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Register a new userHawking-Hayward quasi-local energy under conformal transformations
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We derive a formula describing the transformation of the Hawking-Hayward quasi-local energy under a conformal rescaling of the spacetime metric. A known formula for the transformation of the Misner-Sharp-Hernandez mass is recovered as a special case.
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We consider an approach to the Hawking effect which is free of the asymptotic behavior of the metric or matter fields, and which is not confined to one specific metric configuration. As a result, we find that for a wide class of spacetime horizons there exists an emission of particles out of the horizon. As expected, the energy distribution of the radiating particles turns out to be thermal.
We study how the standard definitions of ADM mass and Brown-York quasi-local energy generalize to pure Lovelock gravity. The quasi-local energy is renormalized using the background subtraction prescription and we consider its limit for large surfaces. We find that the large surface limit vanishes for asymptotically flat fall-off conditions except in Einstein gravity. This problem is avoided by focusing on the variation of the quasi-local energy which correctly approaches the variation of the ADM mass for large surfaces. As a result, we obtain a new simple formula for the ADM mass in pure Lovelock gravity. We apply the formula to spherically symmetric geometries verifying previous calculations in the literature. We also revisit asymptotically AdS geometries.
The weak field limit of scalar tensor theories of gravity is discussed in view of conformal transformations. Specifically, we consider how physical quantities, like gravitational potentials derived in the Newtonian approximation for the same scalar-tensor theory, behave in the Jordan and in the Einstein frame. The approach allows to discriminate features that are invariant under conformal transformations and gives contributions in the debate of selecting the true physical frame. As a particular example, the case of $f(R)$ gravity is considered.
We study timelike and null geodesics in a non-singular black hole metric proposed by Hayward. The metric contains an additional length-scale parameter $ell$ and approaches the Schwarzschild metric at large radii while approaches a constant at small radii so that the singularity is resolved. We tabulate the various critical values of $ell$ for timelike and null geodesics: the critical values for the existence of horizon, marginally stable circular orbit and photon sphere. We find the photon sphere exists even if the horizon is absent and two marginally stable circular orbits appear if the photon sphere is absent and a stable circular orbit for photons exists for a certain range of $ell$. We visualize the image of a black hole and find that blight rings appear even if the photon sphere is absent.
In this paper, we study Joule-Thomson expansion for Hayward-AdS black hole in the extended phase space, and obtain a Joule-Thomson expansion formula for the black hole. We plot the inversion and isenthalpic curves in the T-P plane, and determine the cooling-heating regions. The intersection points of the isenthalpic and inversion curves are exactly the inversion points discriminating the heating process from the cooling one.
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