Emergent de Sitter Cosmology from Decaying Anti–de Sitter Space

Abstract

Recent developments in string compactifications demonstrate obstructions to the simplest constructions of low energy cosmologies with positive vacuum energy. The existence of obstacles to creating scale-separated de Sitter solutions indicates a UV/IR puzzle for embedding cosmological vacua in a unitary theory of quantum gravity. Motivated by this puzzle, we propose an embedding of positive energy Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology within string theory. Our proposal involves confining 4D gravity on a brane which mediates the decay from a non-supersymmetric false AdS5 vacuum to a true vacuum. In this way, it is natural for a 4D observer to experience an effective positive cosmological constant coupled to matter and radiation, avoiding the need for scale separation or a fundamental de Sitter vacuum.

Dark bubbles: decorating the wall

“…This is the result that was derived in [5] demonstrating the appearance of four dimensional gravity with an effective Newton's constant of G 4 := 2G 5 k + k − /(k − − k + ). It is worth mentioning at this point that in this derivation we have worked in a gauge where the brane is placed at ξ = 0.…”

“…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 + .…”

De Sitter cosmology on an expanding bubble

“…Choosing 'our' bubble to be at the center of AdS, this means that at the same time, another bubble will nucleate near the boundary of AdS. Because the bubbles undergo constant proper acceleration, asymptoting to a lightcone, they will collide in a time of order the AdS radius: t col ∼ L + , measured in the global time coordinate (4).…”

“…which can be rearranged to give 9 This can be trace reversed to compute the four-dimensional Einstein tensor G (4) ab := R (4) ab − (R/2)g ab , i.e. , G (4)…”

de Sitter Extrema and the Swampland

“…However, the original KKLT and LVS scenarios have also been criticized throughout the years (see [5][6][7] for details and references). This criticism has cumulated into the recently stated dS swampland conjecture [8]1 1 This conjecture has been further studied and discussed in [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Here the scalar potential V is a function of the scalar fields φ i that arise in any given string theory compactification and the constant c is conjectured to be O (1).…”