Stiff Reheating Scenarios for Starobinsky Inflation Excluded at 1σ by BBN Despite CMB+BAO Alignment
Stiff reheating reconciles Starobinsky with recent CMB+BAO but is excluded by BBN at 1σ; remaining 2σ parameter space predicts GW amplitudes reachable by ET, LISA, DECIGO and BBO, directly linking reheating dynamics to multi-band gravitational-wave astronomy.
Starobinsky inflation yields n_s ≈ 0.965 for instantaneous reheating, but joint ACT DR6 and SPT-3G data favor lower values around 0.96. The paper models three reheating histories: pure stiff domination, matter-to-stiff transition from quadratic oscillations, and radiation-to-stiff transition. Each shifts the pivot-scale n_s downward while blue-tilting the tensor spectrum (n_t > 0), with the stiff phase duration parameterized by the reheating temperature and equation-of-state w.
LISA: no stochastic GW background above Ω_GW h² = 10^{-12} at 3 mHz by 2038 in the surviving 2σ window
Sources (3)
- [1]Primary Source(https://arxiv.org/abs/2606.28502)
- [2]Supporting Source(https://arxiv.org/abs/2503.19436)
- [3]Supporting Source(https://arxiv.org/abs/2307.06394)