- Dipartimento di Fisica, Università di Napoli "Federico II"
- Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Faculty Memberadd
- Full professor in Astrophysics at the University of Naples "Federico II" and at Gran Sasso Science Institute.edit
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We perform a systematic analysis of nonminimally coupled cosmologies in (n+1)-dimensional homogeneous and isotropic spacetimes, searching for Nöther’s symmetries and generalizing the results of our previous works. We obtain (i) the... more
We perform a systematic analysis of nonminimally coupled cosmologies in (n+1)-dimensional homogeneous and isotropic spacetimes, searching for Nöther’s symmetries and generalizing the results of our previous works. We obtain (i) the absence of symmetries when the spatial curvature constant k is nonzero and n=2, 3, but their existence for all the other n; (ii) the existence of such symmetries for every number of spatial dimensions (except n=1) when k=0. In this latter case, we are able to find a general transformation through which we recover the string-dilaton effective action in (n+1) dimensions and the major peculiarity of string cosmology: the scale factor duality. Furthermore, the symmetry fixes a relation among the coupling F(ϕ), the potential V(ϕ) of the scalar field ϕ, the number of spatial dimensions and the spatial curvature constant. When this is the case, it is possible to find a constant of motion and then get the general solution of the dynamics. Finally, in the framework of the so-called Induced Gravity Theories, we are able to obtain the Newton constant at the present time (t→∞) depending on the number of spatial dimensions and directly related to the constant of motion existing in such a model.
It is well known that one cannot construct a self-consistent quantum field theory describing the non-relativistic electromagnetic interaction mediated by massive photons between a point-like electric charge and a magnetic monopole. We... more
It is well known that one cannot construct a self-consistent quantum field theory describing the non-relativistic electromagnetic interaction mediated by massive photons between a point-like electric charge and a magnetic monopole. We show that, indeed, this inconsistency arises in the classical theory itself. No semi-classic approximation or limiting procedure for the Dirac constant approaching to zero is used. As a result, the string attached to the monopole emerges as visible also if finite-range electromagnetic interactions are considered in classical framework.
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The authors study non-flat Friedmann-Robertson-Walker (FRW) cosmologies searching for Noether symmetries in the pointlike Lagrangians derived from a general non-minimally coupled gravitational action. The presence of a quadratic coupling... more
The authors study non-flat Friedmann-Robertson-Walker (FRW) cosmologies searching for Noether symmetries in the pointlike Lagrangians derived from a general non-minimally coupled gravitational action. The presence of a quadratic coupling makes the dynamics degenerate if the spatial-curvature constant is different from zero, while exact solutions, through the existence of the symmetry, are found in the minimally coupled case.
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ABSTRACT The two main classes of ETGs considered in this book, scalar-tensor and f(R) gravity, are the subject of much of this chapter. After exposing the metric formalism, due consideration is given to the Palatini version of f(R)... more
ABSTRACT The two main classes of ETGs considered in this book, scalar-tensor and f(R) gravity, are the subject of much of this chapter. After exposing the metric formalism, due consideration is given to the Palatini version of f(R) theories, emphasizing its bimetric nature. Specifically, we present the actions describing ETGs, derive the field equations from a variational principle, and then discuss their different conformal representations. In this chapter the emphasis is on the general structure of these theories, while their application to astrophysics and cosmology is studied in later chapters.
We study constraints on f(R) dark energy models from solar system experiments combined with experiments on the violation of the equivalence principle. When the mass of an equivalent scalar field degree of freedom is heavy in a region with... more
We study constraints on f(R) dark energy models from solar system experiments combined with experiments on the violation of the equivalence principle. When the mass of an equivalent scalar field degree of freedom is heavy in a region with high density, a spherically symmetric body has a thin shell so that an effective coupling of the fifth force is suppressed through a chameleon mechanism. We place experimental bounds on the cosmologically viable models recently proposed in the literature that have an asymptotic form f(R)=R-λRc[1-(Rc/R)2n] in the regime R≫Rc. From the solar system constraints on the post-Newtonian parameter γ, we derive the bound n>0.5, whereas the constraints from the violations of the weak and strong equivalence principles give the bound n>0.9. This allows a possibility to find the deviation from the Λ-cold dark matter (ΛCDM) cosmological model. For the model f(R)=R-λRc(R/Rc)p with 0<p<1 the severest constraint is found to be p<10-10, which shows that this model is hardly distinguishable from the ΛCDM cosmology.
