Weak field limit of infinite derivative gravity

Kilicarslan, Ercan

doi:10.1103/physrevd.98.064048

Cited by 31 publications

(30 citation statements)

References 40 publications

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“…[12,13] where it was shown that higher derivative gauge theories can be made ghost-free. In the gravitational context the same class of nonlocal actions were useful to obtain ghost-free nonsingular cosmological [14][15][16][17][18] and blackhole [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] solutions. Such nonlocal models were also applied in the framework of inflationary cosmology [34], and thermal field theory [35][36][37].…”

Section: Introductionmentioning

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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Section: Introductionmentioning

confidence: 99%

Nonlocal star as a blackhole mimicker

Buoninfante

Mazumdar

2019

Phys. Rev. D

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“…From Eq. (32), it follows that if p 2 is a solution, then also its complex conjugate (p 2 ) * will be a solution.…”

Section: Pole Structurementioning

confidence: 99%

“…[20] for a more general treatment including some non-maximally symmetric spacetime. It was also noticed that the presence of nonlocality can regularize infinities and many efforts have been made towards the resolution of black hole [17,18,[21][22][23][24][25][26][27][28][29][30][31][32][33] and cosmological [16,[34][35][36][37] singularities. At the quantum level, the high energy behavior of loop integrals has been investigated in [38][39][40][41] and properties of causality and unitarity in [42,43] and [44][45][46][47], respectively.…”

Section: Introductionmentioning

confidence: 99%

Generalized ghost-free propagators in nonlocal field theories

et al. 2020

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In this paper we present an iterative method to generate an infinite class of new nonlocal field theories whose propagators are ghost-free. We first examine the scalar field case and show that the pole structure of such generalized propagators possesses the standard two derivative pole and in addition can contain complex conjugate poles which, however, do not spoil at least tree level unitarity as the optical theorem is still satisfied. Subsequently, we define analogous propagators for the fermionic sector which is also devoid of unhealthy degrees of freedom. As a third case, we apply the same construction to gravity and define a new set of theories whose graviton propagators around the Minkowski background are ghost-free. Such a wider class also includes nonlocal theories previously studied, and Einstein's general relativity as a peculiar limit. Moreover, we compute the linearized gravitational potential generated by a static point-like source for several gravitational theories belonging to this new class and show that the nonlocal nature of gravity regularizes the singularity at the origin.

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“…[12][13][14][15] which demonstrated the possibility of constructing a quadratic curvature theory of gravity that is classically stable and unitary at the quantum level. It has also been noted that nonlocality can regularise infinities, and many efforts have been made to resolve black hole [13,14,[16][17][18][19][20][21][22][23][24][25][26][27]52] and cosmological [12,[28][29][30] singularities. Furthermore, renormalisability [31][32][33], causality [34,35], unitarity [36][37][38][39][40], scattering amplitudes [41][42][43], spontaneous breaking of symmetry [44,45] and counting of initial conditions [46,47] have also been discussed and analysed.…”

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confidence: 99%

Nonlocal gravity with worldline inversion symmetry

Abel

Buoninfante

Mazumdar

2020

J. High Energ. Phys.

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We construct a quadratic curvature theory of gravity whose graviton propagator around the Minkowski background respects wordline inversion symmetry, the particle approximation to modular invariance in string theory. This symmetry automatically yields a corresponding gravitational theory that is nonlocal, with the action containing infinite order differential operators. As a consequence, despite being a higher order derivative theory, it is ghost-free and has no degrees of freedom besides the massless spin-2 graviton of Einstein's general relativity. By working in the linearised regime we show that the point-like singularities that afflict the (local) Einstein's theory are smeared out. IntroductionEinstein's general relativity (GR) is the most widely studied theory of gravity, and its predictions have been tested to very high precision in the infrared (IR) regime, i.e. at large distances and late times [1]. Despite passing these tests, there are unsolved conceptual problems which indicate that Einstein's GR is merely an effective field theory of gravitation: it works very well at low energy but breaks down in the ultraviolet (UV). Indeed at the classical level the Einstein-Hilbert Lagrangian, √ −gR, suffers from the presence of blackhole and cosmological singularities [2] (implying problems in the short-distance regime), while at the quantum level it is non-renormalisable from a perturbative point of view (implying problems in the high-energy regime) [3,4]. Therefore there is a consensus that ultimately GR will need to be extended.One possible extension of GR is to add terms that are quadratic in curvature, such as R 2 and R µν R µν . The resulting actions are power counting renormalisable as shown in Ref. [5]. However they are still non-physical because of the presence of a massive spin-2 ghost degree of freedom which classically causes Hamiltonian instabilities, and which quantum mechanically breaks the unitarity condition of the S-matrix.The appearance of ghost modes is related to the presence of higher order time derivatives in the field equations [6]. However it is known that these unwelcome degrees of freedom can be avoided in higher derivative theories if the order of the derivatives is not finite but infinite. By introducing certain non-polynomial differential operators into the action, for example e /M 2 with M being a new fundamental scale, one can prevent the appearance of extra poles in the physical spectrum [7-10], because the presence of non-polynomial derivatives makes the action nonlocal. In fact such nonlocal models were the subject of very early studies, in which it was noted that they can improve the UV behavior of loop integrals (see Refs. [11]).

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Weak field limit of infinite derivative gravity

Cited by 31 publications

References 40 publications

Nonlocal star as a blackhole mimicker

Nonlocal star as a blackhole mimicker

Generalized ghost-free propagators in nonlocal field theories

Nonlocal gravity with worldline inversion symmetry

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