Linear and nonlinear optical responses in bacteriochlorophyll <i>a</i>

Nonlinear optical responses of bacteriochlorophyll &lt;i&gt;a&lt;/i&gt; (BChl &lt;i&gt;a&lt;/i&gt;) were investigated by means of the three-pulse four-wave mixing (FWM) technique under the resonant excitation into the &lt;i&gt;Q&lt;/i&gt; &lt;i&gt;y&lt;/i&gt; band. The experimental results are explained by a theoretical model calculation including the Brownian oscillation mode of the solvent. We have determined the spectral density, which is the most important function with which to calculate optical signals. The linear absorption spectrum can be reproduced fairly well when the vibronic oscillation modes of the solvent together with those of BChl &lt;i&gt;a&lt;/i&gt; are properly taken into consideration. The FWM signal was also calculated using the spectral density. It was found that a simple two-level model could not explain the experimental result. The effect of the higher-order interactions is discussed

Supernova Model Discrimination with Hyper-Kamiokande

Core-collapse supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants—neutron stars and black holes—are interesting astrophysical objects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. We focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate Hyper-Kamiokandeʼs response to five different supernova models. We show that Hyper-Kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. Once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations toward a precise reproduction of the explosion mechanism observed in nature