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A general approach for finding exact cosmological solutions in f(R) gravity is discussed. Instead of taking into account phenomenological models, we assume, as a physical criterion, the existence of Noether symmetries in the cosmological... more
A general approach for finding exact cosmological solutions in f(R) gravity is discussed. Instead of taking into account phenomenological models, we assume, as a physical criterion, the existence of Noether symmetries in the cosmological f(R) Lagrangian. As a result, the presence of such symmetries leads to the selection of viable models and allows us to solve the equations of motion. We discuss also the case in which no Noether charge is present but general criteria can be used to achieve solutions.
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We construct minisuperspace models for a class of theories of gravity nonminimally coupled with a scalar field. We show that when a Nöther symmetry exists, it is always possible to integrate the Wheeler-DeWitt equation and recover the... more
We construct minisuperspace models for a class of theories of gravity nonminimally coupled with a scalar field. We show that when a Nöther symmetry exists, it is always possible to integrate the Wheeler-DeWitt equation and recover the semiclassical regime for the wave function of the universe. In this sense, we can interpret the Nöther symmetries as a selection rule in the philosophy of the so called Hartle criterion: when they exist, it is possible to select classical universes.
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We investigate the possibility that part of the dark matter is not made out of the usual cold dark matter (CDM) dust-like particles, but is in the form of a fluid of strings with barotropic factor ws = -1/3 of cosmic origin. To this aim,... more
We investigate the possibility that part of the dark matter is not made out of the usual cold dark matter (CDM) dust-like particles, but is in the form of a fluid of strings with barotropic factor ws = -1/3 of cosmic origin. To this aim, we split the dark matter density parameter into two terms and investigate the dynamics of a spatially flat universe filled with baryons, CDM, a fluid of strings and dark energy, modeling the latter as a cosmological constant or a negative pressure fluid with a constant equation of state w < 0. To test the viability of the models and to constrain their parameters, we use the Type Ia supernovae Hubble diagram and data on the gas mass fraction in galaxy clusters. We also discuss the weak field limit of a model comprising a significant fraction of dark matter in the form of a fluid of strings and show that this mechanism makes it possible to reduce the need for the elusive and up to now undetected CDM. We finally find that a model comprising both a cosmological constant and a fluid of strings fits the data very well and eliminates the need for phantom dark energy, thus representing a viable candidate for alleviating some of the problems plaguing the dark side of the universe.
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In the framework of phantom quintessence cosmology, we use the Noether Symmetry Approach to obtain general exact solutions for the cosmological equations. This result is achieved by the quintessential (phantom) potential determined by the... more
In the framework of phantom quintessence cosmology, we use the Noether Symmetry Approach to obtain general exact solutions for the cosmological equations. This result is achieved by the quintessential (phantom) potential determined by the existence of the symmetry itself. A comparison between the theoretical model and observations is worked out. In particular, we use type Ia supernovae and large-scale structure parameters determined from the 2-degree Field Galaxy Redshift Survey and from the Wide part of the VIMOS-VLT Deep Survey ). It turns out that the model is compatible with the presently available observational data. Moreover we extend the approach to include radiation. We show that it is compatible with data derived from recombination and it seems that quintessence do not affect nucleosynthesis results.
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A huge amount of good quality data converges towards the picture of a spatially flat universe undergoing the today observed phase of accelerated expansion. This new observational trend is commonly addressed as Precision Cosmology. Despite... more
A huge amount of good quality data converges towards the picture of a spatially flat universe undergoing the today observed phase of accelerated expansion. This new observational trend is commonly addressed as Precision Cosmology. Despite of the excellent surveys, the nature of dark energy, dominating the matter-energy content of the universe, is still unknown and a lot of different scenarios are viable candidates to explain cosmic acceleration. Methods to test these cosmological models are based on distance measurements and lookback time toward astronomical objects used as standard candles. The related degeneracy problem is the signal that more data at low 0<z<1, medium 1<z<10 and high 10 <z< 1000 redshift are needed to definitively select realistic models.
