Hiroki Matsui

Higgs vacuum metastability in primordial inflation, preheating, and reheating

Current measurements of the Higgs boson mass and top Yukawa coupling suggest that the effective Higgs potential develops an instability below the Planck scale. If the energy scale of inflation is as high as the grand unified theory (GUT) scale, inflationary quantum fluctuations of the Higgs field can easily destabilize the standard electroweak vacuum and produce a lot of anti\char21{}de Sitter (AdS) domains. This destabilization during inflation can be avoided if a relatively large nonminimal Higgs-gravity or inflaton-Higgs coupling is introduced. Such couplings generate a large effective mass term for the Higgs, which can raise the effective Higgs potential and suppress the vacuum fluctuation of the Higgs field. After primordial inflation, however, such effective masses drops rapidly and the nonminimal Higgs-gravity or inflaton-Higgs coupling can cause large fluctuations of the Higgs field to be generated via parametric resonance, thus producing AdS domains in the preheating stage. Furthermore, thermal fluctuations of the Higgs field cannot be neglected in the proceeding reheating epoch. We discuss the Higgs vacuum fluctuations during inflation, preheating, and reheating, and show that the Higgs metastability problem is severe unless the energy scale of the inflaton potential is much lower than the GUT scale.

Higgs sector extension of the neutrino minimal standard model with thermal freeze-in production mechanism

The neutrino minimal Standard Model ({\nu}MSM) is the minimum extension of the standard model. In this model, the Dodelson-Widrow mechanism (DW) produces keV sterile neutrino dark matter (DM) and the degenerate GeV heavy Majorana neutrinos lead to leptogenesis. However, the DW mechanism has been ruled out by Lyman-{\alpha} bounds and X-ray constraints. An alternative scenario that evades these constraints has been proposed, where the sterile neutrino DM is generated by the thermal freeze-in mechanism via a singlet scalar. In this paper, we consider a Higgs sector extension of the {\nu}MSM to improve dark matter sectors and leptogenesis scenarios, focusing on the thermal freeze-in production mechanism. We discuss various thermal freeze-in scenarios for the production of keV-MeV sterile neutrino DM with a singlet scalar, and reinvestigate the Lyman-{\alpha} bounds and the X-ray constraints on the parameter regions. Furthermore, we propose thermal freeze-in leptogenesis scenarios in the extended {\nu}MSM. The singlet scalar needs to be TeV scale in order to generate the observed DM relic density and baryon number density with the thermal freeze-in production mechanism.

Electroweak vacuum instability and renormalized Higgs field vacuum fluctuations in the inflationary universe

In this work, we investigated the electroweak vacuum instability during or after inflation. In the inflationary Universe, i.e., de Sitter space, the vacuum field fluctuations

Cosmological Constant Problem and Renormalized Vacuum Energy Density in Curved Background

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Eternal Inflation and Swampland Conjectures

enlarge in proportion to the Hubble scale

Electroweak Vacuum Instability and Renormalized Vacuum Field Fluctuations in Adiabatic or Non-adiabatic Cosmological Background

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Instability of De Sitter Spacetime below the Planck Scale.

. Therefore, the large inflationary vacuum fluctuations of the Higgs field

Revisiting regularization with Kaluza-Klein states and Casimir vacuum energy from extra dimensional spacetime

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Trans-Planckian quantum corrections and inflationary vacuum fluctuations of non-minimally coupled scalar fields.

are potentially catastrophic to trigger the vacuum transition to the negative-energy Planck-scale vacuum state and cause an immediate collapse of the Universe. However, the vacuum field fluctuations

The UV corrections of the Inflationary Vacuum Field Fluctuation

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