Mariafelicia De Laurentis | Università degli Studi di Napoli "Federico II" (original) (raw)

Books by Mariafelicia De Laurentis

Springer Verlag , 2017

This book offers an excellent introduction to General Relativity and Cosmology. It is designed to... more This book offers an excellent introduction to General Relativity and Cosmology. It is designed to serve as a self-contained text for graduate and advanced undergraduate students and also to provide a basic text for PhD courses. Each of the four parts of the book, two basic and two advanced, can be used as an independent module. In the first part, the main concepts of General Relativity are presented, while the second offers an introduction to the astrophysical applications. The third part is advanced, and discusses the extensions of General Relativity; the contents represent ideal material for a short course at PhD level. The final part of the book provides an introduction to Relativistic Cosmology and its applications. Throughout the text, all mathematical calculations are explained clearly, in step by step detail. Whenever appropriate, the reader is guided to further specialized sources of information.
http://www.springer.com/de/book/9783319327464

Papers by Mariafelicia De Laurentis

The European Physics Journal C, 2018

The study of the dynamics of a two-body system in modified gravity constitutes a more complex pro... more The study of the dynamics of a two-body system in modified gravity constitutes a more complex problem than in Newtonian gravity. Numerical methods are typically needed to solve the equations of geodesics. Despite the complexity of the problem, the study of a two-body system in f (R) gravity leads to a new exciting perspective hinting the right strategy to adopt in order to probe modified gravity. Our results point out some differences between the semiclassical (Newtonian) approach, and the relativistic (geodesic) one thus suggesting that the latter represents the best strategy for future tests of modified theories of gravity. Finally, we have also highlighted the capability of forthcoming observations to serve as smoking gun of modified gravity revealing a departure from GR or further reducing the parameter space of f (R) gravity.

Radio-astronomical observations of the supermassive black-hole candidate in the galactic center w... more Radio-astronomical observations of the supermassive black-hole candidate in the galactic center will soon offer the possibility to study gravity in its strongest regimes and to test different models for these compact objects. Studies based on semi-analytic models and strong-field images of stationary plasma configurations around boson stars have stressed the difficulty to distinguish them from black holes. We here report on the first general-relativistic magnetohydrodynamic simulations of accretion onto a nonrotating boson star and employ general-relativistic radiative-transfer calculations to revisit the appearance of an accreting boson star. We find that the absence of an event horizon in a boson star leads to important differences in the dynamics of the accretion and results in both the formation of a small torus in the interior of the boson star and in the absence of an evacuated high-magnetization funnel in the polar regions. Synthetic reconstructed images considering realistic astronomical observing conditions show that differences in the appearance of the two compact object are large enough to be detectable. These results, which also apply to other horizonless compact objects, strengthen confidence in the ability to determine the presence of an event horizon via radio observations and highlight the importance of self-consistent multidimensional simulations to study the compact object at the galactic center.

Nature Astronomy , 2018

Our Galactic Center, Sagittarius A* (Sgr A*), is believed to harbour a supermassive black hole (B... more Our Galactic Center, Sagittarius A* (Sgr A*), is believed to harbour a supermassive black hole (BH), as suggested by observations tracking individual orbiting stars. Upcoming sub-millimetre very-long-baseline-interferometry (VLBI) images of Sgr A* carried out by the Event-Horizon-Telescope Collaboration (EHTC) are expected to provide critical evidence for the existence of this supermassive BH. We assess our present ability to use EHTC images to determine if they correspond to a Kerr BH as predicted by Einstein's theory of general relativity (GR) or to a BH in alternative theories of gravity. To this end, we perform general-relativistic magnetohydrodynamical (GRMHD) simulations and use general-relativistic radiative transfer (GRRT) calculations to generate synthetic shadow images of a magnetised accretion flow onto a Kerr BH. In addition, and for the first time, we perform GRMHD simulations and GRRT calculations for a dilaton BH, which we take as a representative solution of an alternative theory of gravity. Adopting the VLBI configuration from the 2017 EHTC campaign, we find that it could be extremely difficult to distinguish between BHs from different theories of gravity, thus highlighting that great caution is needed when interpreting BH images as tests of GR.

Physics Letter B

The Noether Symmetry Approach can be used to construct spherically symmetric solutions in f(R) g... more The Noether Symmetry Approach can be used to construct spherically symmetric solutions in f(R) gravity. Specifically, the Noether conserved quantity is related to the gravitational mass and a gravitational radius that reduces to the Schwarzschild radius in the limit f(R)→R.. We show that it is possible to construct the M−R relation for neutron stars depending on the Noether conserved quantity and the associated gravitational radius. This approach enables the recovery of extreme massive stars that could not be stable in the standard Tolman-Oppenheimer-Volkoff based on General Relativity. Examples are given for some power law f(R) gravity models.