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ABSTRACT We tackle the problem of the nucleation of the universe for the case in which the underlying gravity is an induced-gravity with a Ginzburg-Landau potential for the scalar field. In order to make use of Vilenkin’s wave function,... more
ABSTRACT We tackle the problem of the nucleation of the universe for the case in which the underlying gravity is an induced-gravity with a Ginzburg-Landau potential for the scalar field. In order to make use of Vilenkin’s wave function, we cast the theory into its canonical Einstein form through a conformal transformation: by using Vilenkin’s boundary conditions we show that the semiclassical tunnelling from nothing solves the problem of the initial conditions in the induced gravity inflation and then selects the present observed values of the gravitational and the cosmological constants (G eff =G N , Λ eff =0). Therefore our result improves with respect to those obtained by other authors either i) with the assumption of no-boundary conditions for the cosmic wave function, or ii) with the same Ginzburg-Landau potential, but in the standard Einstein gravity.
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We extend the cosmic no-hair theorem to a general class of scalar-tensor nonminimally coupled theories of gravity where ordinary matter is also present in the form of a perfect fluid. We give a set of conditions for obtaining an... more
We extend the cosmic no-hair theorem to a general class of scalar-tensor nonminimally coupled theories of gravity where ordinary matter is also present in the form of a perfect fluid. We give a set of conditions for obtaining an asymptotic de~Sitter expansion, independently of any initial data, by a sort of time-dependent (effective) cosmological constant. Finally we apply the results to some specific models.
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A huge amount of good quality astrophysical data converges towards the picture of a spatially flat universe undergoing the today observed phase of accelerated expansion. This new observational trend is commonly addressed as Precision... more
A huge amount of good quality astrophysical data converges towards the picture of a spatially flat universe undergoing the today observed phase of accelerated expansion. This new observational trend is commonly addressed as Precision Cosmology. Despite of the quality of astrophysical surveys, the nature of dark energy dominating the matter-energy content of the universe is still unknown and a lot of different scenarios are viable candidates to explain cosmic acceleration. Methods to test these cosmological models are based on distance measurements and lookback time toward astronomical objects used as standard candles. I discuss the characterizing parameters and constraints of three different classes of dark energy models pointing out the related degeneracy problem which is the signal that more data at low (z= 0- 1), medium (1<z<10) and high (10 <z< 1000) redshift are needed to definitively select realistic models.
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We use our Nöther Symmetry Approach to study the Einstein equations minimally coupled with a scalar field, in the case of Bianchi universes of class A and B. Possible cases, when such symmetries exist, are found and two examples of exact... more
We use our Nöther Symmetry Approach to study the Einstein equations minimally coupled with a scalar field, in the case of Bianchi universes of class A and B. Possible cases, when such symmetries exist, are found and two examples of exact integration of the equations of motion are given in the cases of Bianchi AI and BV.
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We give conditions to obtain cosmological asymptotic freedom in scalar-tensor theories of gravity. We show that this feature can be achieved in FRW flat spacetimes since we obtain singularity free solutions where the effective... more
We give conditions to obtain cosmological asymptotic freedom in scalar-tensor theories of gravity. We show that this feature can be achieved in FRW flat spacetimes since we obtain singularity free solutions where the effective gravitational constant $G_{eff}\rightarrow 0$ for $t\rightarrow -\infty$ and, for some of them, $G_{eff}\rightarrow G_{N}$ for $t\rightarrow\infty$, where $G_{N}$ is the Newton constant.
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Based on the {\it dynamical} equivalence between higher order gravity and scalar-tensor gravity the PPN-limit of fourth order gravity is discussed. We exploit this analogy developing a fourth order gravity version of the Eddington... more
Based on the {\it dynamical} equivalence between higher order gravity and scalar-tensor gravity the PPN-limit of fourth order gravity is discussed. We exploit this analogy developing a fourth order gravity version of the Eddington PPN-parameters. As a result, Solar System experiments can be reconciled with higher order gravity, if physical constraints descending from experiments are fulfilled.
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We investigate Brans-Dicke cosmology with perfect-fluid matter and give a method for selecting exact solutions parametrized by the constant γ of the state equation p=(γ-1)ρ and the parameter ξ of the nonminimal coupling in which the... more
We investigate Brans-Dicke cosmology with perfect-fluid matter and give a method for selecting exact solutions parametrized by the constant γ of the state equation p=(γ-1)ρ and the parameter ξ of the nonminimal coupling in which the Brans-Dicke theory can be recast. In this sense, we can classify the solutions having and not having inflationary behavior in the presence of ordinary matter.
