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Recently there has been an interesting revival of the idea to use large extradimensions to address the dark energy problem, exploiting the (true)observation that towers of states with masses split, by $M^2_N = f(N) m^2,$with $f$ an unbounded function of the integer $N$, sometimes contribute to thevacuum energy only an amount of order $m^D$ in $D$ dimensions. It has beenargued that this fact is a consequence of swampland conjectures and may requirea departure from Effective Field Theory (EFT) reasoning. We test this claimwith calculations for Casimir energies in extra dimensions. We show why thedomain of validity for EFTs ensures that the tower spacing scale $m$ is alwaysan upper bound on the UV scale for the lower-energy effective theory; use of anEFT with a cutoff part way up a tower is not a controlled approximation. Wehighlight the role played by the sometimes-suppressed contributions from towersin extra-dimensional approaches to the cosmological constant problem, old andnew, and point out difficulties encountered in exploiting it. We compare recentswampland realizations of these arguments with earlier approaches usingstandard EFT examples, discussing successes and limitations of both.

Perils of Towers in the Swamp: Dark Dimensions and the Robustness of Effective Field Theories