Records |
Author ![sorted by Author field, descending order (down)](img/sort_desc.gif) |
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 |
|
Thesis |
|
Publisher |
IOP Publishing Ltd |
Place of Publication |
|
Editor |
|
Language |
English |
Summary Language |
|
Original Title |
|
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
Series Volume |
|
Series Issue |
|
Edition |
|
ISSN |
1475-7516 |
ISBN |
|
Medium |
|
Area |
|
Expedition |
|
Conference |
|
Notes |
WOS:001025410500003 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number |
IFIC @ pastor @ |
Serial |
5583 |
Permanent link to this record |
|
|
|
Author ![sorted by Author field, descending order (down)](img/sort_desc.gif) |
Delhom, A.; Mariz, T.; Nascimento, J.R.; Olmo, G.J.; Petrov, A.Y.; Porfirio, P.J. |
Title |
Spontaneous Lorentz symmetry breaking and one-loop effective action in the metric-affine bumblebee gravity |
Type |
Journal Article |
Year |
2022 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
Volume |
07 |
Issue |
7 |
Pages |
018 - 27pp |
Keywords |
gravity; modified gravity; quantum field theory on curved space; Quantum fields in curved spacetimes |
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. |
Address |
[Delhom, Adria] Univ Tartu, Inst Phys, Lab Theoret Phys, W Ostwaldi 1, EE-50411 Tartu, Estonia, Email: adria.delhom@gmail.com; |
Corporate Author |
|
Thesis |
|
Publisher |
IOP Publishing Ltd |
Place of Publication |
|
Editor |
|
Language |
English |
Summary Language |
|
Original Title |
|
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
Series Volume |
|
Series Issue |
|
Edition |
|
ISSN |
1475-7516 |
ISBN |
|
Medium |
|
Area |
|
Expedition |
|
Conference |
|
Notes |
WOS:000834157900011 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number |
IFIC @ pastor @ |
Serial |
5314 |
Permanent link to this record |
|
|
|
Author ![sorted by Author field, descending order (down)](img/sort_desc.gif) |
Creminelli, P.; Norena, J.; Pena, M.; Simonovic, M. |
Title |
Khronon inflation |
Type |
Journal Article |
Year |
2012 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
Volume |
11 |
Issue |
11 |
Pages |
032 - 16pp |
Keywords |
inflation; modified gravity; non-gaussianity |
Abstract |
We study the possibility that the approximate time shift symmetry during inflation is promoted to the full invariance under time reparametrization t -> (t) over tilde (t), or equivalently under field redefinition of the inflaton phi -> (phi) over tilde(phi). The symmetry allows only two operators at leading order in derivatives, so that all n-point functions of scalar perturbations are fixed in terms of the power spectrum normalization and the speed of sound. During inflation the decaying mode only decays as 1/a and this opens up the possibility to violate some of the consistency relations in the squeezed limit, although this violation is suppressed by the (small) breaking of the field reparametrization symmetry. In particular one can get terms in the 3-point function that are only suppressed by 1/k(L) in the squeezed limit k(L) -> 0 compared to the local shape. |
Address |
[Creminelli, Paolo] Abdus Salam Int Ctr Theoret Phys, I-34151 Trieste, Italy, Email: creminel@ictp.it; |
Corporate Author |
|
Thesis |
|
Publisher |
Iop Publishing Ltd |
Place of Publication |
|
Editor |
|
Language |
English |
Summary Language |
|
Original Title |
|
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
Series Volume |
|
Series Issue |
|
Edition |
|
ISSN |
1475-7516 |
ISBN |
|
Medium |
|
Area |
|
Expedition |
|
Conference |
|
Notes |
WOS:000312263500015 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number |
IFIC @ pastor @ |
Serial |
1274 |
Permanent link to this record |
|
|
|
Author ![sorted by Author field, descending order (down)](img/sort_desc.gif) |
Cervantes-Cota, J.L.; de Putter, R.; Linder, E.V. |
Title |
Induced gravity and the attractor dynamics of dark energy/dark matter |
Type |
Journal Article |
Year |
2010 |
Publication |
Journal of Cosmology and Astroparticle Physics |
Abbreviated Journal |
J. Cosmol. Astropart. Phys. |
Volume |
12 |
Issue |
12 |
Pages |
019 - 20pp |
Keywords |
modified gravity; dark energy theory |
Abstract |
Attractor solutions that give dynamical reasons for dark energy to act like the cosmological constant, or behavior close to it, are interesting possibilities to explain cosmic acceleration. Coupling the scalar field to matter or to gravity enlarges the dynamical behavior; we consider both couplings together, which can ameliorate some problems for each individually. Such theories have also been proposed in a Higgs-like fashion to induce gravity and unify dark energy and dark matter origins. We explore restrictions on such theories due to their dynamical behavior compared to observations of the cosmic expansion. Quartic potentials in particular have viable stability properties and asymptotically approach general relativity. |
Address |
[Cervantes-Cota, Jorge L.] Inst Nacl Invest Nucl, Dept Fis, Mexico City 11801, DF, Mexico, Email: jorge.cervantes@inin.gob.mx |
Corporate Author |
|
Thesis |
|
Publisher |
Iop Publishing Ltd |
Place of Publication |
|
Editor |
|
Language |
English |
Summary Language |
|
Original Title |
|
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
Series Volume |
|
Series Issue |
|
Edition |
|
ISSN |
1475-7516 |
ISBN |
|
Medium |
|
Area |
|
Expedition |
|
Conference |
|
Notes |
ISI:000286930700019 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number |
IFIC @ pastor @ |
Serial |
533 |
Permanent link to this record |
|
|
|
Author ![sorted by Author field, descending order (down)](img/sort_desc.gif) |
Capozziello, S.; Harko, T.; Lobo, F.S.N.; Olmo, G.J.; Vignolo, S. |
Title |
The Cauchy problem in hybrid metric-Palatini f(X)-gravity |
Type |
Journal Article |
Year |
2014 |
Publication |
International Journal of Geometric Methods in Modern Physics |
Abbreviated Journal |
Int. J. Geom. Methods Mod. Phys. |
Volume |
11 |
Issue |
5 |
Pages |
1450042 - 12pp |
Keywords |
Cauchy problem; modified gravity; hybrid metric-Palatini gravity |
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. |
Address |
[Capozziello, Salvatore] Univ Naples Federico II, Dipartimento Sci Fis, Naples, Italy, Email: capozzie@na.infn.it; |
Corporate Author |
|
Thesis |
|
Publisher |
World Scientific Publ Co Pte Ltd |
Place of Publication |
|
Editor |
|
Language |
English |
Summary Language |
|
Original Title |
|
Series Editor |
|
Series Title |
|
Abbreviated Series Title |
|
Series Volume |
|
Series Issue |
|
Edition |
|
ISSN |
0219-8878 |
ISBN |
|
Medium |
|
Area |
|
Expedition |
|
Conference |
|
Notes |
WOS:000336527100003 |
Approved |
no |
Is ISI |
yes |
International Collaboration |
yes |
Call Number |
IFIC @ pastor @ |
Serial |
1813 |
Permanent link to this record |