Trans-Planckian censorship and inflation in grand unified theories

The recently proposed trans-Planckian censorship conjecture (TCC) amounts to the claim that inflation models with an inflationary energy scale larger than Lambda(max)(inf) similar to 10(9) GeV belong to the swampland, i.e., cannot be embedded into a consistent theory of quantum gravity. In this paper, we point out that this constraint can be readily satisfied in D-term hybrid inflation (DHI), which is a well-motivated inflation scenario in the context of supersymmetric grand unification. In DHI, the amplitude of the primordial scalar power spectrum originates from a Fayet-Iliopoulos term of the order of the unification scale, root xi similar to 10(16) GeV. At the same time, the TCC results in an upper bound on the corresponding gauge coupling constant of g(max) similar to 10(-14). We are able to show that this constraint translates into an upper bound on the gravitino mass of m(3/2)(max) similar to 10 MeV, which opens the possibility that dark matter is accounted for by thermally produced gravitinos, if the reheating temperature is close to T-reh similar to 100TeV. Interestingly enough, a somewhat similar gravitino mass range has recently been derived in a model that aims at explaining dark energy in terms of axion quintessence and resolving the Hubble tension by means of decaying gravitino dark matter. (C) 2020 The Author. Published by Elsevier B.V.