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ABSTRACT f(R) gravity is attracting a lot of interest as alternative candidates to explain the observed cosmic acceleration and the missing matter in large scale structures. Very likely, what we call ``Dark Matter&#39;&#39; and... more
ABSTRACT f(R) gravity is attracting a lot of interest as alternative candidates to explain the observed cosmic acceleration and the missing matter in large scale structures. Very likely, what we call ``Dark Matter&#39;&#39; and ``Dark Energy&#39;&#39; are nothing else but signals of the breakdown of General Relativity at large scales. Besides, Solar System experiments do not exclude, a priori, the possibility that such theories could give small observable effects also at these scales. We review some results giving the basic ingredients of such an approach.
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ABSTRACT We discuss the possibility that suitable modifications of gravity could account for some amount of the radiation we observe today, in addition to the possibility of explaining the present speed up of the universe. We start... more
ABSTRACT We discuss the possibility that suitable modifications of gravity could account for some amount of the radiation we observe today, in addition to the possibility of explaining the present speed up of the universe. We start introducing and reviewing cosmological reconstruction methods for metric $f(R)$ theories of gravity that can be considered as one of the straightforward modifications of Einstein&#39;s gravity as soon as $f(R)\neq R$. We then take into account two possible $f(R)$ models which could give rise to (dark) radiation. Constraints on the models are found by using the Planck Collaboration 2015 data within a cosmographic approach and by obtaining the matter power spectrum of those models. The conclusion is that $f(R)$ gravity can only contribute minimally to the (dark) radiation to avoid departures from the observed matter power spectrum at the smallest scales (of the order of $0.01$Mpc$^{-1}$), i.e., precisely those scales that exited the horizon at the radiation dominated epoch. This result could strongly contribute to select reliable $f(R)$ models.
ABSTRACT We adopt a general point of view to obtain the scale factor duality for a class of nonminimally coupled gravitational Lagrangians which comprises the tree-level effective Lagrangian of string-dilaton cosmology. We show that in a... more
ABSTRACT We adopt a general point of view to obtain the scale factor duality for a class of nonminimally coupled gravitational Lagrangians which comprises the tree-level effective Lagrangian of string-dilaton cosmology. We show that in a new system of coordinates the duality is a reflection and the Lagrangians become cyclic with respect to a coordinate. When this is the situation, the dynamics is simplified and it is easier to obtain exact solutions.
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ABSTRACT We construct minisuperspace models for a class of theories of gravity nonminimally coupled with a scalar field. We show that when a Nöther symmetry exists, it is always possible to integrate the Wheeler-DeWitt equation and... more
ABSTRACT We construct minisuperspace models for a class of theories of gravity nonminimally coupled with a scalar field. We show that when a Nöther symmetry exists, it is always possible to integrate the Wheeler-DeWitt equation and recover the semiclassical regime for the wave function of the universe. In this sense, we can interpret the Nöther symmetries as a selection rule in the philosophy of the so called Hartle criterion: when they exist, it is possible to select classical universes.
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ABSTRACT We find the Wheeler-DeWitt equation for a Friedman-Robertson-Walker metric modified according to a model with maximal acceleration and discuss the new conditions in which the wave function of the universe tunnels from the... more
ABSTRACT We find the Wheeler-DeWitt equation for a Friedman-Robertson-Walker metric modified according to a model with maximal acceleration and discuss the new conditions in which the wave function of the universe tunnels from the Euclidean regime to the Lorentzian one. We argue that the acceleration induces a nonminimal coupling of the scalar field with the gravitational degrees of freedom and provides a new dynamical possibility of tunneling through the quantum boundary when .
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The cosmic no-hair theorem is generalized for homogeneous and anisotropic spacetimes in which a scalar field is nonminimally coupled to the geometry. The result is that the Wald proof also holds here for all Bianchi-type universes except... more
The cosmic no-hair theorem is generalized for homogeneous and anisotropic spacetimes in which a scalar field is nonminimally coupled to the geometry. The result is that the Wald proof also holds here for all Bianchi-type universes except Bianchi type-IX. However, considering the asymptotic behaviour of parameters, it is possible to find a class of models where the conjecture holds for Bianchi-IX too.
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Nonperturbative models of quark stars in <mml:math altimg="si1.gif" overflow="scroll" xmlns:xocs="http://www.elsevier.com/xml/xocs/dtd" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.elsevier.com/xml/ja/dtd" xmlns:ja="http://www...more
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gravitational waves ”tuned ” by f(R) gravity
By considering $f(R)$ gravity models, the cosmic evolution is modified with respect to the standard $\Lambda$CDM scenario. In particular, the thermal history of particles results modified. In this paper, we derive the evolution of relics... more
By considering $f(R)$ gravity models, the cosmic evolution is modified with respect to the standard $\Lambda$CDM scenario. In particular, the thermal history of particles results modified. In this paper, we derive the evolution of relics particles (WIMPs) assuming a reliable $f(R)$ cosmological solution and taking into account observational constraints. The connection to the PAMELA experiment is also discussed. Results are consistent with constraints coming from BICEP2 and PLANCK experiments.
