Fresh look at the scalar-tensor theory of gravity in Jordan and Einstein frames from undiscussed standpoints

Bhattacharya, Krishnakanta; Majhi, Bibhas Ranjan

doi:10.1103/physrevd.95.064026

Cited by 44 publications

(49 citation statements)

References 83 publications

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“…The potential V E (ψ) can be rewritten in terms of ψ by using the inverse relation f R = e √ 2κ/3 ψ . Performing the conformal transformation (23), the energy-momentum tensor converts into [72][73][74][75][76][77]…”

Section: Charged Black Hole Solutions In the Einstein Framementioning

confidence: 99%

Spherically symmetric black holes with electric and magnetic charge in extended gravity: physical properties, causal structure, and stability analysis in Einstein’s and Jordan’s frames

et al. 2020

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Novel static black hole solutions with electric and magnetic charges are derived for the class of modified gravities: f (R) = R + 2β √ R, with or without a cosmological constant. The new black holes behave asymptotically as flat or (A)dS space-times with a dynamical value of the Ricci scalar given by R = 1 r 2 and R = 8r 2 Λ+1 r 2 , respectively. They are characterized by three parameters, namely their mass and electric and magnetic charges, and constitute black hole solutions different from those in Einstein's general relativity. Their singularities are studied by obtaining the Kretschmann scalar and Ricci tensor, which shows a dependence on the parameter β that is not permitted to be zero. A conformal transformation is used to display the black holes in Einstein's frame and check if its physical behavior is changed w.r.t. the Jordan one. The thermal stability of the solutions is discussed by using thermodynamical quantities, in particular the entropy, the Hawking temperature, the quasi-local energy, and the Gibbs free energy. Also, the casual structure of the new black holes is studied, and a stability analysis is performed in both frames using the odd perturbations technique and the study of the geodesic deviation. It is concluded that, generically, there is coincidence of the physical properties of the novel black holes in both frames, although this turns not to be the case for the Hawking temperature.

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Section: Charged Black Hole Solutions In the Einstein Framementioning

confidence: 99%

Spherically symmetric black holes with electric and magnetic charge in extended gravity: physical properties, causal structure, and stability analysis in Einstein’s and Jordan’s frames

et al. 2020

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“…The theory.-In R 2 gravity a quadratic curvature term of the form aR 2 is added to the standard Einstein action, where a is a positive constant that controls the deviation from GR. Recasting R 2 gravity into a particular Brans-Dicke STT [38,39,50,51], the resulting action in the Einstein frame with metric g µν and scalar field φ is given by…”

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confidence: 99%

Axial quasinormal modes of neutron stars in R2 gravity

et al. 2018

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The spectrum of frequencies and characteristic times that compose the ringdown phase of gravitational waves emitted by neutron stars carry information about the matter content (the equation of state) and the underlying theory of gravity. Typically, modified theories of gravity introduce additional degrees of freedom/fields, such as scalars, which result in new families of modes composing the ringdown spectrum. One simple but physically promising candidate is R 2 gravity, which effectively introduces an additional massive scalar field that couples non-minimally to gravity, resulting in scalarized neutron stars. Here we show that the ringdown spectrum of R 2 neutron stars is much richer and fundamentally different from the spectrum in GR, possessing for instance ultra long lived modes that can propagate away from the star in the form of scalar gravitational radiation.

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“…It is clear, and important to note here, that extracting entropy according to the prescription (6) does not in any way involve putting the surface gravity factor in by hand, as claimed in Ref [18]…”

mentioning

confidence: 72%

“…Furthermore, this result is actually identical to what has also been found in Refs. [18][19][20][21] by following a different route at the price of introducing the scalar field φ = Ω −2 and then treating the resulting Lagrangian (7) as a scalartensor theory of gravity. However, our approach has the benefit of making transparent the various contributions of the conformal factor to the derivation, first inside the charge and its integral, and then in the final result.…”

Section: Noether Charge and Weyl Rescalingmentioning

confidence: 99%

“…Therefore, although this result seems at odds and contrary to what one expects to find in the conformal frame based on black hole thermodynamics' area law, one can always argue, as was done in Refs. [18][19][20][21], that this comes about because one is not in GR anymore but in its scalar-tensor extension. A far more physically convincing justification for this result, however, is that the latter actually just confirms, as explained in the second paragraph above Eq.…”

Section: Noether Charge and Weyl Rescalingmentioning

confidence: 99%

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More on spacetime thermodynamics in the light of Weyl transformations

Hammad

Dijamco

2019

Phys. Rev. D

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It was recently found that, after performing a Weyl conformal transformation, the familiar analogy between black hole mechanics and black hole thermodynamics becomes ambiguous. It was argued that this fact can be traced back to the fundamental dichotomy between matter and geometry, which is at the heart of Einstein's field equations. As a further study of this issue, we investigate here the general link between spacetime thermodynamics and Weyl transformations from two other angles. We first examine the conformal behaviour of the horizon entropy within Wald's approach based on the fundamental diffeomorphism symmetry of pure geometry. We then revisit -using Weyl transformations -Jacobson's derivation of Einstein's field equations, the starting point of which is precisely built on the fundamental dichotomy between matter and geometry. As a result, we show that in order for Jacobson's approach to be able to yield the right Einstein field equations in the conformal frame, a specific conformal behavior of the horizon temperature and its entropy -different from what Wald's approach implies -is required. The two approaches to spacetime thermodynamics become thus incompatible in the conformal frame. In addition, we show -in greater detail in the conformal frame -that in the presence of a null dust the thermodynamics approach for extracting Einstein's field equations necessarily fails. An extensive discussion of the whole issue is given.

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Fresh look at the scalar-tensor theory of gravity in Jordan and Einstein frames from undiscussed standpoints

Cited by 44 publications

References 83 publications

Spherically symmetric black holes with electric and magnetic charge in extended gravity: physical properties, causal structure, and stability analysis in Einstein’s and Jordan’s frames

Spherically symmetric black holes with electric and magnetic charge in extended gravity: physical properties, causal structure, and stability analysis in Einstein’s and Jordan’s frames

Axial quasinormal modes of neutron stars in R2 gravity

More on spacetime thermodynamics in the light of Weyl transformations

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