Constraints on the non-minimally coupled Witten-O'Raifeartaigh inflation

Abstract

We investigate the impact of a non-minimal coupling of the scalar field with gravity in inflationary models, where a small coupling is allowed. As a concrete example, we consider the Witten-O'Raifeartaigh model, where, in line with other models, the presence of a coupling strength ξ can recover concordance of the inflationary parameters with cosmic microwave background (CMB) constraints, provided by the Planck collaboration. We go beyond the slow-roll regime and investigate the impact in the description of CMB anisotropies by performing a statistical analysis of the model with the most recent Planck + Baryon Acoustic Oscillations (BAO) data to seek for any indication of a non-zero coupling by data within the model. We find that not only the presence of a non-minimal coupling is seen, but the model has a slight statistical preference when compared with the standard ΛCDM one. We also discuss the results on the minimally-coupled model, which in general, favours the simple setting where the associated mass scale is equal to the reduced Planck mass Mp while being, in general, disfavored concerning the standard model.

Is natural inflation in agreement with CMB data?

“…(2.8) was recently well discussed in [29], where both metric and Palatini formalisms were investigated. In general, both formalisms yield almost the same results at the level of inflationary parameters; this is due to the fact that a very small non-minimal coupling of the field is favored by the n s and r restrictions, being of order ξ ∼ 10 −4 -10 −3 (see also [19][20][21], for other models where that is also the case). The most striking aspect is the significant impact that such a small coupling can realize in the slow-roll predictions of the model, being able to restore the concordance of the inflationary parameters with data.…”

“…One of these extensions is the possibility that the inflaton field is non-minimally coupled to gravity [8][9][10][11][12][13][14][15][16][17][18][19][20][21], particularly investigated in the context of chaotic inflation. Such construction has gained more attention, since the proposal that a non-minimally coupled Higgs field can drive inflation [22].…”