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ABSTRACT We perform a systematic analysis of nonminimally coupled cosmologies in (n+1)-dimensional homogeneous and isotropic spacetimes, searching for Nöther&#39;s symmetries and generalizing the results of our previous works. We... more
ABSTRACT We perform a systematic analysis of nonminimally coupled cosmologies in (n+1)-dimensional homogeneous and isotropic spacetimes, searching for Nöther&#39;s symmetries and generalizing the results of our previous works. We obtain (i) the absence of symmetries when the spatial curvature constant k is nonzero and n=2, 3, but their existence for all the other n; (ii) the existence of such symmetries for every number of spatial dimensions (except n=1) when k=0. In this latter case, we are able to find a general transformation through which we recover the string-dilaton effective action in (n+1) dimensions and the major peculiarity of string cosmology: the scale factor duality. Furthermore, the symmetry fixes a relation among the coupling F(varphi), the potential V(varphi) of the scalar field varphi, the number of spatial dimensions and the spatial curvature constant. When this is the case, it is possible to find a constant of motion and then get the general solution of the dynamics. Finally, in the framework of the so-called Induced Gravity Theories, we are able to obtain the Newton constant at the present time (t--&gt;∞) depending on the number of spatial dimensions and directly related to the constant of motion existing in such a model.
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We show that the string cosmology with dilaton can be derived, as a special case, from Caianiello's model of General Relativity with maximal acceleration interpreting the dilaton as an acceleration field. In fact Caianiello's... more
We show that the string cosmology with dilaton can be derived, as a special case, from Caianiello's model of General Relativity with maximal acceleration interpreting the dilaton as an acceleration field. In fact Caianiello's theory allows us to recover the stringdilaton effective action starting from a gravitational action which is minimally coupled to a scalar field by means of a
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Determining H 0 from the time delays in quadruply imaged leng systems needs the knowledge of the deflecting potential y&lt;/font &gt;(r,q&lt;/font &gt;)\psi (r,\theta) . We present two different methods to solve this... more
Determining H 0 from the time delays in quadruply imaged leng systems needs the knowledge of the deflecting potential y&lt;/font &gt;(r,q&lt;/font &gt;)\psi (r,\theta) . We present two different methods to solve this problem. On the one hand, we assume that the potential belongs to a broad class of non-elliptical models and we write down a system of equations which can
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Extended Theories of Gravity can be related to several quantum gravity approaches and unifica- tion schemes. They have recently attracted a lot of interest as alternative candidates to explain the observed cosmic acceleration, the... more
Extended Theories of Gravity can be related to several quantum gravity approaches and unifica- tion schemes. They have recently attracted a lot of interest as alternative candidates to explain the observed cosmic acceleration, the flatness of the rotati on curves of spiral galaxies, the grav- itational potential of galaxy clusters, and other relevant astrophysical phenomena. Very likely, what we call "Dark Matter" and "Dark Energy" are nothing else but signals of the breakdown of General Relativity at large scales. Furthermore, PPN-parameters deduced from Solar System experiments do not exclude, a priori, the possibility that s uch theories could give small observ- able effects also at these scales. We review these results gi ving the basic ingredients of such an approach.
Minisuperspace cosmological models are considered for a class of gravitational theories nonminimally coupled with a scalar field. We show that, when a Noether symmetry exists, it is always possible to integrate the Wheeler–De Witt... more
Minisuperspace cosmological models are considered for a class of gravitational theories nonminimally coupled with a scalar field. We show that, when a Noether symmetry exists, it is always possible to integrate the Wheeler–De Witt equation and to recover the semiclassical regime for the wave function of the universe. In this sense, the Noether symmetries can be regarded as a selection rule in connection with the so called Hartle criterion: when they exist, it is possible to select classical universes.
The authors present a generalization of the "cosmological no-hair theorem" to a wide class of nonminimally coupled scalar-tensor theories of gravity through which it is possible to define a time-dependent "cosmological... more
The authors present a generalization of the "cosmological no-hair theorem" to a wide class of nonminimally coupled scalar-tensor theories of gravity through which it is possible to define a time-dependent "cosmological constant".
