I will discuss some theoretical and experimental topics on eV axion dark matter. The cold axion dark matter can be produced thermally in the early Universe, or alternatively, it can be the inflaton itself. In both cases, the predicted mass range is around eV. The scenario can be probed by observing the dwarf spheroidal galaxies with state-of-the-art infrared spectrographs.
I will discuss anisotropic (patchy) screening induced by the resonant conversion of cosmic microwave background (CMB) photons into light bosons in the dark sector as they cross non-linear large scale structure (LSS). Using kinetically mixed dark photon as an example, I will show how this conversion between CMB photon and light dark photon naturally occurs for a wide range of dark photon...
Dark matter is the dominant matter in the Universe. In this talk, I will introduce two major scenarios of dark matter: Axion dark matter and WIMP (Weakly Interactive Massive Particle) and show how radio telescopes can search and put constraints on their parameters. The first one is Axion, which is a compelling dark matter candidate of increasing scientific interests in recent years, and was...
The coherent oscillation of ultralight Fuzzy dark matter induces changes in gravitational potential with the frequency in the nanohertz range. This effect is known to produce a monochromatic signal in the pulsar timing residuals. Here we discuss a multifield scenario that produces a wide spectrum of frequencies, such that the ultralight particle oscillation can mimic the pulsar timing signal...
This talk is based on the papers arXiv: 2309.01739 and 2307.08185. I present a new mechanism of primordial black hole (PBH) formation from QCD axion in the context of the Peccei-Quinn symmetry breaking during inflation. The axion string-wall network re-enters horizon sufficiently late, so the closed domain walls that naturally arise in the network are sufficiently large to collapse into PBHs....
Vorticity emerges in a class of non-gravitational localised configurations universally displaying the key-essential properties of black holes. Supported by this, I will argue that highly-spinning black holes correspond to graviton condensates endowed with vorticity. As a consequence, potential macroscopic deviations in the gravitational radiation emitted in black hole mergers are...
Precise measurements of the stellar orbits around Sagittarius A* have established the existence of a supermassive black hole (SMBH) at the Galactic center (GC). In addition, the existence of extended mass distribution from dark matter, or novel interactions between dark matter and ordinary matter would imprint on the motions of stars in the innermost region of the GC. Using the Keck and VLT...
I will discuss recent progress on N-body simulations of self-interacting dark matter and their implications within the context of the latest astrophysical observations, including ultra-diffuse galaxies, strong lensing perturbers, and supermassive black holes. We will show that self-interacting dark matter provides a compelling explanation to diverse dark matter distributions in galactic systems.
The primordial black hole (PBH) is a unique candidate for dark matter (DM). It does not require a new particle for DM and the inflationary perturbation explains both the initial condition and the growth promoter of the cosmological perturbation. So far, astrophysical or cosmological observations have constrained the PBH abundance tightly and the window for PBH-DM remains only at the asteroid...
We consider the spike mass density profile in a dark halo by self-consistently solving the relativistic Bondi accretion of dark matter onto a non-spinning black hole. We assume that the dark matter in the halo forming a Bose-Einstein condensate (BEC) is described by a self-interacting scalar field. In the hydrodynamic limit, we find that the accretion rate has a lower bound. The spike density...
When a strong gravitational field is present around an SMBH, dark matter with gravitational interactions can congregate and create an environment that is far more dense than it would be in other regions. In recent years, the orbital dynamics of the S-star near the galactic center (GRAVITY/Keck), the imaging of SMBH (EHT), the nanohertz stochastic gravitational wave (PTA), and the precise...
Fuzzy dark matter (FDM) is made up of a very light axion of mass ~1e-22eV governed by the Schrodinger-Poisson equation. The wave nature of FDM exhibits novel phenomena which can be used to observational probe and constrain the FDM model. In this talk, I will discuss how the wave interference of FDM leads to density fluctuations, the formation of vortices and filaments, and oscillation of the...
Traditionally, Dark Matter (DM) searches are dominantly focused on GeV – TeV mass window. However, though these experiments have reached unprecedented detection sensitivities, the successes only resulted in a push for stronger limits on parameters. This forces people to keep their minds open to other DM candidates, especially in the different mass regimes. If a DM particle is an ultralight...
Dark matter halos host galaxies, but cold dark matter is expected to cluster on much smaller scales as well. Small-scale dark matter structures would host no visible matter but can still leave hints about the nature of dark matter. If the dark matter is a thermal relic, the smallest structures are rho ~ r^-1.5 density cusps that arose at the onset of structure formation in the universe. For...
We explore the possibility that light Dark Matter (DM) existence is related to first order phase transitions (FOPTs) in the early Universe. In particular, DM particles may be pseudo-Goldstone bosons of spontaneously broken global symmetries beyond the Standard Model. In this case, a new scalar field can interact with the Higgs boson and it can be related to a first order electroweak phase...
The environment around the black hole can provide us a promising playground to study the dark matter properties because of the large dark matter density from accretion.
I will explore the multi-messenger probes on the dark matter in the vicinity of black holes. More concretely, I will discuss (1) the gravitational wave signals from a black hole binary whose dynamics is affected by the dark...
Ultralight bosonic fields (ULBFs) are predicted by various theories beyond the standard model of particle physics and are viable candidates of cold dark matter. There have been increasing interests to search for the ULBFs in physical and astronomical experiments. In this paper, we investigate the sensitivity of several planned space-based gravitational-wave interferometers to ultralight scalar...
Since the models of inflation compatible with CMB data require non-renormalizable inflaton potentials, it is natural to have extra couplings between inflaton and gravitons. The suppression scale of such operators can well be lower than the Planck scale. Due to these couplings, inflaton can produce high frequency gravitons during reheating due to both decay and bremsstrahlung process. In my...
