The Case for Nonlocal Modifications of Gravity

Woodard, R. P.

doi:10.3390/universe4080088

Cited by 28 publications

(33 citation statements)

References 142 publications

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“…In this paper we will only consider analytic form-factors. However, it is worth mentioning that nonlocal models with nonanalytic differential operators have been investigated by many authors; see, for example, Refs [59][60][61][62][63][64]…”

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confidence: 99%

Nonlocal star as a blackhole mimicker

Buoninfante

Mazumdar

2019

Phys. Rev. D

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In the context of ghost-free, infinite derivative gravity, we will provide a quantum mechanical framework in which we can describe astrophysical objects devoid of curvature singularity and event horizon. In order to avoid ghosts and singularity, the gravitational interaction has to be nonlocal, therefore, we call these objects as nonlocal stars. Quantum mechanically a nonlocal star is a selfgravitational bound system of many gravitons interacting nonlocally. Outside the nonlocal star the spacetime is well described by the Schwarzschild metric, while inside we have a non-vacuum spacetime metric which tends to be conformally flat at the origin. Remarkably, in the most compact scenario the radius of a nonlocal star is of the same order of the Buchdahl limit, therefore slightly larger than the Schwarzschild radius, such that there can exist a photosphere. These objects live longer than a Schwarzschild blackhole and they are very good absorbers, due to the fact that the number of available states is larger than that of a blackhole. As a result nonlocal stars, not only can be excellent blackhole mimickers, but can also be considered as dark matter candidates. In particular, nonlocal stars with masses below 10 14 g can be made stable compared to the age of the Universe.

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confidence: 99%

Nonlocal star as a blackhole mimicker

Buoninfante

Mazumdar

2019

Phys. Rev. D

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“…Nonlocal effective gravitational actions have very interesting cosmological phenomenology such as explaining problems of dark matter [52], dark energy [52,53] and inflation [54]. It has quite unusual classical features [55,56]. A comprehensive review of its quantum properties can be found in [57].…”

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confidence: 99%

Effective action from the functional renormalization group

Ohta

Rachwał

2020

Eur. Phys. J. C

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We study the quantum gravitational system coupled to a charged scalar, Dirac fermions, and electromagnetic fields. We use the “exact” or “functional” renormalization group equation to derive the effective action $$\Gamma _0$$ Γ 0 by integrating the flow equation from the ultraviolet scale down to $$k=0$$ k = 0 . The resulting effective action consists of local terms and nonlocal terms with unique coefficients.

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“…The justification for nonlocality comes from quantum field theory, in which nonlocality inevitably arises as quantum loop corrections of massless particles; see, for example [23]. It has been suggested that a nonlocal quantum effective action might derive from fundamental theory through the gravitational vacuum polarization of infrared gravitons vastly produced during primordial inflation [24,25]. However, since no such derivation is currently available, one may take a phenomenological approach, that is to guess what form of nonlocal actions would do the job of generating an accelerated expansion without dark energy [26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Does nonlocal gravity yield divergent gravitational energy-momentum fluxes?

Chu

Park

2019

Phys. Rev. D

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Energy-momentum conservation requires the associated gravitational fluxes on an asymptotically flat spacetime to scale as 1/r 2 , as r → ∞, where r is the distance between the observer and the source of the gravitational waves. We expand the equations-of-motion for the Deser-Woodard nonlocal gravity model up to quadratic order in metric perturbations, to compute its gravitational energy-momentum flux due to an isolated system. The contributions from the nonlocal sector contains 1/r terms proportional to the acceleration of the Newtonian energy of the system, indicating such nonlocal gravity models may not yield well-defined energy fluxes at infinity. In the case of the Deser-Woodard model, this divergent flux can be avoided by requiring the first and second derivatives of the nonlocal distortion function f [X] at X = 0 to be zero, i.e., f ′ [0] = 0 = f ′′ [0]. It would be interesting to investigate whether other classes of nonlocal models not involving such an arbitrary function can avoid divergent fluxes.

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The Case for Nonlocal Modifications of Gravity

Cited by 28 publications

References 142 publications

Nonlocal star as a blackhole mimicker

Nonlocal star as a blackhole mimicker

Effective action from the functional renormalization group

Does nonlocal gravity yield divergent gravitational energy-momentum fluxes?

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