Gravitational Wave Background from Population III Stars

We estimate the gravitational wave (GW) background from Population III (Pop III) stars using the results from our hydrodynamic simulations (Suwa et al. 2007). We calculate gravitational waveforms from matter motions and anisotropic neutrino emissions for single Pop III stars. We find that the GW amplitudes from matter motions are dominant until just after bounce, but those from neutrinos dominate later on at frequencies below $\sim 10$ Hz in the GW spectrum. Computing the overall signal produced by the ensemble of such Pop III stars, we find that the resultant density parameter of the GW background peaks at the amplitude of $\Omega_\mathrm{GW}\sim 10^{-10}$ in the frequency interval $\sim 1-10$ Hz. We show that such signals, depending on the formation rate of Pop III stars, can be within the detection limits of future planned interferometers such as DECIGO and BBO in the frequency interval of $\sim 0.1-1$ Hz. Our results suggest that the detection of the GW background from Pop III stars can be an important tool to supply the information about the star formation history in the early universe.Comment: 4 pages, 3 figures, accepted for publication in ApJ

Explosion geometry of a rotating 13 M⊙M_{\odot} star driven by the SASI-aided neutrino-heating supernova mechanism

By performing axisymmetric hydrodynamic simulations of core-collapse supernovae with spectral neutrino transport based on the isotropic diffusion source approximation scheme, we support the assumption that the neutrino-heating mechanism aided by the standing accretion shock instability and convection can initiate an explosion of a 13 $M_{\odot}$ star. Our results show that bipolar explosions are more likely to be associated with models which include rotation. We point out that models, which form a north-south symmetric bipolar explosion, can lead to larger explosion energies than for the corresponding unipolar explosions.Comment: 5 pages, 4 figures; accepted for publication in PASJ Letter

Non-thermal neutrinos from supernovae leaving a magnetar

Under the fossil field hypothesis of the origin of magnetar magnetic fields, the magnetar inherits its magnetic field from its progenitor. We show that during the supernova of such a progenitor, protons may be accelerated to ∼10^4 GeV as the supernova shock propagates in the stellar envelope. Inelastic nuclear collisions of these protons produce a flash of high-energy neutrinos arriving a few hours after thermal (10 MeV) neutrinos. The neutrino flash is characterized by energies up to O(100) GeV and durations seconds to hours, depending on the progenitor: those from smaller Type Ibc progenitors are typically shorter in duration and reach higher energies compared to those from larger Type II progenitors. A Galactic Type Ib supernova leaving behind a magnetar remnant will yield up to ∼160 neutrino-induced muon events in Super-Kamiokande, and up to ∼7000 in a km^3 class detector such as IceCube, providing a means of probing supernova models and the presence of strong magnetic fields in the stellar envelope

Space laser interferometers can determine the thermal history of the early Universe

It is shown that space-based gravitational wave detectors such as DECIGO and/or Big Bang Observer (BBO) will provide us with invaluable information on the cosmic thermal history after inflation and they will be able to determine the reheat temperature $T_R$ provided that it lies in the range preferred by the cosmological gravitino problem, $T_R\sim 10^{5-9}$ GeV. Therefore it is strongly desired that they will be put into practice as soon as possible.Comment: 5 page

Impact of Rotation on Neutrino Emission and Relic Neutrino Background from Population III Stars

We study the effects of rotation on the neutrino emission from Population III (Pop III) stars by performing a series of two-dimensional rotational collapse simulations of Pop III stellar cores. Our results show that rotation enhances the neutrino luminosities and the average energies of emitted neutrinos. This is because the thermalized inner core, which is the dominant neutrino source from Pop III stars, can be enlarged, due to rotational flattening, enough to extend the inner core outside the neutrinospheres. This is in sharp contrast to the case of spherical collapse, in which the case of inner core shrinks deeper inside the neutrinospheres before black hole formation, which hinders the efficient neutrino emission. In the case of rotational core-collapse, the emitted neutrino energies are found to become larger in the vicinity near the pole than the ones near the equatorial plane. These factors make the emergent neutrino spectrum broader and harder than the spherical collapse case. By computing the overall neutrino signals produced by the ensemble of individual rotating Pop III stars, we find that the amplitudes of the relic neutrinos, depending on their star formation rates, can dominate over the contributions from ordinary core-collapse supernovae below a few MeV. A detection of this signal could be an important tool to probe star formation history in the early universe.Comment: 28 pages, 12figures; High resolution version can be found at http://www-utap.phys.s.u-tokyo.ac.jp/~suwa/paper/pop3neu.pd

Simple way of finding Ba to Si deposition rate ratios for high photoresponsivity in BaSi2 films by Raman spectroscopy

Since the photoresponsivity of BaSi2 is sensitive to a Ba-to-Si deposition rate ratio (R Ba/R Si), there is a need to determine the optimum value of R Ba/R Si. We grew 0.5 μm thick BaSi2 films with R Ba/R Si varied from 1.1–3.6 at 580 °C and 0.4–4.7 at 650 °C. The photoresponsivity reached a maximum at R Ba/R Si = 2.2 and 1.2, respectively. Raman spectroscopy revealed that the crystalline quality of BaSi2 became better with decreasing R Ba/R Si. However, as R Ba/R Si decreased further beyond these values, excess Si precipitated, showing that the optimum value of R Ba/R Si should be as small as possible without causing Si precipitates to form

Investigation of native defects in BaSi2 epitaxial films by electron paramagnetic resonance

We investigated photoresponse, photoluminescence (PL), and electron paramagnetic resonance (EPR) spectra of 0.5 μm thick BaSi2 films grown by molecular beam epitaxy using various Ba-to-Si deposition rate ratios (R Ba/R Si). BaSi2 films (R Ba/R Si = 2.2) showed the highest photoresponsivity at room temperature. In contrast, BaSi2 films with R Ba/R Si away from 2.2 showed low photoresponsivity but intense sub-bandgap PL at 9 K. An anisotropic EPR line was observed below 20 K for such BaSi2 films. The EPR line disappeared for BaSi2 films passivated with atomic hydrogen. Thereby, the PL and EPR signals are interpreted to originate from native defects in the BaSi2 films

Low Surface Potential with Glycoconjugates Determines Insect Cell Adhesion at Room Temperature

Cell-coupled field-effect transistor (FET) biosensors have attracted considerable attention because of their high sensitivity to biomolecules. The use of insect cells (Sf21) as a core sensor element is advantageous due to their stable adhesion to sensors at room temperature. Although visualization of the insect cell-substrate interface leads to logical amplification of signals, the spatiotemporal processes at the interfaces have not yet been elucidated. We quantitatively monitored the adhesion dynamics of Sf21 using interference reflection microscopy (IRM). Specific adhesion signatures with ring-like patches along the cellular periphery were detected. A combination of zeta potential measurements and lectin staining identified specific glycoconjugates with low electrostatic potentials. The ring-like structures were disrupted after cholesterol depletion, suggesting a raft domain along the cell periphery. Our results indicate dynamic and asymmetric cell adhesion is due to low electrostatic repulsion with fluidic sugar rafts. We envision the logical design of cell-sensor interfaces with an electrical model that accounts for actual adhesion interfaces.Matsuzaki T., Terutsuki D., Sato S., et al. Low Surface Potential with Glycoconjugates Determines Insect Cell Adhesion at Room Temperature. Journal of Physical Chemistry Letters 2022 13(40), 9494-9500. DOI: 10.1021/acs.jpclett.2c01673. Copyright © 2022 American Chemical Society