Abstract
We analyze four-dimensional Friedmann-Lemaître-Robertson-Walker cosmologies in type IIB, arising from a M-theory dual, and find that the null energy condition (NEC) has to be obeyed by them (except for the negatively curved case) in order for the M-theory action to have a Wilsonian effective description. However, this does not imply that the M-theory metric has to obey the 11D NEC. Thus, we propose a new swampland conjecture-the 4D NEC is a consistency condition for any theory to have a completion within M theory-with an explicit derivation of it for cosmological backgrounds from a top-down perspective. We briefly discuss the cosmological consequences of such a condition derived from M theory.
Highlights
Introduction.—Energy conditions are considered important for constraining physically viable solutions of Einstein’s equations
We find a compelling reason to elevate the status of the 4D null energy condition (NEC) to a swampland conjecture—a necessary condition that any 4D effective field theories (EFTs) has to satisfy in order to have a UV completion within string theory
An important implication of this is that since it is well known that violating the NEC is a necessary condition for the existence of bounces in flat Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmologies, we show that such bounces cannot arise in theories descending from M theory with a well-defined Wilsonian effective action, supporting previous similar claims from other considerations [33,34,35,36]
Summary
Introduction.—Energy conditions are considered important for constraining physically viable solutions of Einstein’s equations. One starts with an 11D M-theory metric which allows for a 4D FLRW spacetime and a time-dependent (warped) internal spacetime (in the dual type IIB side) and includes all types of (time-dependent) fluxes and local and nonlocal quantum corrections (including higher curvature terms) that are needed to support such a spacetime [37,38,39].
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