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Author Borja, E.F.; Diaz-Polo, J.; Garay, I.; Livine, E.R.
Title Dynamics for a 2-vertex quantum gravity model Type Journal Article
Year 2010 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 27 Issue 23 Pages 235010 - 34pp
Keywords (up)
Abstract We use the recently introduced U(N) framework for loop quantum gravity to study the dynamics of spin network states on the simplest class of graphs: two vertices linked with an arbitrary number N of edges. Such graphs represent two regions, in and out, separated by a boundary surface. We study the algebraic structure of the Hilbert space of spin networks from the U(N) perspective. In particular, we describe the algebra of operators acting on that space and discuss their relation to the standard holonomy operator of loop quantum gravity. Furthermore, we show that it is possible to make the restriction to the isotropic/homogeneous sector of the model by imposing the invariance under a global U(N) symmetry. We then propose a U(N)-invariant Hamiltonian operator and study the induced dynamics. Finally, we explore the analogies between this model and loop quantum cosmology and sketch some possible generalizations of it.
Address [Borja, Enrique F.; Garay, Inaki] Univ Erlangen Nurnberg, Inst Theoret Phys 3, D-91058 Erlangen, Germany, Email: etera.livine@ens-lyon.fr
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes ISI:000284211600011 Approved no
Is ISI yes International Collaboration yes
Call Number IFIC @ elepoucu @ Serial 341
Permanent link to this record
 
 
Author Borja, E.F.; Freidel, L.; Garay, I.; Livine, E.R.
Title U(N) tools for loop quantum gravity: the return of the spinor Type Journal Article
Year 2011 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 28 Issue 5 Pages 055005 - 28pp
Keywords (up)
Abstract We explore the classical setting for the U(N) framework for SU(2) intertwiners for loop quantum gravity and describe the corresponding phase space in terms of spinors with the appropriate constraints. We show how its quantization leads back to the standard Hilbert space of intertwiner states defined as holomorphic functionals. We then explain how to glue these intertwiners states in order to construct spin network states as wavefunctions on the spinor phase space. In particular, we translate the usual loop gravity holonomy observables to our classical framework. Finally, we propose how to derive our phase space structure from an action principle which induces non-trivial dynamics for the spin network states. We conclude by applying explicitly our framework to states living on the simple 2-vertex graph and discuss the properties of the resulting Hamiltonian.
Address [Borja, Enrique F.; Garay, Inaki] Univ Erlangen Nurnberg, Inst Theoret Phys 3, D-91058 Erlangen, Germany, Email: etera.livine@ens-lyon.fr
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes ISI:000287308700005 Approved no
Is ISI yes International Collaboration yes
Call Number IFIC @ pastor @ Serial 579
Permanent link to this record
 
 
Author Lledo, M.A.; Sommovigo, L.
Title Torsion formulation of gravity Type Journal Article
Year 2010 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 27 Issue 6 Pages 065014 - 16pp
Keywords (up)
Abstract We explain precisely what it means to have a connection with torsion as a solution of the Einstein equations. While locally the theory remains the same, the new formulation allows for topologies that would have been excluded in the standard formulation of gravity. In this formulation it is possible to couple arbitrary torsion to gauge fields without breaking the gauge invariance.
Address [Lledo, M. A.; Sommovigo, L.] Univ Valencia, Dept Fis Teor, E-46100 Valencia, Spain, Email: Maria.Lledo@ific.uv.es
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes ISI:000275120600015 Approved no
Is ISI yes International Collaboration yes
Call Number IFIC @ elepoucu @ Serial 498
Permanent link to this record
 
