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 gravity with torsion and the Immirzi field: Signature for gravitational wave detection

Bombacigno, Flavio; Montani, Giovanni

doi:10.1103/physrevd.97.124066

Cited by 15 publications

(34 citation statements)

References 37 publications

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“…Similar results have been found in teleparallel gravity theories[70][71][72] and in f (R) theories with a nonminimal coupling to the Nieh-Yan term[73,74].…”

supporting

confidence: 87%

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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“…Similar results have been found in teleparallel gravity theories[70][71][72] and in f (R) theories with a nonminimal coupling to the Nieh-Yan term[73,74].…”

supporting

confidence: 87%

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

et al. 2019

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“…Instead, the cross polarization, beyond possessing an expansion mode, is characterized by an angle between the two main axes slightly different from π/2. Such phenomenological issues are qualitatively similar to those ones observed in a theory based on a Nieh-Yan term, as in [20], and the two signature are distinct in their specific morphology, so that a study of the real incoming signals could discriminate between these two models and among them and other modified theories of gravity. On the present level of sensitivity also the different character of the upper limit that we could put on these scenarios could constitute a preliminar, but intriguing feature from a theoretical point of view.…”

Section: Introductionsupporting

confidence: 67%

“…where square brackets denote anti-symmetrization on the indices, namely A [µν] ≡ 1/2(A µν − A µν ). Now, plugging (9) in (4) (see [20]), it is possible to recast (6) in the more suitable form:…”

Section: The Holst-f (R) Modelsmentioning

confidence: 99%

“…of (15) is not vanishing, but a coupling between the Immirzi field and ϕ arises. Though, in principle, it allows us to solve ϕ in terms of β once we chose a specific f (R) model (see [20,28]), to accomplish such a purpose is not in general feasible. Therefore, the weak field limit represents a simpler and not less significant context where the effects of the Immirzi field could be studied, regarding both the static (Newtonian) case and the gravitational waves propagation.…”

Section: The Holst-f (R) Modelsmentioning

confidence: 99%

“…This interesting and, to some extent, puzzling feature is suggesting that a coherent Palatini formulation of the theory requires the introduction of a torsion field [16][17][18][19] ab initio in the Lagrangian model. This idea was successifully pursued in [20], where a Nieh-Yan term [21][22][23] is included in the modified Lagrangian, also in the presence of an Immirzi field [24][25][26][27] The implications for the morphology of the gravitational * flavio.bombacigno@uniroma1.it † giovanni.montani@enea.it waves and possible phenomenological signature of the theory have been also discussed there. Furthermore, the cosmological implementation of the proposed theory of modified gravity on a cosmological setting has been also addressed, for viable form of the f (R), in [28].…”

Section: Introductionmentioning

confidence: 99%

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Implications of the Holst term in a f(R) theory with torsion

Bombacigno

Montani

2019

Phys. Rev. D

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We analyze a modified f (R) theory of gravity in the Palatini formulation, when an Holst term endowed with a dynamical Immirzi field is included. We study the basic features of the model, especially in view of eliminating the torsion field via the Immirzi field and the scalar-tensor degrees of freedom of the f (R) model. The main task of this study is the investigation of the morphology of the gravitational wave polarization when their coupling to a circle of test particles is considered. We first observe that the dynamics of the scalar mode of the f (R) Lagrangian is frozen out, since its first order term identically vanishes. This allows a detailed characterization of the linearized theory, which outlines the emergence of a modified Newtonian potential in the static limit, and when time independence is relaxed a standard gravitational wave plus the scalar wave associated to the Immirzi field. Investigating the effect of the coupling of this scalar-tensor wave on a circle of test particles, we arrive to define two effective gravitational polarizations, corresponding to an equivalent phenomenological wave, whose morphology is anomalous with respect the standard case of General Relativity. In fact, the particle circle suffers modifications as it was subjected to modified plus and cross modes, whose specific features depend on the model free parameters and are, in principle, detectable via a data analysis procedure.

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