We discuss non-minimal quadratic inflation in supersymmetric ( SUSY ) and non-SUSY models which entails a linear coupling of the inflaton to gravity .
Imposing a lower bound on the parameter c _ { \cal R } , involved in the coupling between the inflaton and the Ricci scalar curvature , inflation can be attained even for subplanckian values of the inflaton while the corresponding effective theory respects the perturbative unitarity up to the Planck scale .
Working in the non-SUSY context we also consider radiative corrections to the inflationary potential due to a possible coupling of the inflaton to bosons or fermions .
We find ranges of the parameters , depending mildly on the renormalization scale , with adjustable values of the spectral index n _ { s } , tensor-to-scalar ratio r \simeq ( 2 - 4 ) \cdot 10 ^ { -3 } , and an inflaton mass close to 3 \cdot 10 ^ { 13 } ~ { } { \mbox { GeV } } .
In the SUSY framework we employ two gauge singlet chiral superfields , a logarithmic Kähler potential including all the allowed terms up to fourth order in powers of the various fields , and determine uniquely the superpotential by applying a continuous R and a global U ( 1 ) symmetry .
When the Kähler manifold exhibits a no-scale-type symmetry , the model predicts n _ { s } \simeq 0.963 and r \simeq 0.004 .
Beyond no-scale SUGRA , n _ { s } and r depend crucially on the coefficient involved in the fourth order term , which mixes the inflaton with the accompanying non-inflaton field in the Kähler potential , and the prefactor encountered in it .
Increasing slightly the latter above ( -3 ) , an efficient enhancement of the resulting r can be achieved putting it in the observable range .
The inflaton mass in the last case is confined in the range ( 5 - 9 ) \cdot 10 ^ { 13 } ~ { } { \mbox { GeV } } . Keywords : Cosmology , Supersymmetric models , Supergravity ; PACS codes : 98.80.Cq , 11.30.Qc , 12.60.Jv , 04.65.+e Published in J. Cosmol .
Astropart .
Phys . 03 , 023 ( 2015 )