Alternative theories of gravity may serve to overcame several shortcomings of the standard cosmol... more Alternative theories of gravity may serve to overcame several shortcomings of the standard cosmological model but, in their weak field limit, they must recover General Relativity to match the tight constraints at Solar System scale. Therefore, testing such alternative models at scale of stellar systems could give a unique opportunity to confirm or rule them out. One of the most straightforward modifications is represented by analytical f(R)-gravity models that introduce a Yukawa-like modification to the Newtonian potential that modify the dynamics of particles. Using the geodesic equations, we have illustrated the amplitude of these modifications. First, we have numerically integrated the equations of motion showing the orbital precession of a particle around a massive object. Second, we have computed an analytic expression for the periastron advance of systems having semi-major axis much lower than the Yukawa-scale length. Finally, we have extended our results to the case of a binary system composed of two massive objects. Our analysis provides a powerful tool to obtain constraints on the underlying theory of gravity using current and forthcoming dataset.

The concordance cosmological model has been successfully tested throughout the last decades. Desp... more The concordance cosmological model has been successfully tested throughout the last decades. Despite its successes, the fundamental nature of dark matter and dark energy is still unknown. Modifications of the gravitational action have been proposed as an alternative to these dark components. The straightforward modification of gravity is to generalize the action to a function, f(R), of the scalar curvature. Thus one is able to describe the emergence and the evolution of the Large Scale Structure without any additional (unknown) dark component. In the weak field limit of the f(R)-gravity, a modified Newtonian gravitational potential arises. This gravitational potential accounts for an extra force, generally called fifth force, that produces a precession of the orbital motion even in the classic mechanical approach. We have shown that the orbits in the modified potential can be written as Keplerian orbits under some conditions on the strength and scale length of this extra force. Nevertheless, we have also shown that this extra term gives rise to the precession of the orbit. Thus, comparing our prediction with the measurements of the precession of some planetary motions, we have found that the strength of the fifth force must be in the range [2.70−6.70]×10−9 whit the characteristic scale length to fixed to the fiducial values of ∼5000 AU.

To date, the most precise tests of general relativity have been achieved through pulsar timing, a... more To date, the most precise tests of general relativity have been achieved through pulsar timing, albeit in the weak-field regime. Since pulsars are some of the most precise and stable "clocks" in the Universe, present observational efforts are focused on detecting pulsars in the vicinity of supermassive black holes (most notably in our Galactic Centre), enabling pulsar timing to be used as an extremely precise probe of strong-field gravity. In this paper a mathematical framework to describe test-particle dynamics in general black hole spacetimes is presented, and subsequently used to study a binary system comprising a pulsar orbiting a black hole. In particular, taking into account the parameterization of a general spherically symmetric black hole metric, general analytic expressions for both the advance of the periastron and for the orbital period of a massive test particle are derived. Furthermore, these expressions are applied to four representative cases of solutions arising in both general relativity and in alternative theories of gravity. Finally, this framework is applied to the Galactic Centre S-stars and four distinct pulsar toy models. It is shown that by adopting a fully general-relativistic description of test-particle motion which is independent of any particular theory of gravity, observations of pulsars can help impose better constraints on alternative theories of gravity than is presently possible.

In its weak field limit, Scalar-tensor-vector gravity theory introduces a Yukawa-correction to th... more In its weak field limit, Scalar-tensor-vector gravity theory introduces a Yukawa-correction to the gravitational potential. Such a correction depends on the two parameters, α which accounts for the modification of the gravitational constant, and 1/µ * which represents the scale length on which the scalar field propagates. These parameters were found to be universal when the modified gravitational potential was used to fit the galaxy rotation curves and the mass profiles of galaxy clusters, both without Dark Matter. We test the universality of these parameters using the the temperature anisotropies due to the thermal Sunyaev-Zeldovich effect. In our model the intra-cluster gas is in hydrostatic equilibrium within the modified gravitational potential well and it is described by a polytropic equation of state. We predict the thermal Sunyaev-Zeldovich temperature anisotropies produced by Coma cluster, and we compare them with those obtained using the Planck 2013 Nominal maps. In our analysis, we find α and the scale length, respectively, to be consistent and to depart from their universal values. Our analysis points out that the assumption of the universality of the Yukawa-correction to the gravitational potential is ruled out at more than 3.5σ at galaxy clusters scale, while demonstrating that such a theory of gravity is capable to fit the cluster profile if the scale dependence of the gravitational potential is restored.

