181229 Enhanced Photon Coupling of ALP Dark Matter Adiabatically Converted From the QCD Axion

Title:
Enhanced Photon Coupling of ALP Dark Matter Adiabatically Converted From the QCD Axion

Speaker:
何書宇 (Shu-Yu Ho), PhD student, 日本東北大學 (Tohoku University)

Time:
12/29 (Sat.) 6 pm PST, 7 pm MST, 8 pm CST, 9 pm EST
12/30 (Sun.) 10 am Taiwan

Keywords:
Physics, Particle cosmology, Dark matter, Axion

Abstract:
We revisit the adiabatic conversion between the QCD axion and axion-like particle (ALP) at level crossing, which can occur in the early universe as a result of the existence of a hypothetical mass mixing. This is similar to the Mikheyev-Smirnov-Wolfenstein effect in neutrino oscillations. After refining the conditions for the adiabatic conversion to occur, we focus on a scenario where the ALP produced by the adiabatic conversion of the QCD axion explains the observed dark matter abundance. Interestingly, we find that the ALP decay constant can be much smaller than the ordinary case in which the ALP is produced by the realignment mechanism. As a consequence, the ALP-photon coupling is enhanced by a few orders of magnitude, which is advantageous for the future ALP and axion-search experiments using the ALP-photon coupling.

181208 The Birth of Solar-Like Stars: an Inseparable Entanglement of Dynamics and Chemistry

Title:
The Birth of Solar-Like Stars: an Inseparable Entanglement of Dynamics and Chemistry

Speaker:
楊燿綸 (Yao-Lun Yang), PhD candidate, UT Austin

Time:
12/08 (Sat.) 6 pm PST, 7 pm MST, 8 pm CST, 9 pm EST
12/09 (Sun.) 10 am Taiwan

Keywords:
Astronomy, Star formation, Infall, Radiative Transfer, Astrochemistry

Abstract:
How did we get here? For decades, this question drives us to explore star-forming regions, protoplanetary disks, and exoplanets. Molecular emission is a powerful tool for probing the kinematics during the star formation; however, star formation processes not only regulate the dynamics but also increase the complexity of molecules; thus, we need to consider the chemical processing, such as freeze-out and dissociation, simultaneously when using the molecular emission to probe gas kinematics. I will focus on the infall, which dominates the conversion from dense clouds to protostars, and how the infall may also determine the formation of complex organic molecules, such as methanol. We use the line profile of molecular emission to traces the infall, which can be modeled with radiative transfer calculations. Furthermore, we developed an observing strategy to probe the dynamics (infall) and chemistry (complex organics molecules) within a single shot of ALMA observations. By following the trails of dynamics and chemistry, we will start to constrain the formation history of our own solar system.