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Author |
Bombacigno, F.; Boudet, S.; Olmo, G.J.; Montani, G. |
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Title |
Big bounce and future time singularity resolution in Bianchi I cosmologies: The projective invariant Nieh-Yan case |
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Journal Article |
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Year |
2021 |
Publication |
Physical Review D |
Abbreviated Journal |
Phys. Rev. D |
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Volume |
103 |
Issue |
12 |
Pages |
124031 |
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Abstract |
We extend the notion of the Nieh-Yan invariant to generic metric-affine geometries, where both torsion and nonmetricity are taken into account. Notably, we show that the properties of projective invariance and topologicity can be independently accommodated by a suitable choice of the parameters featuring this new Nieh-Yan term. We then consider a special class of modified theories of gravity able to promote the Immirzi parameter to a dynamical scalar field coupled to the Nieh-Yan form, and we discuss in more detail the dynamics of the effective scalar tensor theory stemming from such a revised theoretical framework. We focus, in particular, on cosmological Bianchi I models and we derive classical solutions where the initial singularity is safely removed in favor of a big bounce, which is ultimately driven by the nonminimal coupling with the Immirzi field. These solutions, moreover, turn out to be characterized by finite time singularities, but we show that such critical points do not spoil the geodesic completeness and wave regularity of these spacetimes. |
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2470-0010 |
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WOS:000661819200005 |
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no |
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yes |
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yes |
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Call Number |
IFIC @ pastor @ |
Serial |
4870 |
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Author |
Schiavone, T.; Montani, G.; Bombacigno, F. |
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Title |
f(R) gravity in the Jordan frame as a paradigm for the Hubble tension |
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Journal Article |
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Year |
2023 |
Publication |
Monthly Notices of the Royal Astronomical Society |
Abbreviated Journal |
Mon. Not. Roy. Astron. Soc. |
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Volume |
522 |
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1 |
Pages |
L72-L77 |
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Keywords |
supernovae: general; galaxies: distances and redshifts; cosmological parameters; dark energy; cosmology: theory |
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Abstract |
We analyse the f(R) gravity in the so-called Jordan frame, as implemented to the isotropic Universe dynamics. The goal of the present study is to show that according to recent data analyses of the supernovae Ia Pantheon sample, it is possible to account for an effective redshift dependence of the Hubble constant. This is achieved via the dynamics of a non-minimally coupled scalar field, as it emerges in the f(R) gravity. We face the question both from an analytical and purely numerical point of view, following the same technical paradigm. We arrive to establish that the expected decay of the Hubble constant with the redshift z is ensured by a form of the scalar field potential, which remains essentially constant for z less than or similar to 0.3, independently if this request is made a priori, as in the analytical approach, or obtained a posteriori, when the numerical procedure is addressed. Thus, we demonstrate that an f(R) dark energy model is able to account for an apparent variation of the Hubble constant due to the rescaling of the Einstein constant by the f(R) scalar mode. |
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[Schiavone, Tiziano] Univ Pisa, Dept Phys Fermi, Largo Bruno Pontecorvo 3, I-56127 Pisa, Italy, Email: tschiavone@fc.ul.pt |
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Oxford Univ Press |
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English |
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0035-8711 |
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WOS:001066034100015 |
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no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5672 |
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Author |
Bombacigno, F.; Boudet, S.; Montani, G. |
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Title |
Generalized Ashtekar variables for Palatini f(R) models |
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Journal Article |
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Year |
2021 |
Publication |
Nuclear Physics B |
Abbreviated Journal |
Nucl. Phys. B |
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963 |
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Pages |
115281 - 21pp |
