Cosimo Stornaiolo

f(R) gravity with torsion: the metric-affine approach

The role of torsion in f(R) gravity is considered in the framework of metric-affine formalism. We discuss the field equations in empty space and in the presence of perfect fluid matter, taking into account the analogy with the Palatini formalism. As a result, the extra curvature and torsion degrees of freedom can be dealt as an effective scalar field of a fully geometric origin. From a cosmological point of view, such a geometric description could account for the whole dark side of the universe.

Space-time covariant form of Ashtekar’s constraints

SummaryThe Lagrangian formulation of classical field theories and, in particular, general relativity leads to a coordinate-free, fully covariant analysis of these constrained systems. This paper applies multisymplectic techniques to obtain the analysis of Palatini and self-dual gravity theories as constrained systems, which have been studied so far in the Hamiltonian formalism. The constraint equations are derived while paying attention to boundary terms, and the Hamiltonian constraint turns out to be linear in the multimomenta. The equivalence with Ashtekar’s formalism is also established. The whole constraint analysis, however, remains covariant in that the multimomentum map is evaluated onany space-like hypersurface. This study is motivated by the non-perturbative quantization programme of general relativity.

Fermion helicity flip induced by torsion field

We show that in theories of gravitation with torsion the helicity of fermion particles is not conserved and we calculate the probability of spin flip, which is related to the anti-symmetric part of affine connection. Some cosmological consequences are discussed.

New exact solutions of cosmological equations with considerations upon the cosmological constant

Abstract The cosmological equations of a gravitational field, minimally coupled witha scalar field, are exactly integrated, provided that the potential of the scalar field belongs to a special class of exponentials. A particular solution is given, exhibiting the damping of the effective cosmological constant and a power-law inflation.

SPACE-TIME DEFORMATIONS AS EXTENDED CONFORMAL TRANSFORMATIONS

A definition of space-time metric deformations on an n-dimensional manifold is given. We show that such deformations can be regarded as extended conformal transformations. In particular, their features can be related to the perturbation theory giving a natural picture by which gravitational waves are described by small deformations of the metric. As further result, deformations can be related to approximate Killing vectors (approximate symmetries) by which it is possible to parameterize the deformed region of a given manifold. The perspectives and some possible physical applications of such an approach are discussed.

Peierls Brackets in Field Theory

Peierls brackets are part of the space-time approach to quantum field theory, and provide a Poisson bracket which, being defined for pairs of observables which are group invariant, is group invariant by construction. It is therefore well suited for combining the use of Poisson brackets and the full diffeomorphism group in general relativity. The present paper provides an introduction to the topic, with applications to gauge field theory.

Cosmological Black Holes

In this paper we propose a model for the formation of the cosmological voids. We show that cosmological voids can form directly after the collapse of extremely large wavelength perturbations into low-density black holes or cosmological black holes (CBH). Consequently the voids are formed by the comoving expansion of the matter that surrounds the collapsed perturbation. It follows that the universe evolves, in first approximation, according to the Einstein-Straus cosmological model. We discuss finally the possibility to detect the presence of these black holes through their weak and strong lensing effects and their influence on the cosmic background radiation.

Cosmological black holes as seeds of voids in the galaxy distribution

Deep surveys indicate a bubbly structure on cosmological large scales which should be the result of evolution of primordial density perturbations. Several models have been proposed to explain the origin and dynamics of such features but, till now, no exhaustive and fully consistent theory has been found. We discuss a model where cosmological black holes, deriving from primordial perturbations, are the seeds for large-scale-structure voids. We give details of the dynamics and accretion of the system voids-cosmological black holes from the epoch z � 10 3 till now, finding that a void of 40 h −1 Mpc diameter and under-density of −0.9 fits the observations without conflicting with the homogeneity and isotropy of the cosmic microwave background radiation.

Inflationary models in ECSK theory

Abstract We have extended the Guth inflationary model of the universe to the Einstein-Cartan theory of gravitation. In this model the initial singularity is avoided; moreover, the minimal radius of the universe is influenced by the fals vacuum energy.

Tomographic representation of minisuperspace quantum cosmology and noether symmetries

The probability representation, in which cosmological quantum states are described by a standard positive probability distribution, is constructed for minisuperspace models selected by Noether symmetries. In such a case, the tomographic probability distribution provides the classical evolution for the models and can be considered an approach to select “observable” universes. Some specific examples, derived from Extended Theories of Gravity, are worked out. We discuss also how to connect tomograms, symmetries and cosmological parameters.