Conditions for defocusing around more general metrics in infinite derivative gravity

Abstract

Infinite Derivative Gravity is able to resolve the Big Bang curvature singularity present in general relativity by using a simplifying ansatz. We show that it can also avoid the Hawking-Penrose singularity, by allowing defocusing of null rays through the Raychaudhuri equation. This occurs not only in the minimal case where we ignore the matter contribution, but also in the case where matter plays a key role. We investigate the conditions for defocusing for the general case where this ansatz applies and also for more specific metrics, including a general Friedmann-Robertson-Walker (FRW) metric and three specific choices of the scale factor which produce a bouncing FRW universe.

Black-hole stability in non-local gravity

“…The case of black holes is especially interesting because, currently, there are three different views: black holes in nonlocal gravity may form but are singular [6,7], they form and are regular [8][9][10][11][12][13][14][15], or they may not even form as asymptotic, classically stable states [16,17]. The first view is the subject of the present paper (we will comment about the second view in the concluding section).…”

Non-perturbative spectrum of non-local gravity

“…wrong sign (analogous to Stelle's Pauli-Fierz massive ghost field), and a scalar field. On the other hand, the gauge-invariant terms of the propagators for χ and Ψ µν are both proportional to the inverse of (31), γ e −H , which has no poles by definition of H. The conclusion is that the spin-2 ghost and the scalar present in Stelle local theory [41] do not propagate at the perturbative level in non-local gravity.…”

“…Causality is not violated in the usual eikonal limit [16] and one expects nonoffensive microcausality violations at the non-locality scale. The Email addresses: g.calcagni@csic.es (Gianluca Calcagni), lmodesto@sustc.edu.cn (Leonardo Modesto), giuseppe.nardelli@unicatt.it (Giuseppe Nardelli) theory may resolve the big bang [17][18][19][20][21][22][23][24][25] and black-hole singularities [26][27][28][29][30][31], and its cosmological solutions may unravel interesting bottom-up scenarios in the early universe (inflation) and at late times (dark energy). Surprisingly, these encouraging features are accompanied by a number of appalling gaps of knowledge on basic questions on the classical theory, such as how to find solutions of the dynamics and whether they match the singularity-free geometries found when linearizing the equations of motion.…”

“…Causality is not violated in the usual eikonal limit [16] and one expects nonoffensive microcausality violations at the non-locality scale. The theory may resolve the big bang [17][18][19][20][21][22][23][24][25] and black-hole singularities [26][27][28][29][30][31], and its cosmological solutions may unravel interesting bottom-up scenarios in the early universe (inflation) and at late times (dark energy).…”

Big Bounce or Double Bang? A Reply to Craig and Sinclair on the Interpretation of Bounce Cosmologies

“…The BGV theorem applies only to classical space-times. Models that modify the Einstein Field Equations to produce a non-classical space-time can produce a non-singular "bounce" (Pop lawski [2010(Pop lawski [ , 2016, Starobinsky [1980], Sotiriou and Faraoni [2010], Corda and Cuesta [2011], Edholm [2018], Lilley and Peter [2015], Kehagias et al [2014], Ijjas and Steinhardt [2017]). In this section, I consider two models -Lee Smolin's evolving universe scenario (2006,1992) and Nikodem Poplawski's model (2010,2016) -in which Einstein's gravity is modified in ways that allow the interior of a black hole to "bounce" and produce a baby universe.…”