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Author |
Capozziello, S.; Harko, T.; Lobo, F.S.N.; Olmo, G.J.; Vignolo, S. |
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Title  |
The Cauchy problem in hybrid metric-Palatini f(X)-gravity |
Type |
Journal Article |
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Year |
2014 |
Publication |
International Journal of Geometric Methods in Modern Physics |
Abbreviated Journal |
Int. J. Geom. Methods Mod. Phys. |
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Volume |
11 |
Issue |
5 |
Pages |
1450042 - 12pp |
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Keywords |
Cauchy problem; modified gravity; hybrid metric-Palatini gravity |
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Abstract |
The well-formulation and the well-posedness of the Cauchy problem are discussed for hybrid metric-Palatini gravity, a recently proposed modified gravitational theory consisting of adding to the Einstein-Hilbert Lagrangian an f(R)-term constructed a la Palatini. The theory can be recast as a scalar-tensor one predicting the existence of a light long-range scalar field that evades the local Solar System tests and is able to modify galactic and cosmological dynamics, leading to the late-time cosmic acceleration. In this work, adopting generalized harmonic coordinates, we show that the initial value problem can always be well-formulated and, furthermore, can be well-posed depending on the adopted matter sources. |
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Address |
[Capozziello, Salvatore] Univ Naples Federico II, Dipartimento Sci Fis, Naples, Italy, Email: capozzie@na.infn.it; |
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Publisher |
World Scientific Publ Co Pte Ltd |
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Language |
English |
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ISSN |
0219-8878 |
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Conference |
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Notes |
WOS:000336527100003 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
1813 |
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Author |
Beltran Jimenez, J.; Heisenberg, L.; Olmo, G.J. |
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Title |
Tensor perturbations in a general class of Palatini theories |
Type |
Journal Article |
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Year |
2015 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
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Volume |
06 |
Issue |
6 |
Pages |
026 - 16pp |
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Keywords |
modified gravity; inflation; gravity; dark energy theory |
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Abstract |
We study a general class of gravitational theories formulated in the Palatini approach and derive the equations governing the evolution of tensor perturbations. In the absence of torsion, the connection can be solved as the Christoffel symbols of an auxiliary metric which is non-trivially related to the space-time metric. We then consider background solutions corresponding to a perfect fluid and show that the tensor perturbations equations (including anisotropic stresses) for the auxiliary metric around such a background take an Einstein-like form. This facilitates the study in a homogeneous and isotropic cosmological scenario where we explicitly establish the relation between the auxiliary metric and the spacetime metric tensor perturbations. As a general result, we show that both tensor perturbations coincide in the absence of anisotropic stresses. |
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Address |
[Jimenez, Jose Beltran] Univ Louvain, Inst Math & Phys, Ctr Cosmol Particle Phys & Phenomenol, B-1318 Louvain, Belgium, Email: jose.beltran@cpt.univ.mrs.fr; |
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Publisher |
Iop Publishing Ltd |
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English |
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Edition |
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ISSN |
1475-7516 |
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Expedition |
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Conference |
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Notes |
WOS:000359215400027 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
2368 |
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Author |
Lobo, F.S.N.; Olmo, G.J.; Orazi, E.; Rubiera-Garcia, D.; Rustam, A. |
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Title |
Structure and stability of traversable thin-shell wormholes in Palatini f(R) gravity |
Type |
Journal Article |
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Year |
2020 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
102 |
Issue |
10 |
Pages |
104012 - 11pp |
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Keywords |
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Abstract |
We study the structure and stability of traversable wormholes built as (spherically symmetric) thin shells in the context of Palatini f(R) gravity. Using a suitable junction formalism for these theories we find that the effective number of degrees of freedom on the shell is reduced to a single one, which fixes the equation of state to be that of massless stress-energy fields, contrary to the general relativistic and metric f(R) cases. Another major difference is that the surface energy density threading the thin shell, needed in order to sustain the wormhole, can take any sign and may even vanish, depending on the desired features of the corresponding solutions. We illustrate our results by constructing thin-shell wormholes by surgically grafting Schwarzschild space-times and show that these configurations are always linearly unstable. However, surgically joined Reissner-Nordstrom space-times allow for linearly stable, traversable thin-shell wormholes supported by a positive energy density provided that the (squared) mass-to-charge ratio, given by y = Q(2)/M-2, satisfies the constraint 1 < y < 9/8 (corresponding to overcharged Reissner-Nordstrom configurations having a photon sphere) and lies in a region bounded by specific curves defined in terms of the (dimensionless) radius of the shell x(0) = R/M. |
