AdS swampland conjectures and light fermions

We consider constraints on D-dimensional theories in M-D, dS(D) and AdS(D) backgrounds in the light of AdS swampland conjectures as applied to their compactification in a circle. In particular we consider the non-SUSY AdS instability conjecture and the AdS distance conjecture. For M-D and dS(D) vacua the results may be summarized by a light fermion conjecturewhich states that in theories with Lambda(D)> 0 and a positive first non-vanishing supertrace (-1)(k+1)StrM(2k) > 0, a surplus of light fermions with mass m(f) less than or similar to Lambda(1/D)(D) must be present. For dSDthis is supported by both AdS swampland conjectures. On the contrary, the cases of M-D and AdS(D) can be made consistent with the mild but not the strong version of the AdS Distance conjecture, since the KK tower in the lower d-dim theory will scale as m less than or similar to Lambda(alpha)(d) with alpha = 1/d. The above constraints also suggest that the Standard Model of particle physics would be inconsistent in Minkowski space but consistent in dS if the lightest neutrino is Dirac and lighter than the cosmological constant scale. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

This study examines the constraints on D-dimensional theories in M-D, dS(D) and AdS(D) backgrounds in the context of AdS swampland conjectures, particularly focusing on the non-SUSY AdS instability conjecture and the AdS distance conjecture. The results suggest the importance of the light fermion conjecture for M-D and dS(D) vacua, indicating the presence of a surplus of light fermions in certain conditions.