Gravitational waves are useful probe for the physics of the early Universe. I will discuss several sources of stochastic gravitational wave background from the early Universe and provide a historical overview of this fascinating research field.
Gravitational wave (GW) observations offer a powerful tool for testing the fundamental Lorentz and parity symmetries of gravity. Any violation of these symmetries could manifest as deviations in GW propagation. In this talk, I will explore how current and future GW detections can constrain Lorentz- and parity-violating effects in gravity. I will introduce a systematic parameterization...
Non-minimal matter-curvature couplings arise in many different contexts, and modify solutions of general relativity. If dark matter (DM) experiences non-minimal couplings, the imprint can be see in gravitational waves (GWs) emitted from binary black hole mergers, where DM densities are expected to be large. In this talk, we explore effects of various non-minimal couplings on GWs by working...
I present an analytical computation of the energy emitted by a scalar particle radially infalling into a Schwarzschild black hole spacetime within the framework of the gravitational self-force. The results are expressed in Post-Newtonian expanded form, as is customary.
In this talk, I will report our progresses on the simulation of Gravitational wave and particle productions from cosmic strings.
We propose a two-field model where the inflaton χ is non-minimally coupled to the instanton ϕ. By choosing an appropriate coupling function, we realize the scenario where the difference of the values of potential between false vacuum (FV) and true vacuum (TV) is maximized during inflation. Most of the bubbles are created at this time. After inflation ends, the potential value of FV...
The polarized light of the cosmic microwave background is sensitive to new physics that violates parity symmetry. In this presentation, we present a tantalizing hint of parity violation from the polarization data of two satellite missions, WMAP and Planck, with a statistical significance of 3 sigma. This signal has also been observed in recent data from the Atacama Cosmology Telescope. Taken...
It is not easy to have a healthy parity violating gravity models within Riemannian geometry. The famous Chern-Simons modified general relativity and its extensions are pathological due to the ghost modes appeared at high energy scales. In this talk, I will introduce some parity violating models within the framework of teleparallel gravity, especially the Nieh-Yan modified teleparallel gravity...
In this presentation, I will talk about a framework for analysing gravitational waves in thermal environments, such as the radiation-dominant early universe, from a symmetry perspective. I will focus on the effective dynamics of gravitational waves in the interaction picture of quantum field theory and discuss the symmetry constraints on the theory.
We investigate a cosmological scenario in which the Peccei-Quinn (PQ) symmetry remains broken in the entire history of the Universe, thereby avoiding the formation of axion strings and domain walls. Contrary to the conventional expectation, it is demonstrated that appropriately chosen scalar
interactions are able to keep the PQ symmetry broken at arbitrarily high temperatures. We carefully...
We investigate the possibility of using the cosmic gravitational focusing (CGF) to probe the minor light dark matter (DM) component whose mass is in the range of $(0.1 \sim 100)$\,eV. Being a purely gravitational effect, the CGF offers a mode-independent probe that is complementary to the existing ways such as Lyman-$\alpha$ and $\Delta N_{\rm eff}$. Such effect finally leads to a dipole...
We discuss the intriguing possibility that the recently reported nano-Hz gravitational wave signal by Pulsar Timing Array (PTA) experiments is sourced by a strong first-order phase transition in a dark sector. The phase transition has to be strongly supercooled to explain the signal amplitude. However, such strong supercooling exponentially dilutes away any pre-existing baryon asymmetry and...
A complex singlet extension of the Standard Model not only incorporates scalar dark matter candidates but also enables the realization of a strong electroweak first-order phase transition essential for electroweak baryogenesis. This phase transition may generate gravitational waves and primordial black holes. We discuss the correlation between the strength of the phase transition and these...
In this talk we will present the formation of multiple vacuum states in axion models with non-degenerate vacua, which originate from vacuum fluctuations amplified via parametric resonance. The domains are classified as sub-horizon, cross-horizon, or super-horizon on their scale upon formation, leading to the different cosmic evolution as well as gravitational wave spectrum
Spin-2 ultralight dark matter (ULDM) is a viable dark matter candidate, and it can be constrained using gravitational wave (GW) observations. The pulsar timings are sensitive to both the nanohertz gravitational-wave background and the oscillation of ultralight dark matter. We study the angular correlation of the timing residuals induced by spin-2 ultralight dark matter, which differs from the...
