Induced-Gravity Higgs Inflation in Palatini Supergravity Confronts ACT DR6

TL;DR

The paper presents a Palatini supergravity realization of induced-gravity Higgs inflation where the inflaton is part of a B-L Higgs pair, with gravity effectively generated in the vacuum via a frame function in the Kähler potential. A shift-symmetric real part and logarithmic couplings to gravity produce a plateau-like potential that yields sub-Planckian inflaton values and inflationary observables in line with ACT DR6, while linking the inflationary scale to GUT physics through the IG condition. Embedding this framework in a B-L extension of the MSSM enables a mechanism to generate the MSSM μ term and realize non-thermal leptogenesis, ultimately predicting split SUSY with $m_{3/2} \\sim (40-60)\,\mathrm{PeV}$ and a high reheating temperature compatible with gravitino cosmology. The model constrains the GUT scale and non-minimal coupling via gauge unification, providing a tightly constrained parameter space that connects early-universe dynamics to low-energy SUSY phenomenology and baryogenesis. Overall, the approach delivers inflation compatible with ACT DR6 without tuning and establishes a coherent link between high-scale inflation, IG, GUT physics, and post-inflationary cosmology.

Abstract

We formulate within Palatini Supergravity a model of induced-gravity inflation excellently consistent with ACT DR6. The inflaton belongs in the decomposition of a conjugate pair of Higgs superfields which lead to the spontaneous breaking of a U(1)B-L symmetry at a scale close to the range (0.102-5.85)x10^16 GeV. The inflaton field is canonically normalized thanks to a real and shift-symmetric contribution into the Kaehler potential. It also includes two separate holomorphic and antiholomorphic logarithmic terms, the argument of which can be interpreted as the coupling of the inflaton to the Ricci scalar. The attainment of inflation allows for subplanckian inflaton values and energy scales below the cut-off scale of the corresponding effective theory. Embedding the model in a B-L extension of the MSSM we show how the mu parameter can be generated and non-thermal leptogenesis can be successfully realized. An outcome of our scheme is split SUSY with gravitino mass in the range (40-60) PeV, which is consistent with the results of LHC on the Higgs boson mass.