Some cosmological models coming from gravitational theories having torsional degrees of freedom

Espiro, J. Lorca; Vásquez, Yerko

doi:10.1007/s10714-016-2113-7

Cited by 11 publications

(9 citation statements)

References 41 publications

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“…2.1, and α i are dimensionful coupling constants. These models have been considered in cosmological scenarios presenting interesting phenomenology [30,31,33]. The field equations are obtained by performing stationary variations of (33) with respect to the vierbein, Lorentz connection, and scalar fields giving…”

Section: First-order Chern-simons Modified Gravitymentioning

confidence: 99%

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Static and rotating black strings in dynamical Chern–Simons modified gravity

2019

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Four-dimensional homogeneous static and rotating black strings in dynamical Chern-Simons modified gravity, with and without torsion, are presented. Each solution is supported by a scalar field that depends linearly on the coordinate that span the string. The solutions are locally AdS 3 × R and they represent the continuation of the Bañados-Teitelboim-Zanelli black hole. Moreover, they belong to the so-called Chern-Simons sector of the space of solutions of the theory, since the Cotton tensor contributes nontrivially to the field equations. The case with nonvanishing torsion is studied within the firstorder formalism of gravity, and it considers nonminimal couplings of the scalar fields to three topological invariants: Nieh-Yan, Pontryagin and Gauss-Bonnet terms, which are studied separately. These nonminimal couplings generate torsion in vacuum, in contrast to Einstein-Cartan theory. In all cases, torsion contributes to an effective cosmological constant that, in particular cases, can be set to zero by a proper choice of the parameters.

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Section: First-order Chern-simons Modified Gravitymentioning

confidence: 99%

“…[25,26], and it might offer a solution to the strong CP problem [27][28][29]. Finally, cosmological scenarios have been studied in the first-order formulation of scalar-Gauss-Bonnet gravity [30][31][32][33], motivated by dimensional reductions of Lovelock gravity, which appears as low-energy corrections of string theory [34].…”

Section: Introductionmentioning

confidence: 99%

Static and rotating black strings in dynamical Chern–Simons modified gravity

2019

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“…When V = const., this last term becomes a topological invariant proportional to the Euler characteristic and does not contribute to the field dynamics in the bulk, although it becomes relevant in the regularization of Noether charges for asymptotically locally anti-de Sitter spacetimes [82,83]. In the general case, namely V = const., this term contributes to the field equations acting as a source of torsion [51,[58][59][60][61][62][63][64]66]. The particular nonminimal coupling with the GB term we use is but one choice; the results regarding the speed of GWs are still valid even if the 1/ (Λ + κ 4 V ) coupling is replaced by an arbitrary function of (the magnitude of) the scalar field, f (|φ|).…”

Section: Scalar-tensor Model With Gauss-bonnet Couplingmentioning

confidence: 99%

“…When scalar fields are coupled to the Nieh-Yan topological invariant [52], a regularization procedure of the axial anomaly in RC spacetimes can be prescribed [53][54][55][56][57], and a torsion-descendent axion that might solve the strong CP problem in a gravitational fashion is predicted [58][59][60]. The nonminimal coupling to the Gauss-Bonnet invariant, on the other hand, can be motivated from dimensional reduction of stringgenerated gravity models [61], and it could drive the latetime acceleration of the Universe in the absence of the cosmological constant [62][63][64]. The first-order formulation of Chern-Simons modified gravity produces interesting phenomenology when coupled with fermions [65], and it has been shown that the different nonminimal couplings support four-dimensional black string configurations in vacuum, possessing locally AdS 3 × R geometries with nontrivial torsion [66].…”