The paradox of a free falling radiating charged particle in a gravitational field, is a well-know... more The paradox of a free falling radiating charged particle in a gravitational field, is a well-known fascinating conceptual challenge that involves classical electrodynamics and general relativity. We discuss this paradox considering the emission of radiation as a consequence of an explicit space/time symmetry breaking involving the electric field within the trajectory of the particle seen from an external observer. This occurs in certain particular cases when the relative motion of the charged particle does not follow a geodesic of the motion dictated by the explicit Lagrangian formulation of the problem and thus from the metric of spacetime. The problem is equivalent to the breaking of symmetry within the spatial configuration of a radiating system like an antenna: when the current is not conserved at a certain instant of time within a closed region then emission of radiation occurs [1]. Radiation from a system of charges is possible only when there is explicit breaking of symmetry in the electric field in space and time.

The Hawking-Perry-Strominger (HPS) work [1] states a new controversial idea about the black hole ... more The Hawking-Perry-Strominger (HPS) work [1] states a new controversial idea about the black hole (BH) information paradox [2-5] where BHs maximally entropize and encode information in their event horizon area [6,7], with no "hair" were thought to reveal information outside but angular momentum, mass and electric charge only [8,9] in a unique quantum gravity (QG) vacuum state. This new idea invokes new conservation laws involving gravitation and electromagnetism [10,11], to generate different QG vacua and preserve more information in hair implants. In the context of black holes and the HPS proposal we find that BH photon hair implants can be spatially shaped ad hoc and encode structured and densely organized information on the event horizon involving novel aspect in the discussion a particular aspect of EM fields, namely the spatial information of the field associated to its orbital angular momentum. BHs can have "curly", twisted, soft-hair implants with vorticity where structured information is holographically encoded in the event horizon in an organized way.

The recently reported gravitational wave events GW150914 and GW151226 caused by the merg- ers of ... more The recently reported gravitational wave events GW150914 and GW151226 caused by the merg- ers of binary black holes [1–3] provide a formidable way to set constraints on alternative metric theories of gravity in the strong field regime. In this paper, we develop an approach where an arbitrary theory of gravity can be parametrised by an effective coupling Geff and an effective grav- itational potential Φ(r). The standard Newtonian limit of General Relativity is recovered as soon as Geff → GN and Φ(r) → ΦN. The upper bound on the graviton mass and the gravitational interaction length, reported by the LIGO-VIRGO collaboration, can be directly recast in terms of the parameters of the theory which allows an analysis where the gravitational wave frequency modulation sets constraints on the range of possible alternative models of gravity. Numerical results based on published parameters for the binary black hole mergers are also reported. Comparison of the observed phase of the GW150914 and GW151226 with the modulated phase in alternative theories of gravity does not give reasonable constraints due the large uncertainties in the estimated parameters for the coalescing black holes. In addition to these general considerations, we obtain limits for the frequency dependence of the α parameter in scalar tensor theories of gravity.

Einstein's General Theory of Relativity (GR) successfully describes gravity. The most fundamental... more Einstein's General Theory of Relativity (GR) successfully describes gravity. The most fundamental predictions of GR are black holes (BHs), but in spite of many convincing BH candidates in the Universe, there is no conclusive experimental proof of their existence using astronomical observations. Are BHs real astrophysical objects? Does GR hold in its most extreme limit or are alternatives needed? The prime target to address these fundamental questions is in the center of our own Galaxy, which hosts the closest and best-constrained supermassive BH candidate in the Universe, Sagittarius A* (Sgr A*). Three different types of experiments hold the promise to test GR in a strong-field regime using observations of Sgr A* with new-generation instruments. The first experiment aims to image the relativistic plasma emission which surrounds the event horizon and forms a "shadow" cast against the background, whose predicted size (~50 microarcseconds) can now be resolved by upcoming VLBI experiments at mm-waves such as the Event Horizon Telescope (EHT). The second experiment aims to monitor stars orbiting Sgr A* with the upcoming near-infrared interferometer GRAVITY at the Very Large Telescope (VLT). The third experiment aims to time a radio pulsar in tight orbit about Sgr A* using radio telescopes (including the Atacama Large Millimeter Array or ALMA). The BlackHoleCam project exploits the synergy between these three different techniques and aims to measure the main BH parameters with sufficient precision to provide fundamental tests of GR and probe the spacetime around a BH in any metric theory of gravity. Here, we review our current knowledge of the physical properties of Sgr A* as well as the current status of such experimental efforts towards imaging the event horizon, measuring stellar orbits, and timing pulsars around Sgr A*.

