Records |
Author |
Delhom, A.; Olmo, G.J.; Singh, P. |
Title |
A diffeomorphism invariant family of metric-affine actions for loop cosmologies |
Type |
Journal Article |
Year |
2023 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
Volume |
06 |
Issue |
6 |
Pages |
059 - 21pp |
Keywords |
quantum cosmology; modified gravity; cosmic singularity |
Abstract |
In loop quantum cosmology (LQC) the big bang singularity is generically resolved by a big bounce. This feature holds even when modified quantization prescriptions of the Hamiltonian constraint are used such as in mLQC-I and mLQC-II. While the later describes an effective description qualitatively similar to that of standard LQC, the former describes an asymmetric evolution with an emergent Planckian de-Sitter pre-bounce phase even in the absence of a potential. We consider the potential relation of these canonically quantized non-singular models with effective actions based on a geometric description. We find a 3-parameter family of metric-affine f (R) theories which accurately approximate the effective dynamics of LQC and mLQC-II in all regimes and mLQC-I in the post-bounce phase. Two of the parameters are fixed by enforcing equivalence at the bounce, and the background evolution of the relevant observables can be fitted with only one free parameter. It is seen that the non-perturbative effects of these loop cosmologies are universally encoded by a logarithmic correction that only depends on the bounce curvature of the model. In addition, we find that the best fit value of the free parameter can be very approximately written in terms of fundamental parameters of the underlying quantum description for the three models. The values of the best fits can be written in terms of the bounce density in a simple manner, and the values for each model are related to one another by a proportionality relation involving only the Barbero-Immirzi parameter. |
Address |
[Delhom, Adria; Singh, Parampreet] Louisiana State Univ, Dept Phys & Astron, Baton Rouge, LA 70803 USA, Email: adria.delhom@gmail.com; |
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 |
1475-7516 |
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:001025410500003 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number ![sorted by Call Number field, descending order (down)](img/sort_desc.gif) |
IFIC @ pastor @ |
Serial |
5583 |
Permanent link to this record |
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Author |
Belchior, F.M.; Moreira, A.R.P.; Maluf, R.V.; Almeida, C.A.S. |
Title |
5D Elko spinor field non-minimally coupled to nonmetricity in f (Q) gravity |
Type |
Journal Article |
Year |
2023 |
Publication |
Physics Letters B |
Abbreviated Journal |
Phys. Lett. B |
Volume |
843 |
Issue |
|
Pages |
138029 - 8pp |
Keywords |
Elko field; Dark matter; Thick brane; Symmetric teleparallel gravity |
Abstract |
This paper aims to investigate the localization of the five-dimensional spinor field known as Elko (dual-helicity eigenspinors of the charge conjugation operator) by employing a Yukawa-like geometrical coupling in which the Elko field is non-minimally coupled to nonmetricity scalar Q. We adopt the braneworld scenarios in which the first-order formalism with sine-Gordon and linear superpotentials is employed to obtain the warp factors. A linear function supports the zero-mode trapping within the geometric coupling, leading to the same effective potential as the scalar field. Moreover, an exotic term must be added to obtain real-valued massive modes. Such modes are investigated through the Schrodinger-like approach. |
Address |
[Belchior, F. M.; Moreira, A. R. P.; Maluf, R. V.; Almeida, C. A. S.] Univ Fed Ceara UFC, Dept Fis, Campus Pico,CP 6030, BR-60455760 Fortaleza, CE, Brazil, Email: belchior@fisica.ufc.br; |
Corporate Author |
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Thesis |
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Publisher |
Elsevier |
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 |
0370-2693 |
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:001039072300001 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number ![sorted by Call Number field, descending order (down)](img/sort_desc.gif) |
IFIC @ pastor @ |
Serial |
5594 |
Permanent link to this record |
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Author |
Olmo, G.J.; Rosa, J.L.; Rubiera-Garcia, D.; Saez-Chillon Gomez, D. |
Title |
Shadows and photon rings of regular black holes and geonic horizonless compact objects |
Type |
Journal Article |
Year |
2023 |
Publication |
Classical and Quantum Gravity |
Abbreviated Journal |
Class. Quantum Gravity |
Volume |
40 |
Issue |
17 |
Pages |
174002 - 37pp |
Keywords |
black holes; compact objects; photon rings; shadows; metric-affine gravity; Born-Infeld gravity; regular solutions |
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. |
Address |
[Olmo, Gonzalo J.] Univ Valencia, Ctr Mixto Univ Valencia, Dept Fis Teor, CSIC, Burjassot 46100, Valencia, Spain, Email: drubiera@ucm.es |
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 |
Is ISI |
yes |
International Collaboration |
yes |
Call Number ![sorted by Call Number field, descending order (down)](img/sort_desc.gif) |
IFIC @ pastor @ |
Serial |
5600 |
Permanent link to this record |
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Author |
Bombacigno, F.; Moretti, F.; Boudet, S.; Olmo, G.J. |
Title |
Landau damping for gravitational waves in parity-violating theories |
Type |
Journal Article |
Year |
2023 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
Volume |
02 |
Issue |
2 |
Pages |
009 - 29pp |
Keywords |
Gravitational waves in GR and beyond: theory; modified gravity; gravitational waves / experiments; dark matter experiments |
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. |
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; |
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 |
1475-7516 |
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:001040875600002 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number ![sorted by Call Number field, descending order (down)](img/sort_desc.gif) |
IFIC @ pastor @ |
Serial |
5624 |
Permanent link to this record |
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Author |
Araujo Filho, A.A.; Furtado, J.; Hassanabadi, H.; Reis, J.A.A.S. |
Title |
Thermal analysis of photon-like particles in rainbow gravity |
Type |
Journal Article |
Year |
2023 |
Publication |
Physics of the Dark Universe |
Abbreviated Journal |
Phys. Dark Universe |
Volume |
42 |
Issue |
|
Pages |
101310 - 8pp |
Keywords |
Rainbow gravity; Thermodynamics; Bounds |
Abstract |
This work is devoted to study the thermodynamic behavior of photon-like particles within the rainbow gravity formalism. To to do this, we chose two particular ansatzs to accomplish our calculations. First, we consider a dispersion relation which avoids UV divergences, getting a positive effective cosmological constant. We provide numerical analysis for the thermodynamic functions of the system and bounds are estimated. Furthermore, a phase transition is also expected for this model. Second, we consider a dispersion relation employed in the context of Gamma Ray Bursts. Remarkably, for this latter case, the thermodynamic properties are calculated in an analytical manner and they turn out to depend on the harmonic series Hn, gamma & UGamma; (z), polygamma & psi;n(z) and zeta Riemann functions & zeta;(z). |
Address |
[Araujo Filho, A. A.] Univ Valencia, CSIC, Dept Fis Teor & IFIC, Ctr Mixto Univ Valencia, Valencia 46100, Spain, Email: dilto@fisica.ufc.br; |
Corporate Author |
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Thesis |
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Publisher |
Elsevier |
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:001062674000001 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number ![sorted by Call Number field, descending order (down)](img/sort_desc.gif) |
IFIC @ pastor @ |
Serial |
5667 |
Permanent link to this record |