 
Author Borja, E.F.; Garay, I.; Strobel, E.
Title Revisiting the quantum scalar field in spherically symmetric quantum gravity Type Journal Article
Year 2012 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 29 Issue 14 Pages 145012 - 19pp
Keywords (up)
Abstract We extend previous results in spherically symmetric gravitational systems coupled with a massless scalar field within the loop quantum gravity framework. As a starting point, we take the Schwarzschild spacetime. The results presented here rely on the uniform discretization method. We are able to minimize the associated discrete master constraint using a variational method. The trial state for the vacuum consists of a direct product of a Fock vacuum for the matter part and a Gaussian centered around the classical Schwarzschild solution. This paper follows the line of research presented by Gambini et al (2009 Class. Quantum Grav. 26 215011 (arXiv: 0906.1774v1)) and a comparison between their result and the one given in this work is made.
Address [Borja, Enrique F.; Garay, Inaki; Strobel, Eckhard] Univ Erlangen Nurnberg, Inst Theoret Phys 3, D-91058 Erlangen, Germany, Email: eckhard@bebsdb.dnsalias.net
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes WOS:000305810600013 Approved no
Is ISI yes International Collaboration yes
Call Number IFIC @ pastor @ Serial 1087
Permanent link to this record
 
 
Author Babichev, E.; Fabbri, A.
Title Instability of black holes in massive gravity Type Journal Article
Year 2013 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 30 Issue 15 Pages 152001 - 7pp
Keywords (up)
Abstract We show that linear perturbations around the simplest black hole solution of massive bi-gravity theories, the bi-Schwarzschild solution, exhibit an unstable mode featuring the Gregory-Laflamme instability of higher dimensional black strings. The result is obtained for the massive gravity theory which is free from the Boulware-Deser ghost, as well as for its extension with two dynamical metrics. These results may indicate that static black holes in massive gravity do not exist. For the graviton mass of the order of the Hubble scale, however, the instability timescale is of order of the Hubble time.
Address [Babichev, Eugeny] Univ Paris 11, Lab Phys Theor Orsay, F-91405 Orsay, France, Email: eugeny.babichev@th.u-psud.fr;
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes WOS:000321692600001 Approved no
Is ISI yes International Collaboration yes
Call Number IFIC @ pastor @ Serial 1498
Permanent link to this record
 
 
Author Beltran Jimenez, J.; de Andres, D.; Delhom, A.
Title Anisotropic deformations in a class of projectively-invariant metric-affine theories of gravity Type Journal Article
Year 2020 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 37 Issue 22 Pages 225013 - 25pp
Keywords (up) alternative theories of gravity; metric-affine gravity; anisotropic solutions
Abstract Among the general class of metric-affine theories of gravity, there is a special class conformed by those endowed with a projective symmetry. Perhaps the simplest manner to realise this symmetry is by constructing the action in terms of the symmetric part of the Ricci tensor. In these theories, the connection can be solved algebraically in terms of a metric that relates to the spacetime metric by means of the so-called deformation matrix that is given in terms of the matter fields. In most phenomenological applications, this deformation matrix is assumed to inherit the symmetries of the matter sector so that in the presence of an isotropic energy-momentum tensor, it respects isotropy. In this work we discuss this condition and, in particular, we show how the deformation matrix can be anisotropic even in the presence of isotropic sources due to the non-linear nature of the equations. Remarkably, we find that Eddington-inspired-Born-Infeld (EiBI) theories do not admit anisotropic deformations, but more general theories do. However, we find that the anisotropic branches of solutions are generally prone to a pathological physical behaviour.
Address [Jimenez, Jose Beltran] Univ Salamanca, Dept Fis Fundamental, E-37008 Salamanca, Spain, Email: jose.beltran@usal.es;
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes WOS:000580878200001 Approved no
Is ISI yes International Collaboration no
Call Number IFIC @ pastor @ Serial 4576
Permanent link to this record
 
 
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 (up) 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 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 0264-9381 ISBN Medium
Area Expedition Conference
Notes WOS:001043720300001 Approved no
Is ISI yes International Collaboration yes
Call Number IFIC @ pastor @ Serial 5600
Permanent link to this record
 