Modern Physics Letters A, 2008

MNRAS, May 5, 2014

Models of f(R)f(R)f(R) gravity that introduce corrections to the Newtonian potential in the weak field ... more Models of f(R)f(R)f(R) gravity that introduce corrections to the Newtonian potential in the weak field limit are tested at the scale of galaxy clusters. These models can explain the dynamics of spiral and elliptical galaxies without resorting to dark matter. We compute the pressure profiles of 579 galaxy clusters assuming that the gas is in hydrostatic equilibrium within the potential well of the modified gravitational field. The predicted profiles are compared with the average profile obtained by stacking the data of our cluster sample in the Planck foreground clean map SMICA. We find that the resulting profiles of these systems fit the data without requiring a dominant dark matter component, with model parameters similar to those required to explain the dynamics of galaxies. Our results do not rule out that clusters are dynamically dominated by Dark Matter but support the idea that Extended Theories of Gravity could provide an explanation to the dynamics of self-gravitating systems and to the present period of accelerated expansion, alternative to the concordance cosmological model.

2009 Sixth International Conference on Fuzzy Systems and Knowledge Discovery, 2009

Springer Verlag , 2017

The European Physics Journal C, 2018

Nature Astronomy , 2018

Physics Letter B

Modern Physics Letters A, 2008

MNRAS, May 5, 2014

2009 Sixth International Conference on Fuzzy Systems and Knowledge Discovery, 2009

The European Physical Journal C, 2012

The European Physical Journal C, 2010

To explain the extremely high energy release, > 10 53 erg, suggested by the observations of some ... more To explain the extremely high energy release, > 10 53 erg, suggested by the observations of some Gamma-Ray Bursts (GRBs), we propose a new energy extraction mechanism from the rotational energy of a Kerr-Newman black hole (BH) by a massive photon field. Numerical studies show that this mechanism is stable with respect to the black hole rotation parameter, a, with a clear dependence on the BH mass, M, and charge, Q, and can extract energies up to 10 54 erg. The controversial " energy crisis " problem of GRBs that does not show evidence for collimated emission may benefit from this energy extraction mechanism. With these results we set a lower bound on the coupling between electromagnetic and gravitational fields.

The aim of the school is to bring together PhD students, Post-docs and researchers with inter... more The aim of the school is to bring together PhD students, Post-docs and researchers with interests in the new approaches and trends in Theoretical Cosmology. In particular, the lectures will be devoted to the so called back reaction in cosmology, the cosmic acceleration and the theory of cosmological perturbations. The lectures are also devoted to the formation of INFN researchers.

The biennial Conference of the Italian Society of General Relativity and Gravitation (SIGRAV) is... more The biennial Conference of the Italian Society of General Relativity and Gravitation (SIGRAV) is devoted to all aspects of gravitational physics, such as Classical and Quantum Gravity, Relativistic Astrophysics and Cosmology, as well as Experimental Gravity.
The five day Conference will host about twenty invited plenary talks and shorter invited and contributed talks in three parallel workshops. A science divulgation/outreach session will be hosted during the Conference.
The Conference will take place at the Osservatorio Astronomico di Capodimonte (Napoli), in the framework of the celebrations of 200 years since its foundation.
During the Conference, the AMALDI MEDAL and the SIGRAV Prizes will be awarded to outstanding Senior and Junior scientists.

"The meeting is in the Series of the DSU workshops previeusly held in Seoul (2005), Madrid (2006)... more "The meeting is in the Series of the DSU workshops previeusly held in Seoul (2005), Madrid (2006), Minnesota (2007), Cairo (2008), Melbourne (2009), Leon (2010), Beijing (2011) and Buzios, Rio de Janeiro (2012). For more info, seehttp://dark.ft.uam.es/dsu/ DSU are a series of international workshops bringing together a wide range of theorists and experimentalists to discuss current ideas on models of the dark side and relate them to current and future experiments. Topics covered include: dark matter, dark energy, cosmic rays, neutrino physics, cosmology, astrophysical analysis of galactic halos, physics beyond the standard model, etc. Topics of the workshop: Observational Cosmology. Planck results. Dark Energy: origin, evolution and observational properties. Observational properties of Galaxies. Dark Matter in Galaxies, Groups and Clusters. Old and New Dark Matter candidates. Direct and Indirect Dark Matter searches. Simulations in Galaxy/Cluster Formation. Abandoning the LCDM Universe paradigm? Ultra high energy cosmic rays. Modifying Newton-Einstein Theory of Gravity?
Scientific Organizing Committee:
Pyungwon Ko (KIAS, South Korea)
Carlos Muñoz (UAM/IFT, Spain)
Christiane Frigerio Martins (UFF Brasil)
Shaban Khalil (BUE, Egypt)
Keith Olive (Minnesota University, USA)
Csaba Balazs (Monash University, Australia)
David Delepine (Guanajauato University, Mexico)
Qaisar Shafi (Delaware University, USA)
Yu-Feng Zhou (KITPC/ITP-CAS, China)
Paolo Salucci (SISSA, Italy)

