Four-Dimensional Null Energy Condition as a Swampland Conjecture

We analyze four-dimensional Friedmann-Lemaistre-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.

Automated summary

The article analyzes the null energy condition in four-dimensional cosmological theories and proposes a new swampland conjecture that 4D NEC is a consistency requirement for any theory to be complete within M theory. It also briefly discusses the cosmological implications of this condition derived from M theory.