 
Author Navarro-Salas, J.
Title Black holes, conformal symmetry, and fundamental fields Type Journal Article
Year 2024 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 41 Issue 8 Pages 085003 - 14pp
Keywords (up) black holes; horizons; singularities; conformal symmetry; quantum fields; Standard Model
Abstract Cosmic censorship protects the outside world from black hole singularities and paves the way for assigning entropy to gravity at the event horizons. We point out a tension between cosmic censorship and the quantum backreacted geometry of Schwarzschild black holes, induced by vacuum polarization and driven by the conformal anomaly. A similar tension appears for the Weyl curvature hypothesis at the Big Bang singularity. We argue that the requirement of exact conformal symmetry resolves both conflicts and has major implications for constraining the set of fundamental constituents of the Standard Model.
Address [Navarro-Salas, Jose] Univ Valencia, Dept Fis Teor, IFIC, CSIC, E-46100 Burjassot, Valencia, Spain, Email: jnavarro@ific.uv.es
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes WOS:001187435100001 Approved no
Is ISI yes International Collaboration no
Call Number IFIC @ pastor @ Serial 6029
Permanent link to this record
 
 
Author Bazeia, D.; Losano, L.; Olmo, G.J.; Rubiera-Garcia, D.
Title Geodesically complete BTZ-type solutions of 2+1 Born-Infeld gravity Type Journal Article
Year 2017 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 34 Issue 4 Pages 045006 - 21pp
Keywords (up) Born-Infeld gravity; BTZ; wormholes; nonsingular solutions; geodesic completeness
Abstract We study Born-Infeld gravity coupled to a static, non-rotating electric field in 2 + 1 dimensions and find exact analytical solutions. Two families of such solutions represent geodesically complete, and hence nonsingular, spacetimes. Another family represents a point-like charge with a singularity at the center. Despite the absence of rotation, these solutions resemble the charged, rotating BTZ solution of general relativity but with a richer structure in terms of horizons. The nonsingular character of the first two families turn out to be attached to the emergence of a wormhole structure on their innermost region. This seems to be a generic prediction of extensions of general relativity formulated in metric-affine (or Palatini) spaces, where metric and connection are regarded as independent degrees of freedom.
Address [Bazeia, D.; Losano, L.; Olmo, Gonzalo J.] Univ Fed Paraiba, Dept Fis, BR-58051900 Joao Pessoa, Paraiba, Brazil, Email: bazeia@fisica.ufpb.br;
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes WOS:000395398800002 Approved no
Is ISI yes International Collaboration yes
Call Number IFIC @ pastor @ Serial 3013
Permanent link to this record
 
 
Author Maso-Ferrando, A.; Sanchis-Gual, N.; Font, J.A.; Olmo, G.J.
Title Boson stars in Palatini f(R) gravity Type Journal Article
Year 2021 Publication Classical and Quantum Gravity Abbreviated Journal Class. Quantum Gravity
Volume 38 Issue 19 Pages 194003 - 25pp
Keywords (up) boson stars; Palatini formalism; modified gravity
Abstract We explore equilibrium solutions of spherically symmetric boson stars in the Palatini formulation of f (R) gravity. We account for the modifications introduced in the gravitational sector by using a recently established correspondence between modified gravity with scalar matter and general relativity with modified scalar matter. We focus on the quadratic theory f (R) = R + xi R-2 and compare its solutions with those found in general relativity, exploring both positive and negative values of the coupling parameter xi. As matter source, a complex, massive scalar field with and without self-interaction terms is considered. Our results show that the existence curves of boson stars in Palatini f (R) gravity are fairly similar to those found in general relativity. Major differences are observed for negative values of the coupling parameter which results in a repulsive gravitational component for high enough scalar field density distributions. Adding self-interactions makes the degeneracy between f (R) and general relativity even more pronounced, leaving very little room for observational discrimination between the two theories.
Address [Maso-Ferrando, Andreu; Olmo, Gonzalo J.] Univ Valencia, Dept Fis Teor, Ctr Mixto Univ Valencia CSIC, Valencia 46100, Spain, Email: andreu.maso@uv.es
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 0264-9381 ISBN Medium
Area Expedition Conference
Notes WOS:000695280300001 Approved no
Is ISI yes International Collaboration yes
Call Number IFIC @ pastor @ Serial 4964
Permanent link to this record