Pyungwon Ko
The chiral Lagrangian is a cornerstone of modern particle physics, offering a systematic and quantitative description of low-energy pions. Using tools from the modern scattering amplitudes program, we show that consistent multiparticle…
We explicitly present all coupling conditions required for tree-level unitarity (tree unitarity) in theories with a finite number of massive and massless particles of spin up to 1. They allow us to diagnose tree unitarity of a system using…
We investigate dark matter (DM) phenomenology and cosmic inflation within a unified framework based on a dark $U(1)_D$ gauge extension of the Standard Model (SM). The associated dark gauge boson, namely the dark photon, serves as a viable…
In 2023, Belle II collaboration announced the observarion of the $B^+ \to K^+ \nu\bar{\nu}$ decay channel for the first time. This decay channel provides a clean signal with high precision in theoretical calculation. However, we encounter…
The KM3NeT collaboration recently reported the detection of an ultra-high-energy (UHE) neutrino event, dubbed KM3-230213A. This is the first observed neutrino event with energy of the order of $\mathcal{O}(100) {\rm PeV}$, the origin of…
Motivated by recent results from particle physics analyses, we investigate the Next-to-Minimal Supersymmetric Standard Model (NMSSM) as a framework capable of accommodating a range of current data anomalies across low- and high-energy…
This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $t$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more…
We study multi-component dark matter scenarios and the Galactic 511 keV $\gamma$-ray emission line signal in the framework of a local, dark $U(1)_D$ extension of the Standard Model. A light vector dark matter particle associated with the…
The Belle II collaboration recently announced that they observed the $B^+ \!\to K^+\nu\bar{\nu}$ decay process for the first time. This dineutrino mode of $B^+ \!\to K^+\nu\bar{\nu}$ has been theoretically identified as a very clean…
This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers…
Gravitational positivity bounds provide consistency conditions for effective field theories with gravity. They turn out to be phenomenologically useful by providing lower bounds in parameters of new physics beyond the Standard Models (BSM).…
The details of the minimal cosmological standard model (MCSM) proposed in [arXiv:2403.05390.] are discussed. The model is based on the scale-symmetry and the global Peccei-Quinn(PQ) symmetry with a key assumption that the latter is broken…
As a new type of dynamical dark matter mechanism, we discuss the stability of the gauged Q-ball dark matter and its production mechanism through a cosmological first-order phase transition. This work delves into the study of gauged Q-ball…
We investigate dark matter phenomenology and Higgs inflation in a dark $U(1)_D$-extended model. The model features two dark matter candidates, a dark fermion and a dark vector boson. When the fermion dark matter $\psi$ is heavier than the…
In this paper, we construct a viable model for a GeV scale self-interacting dark matter (DM), where the DM was thermally produced in the early universe. Here, a new vector-like fermion with a dark charge under the $U(1)_{D}$ gauge symmetry…
The presence of dark matter overdensities surrounding a black hole can influence the evolution of a binary system. The gravitational wave signals emitted by a black hole binary offer a promising means to probe the dark matter environments…
We consider $U(1)_H$ extensions of Type-I 2HDM plus a singlet scalar $\phi_H$, introducing a new Higgs doublet $H_2$ and a singlet $\phi_H$ charged under $U(1)_H$. The SM Higgs doublet $H_1$ as well as all the SM fermions and three…
We propose a deep learning-based search strategy for pair production of doubly charged scalars undergoing three-body decays to $W^+ t\bar b$ in the same-sign lepton plus multi-jet final state. This process is motivated by composite Higgs…
In this paper, we evaluate the energy loss rate of supernovae induced by the axion emission process $\pi^- + p \to n + a$ with the $\Delta(1232)$ resonance in the heavy baryon chiral perturbation theory for the first time. Given the…
Multi-component dark matter scenarios are studied in the model with $U(1)_X$ dark gauge symmetry that is broken into its product subgroup $Z_2 \times Z_3$ \'{a} la Krauss-Wilczek mechanism. In this setup, there exist two types of dark…