Hearing Higgs with gravitational wave detectors

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A pseudo Nambu-Goldstone boson (such as an axion-like particle) is a theoretically well-motivated inflaton as it features a naturally flat potential (natural inflation). This is because Goldstone's theorem protects its potential from sizable quantum corrections. Such corrections, however, generically generates an R 2 term in the action, which leads to another inflaton candidate because of the equivalence between the R 2 term and a scalar field, the scalaron, with a quasi flat potential (Starobinsky inflation). Here it is investigated a new multifield scenario in which both the scalaron and a pseudo Nambu-Goldstone boson are active (natural-scalaron inflation). For generality, also a non-minimal coupling is included, which is shown to emerge from microscopic theories. It is demonstrated that a robust inflationary attractor is present even when the masses of the two inflatons are comparable. Moreover, the presence of the scalaron allows to satisfy all observational bounds in a large region of the parameter space, unlike what happens in pure-natural inflation.

Section: Discussionmentioning

confidence: 99%

Natural-scalaron inflation

Salvio

2021

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“…For these reasons it is more realistic to consider CHI in some economical SM extension that can account for all observations. As a benchmark model we consider here the aνMSM one [37][38][39][40], which can account for all the experimentally confirmed signals of beyond-the-SM physics (neutrino oscillations and dark matter) and can solve other important issues of the SM (baryon asymmetry, the strong CP problem, 3 the metastability of the EW vacuum and inflation) at the same time.…”

Section: Jcap09(2022)027mentioning

confidence: 99%

BICEP/Keck data and quadratic gravity

Salvio¹

2022

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The recent results of the BICEP and Keck collaborations have put stringent bounds on many inflationary models, including some well-motivated ones. This is certainly the case when gravity remains described by Einstein's theory up to the inflationary scale, but can be avoided by introducing quadratic-in-curvature terms that are effective at that scale. Recently it has also been shown that these terms can UV complete gravity respecting stability and unitarity. Here the predictions of such quadratic gravity are computed and compared with the BICEP/Keck constraints by focusing on some of the inflationary scenarios that are best-motivated from the particle physics point of view and are already ruled out in Einstein gravity: (critical) Higgs inflation and natural inflation. The first scenario can be considered as the most economical option as the inflaton is identified with the only known elementary scalar field in the Standard Model and the near criticality of the Standard Model is used to remain in the perturbative regime. In the second one a pseudo-Nambu-Goldstone boson contributes to the inflationary dynamics and its potential is naturally flat. It is shown that in both scenarios one can restore the agreement with the observational constraints in quadratic gravity.

“…For this reason we think it is important to focus on those that are best motivated from the particle-physics perspective. The SM Higgs field is a well-motivated inflaton candidate [24][25][26][27][28] (being the sole fundamental scalar within the SM) and the comparison between its theoretical predictions for the inflationary GW spectrum and the expected sensitivities of future detectors has been performed in [29].…”

Section: Introductionmentioning

confidence: 99%

(Multi-field) natural inflation and gravitational waves

Salvio,

Sciusco

2024

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We provide a detailed study of natural inflation with a periodic non-minimal coupling, which is a well-motivated inflationary model that admits an explicit UV completion. We demonstrate that this construction can satisfy the most recent observational constraints from Planck and the BICEP/Keck collaborations. We also compute the corresponding relic gravitational wave background due to tensor perturbations and show that future space-borne interferometers, such as DECIGO, BBO and ALIA, may be able to detect it. Next, we extend this analysis and establish the validity of these results in a multi-field model featuring an additional R 2 term in the action, which allows us to interpolate between natural and scalaron (a.k.a. Starobinsky) inflation. We investigate the conditions under which the aforementioned future interferometers will have the capability to differentiate between pure natural inflation and natural-scalaron inflation. The latter analysis could open the door to distinguishing between single-field and multi-field inflation through gravitational wave observations in more general contexts.