Improved Predictions on Higgs-Starobinsky Inflation and Reheating with ACT DR6 and Primordial Gravitational Waves

2025/05/07 by Haque, Md Riajul, Pal, Sourav, Paul, Debarun · 16 citations
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph)

paper · doi:10.48550/arxiv.2505.04615

Abstract

We investigate the implications of recent CMB observations for Higgs-Starobinsky inflationary models and their associated reheating dynamics, utilizing data from ACT DR6, Planck 2018, BICEP/Keck 2018, and DESI, collectively referred to as P-ACT-LB-BK18. In addition to direct CMB constraints, we incorporate indirect bounds arising from the potential overproduction of primordial gravitational waves (PGWs), particularly through limits on the effective number of relativistic species, ΔN_{\rm eff}, during Big Bang Nucleosynthesis (BBN). These constraints become especially relevant in scenarios featuring a stiff post-inflationary equation of state w_{\rm RH}≥ 0.58. Our analysis shows that, when both P-ACT-LB-BK18 data and ΔN_{\rm eff} bounds are considered, the viable number of inflationary e-folds is restricted to the range (57.9-62.2) at the 2σ confidence level (C.L.). Correspondingly, the reheating temperature is constrained to lie between the BBN energy scale and 10¹² GeV, with the post-inflationary equation-of-state parameter satisfying w_{\rm RH} > 0.41. However, no parameter space remains viable at the 1σ C.L. once ΔN_{\rm eff} constraints from PGWs are included, rendering the Higgs-Starobinsky model highly restricted.

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