Trans-Planckian censorship and inflation in grand unified theories

Abstract

The recently proposed trans-Planckian censorship conjecture (TCC) amounts to the claim that inflation models with an inflationary energy scale larger than Λ max inf ∼ 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, √ ξ ∼ 10 16 GeV. At the same time, the TCC results in an upper bound on the corresponding gauge coupling constant of gmax ∼ 10 −14 . We are able to show that this constraint translates into an upper bound on the gravitino mass of m max 3/2 ∼ 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 ∼ 100 TeV. 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.

de Sitter Bubbles and the Swampland

“…In [5] it was shown that the simplest TCC-compatible potential that could fit the observations such as the CMB power spectrum is an inverted parabola. A similar hilltop model was discussed in [36]. A concrete example of this can be taken to…”

“…In [5] it was shown that the simplest TCC‐compatible potential that could fit the observations such as the CMB power spectrum is an inverted parabola. A similar hilltop model was discussed in [36]. A concrete example of this can be taken to be defined over where is fixed by observation to be Plugging this into the potential gives For small enough V 0 and large enough the above potential is consistent with the no‐eternal inflation condition as well as the TCC.…”

Trans-Planckian censorship and other swampland bothers addressed in warm inflation

“…This restricts the energy scale of a phase of inflation to be fairly low, hence placing a bound on the tensor-to-scalar ratio of r < O(10 −30 ), as shown in [16]. Even though there are models that satisfy this constraint [18][19][20][21], it has been also pointed out that the bound is less demanding for bouncing cosmologies and other pre-inflationary scenarios, basically for the same reasons that they are less sensitive to the TP problem [16,22]. Along those lines, other scenarios like a multi-stage inflation [23], excited initial states [24] or non-standard expansion histories [25,26] can also mitigate the TCC constraints.…”

Swampland Conjecture and Inflation Model from Brane Perspective

“…Of course, there are models that are compatible with these criteria, but they are always associated with the problems in the initial conditions which has been extensively discussed in Refs. [45] and [46]. The objective of this paper is to improve the aforementioned situation.…”