general relativity (n=1).     

Nonstandard canonical quantization of local field theories

A recent new approach to classical local field theories (CLFT) offers a new, alternative quantization procedure of fields. A brief discussion of this nonstandard field quantization is given.Presented at the International Conference Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 23–27, 1986.     

Radion tunneling in modified theories of gravity

We consider a five dimensional warped spacetime where the bulk geometry is governed by higher curvature F(R) gravity. In this model, we determine the modulus potential originating from the scalar degree of freedom of higher curvature gravity. In the presence of this potential, we investigate the possibility of modulus (radion) tunneling leading to an instability in the brane configuration. Our results reveal that the parametric regions where the tunneling probability is highly suppressed, corresponds to the parametric values required to resolve the gauge hierarchy problem.     

Lie groups and gravity theories

Generalized theories of gravitation using the group manifold approach are outlined. It is suggested that free differential algebras should take the place of Lie algebras in current physical theory.