The inflaton that could: primordial black holes and second order gravitational waves from tachyonic instability induced in Higgs-R<sup>2</sup>inflation

The general scalar-tensor theory that includes all the dimension-four terms has parameter regions that can produce successful inflation consistent with cosmological observations. This theory is in fact the same as the Higgs-Starobinsky inflation, when the scalar is identified with the Standard Model Higgs boson. We consider possible dimension-six operators constructed from non-derivative terms of the scalar field and the Ricci scalar as perturbations. We investigate how much suppression is required for these operators to avoid disrupting the successful inflationary predictions. To ensure viable cosmological predictions, the suppression scale for the sixth power of the scalar should be as high as the Planck scale. For the other terms, much smaller scales are sufficient.

Section: Higgs-r 2 Inflationmentioning

confidence: 99%

Ultraviolet sensitivity in Higgs-Starobinsky inflation

Lee,

Modak,

Oda

et al. 2023

“…can realize a large enhancement on the power spectrum and produce PBHs if the parameter h is large enough [45,50]. Besides the noncanonical single field inflation models, the multi-filed inflationary models are another important way to enhance the power spectrum [68][69][70], especially those with tachyonic instabilities [71][72][73]. In this paper, we focus on the scalar-tensor inflation and find that with the Ricci scalar coupling function being a quadratic form Ω(φ) = 1 − 2φ/φ c + (1 + δ 2 )(φ/φ c ) 2 , the ultra-slow-roll condition can be satisfied transiently at the critical point φ c , and the power spectrum can be enhanced enough to produce PBHs.…”

Section: Jcap03(2023)048mentioning

confidence: 99%

Primordial black holes and scalar-induced gravitational waves from the generalized Brans-Dicke theory

Zhu

2023

The power spectrum of the scalar-tensor inflation with a quadratic form Ricci scalar coupling function Ω(ϕ) = 1 - 2ϕ/ϕ c + (1 + δ 2)(ϕ/ϕ c )2 can be enhanced enough to produce primordial black holes and generate scalar-induced gravitational waves. The masses of primordial black holes and the frequencies of scalar-induced gravitational waves are controlled by the parameter ϕ c , and their amplitudes are determined by the parameter δ. Primordial black holes with stellar masses, planetary masses, and masses around 10-12 M ⊙ are produced and their abundances are obtained from the peak theory. The frequencies of the corresponding scalar-induced gravitational waves are around 10-9 Hz, 10-6 Hz, and 10-3 Hz, respectively. The primordial black holes with masses around 10-12 M ⊙ can account for almost all of the dark matter, and the scalar-induced gravitational waves with frequencies around 10-9 Hz can explain the NANOGrav 12.5 yrs signal.

“…See, e.g., refs. [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] for such works.…”

Section: Modelmentioning

confidence: 99%

Nonminimally assisted inflation: a general analysis

Hyun

Kim

Kodama

et al. 2023

Self Cite

The effects of a scalar field, known as the “assistant field,” which nonminimally couples to gravity, on single-field inflationary models are studied. The analysis provides analytical expressions for inflationary observables such as the spectral index (ns ), the tensor-to-scalar ratio (r), and the local-type nonlinearity parameter (f NL (local)). The presence of the assistant field leads to a lowering of ns and r in most of the parameter space, compared to the original predictions. In some cases, ns may increase due to the assistant field. This revives compatibility between ruled-out single-field models and the latest observations by Planck-BICEP/Keck. The results are demonstrated using three example models: loop inflation, power-law inflation, and hybrid inflation.