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The authors construct a cosmological toy model in which a "cosmological constant" depending on time as a step-function is taken into consideration besides ordinary matter. They assume that Lambda takes two values depending on... more
The authors construct a cosmological toy model in which a "cosmological constant" depending on time as a step-function is taken into consideration besides ordinary matter. They assume that Lambda takes two values depending on the epoch, and matter goes from a radiation-dominated era to a dust-dominated era. The model is exactly solvable and it can be compared with recent observations.
The Dark Matter problem from f (R) gravity viewpoint Contents 1 Introduction 1 2 Extended Gravity and Conformal trasformations 4 3 Yukawa-like corrections to the gravitational potential from the weak-field limit of the theory 9 4 Solar system and Equivalence Principle constraints 11 5 Stellar str...more
An alternative view to the dark matter puzzle is represented by Extended Theories of Gravity. The approach consists in addressing issues like dark components from the point of view of gravitational field instead of requiring new material... more
An alternative view to the dark matter puzzle is represented by Extended Theories of Gravity. The approach consists in addressing issues like dark components from the point of view of gravitational field instead of requiring new material ingredients that, up to now, have not been detected at fundamental level. In this review paper, by extending the Hilbert-Einstein action of gravitational field to more general actions (e.g. f (R) gravity), we show that several gravitating structures like stars, spiral galaxies, elliptical galaxies and clusters of galaxies can be self-consistently described without asking for dark matter. We show also that standard General Relativity tests and Equivalence Principle constraints can be evaded at Solar System scales.
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The extreme physical conditions of Gamma Ray Bursts can constitute a useful observational laboratory to test theories of gravity where very high curvature regimes are involved. Here we propose a sort of curvature engine capable, in... more
The extreme physical conditions of Gamma Ray Bursts can constitute a useful observational laboratory to test theories of gravity where very high curvature regimes are involved. Here we propose a sort of curvature engine capable, in principle, of explaining the huge energy emission of Gamma Ray Bursts. Specifically, we investigate the emission of radiation by charged particles non-minimally coupled to the gravitational background where higher order curvature invariants are present. The coupling gives rise to an additional force inducing a non-geodesics motion of particles. This fact allows a strong emission of radiation by gravitationally accelerated particles. As we will show with some specific model, the energy emission is of the same order of magnitude of that characterizing the Gamma Ray Burst physics. Alternatively, strong curvature regimes can be considered as a natural mechanism for the generation of highly energetic astrophysical events.
Cosmological inflation is discussed in the framework of $F(R,{\cal G})$ gravity where $F$ is a generic function of the curvature scalar $R$ and the Gauss-Bonnet topological invariant $\cal G$. The main feature that emerges in this... more
Cosmological inflation is discussed in the framework of $F(R,{\cal G})$ gravity where $F$ is a generic function of the curvature scalar $R$ and the Gauss-Bonnet topological invariant $\cal G$. The main feature that emerges in this analysis is the fact that this kind of theory can exhaust all the curvature budget related to curvature invariants without considering derivatives of $R,$ $R_{\mu\nu}$, $R^{\lambda}_{\sigma\mu\nu}$ etc. in the action. Cosmological dynamics results driven by two effective masses (lenghts) related to the $R$ scalaron and the $\cal G$ scalaron working respectively at early and very early epochs of cosmic evolution. In this sense, a double inflationary scenario naturally emerges.
We show that a Lagrangian density proportional to $\sqrt{-g} \mathcal{L}_m^2/R$ reduces to a pressuron theory of gravity that is indistinguishable from General Relativity in weak pressure regimes. The unification of matter and geometry in... more
We show that a Lagrangian density proportional to $\sqrt{-g} \mathcal{L}_m^2/R$ reduces to a pressuron theory of gravity that is indistinguishable from General Relativity in weak pressure regimes. The unification of matter and geometry in the same Lagrangian term intrinsically satisfies Mach's Principle --- since matter cannot exist without curvature and vice versa --- while it may have the correct phenomenology in order to describe actual gravity.
Gravitational waves detected from well-localized inspiraling binaries would allow us to determine, directly and independently, binary luminosity and redshift. In this case, such systems could behave as "standard candles" providing an... more
Gravitational waves detected from well-localized inspiraling binaries would allow us to determine, directly and independently, binary luminosity and redshift. In this case, such systems could behave as "standard candles" providing an excellent probe of cosmic distances up to z <0.1 and complementing other indicators of cosmological distance ladder.