CARLONI S.

We explore the idea that the coupling between matter and spacetime is more complex than the one originally envisioned by Einstein. We propose that such coupling takes the form of a new fundamental tensor in the Einstein field equations. We then show that the introduction of this tensor can account for dark phenomenology in General Relativity,...

We present a general method to reconstruct static spherically symmetric metrics in general relativity based on the 1+1+2 covariant approach. This method allows a more complete exploration of the properties of these metrics in the case of a generic fluid and in the presence of a scalar field. A number of new exact solutions are reconstructed in...

We propose a new dynamical system formalism for the analysis of f(R) cosmologies. The new approach eliminates the need for cumbersome inversions to close the dynamical system and allows the analysis of the phase space of f(R)-gravity models which cannot be investigated using the standard technique. Differently form previously proposed similar...

The 1+3 covariant approach and the covariant gauge-invariant approach to perturbations are used to analyze in depth conformal transformations in cosmology. Such techniques allow us to obtain insights on the physical meaning of these transformations when applied to non-standard gravity. The results obtained lead to a number of general...

The evolution equations for tensor perturbations in a generic scalar-tensor theory of gravity are presented. Exact solutions are given for a specific class of theories and Friedmann-Lemaître-Robertson-Walker backgrounds. In these cases it is shown that, although the evolution of tensor models depends on the choice of parameters of the theory,...

The propagation of a boson particle in the Janis-Newman-Winicour-Wyman (JNWW) gravitational field is analyzed. We derive the wave function of the scalar particle, and the effective potential experienced by quantum particles. Besides, we show that the probability to find the scalar particle near the region where the naked singularity is finite....

We use the 1+ 1+ 2 covariant approach to clarify a number of aspects of spherically symmetric solutions of non-minimally coupled scalar tensor theories. Particular attention is focused on the extension of Birkhoff's theorem and the nature of quasi-local horizons in this context.

The dynamical system approach has recently acquired great importance in the investigation on higher order theories of gravity. In this talk I review some of the main results obtained with this method and I consider briefly a number of further developments. © 2007 IOP Publishing Ltd.

In this article, we develop the formalism for singular hypersurfaces and junction conditions in generalized coupling theories using a variational approach. We then employ this formalism to examine the behavior of sharp matter density gradients in generalized coupling theories. We find that such gradients do not necessarily lead to the...

A detailed analysis of dynamics of cosmological models based on R n gravity is presented. We show that the cosmological equations can be written as a first-order autonomous system and analysed using the standard techniques of dynamical system theory. In the absence of perfect fluid matter, we find exact solutions whose behaviour and stability...

We investigate the conditions for a bounce to occur in Friedmann-Robertson-Walker cosmologies for the class of fourth-order gravity theories. The general bounce criterion is determined and constraints on the parameters of three specific models are given in order to obtain bounce solutions. Furthermore, unlike the case of general relativity, a...

We give a rigorous and mathematically well defined presentation of the covariant and gauge invariant theory of scalar perturbations of a Friedmann-Lemaître-Robertson-Walker universe for fourth order gravity, where the matter is described by a perfect fluid with a barotropic equation of state. The general perturbations equations are applied to a...

The covariant gauge-invariant perturbation theory of scalar cosmological perturbations is developed for a general scalar-tensor Friedmann-Lemaitre- Robertson-Walker cosmology in a vacuum. The perturbation equations are then solved exactly in the long wavelength limit for a specific coupling, potential, and background. Differences with the...

We present a new approach of the reconstruction method based on the use of the cosmic parameters instead of a time law for the scale factor. This solution generating technique allows the derivation and analysis of a set of new non-trivial exact cosmological solutions for f(R)-gravity. Specifically, we find two new cyclic solutions and we...

The so-called f(X) hybrid metric-Palatini gravity, where X=R+T, with T the stress-energy trace and R the Ricci scalar, presents a unique viable generalization of the f(R) theories within the metric-affine formalism. In this paper, the cosmology of the f(X) theories is studied using the dynamical system approach. The method consists of...

Building on earlier work, we discuss a general framework for exploring the cosmological dynamics of Higher Order Theories of Gravity. We show that once the theory of gravity has been specified, the cosmological equations can be written as a first-order autonomous system and we give several examples which illustrate the utility of our method. We...

We present a detailed investigation of the cosmological dynamics based on exp(-R/Λ) gravity. We apply the dynamical system approach to both the vacuum and matter cases and obtain exact solutions and their stability in the finite and asymptotic regimes. The results show that cosmic histories exist which admit a double de Sitter phase which could...

We construct a covariant version of the Tolman-Oppenheimer-Volkoff equations in the case of isotropic sources. The new equations make evident the mathematical problems in the determination of interior solutions of relativistic stellar objects. Using a reconstruction algorithm, we find two physically interesting generalizations of previously...

Gamma-Ray Bursts (GRBs) production is discussed in the framework of the Brans-Dicke (BD) theory of gravity. We derive the effective potential and the acceleration of a scalar particle propagating in a gravitational field described by BD theory. The rate of the energy radiated by charged particles is also calculated. Constraints on parameters...

We generalize the Tolman-Oppenheimer-Volkoff equations for space-times endowed with a Weyssenhof-like torsion field in the Einstein-Cartan theory. The new set of structure equations clearly show how the presence of torsion affects the geometry of the space-time. We obtain new exact solutions for compact objects with non-null intrinsic spin...

We discuss a mechanism that induces a time-dependent vacuum energy on cosmological scales. It is based on the instability-induced renormalization triggered by the low-energy quantum fluctuations in a Universe with a positive cosmological constant. We use the dynamical systems approach to study the qualitative behavior of the...

Building on the results of a previous paper, we compute for the first time a full first-order perturbative solution for the angular coordinates in the restricted post-Newtonian two-body problem with spin. The analytical integration of the angular coordinates, based on the theory of the Weierstrassian functions, allows us to investigate...

We revisit the relativistic restricted two-body problem with spin employing a perturbation scheme based on Lie series. Starting from a post-Newtonian expansion of the field equations, we develop a first-order secular theory that reproduces well-known relativistic effects such as the precession of the pericentre and the Lense-Thirring and...

We find a reconstruction algorithm able to generate all the static spherically symmetric interior solutions in the framework of Hořava gravity and Einstein-æther theory in the presence of anisotropic fluids. We focus for simplicity on the case of a static æther finding a large class of possible viable interior star solutions which present a...

We generalize the covariant Tolman-Oppenheimer-Volkoff equations proposed in Carloni and Vernieri [Phys. Rev. D 97, 124056 (2018).PRVDAQ0556-282110.1103/PhysRevD.97.124056]. to the case of static and spherically symmetric spacetimes with anisotropic sources. The extended equations allow a detailed analysis of the role of the anisotropic terms...