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Address |
[Lobo, Francisco S. N.] Univ Lisbon, Fac Ciencias, Inst Astrofis & Ciencias Espaco, Edificio C8,Campo Grande, P-1749016 Lisbon, Portugal, Email: fslobo@fc.ul.pt; |
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Publisher |
Amer Physical Soc |
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Language |
English |
Summary Language |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
2470-0010 |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000587286200006 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
4596 |
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Author |
Olmo, G.J.; Rubiera-Garcia, D.; Wojnar, A. |
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Title |
Stellar structure models in modified theories of gravity: Lessons and challenges |
Type |
Journal Article |
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Year |
2020 |
Publication |
Physics Reports |
Abbreviated Journal |
Phys. Rep. |
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Volume |
876 |
Issue |
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Pages |
1-75 |
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Keywords |
Stellar structure; Modified gravity; Palatini formalism; Neutron stars; Brown dwarfs; Relativistic stars; Weak field; f(R) theories; Born-Infeld theory; Horndeski theory |
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Abstract |
The understanding of stellar structure represents the crossroads of our theories of the nuclear force and the gravitational interaction under the most extreme conditions observably accessible. It provides a powerful probe of the strong field regime of General Relativity, and opens fruitful avenues for the exploration of new gravitational physics. The latter can be captured via modified theories of gravity, which modify the Einstein-Hilbert action of General Relativity and/or some of its principles. These theories typically change the Tolman-Oppenheimer-Volkoff equations of stellar's hydrostatic equilibrium, thus having a large impact on the astrophysical properties of the corresponding stars and opening a new window to constrain these theories with present and future observations of different types of stars. For relativistic stars, such as neutron stars, the uncertainty on the equation of state of matter at supranuclear densities intertwines with the new parameters coming from the modified gravity side, providing a whole new phenomenology for the typical predictions of stellar structure models, such as mass-radius relations, maximum masses, or moment of inertia. For non-relativistic stars, such as white, brown and red dwarfs, the weakening/strengthening of the gravitational force inside astrophysical bodies via the modified Newtonian (Poisson) equation may induce changes on the star's mass, radius, central density or luminosity, having an impact, for instance, in the Chandrasekhar's limit for white dwarfs, or in the minimum mass for stable hydrogen burning in high-mass brown dwarfs. This work aims to provide a broad overview of the main such results achieved in the recent literature for many such modified theories of gravity, by combining the results and constraints obtained from the analysis of relativistic and non-relativistic stars in different scenarios. Moreover, we will build a bridge between the efforts of the community working on different theories, formulations, types of stars, theoretical modelings, and observational aspects, highlighting some of the most promising opportunities in the field. |
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Address |
[Olmo, Gonzalo J.] Univ Valencia, Dept Fis Teor, Ctr Mixto, CSIC, Valencia 46100, Spain, Email: gonzalo.olmo@uv.es; |
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Publisher |
Elsevier |
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English |
Summary Language |
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ISSN |
0370-1573 |
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Conference |
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Notes |
WOS:000570298900001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
4531 |
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Author |
Olmo, G.J.; Sanchis-Alepuz, H.; Tripathi, S. |
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Title |
Stellar structure equations in extended Palatini gravity |
Type |
Journal Article |
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Year |
2012 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
86 |
Issue |
10 |
Pages |
104039 - 8pp |
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Keywords |
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Abstract |
We consider static spherically symmetric stellar configurations in Palatini theories of gravity in which the Lagrangian is an unspecified function of the form f(R, R μnu R μnu). We obtain the Tolman-Oppenheimer-Volkov equations corresponding to this class of theories and show that they recover those of f(R) theories and general relativity in the appropriate limits. We show that the exterior vacuum solutions are of Schwarzschild-de Sitter type and comment on the possible expected modifications, as compared to general relativity, of the interior solutions. |
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Address |
[Olmo, Gonzalo J.; Sanchis-Alepuz, Helios] Univ Valencia, CSIC, Fac Fis, Dept Fis Teor, E-46100 Valencia, Spain, Email: gonzalo.olmo@csic.es; |
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Corporate Author |
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Thesis |
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Publisher |
Amer Physical Soc |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
1550-7998 |
ISBN |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000311143500004 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
1222 |
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Author |
Delhom, A.; Mariz, T.; Nascimento, J.R.; Olmo, G.J.; Petrov, A.Y.; Porfirio, P.J. |
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Title |
Spontaneous Lorentz symmetry breaking and one-loop effective action in the metric-affine bumblebee gravity |
Type |
Journal Article |