Local Organizing Committee:
Paolo Salucci (SISSA, Italy)
Andrea Lapi (SISSA, Italy)
Mariafelicia De Laurentis (SISSA, Italy)
Gigi Danese (SISSA, Italy)
Piero Ullio (SISSA, Italy)"

f(R) gravity is an extension of Einstein's General Relativity derived from relaxing the hypotesis... more f(R) gravity is an extension of Einstein's General Relativity derived from relaxing the hypotesis that the Hilbert-Einstein action for the gravitational field is strictly linear in the Ricci curvature scalar R, i.e. f(R)=R. In this sense, f(R) gravity represents a class of theories defined as arbitrary functions of R. It can be considered as the simplest example of Extended Theory of Gravity (Capozziello and De Laurentis, 2011)....

Over the past decades, General Relativity and the concordance ΛCDM model have been successfully t... more Over the past decades, General Relativity and the concordance ΛCDM model have been successfully tested using several different astrophysical and cosmological probes based on large datasets ({\it precision cosmology}). Despite their successes, some shortcomings emerge due to the fact that General Relativity should be revised at infrared and ultraviolet limits and to the fact that the fundamental nature of Dark Matter and Dark Energy is still a puzzle to be solved. In this perspective, f(R) gravity have been extensively investigated being the most straightforward way to modify General Relativity and to overcame some of the above shortcomings. In this paper, we review various aspects of f(R) gravity at extragalactic and cosmological levels. In particular, we consider cluster of galaxies, cosmological perturbations, and N-Body simulations, focusing on those models that satisfy both cosmological and local gravity constraints. The perspective is that some classes of f(R) models can be consistently constrained by Large Scale Structure.

AIP Conf. Proc. 1458, pp. 475-478

Gravitational waves detected from well-localized inspiraling binaries would allow us to determine... 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.

Models of f(R) gravity that introduce corrections to the Newtonian potential in the weak field li... more Models of f(R) gravity that introduce corrections to the Newtonian potential in the weak field limit are tested at the scale of galaxy clusters. These models can explain the dynamics of spiral and elliptical galaxies without resorting to dark matter. We compute the pressure profiles of 579 galaxy clusters assuming that the gas is in hydrostatic equilibrium within the potential well of the modified gravitational field. The predicted profiles are compared with the average profile obtained by stacking the data of our cluster sample in the Planck foreground clean map SMICA. We find that the resulting profiles of these systems fit the data without requiring a dominant dark matter component, with model parameters similar to those required to explain the dynamics of galaxies. Our results do not rule out that clusters are dynamically dominated by Dark Matter but support the idea that Extended Theories of Gravity could provide an explanation to the dynamics of self-gravitating systems and to the present period of accelerated expansion, alternative to the concordance cosmological model.

"Einstein and Others: Unification" Editors: Valeriy V. Dvoeglazov, ISBN: 978-1-63463-278-2., 2014

Starting from a 5D-Riemannian manifold, we show that a reduction mechanism to 4D-spacetimes repro... more Starting from a 5D-Riemannian manifold, we show that a reduction mechanism to 4D-spacetimes reproduces Extended Theories of Gravity (ETGs) that are direct generalizations of Einstein's gravity. In this context, the gravitational degrees of freedom can be dealt under the standard of spacetime deformations. Besides, such deformations can be related to the mass spectra of particles. The intrinsic non-linearity of ETGs gives an energy-dependent running coupling, while torsion gives rise to interactions among spinors displaying the structure of the weak forces among fermions. We discuss how this scheme is compatible with the known observational evidence and suggest that eventual discrepancies could be detected in experiments, as ATLAS and CMS, today running at LHC (CERN). We finally discuss the consequences of the present approach in view of unification of physical interactions.