Masahiro Takimoto

Gravitational waves from bubble collisions: An analytic derivation

We consider gravitational wave production by bubble collisions during a cosmological first-order phase transition. In the literature, such spectra have been estimated by simulating the bubble dynamics, under so-called thin-wall and envelope approximations in a flat background metric. However, we show that, within these assumptions, the gravitational wave spectrum can be estimated in an analytic way. Our estimation is based on the observation that the two-point correlator of the energy-momentum tensor

Non-thermal production of Wino dark matter via the decay of long-lived particles

\langle T(x)T(y)\rangle

Thermal effects on saxion in supersymmetric model with Peccei–Quinn symmetry

can be expressed analytically under these assumptions. Though the final expressions for the spectrum contain a few integrations that cannot be calculated explicitly, we can easily estimate it numerically. As a result, it is found that the most of the contributions to the spectrum come from single-bubble contribution to the correlator, and in addition the fall-off of the spectrum at high frequencies is found to be proportional to

Gravitational waves from the first order phase transition of the Higgs field at high energy scales

f^{-1}

Fate of Z 2 symmetric scalar field

. We also provide fitting formulae for the spectrum.

Scalar trapping and Saxion cosmology

A bstractWe consider supersymmetric models in which the neutral Wino is the lightest superparticle (LSP), and study the possibility that non-thermally produced Wino plays the role of dark matter. The thermal relic density of Wino is smaller than the present mass density of dark matter if

Gravitational waves from first-order phase transitions: Towards model separation by bubble nucleation rate

{m_{{\widetilde{W}}}}

Curvaton dynamics revisited

≲ 2.9 TeV; however, even with smaller Wino mass, the Wino can be the dominant component of dark matter if it is non-thermally produced by the decay of a long-lived particle. In order to study such a possibility in detail, we perform a precise calculation of the present mass density of Wino produced by the decay of a long- lived particle, taking account of the following effects: (i) coannihilation among charged and neutral Winos, and (ii) Sommerfeld effect on the pair annihilation cross section of Winos. We consider several well-motivated cases where the long-lived particle corresponds to cosmological moduli fields, gravitino, or axino, and discuss the implication of the Wino LSP for these cases.

Higgs inflation and suppression of axion isocurvature perturbation

Abstract We consider supersymmetric model with Peccei–Quinn symmetry and study effects of saxion on the evolution of the universe, paying particular attention to the effects of thermal bath. The axion multiplet inevitably couples to colored particles, which induces various thermal effects. In particular, (i) saxion potential is deformed by thermal effects, and (ii) coherent oscillation of the saxion dissipates via the interaction with hot plasma. These may significantly affect the evolution of the saxion in the early universe.

Cosmic rays, anti-helium, and an old navy spotlight

In a wide class of new physics models, there exist scalar fields that obtain vacuum expectation values of high energy scales. We study the possibility that the standard model Higgs field has experienced first order phase transition at the high energy scale due to the couplings with these scalar fields. We estimate the amount of gravitational waves produced by the phase transition, and discuss observational consequences.