Papers by Salvatore Capozziello
Classical and Quantum Gravity, 2007
In the framework of ADM formalism, it is possible to find out eigenvalues of the WDW equation wit... more In the framework of ADM formalism, it is possible to find out eigenvalues of the WDW equation with the meaning of vacuum states, i.e. cosmological constants, for f (R) theories of gravity, where f (R) is a generic analytic function of the Ricci curvature scalar R. The explicit calculation is performed for a Schwarzschild metric where one-loop energy is derived by the zeta function regularization method and a renormalized running Λ0 constant is obtained.
AIP Conference Proceedings, 2009
We present an f (R)-cosmological model with an exact analytic solution, coming from the request o... more We present an f (R)-cosmological model with an exact analytic solution, coming from the request of the existence of a Noether symmetry, which is able to describe a dust-dominated decelerated phase before the current accelerated phase of the universe.
Classical and Quantum Gravity, 2007
Int J Mod Phys D, 1993
We perform a systematic analysis of nonminimally coupled cosmologies in (n+1)-dimensional homogen... 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.
Advances in High Energy Physics, Jan 23, 2007
It is well known that one cannot construct a self-consistent quantum field theory describing the ... 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.
Il Nuovo Cimento B, 1994
The authors study non-flat Friedmann-Robertson-Walker (FRW) cosmologies searching for Noether sym... 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.
Physical Review D, 2014
Spherically symmetric solutions for f (T ) gravity models are derived by the so called Noether Sy... more Spherically symmetric solutions for f (T ) gravity models are derived by the so called Noether Symmetry Approach. First, we present a full set of Noether symmetries for some minisuperspace models. Then, we compute analytical solutions and find that spherically symmetric solutions in f (T ) gravity can be recast in terms of Schwarzschild-like solutions modified by a distortion function depending on a characteristic radius. The obtained solutions are more general than those obtained by the usual solution methods.
ABSTRACT The two main classes of ETGs considered in this book, scalar-tensor and f(R) gravity, ar... 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.
Phys Rev D, 2008
We study constraints on f(R) dark energy models from solar system experiments combined with exper... 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.
Jcap, 2008
A general approach for finding exact cosmological solutions in f(R) gravity is discussed. Instead... 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.
Int J Mod Phys D, 1994
We construct minisuperspace models for a class of theories of gravity nonminimally coupled with a... 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.
Int J Geom Methods Mod Phys, 2009
Int J Mod Phys D, 2006
We investigate the possibility that part of the dark matter is not made out of the usual cold dar... 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.
Physical Review D Particles and Fields, Aug 15, 2009
In the framework of phantom quintessence cosmology, we use the Noether Symmetry Approach to obtai... 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.
A huge amount of good quality data converges towards the picture of a spatially flat universe und... 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.
ABSTRACT We tackle the problem of the nucleation of the universe for the case in which the underl... 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.
We propose a cosmological model that unifies inflation, deceleration and acceleration phases of e... more We propose a cosmological model that unifies inflation, deceleration and acceleration phases of expansion history by a BIonic system. At the beginning, there are k black fundamental strings that transited to the BIon configuration at a given corresponding point. Here, two coupled universes, brane and antibrane, are created interacting each other through a wormhole and inflate. With decreasing temperature, the energy of this wormhole flows into the universe branes and leads to inflation. After a short time, the wormhole evaporates, the inflation ends and a deceleration epoch starts. By approaching the brane and antibrane universes together, a tachyon is born, grows and causes the creation of a new wormhole. At this time, the brane and antibrane universes result connected again and the late-time acceleration era of the universe begins. We compare our model with previous unified phantom models and observational data obtaining some cosmological parameters like temperature in terms of time. We also find that deceleration parameter is negative during inflation and late-time acceleration epochs, while it is positive during the deceleration era. This means that the model is consistent, in principle, with cosmological observations.
Gen Relativ Gravit, 1997
We extend the cosmic no-hair theorem to a general class of scalar-tensor nonminimally coupled the... 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.
A huge amount of good quality astrophysical data converges towards the picture of a spatially fla... 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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Papers by Salvatore Capozziello