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Year |
2022 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
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Volume |
07 |
Issue |
7 |
Pages |
018 - 27pp |
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Keywords |
gravity; modified gravity; quantum field theory on curved space; Quantum fields in curved spacetimes |
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Abstract |
The metric-affine bumblebee model in the presence of fermionic matter minimally coupled to the connection is studied. We show that the model admits an Einstein frame representation in which the matter sector is described by a non-minimal Dirac action without any analogy in the literature. Such non-minimal terms involve unconventional couplings between the bumblebee and the fermion field. We then rewrite the quadratic fermion action in the Einstein frame in the basis of 16 Dirac matrices in order to identify the coefficients for Lorentz/CPT violation in all orders of the non-minimal coupling xi. The exact result for the fermionic determinant in the Einstein frame, including all orders in xi, is also provided. We demonstrate that the axial contributions are at least of second order in the perturbative expansion of xi. Furthermore, we compute the one-loop effective potential within the weak field approximation. |
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Address |
[Delhom, Adria] Univ Tartu, Inst Phys, Lab Theoret Phys, W Ostwaldi 1, EE-50411 Tartu, Estonia, Email: adria.delhom@gmail.com; |
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Corporate Author |
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Publisher |
IOP Publishing Ltd |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
1475-7516 |
ISBN |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000834157900011 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5314 |
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Author |
Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Some recent results on Ricci-based gravity theories |
Type |
Journal Article |
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Year |
2022 |
Publication |
International Journal of Modern Physics D |
Abbreviated Journal |
Int. J. Mod. Phys. D |
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Volume |
31 |
Issue |
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Pages |
2240012 - 15pp |
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Keywords |
Metric-affine gravity; scalar fields; stellar models; junction conditions; compact objects |
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Abstract |
In this paper, metric-afline theories in which the gravity Lagrangian is built using (projectively invariant) contractions of the Ricci tensor with itself and with the metric (Ricci-based gravity theories, or RBGs for short) are reviewed. The goal is to provide a contextualized and coherent presentation of some recent results. In particular, we focus on the correspondence that exists between the field equations of these theories and those of general relativity, and comment on how this can be used to build new solutions of physical interest. We also discuss the formalism of junction conditions in the f (R) case, and provide a brief summary on current experimental and observational bounds on model parameters. |
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Address |
[Olmo, Gonzalo J.] Univ Valencia, CSIC, Ctr Mixto, Dept Fis Teor, Valencia 46100, Spain, Email: gonzalo.olmo@uv.es; |
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Corporate Author |
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Thesis |
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Publisher |
World Scientific Publ Co Pte Ltd |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0218-2718 |
ISBN |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000848888900001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5350 |
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Author |
Bazeia, D.; Marques, M.A.; Olmo, G.J. |
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Title |
Small and hollow magnetic monopoles |
Type |
Journal Article |
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Year |
2018 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
98 |
Issue |
2 |
Pages |
025017 - 8pp |
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Keywords |
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Abstract |
We deal with the presence of magnetic monopoles in a non-Abelian model that generalizes the standard 't Hooft-Polyakov model in three spatial dimensions. We investigate the energy density of the static and spherically symmetric solutions to find first order differential equations that solve the equations of motion. The system is further studied and two distinct classes of solutions are obtained, one that can also be described by analytical solutions and is called a small monopole, since it is significantly smaller than the standard 't Hooft-Polyakov monopole. The other type of structure is the hollow monopole, since the energy density is endowed with a hole at its core. The hollow monopole can be smaller or larger than the standard monopole, depending on the value of the parameter that controls the magnetic permeability of the model. |
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Address |
[Bazeia, D.; Marques, M. A.; Olmo, Gonzalo J.] Univ Fed Paraiba, Dept Fis, BR-58051970 Joao Pessoa, Paraiba, Brazil |
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Publisher |
Amer Physical Soc |
Place of Publication |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
2470-0010 |
ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000439545000007 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
3672 |
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Author |
Benisty, D.; Olmo, G.J.; Rubiera-Garcia, D. |
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Title |
Singularity-Free and Cosmologically Viable Born-Infeld Gravity with Scalar Matter |
Type |
Journal Article |
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Year |
2021 |
Publication |
Symmetry-Basel |
Abbreviated Journal |
Symmetry-Basel |
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Volume |
13 |
Issue |
11 |
Pages |
