Abstract

Inspired by the recent detection of the 21-cm absorption signal from primordial neutral hydrogen at z~17 by EDGES, a class of dark matter (DM) models with non-gravitational baryon-DM scattering (BDMS) becomes more appealing. The intergalactic medium (IGM) can be cooler in these BDMS models compared with the case of the standard cold DM, producing deep absorption depths as measured by EDGES. The effect of BDMS previously has only been studied in the linear regime for the IGM, and the constraints on parameters are incomplete, leaving a open region in the phenomenological parameter space consistent with the EDGES signal. We investigate the effect of BDMS in the non-linear regime of early structure formation to place new constraints on BDMS. We find that BDMS can significantly affect the abundance of star-forming minihaloes, and a large region in the parameter space is ruled out, in which star formation is significantly suppressed at zgtrsim 20, inconsistent with the timing of the EDGES signal. Our work is exploratory (semi-analytical) and far from a full answer. However, with future detailed cosmological simulations and improved 21-cm observations, more insights into the particle-physics nature of DM will be obtained from the perspective of early structure formation.

If you would like to know more details of this work, please read our paper: https://arxiv.org/abs/1902.09650

Abstract

Most detected exoplanets orbit FGKM dwarfs, largely because detecting planets that orbit hotter stars, namely A stars, is difficult due to their rotationally-broadened spectra and large radii. This study explores the planet occurrence rates around hot A-stars in the Kepler data set, in order to investigate the role of stellar evolution on planetary formation. Kepler is the first astronomical survey to have photometric precision necessary to detect Jupiter-size planets transiting A-star hosts. We limit our stellar host samples to stars with over 6500K, matching late F-star and A-star stellar temperatures. Using both the spectroscopic and photometric data, we re-characterize the planetary system to obtain reliable, homogeneous properties. We infer the population level statistics on the planetary candidates using a hierarchical probabilistic framework. Finally, we sampling using MCMC to get the population parameters in order to constrain our planet occurrence rates.