ABSTRACT
Axion-like particles (ALPs) are hypothetical extensions of the Standard Model, with the potential to account for both dark matter and various astrophysical phenomena. This seminar will explore two distinct detection approaches for ALPs: one focusing on ALPs as long-lived particles and the other considering them as dark matter candidates. The first study (2410.16065) investigates the production of long-lived ALPs in stellar cores, particularly their decay into monochromatic X-rays detectable in nearby stellar systems. Using data from the Alpha Centauri binary system, we establish the most stringent limits on ALP interactions, improving constraints on the ALP-photon coupling by up to two orders of magnitude for masses between 0.25 keV and 5 keV. The second study (2507.07786) examines ALPs as dark matter candidates, exploring their conversion into photons via the Primakoff effect. By analyzing 16.5 years of Fermi-LAT data from the galaxy NGC 1275, we refine exclusion limits on the photon-ALP coupling for masses between 4e-10 eV and 5e-9 eV. We also highlight the potential of the upcoming Very Large Area Gamma-ray Space Telescope (VLAST) to surpass the sensitivity of future observatories like IAXO.
Inelastic self-interacting dark matter (iSIDM) provides a well-motivated extension of the cold dark matter paradigm, featuring multiple internal states connected by inelastic conversion processes. In this seminar, I will present a linear-cosmology framework for iSIDM, starting from a model-independent microphysical parameterization of the inelastic cross section and deriving the corresponding background and perturbation equations in an effective Boltzmann-code description. I will then discuss the resulting cosmological evolution, including the homogeneous chemical evolution and thermal history of the dark sector, demonstrating how these dynamics imprint characteristic signatures on the growth of density perturbations and the linear matter power spectrum. Finally, I will illustrate how the linear-theory predictions of iSIDM can be connected to existing data by translating the modified transfer function into two commonly used phenomenological constraints—those derived from the Lyman-α forest and high-redshift UV luminosity functions—thereby obtaining a preliminary mapping of the viable parameter space.
BIOGRAPHY
Dr. Yue-Lin Sming Tsai is currently a senior Research Fellow at Purple Mountain Observatory (PMO). He received his Ph.D. in Physics and Astronomy from the University of Sheffield in 2011, specializing in particle astrophysics. Before joining PMO, he has held postdoc positions at the NCBJ in Poland (2011–2013), the Kavli IPMU of Tokyo University (2013–2016), the National Center for Theoretical Sciences in Taiwan
(2016–2017), the Institute of Physics at Academia Sinica as a visiting associate professor (2017–2020), and National Tsing Hua University as a research scholar (2020–2021).
His research focuses on dark matter phenomenology, aiming to probe the particle properties of dark matter by connecting theoretical models with experimental data. He specializes in testing high-dimensional theoretical models using diverse datasets. His current interests include indirect and direct detection of dark matter, cosmological implications of dark matter (including linear theory and non-linear N-body simulations), and dark matter model testing. He has published 76 papers in the field of dark matter research, with an h-index of 33.
Xinchen Duan is a Ph.D. student at the Purple Mountain Observatory (PMO), specializing in cosmology and particle astrophysics. Her research focuses on dark-sector phenomenology, particularly on connecting microphysical dark matter interactions to cosmological observables .
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