2108 - 24pp |
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Keywords |
metric-affine gravity; non-singular cosmologies; born-infeld gravity; observational constraints; scalar fields |
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Abstract |
The early cosmology, driven by a single scalar field, both massless and massive, in the context of Eddington-inspired Born-Infeld gravity, is explored. We show the existence of nonsingular solutions of bouncing and loitering type (depending on the sign of the gravitational theory's parameter, epsilon) replacing the Big Bang singularity, and discuss their properties. In addition, in the massive case, we find some new features of the cosmological evolution depending on the value of the mass parameter, including asymmetries in the expansion/contraction phases, or a continuous transition between a contracting phase to an expanding one via an intermediate loitering phase. We also provide a combined analysis of cosmic chronometers, standard candles, BAO, and CMB data to constrain the model, finding that for roughly |epsilon|& LSIM;5 & BULL;10-8m2 the model is compatible with the latest observations while successfully removing the Big Bang singularity. This bound is several orders of magnitude stronger than the most stringent constraints currently available in the literature. |
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Address |
[Benisty, David] Univ Cambridge, Ctr Math Sci, DAMTP, Wilberforce Rd, Cambridge CB3 0WA, England, Email: benidav@post.bgu.ac.il; |
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Publisher |
Mdpi |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
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ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:000726717400001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5040 |
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Author |
Olmo, G.J.; Rosa, J.L.; Rubiera-Garcia, D.; Saez-Chillon Gomez, D. |
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Title |
Shadows and photon rings of regular black holes and geonic horizonless compact objects |
Type |
Journal Article |
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Year |
2023 |
Publication |
Classical and Quantum Gravity |
Abbreviated Journal |
Class. Quantum Gravity |
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Volume |
40 |
Issue |
17 |
Pages |
174002 - 37pp |
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Keywords |
black holes; compact objects; photon rings; shadows; metric-affine gravity; Born-Infeld gravity; regular solutions |
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Abstract |
The optical appearance of a body compact enough to feature an unstable bound orbit, when surrounded by an accretion disk, is expected to be dominated by a luminous ring of radiation enclosing a central brightness depression typically known as the shadow. Despite observational limitations, the rough details of this picture have been now confirmed by the results of the Event Horizon Telescope (EHT) Collaboration on the imaging of the M87 and Milky Way supermassive central objects. However, the precise characterization of both features-ring and shadow-depends on the interaction between the background geometry and the accretion disk, thus being a fertile playground to test our theories on the nature of compact objects and the gravitational field itself in the strong-field regime. In this work we use both features in order to test a continuous family of solutions interpolating between regular black holes and horizonless compact objects, which arise within the Eddington-inspired Born-Infeld theory of gravity, a viable extension of Einstein's general relativity (GR). To this end we consider seven distinctive classes of such configurations (five black holes and two traversable wormholes) and study their optical appearances under illumination by a geometrically and optically thin accretion disk, emitting monochromatically with three analytic intensity profiles previously suggested in the literature. We build such images and consider the sub-ring structure created by light rays crossing the disk more than once and existing on top of the main ring of radiation. We discuss in detail the modifications as compared to their GR counterparts, the Lyapunov exponents of unstable nearly-bound orbits, as well as the differences between black hole and traversable wormholes for the three intensity profiles. In addition we use the claim by the EHT Collaboration on the radius of the bright ring acting (under proper calibrations) as a proxy for the radius of the shadow itself to explore the parameter space of our solutions compatible with such a result. |
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Address |
[Olmo, Gonzalo J.] Univ Valencia, Ctr Mixto Univ Valencia, Dept Fis Teor, CSIC, Burjassot 46100, Valencia, Spain, Email: drubiera@ucm.es |
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Corporate Author |
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Thesis |
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Publisher |
IOP Publishing Ltd |
Place of Publication |
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Editor |
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Language |
English |
Summary Language |
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Original Title |
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Series Editor |
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Series Title |
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Abbreviated Series Title |
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Series Volume |
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Series Issue |
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Edition |
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ISSN |
0264-9381 |
ISBN |
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Medium |
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Area |
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Expedition |
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Conference |
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Notes |
WOS:001043720300001 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5600 |
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