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We consider special classes of Palatini f(R) theories, featured by additional Loop Quantum Gravity inspired terms, with the aim of identifying a set of modified Ashtekar canonical variables, which still preserve the SU(2) gauge structure of the standard theory. In particular, we allow for affine connection to be endowed with torsion, which turns out to depend on the additional scalar degree affecting Palatini f( R) gravity, and in this respect we successfully construct a novel Gauss constraint. We analyze the role of the additional scalar field, outlining as it acquires a dynamical character by virtue of a non vanishing Immirzi parameter, and we describe some possible effects on the area operator stemming from such a revised theoretical framework. Finally, we compare our results with earlier studies in literature, discussing differences between metric and Palatini approaches. It is worth noting how the Hamiltonian turns out to be different in the two cases. The results can be reconciled when the analysis is performed in the Einstein frame. |
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[Bombacigno, Flavio] Univ Valencia, CSIC, Ctr Mixto, Dept Fis Teor, Valencia 46100, Spain, Email: flavio.bombacigno@ext.uv.es; |
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Elsevier |
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English |
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ISSN |
0550-3213 |
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Notes |
WOS:000613579500003 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
4706 |
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Author |
Moretti, F.; Bombacigno, F.; Montani, G. |
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Title |
Gravitational Landau damping for massive scalar modes |
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Journal Article |
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Year |
2020 |
Publication |
European Physical Journal C |
Abbreviated Journal |
Eur. Phys. J. C |
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80 |
Issue |
12 |
Pages |
1203 - 9pp |
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We establish the possibility of Landau damping for gravitational scalar waves which propagate in a non-collisional gas of particles. In particular, under the hypothesis of homogeneity and isotropy, we describe the medium at the equilibrium with a Juttner-Maxwell distribution, and we analytically determine the damping rate from the Vlasov equation. We find that damping occurs only if the phase velocity of the wave is subluminal throughout the propagation within the medium. Finally, we investigate relativistic media in cosmological settings by adopting numerical techniques. |
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[Moretti, Fabio; Montani, Giovanni] Sapienza Univ Rome, Phys Dept, Ple Aldo Moro 5, I-00185 Rome, Italy, Email: fabio.moretti@uniroma1.it; |
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Springer |
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English |
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ISSN |
1434-6044 |
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Notes |
WOS:000615196900004 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
4707 |
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Permanent link to this record |
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Author |
Bombacigno, F.; Moretti, F.; Boudet, S.; Olmo, G.J. |
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Title |
Landau damping for gravitational waves in parity-violating theories |
Type |
Journal Article |
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Year |
2023 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
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Volume |
02 |
Issue |
2 |
Pages |
009 - 29pp |
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Keywords |
Gravitational waves in GR and beyond: theory; modified gravity; gravitational waves / experiments; dark matter experiments |
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Abstract |
We discuss how tensor polarizations of gravitational waves can suffer Landau damping in the presence of velocity birefringence, when parity symmetry is explicitly broken. In particular, we analyze the role of the Nieh-Yan and Chern-Simons terms in modified theories of gravity, showing how the gravitational perturbation in collisionless media can be characterized by a subluminal phase velocity, circumventing the well-known results of General Relativity and allowing for the appearance of the kinematic damping. We investigate in detail the connection between the thermodynamic properties of the medium, such as temperature and mass of the particles interacting with the gravitational wave, and the parameters ruling the parity violating terms of the models. In this respect, we outline how the dispersion relations can give rise in each model to different regions of the wavenumber space, where the phase velocity is subluminal, superluminal or does not exist. Quantitative estimates on the considered models indicate that the phenomenon of Landau damping is not detectable given the sensitivity of present-day instruments. |
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Address |
[Bombacigno, F.; Moretti, F.; Olmo, Gonzalo J.] Ctr Mixto Univ Valencia, CSIC, Dept Fis Teor, Carrer Doctor Moliner 50, Valencia 46100, Spain, Email: flavio2.bombacigno@uv.es; |
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IOP Publishing Ltd |
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English |
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ISSN |
1475-7516 |
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Notes |
WOS:001040875600002 |
Approved |
no |
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Is ISI |
yes |
International Collaboration |
yes |
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Call Number |
IFIC @ pastor @ |
Serial |
5624 |
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Permanent link to this record |