Section: Introductionmentioning

confidence: 99%

Luminal propagation of gravitational waves in scalar-tensor theories: The case for torsion

et al. 2019

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Scalar-tensor gravity theories with a nonminimal Gauss-Bonnet coupling typically lead to an anomalous propagation speed for gravitational waves, and have therefore been tightly constrained by multimessenger observations such as GW170817/GRB170817A. In this paper we show that this is not a general feature of scalar-tensor theories, but rather a consequence of assuming that spacetime torsion vanishes identically. At least for the case of a nonminimal Gauss-Bonnet coupling, removing the torsionless condition restores the canonical dispersion relation and therefore the correct propagation speed for gravitational waves. To achieve this result we develop a new approach, based on the first-order formulation of gravity, to deal with perturbations on these Riemann-Cartan geometries.topological invariants, e.g., the Pontryagin or Gauss-Bonnet (GB) terms, motivated by effective field theories, string theory, and particle physics [15]. From a phenomenological viewpoint, the scalar-Pontryagin modification to GR-also known as Chern-Simons modified gravity-is an interesting extension that might explain the flat galaxy rotation curves dispensing with dark matter [16], while leaving the propagation speed of GWs unaffected [17]. This interaction generates nontrivial effects when rotation is included [18][19][20][21][22][23], providing a smoking gun in future GW detectors [24][25][26][27]. The couplings between scalar fields and the GB term, on the other hand, have been studied in different setups and several solutions that exhibit spontaneous scalarization have been reported [28][29][30][31][32][33][34][35][36][37][38][39][40][41]. Their stability, however, depends on the choice of the coupling between the scalar field and the GB term [42][43][44]. In spite of this, the theory is experimentally disadvantaged from an astrophysical viewpoint, since it develops an anomalous propagation speed for GWs [45].Scalar-tensor theories have been formulated in geometries that depart from the pseudo-Riemannian framework several times in the past. In particular, the gravitational role of Riemann-Cartan (RC) geometries, characterized by curvature and torsion, was first discussed by Cartan and Einstein themselves [46], and later on in the framework of gauge theories of gravitation [47][48][49][50]. Within its simplest formulation-the Einstein-Cartan-Sciama-Kibble (ECSK) theory-torsion is a nonpropagating field sourced only by the spin density of matter. The nonminimal coupling of scalar fields to geometry dramati-arXiv:1910.00148v3 [gr-qc]

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“…In principle, however, one could consider a firstorder action such that an arbitrary dependence on χ is allowed within a generic gravitational action, as expected from well-known results in scalar-tensor theories [60]. In general, this class of theories can introduce interesting effects associated with the torsion [61][62][63][64]. Even though this possibility is worth exploring, we focus on the UEC theory for the sake of simplicity, and relegate the general dependence on χ to the matter action only.…”

Section: Unimodular Einstein-cartan Theory With Spin Densitymentioning

confidence: 99%

Unimodular Einstein-Cartan gravity: Dynamics and conservation laws

Bonder

Corral

2018

Phys. Rev. D

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Unimodular gravity is an interesting approach to address the cosmological constant problem, since the vacuum energy density of quantum fields does not gravitate in this framework, and the cosmological constant appears as an integration constant. These features arise as a consequence of considering a constrained volume element 4-form that breaks the diffeomorphisms invariance down to volume preserving diffeomorphisms. In this work, the first-order formulation of unimodular gravity is presented by considering the spin density of matter fields as a source of spacetime torsion. Even though the most general matter Lagrangian allowed by the symmetries is considered, dynamical restrictions arise on their functional dependence. The field equations are obtained and the conservation laws associated with the symmetries are derived. It is found that, analogous to torsion-free unimodular gravity, the field equation for the vierbein is traceless, nevertheless, torsion is algebraically related to the spin density as in standard Einstein-Cartan theory. The particular example of massless Dirac spinors is studied, and comparisons with standard Einstein-Cartan theory are shown.

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Some cosmological models coming from gravitational theories having torsional degrees of freedom

Cited by 11 publications

References 41 publications

Static and rotating black strings in dynamical Chern–Simons modified gravity

Static and rotating black strings in dynamical Chern–Simons modified gravity

Luminal propagation of gravitational waves in scalar-tensor theories: The case for torsion

Unimodular Einstein-Cartan gravity: Dynamics and conservation laws

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