De Sitter cosmology on an expanding bubble

Abstract

Constructing an explicit compactification yielding a metastable de Sitter (dS) vacuum in a UV consistent string theory is an incredibly difficult open problem. Motivated by this issue, as well as the conjecture that all non-supersymmetric AdS vacua must decay, we discuss the alternative possibility of realizing an effective four-dimensional dS cosmology on a codimensionone bubble wall separating two AdS 5 vacua. The construction further elaborates on the scenario of arXiv:1807.01570, where the aforementioned cosmology arises due to a non-perturbative decay and is embedded in a five-dimensional bulk in a time-dependent way. In this paper we discuss the relation between this scenario and the weak gravity conjecture and further develop the details of the four-dimensional cosmology. We provide a bulk interpretation for the dS temperature as the Unruh temperature experienced by an accelerated observer riding the bubble.A source of four-dimensional matter arises from a string cloud in the bulk, and we examine the consequences for the particle mass spectrum. Furthermore, we show how effective fourdimensional Einstein gravity on the bubble is obtained from the five-dimensional Gauss equation.We conclude by outlining some implications that this paradigm will have for holography, inflation, the standard model, and black holes. arXiv:1907.04268v1 [hep-th] 9 Jul 2019 The decay of AdS 2 Cosmology on a bubble 4 Bulk acceleration and induced temperature 6

Geometries with mismatched branes

“…We also note that such setups generally contain time-dependence that cannot be neglected. In some cases Newton's constant itself has strong time-dependence, showing that constructions of the type presented in [11,12] will need some refinement to be viable. However, we also observe that precisely the time-dependence of the solutions might suggest properties that have the potential to address outstanding cosmological issues.…”

“…Recently RS brane worlds have been employed to understand the evaporation of black holes [3,4] in the context of the AdS/BCFT correspondence [5][6][7]. RS branes also play a crucial role in realizing accelerating universes in string theory, both the classic KKLT construction [8,9] as well as in the recent proposals of [10][11][12]. In particular in the latter context one question that has been raised is that of "mismatched" branes.…”

Dark bubbles: decorating the wall

“…Let us begin by summarizing the shellworld construction of [5,6]. Consider a theory that has two AdS 5 vacua with cosmological constants Λ + (= −6k 2 + = −6/L 2 + ) and Λ − (= −6k 2 − = −6/L 2 − ) with k − > k + .…”

“…The vacuum with higher energy Λ + can decay into the vacuum with lower energy Λ − non-perturbatively via the nucleation of a Brown-Teitelboim instanton. 1 The decay AdS vacua supported by flux through the nucleation of charged membranes, and its relation to the Weak Gravity Conjecture [13] in the context of shellworlds, was discussed in [6]. Let us consider these AdS vacua in global coordinates (where the subscripts + and − denote quantities outside and inside 2 the bubble respectively) '…”

“…5 Interested readers are referred to the elaborate review [18] and references therein. 6 The Bianchi identities require the stress tensor to be covariantly conserved in order for Einstein's equations to be consistent. This is a constraint on the components of the stress tensor that we will use here Figure 1: A schematic representation of the brane, showing the effect of various forms of stress tensor.…”