A strong first-order electroweak phase transition (EWPT) can be realized through the introduction of a light scalar that is weakly coupled to the Higgs boson. Such weak couplings can result in a macroscopic lifetime, leading to displaced decays that provide a distinctive experimental signature. In this talk, we investigate the sensitivity of future lepton colliders to long-lived scalars "s"...
The search for dark matter at accelerators has a long history, dating back to the first proposals for the LHC and even earlier. While complementary to direct detection in certain respects, accelerator-based searches offer distinct advantages, particularly when investigating a complex dark sector and multi-step processes. As a precision machine with unique potential, the planned CEPC...
A number of excesses observed in LHC data have motivated the hypothesis of a new Higgs-like scalar with a mass near 152 GeV. This presentation will begin with a brief introduction to the history of the 152 GeV candidate, from the multi-lepton anomalies and the prediction of a scalar mass near 150 GeV to the subsequent excesses observed in the \gamma\gamma, Z\gamma, and WW channels.
The main...
The invisible width of the Z boson was measured with high accuracy at LEP. Within the Standard Model, this value indicates three active neutrino families. However, New physics models can lead to deviations from this estimate. Therefore, it is important to measure the Z decay branching fraction for a specific neutrino flavor. We propose a new method to precisely measure the Z decay branching...
We investigate the phenomenology of 2 Higgs doublet models (2HDMs) with a new $U(1)$ gauge symmetry, $U(1)_X$, by which flavor changing neutral currents are forbidden at tree level. As an important consequence of the spontaneous breaking of both the $U(1)_X$ and electroweak symmetries by electroweak vacuum expectation values, upper limits appear on masses of an additional gauge boson $Z'$ and...
Higgs precision measurements provide an opportunity to test various extended Higgs models. To exploit the high precision of future experimental measurements, theoretical predictions must be calculated with comparable precision by including higher-order corrections. To probe the structure of the Higgs sector through future precision measurements, we have developed a program, H-COUP, which...
In this talk, I will cover both the Axion-Like Particles and Tau weak electric dipole moments. Our combined analysis shows that mono-V and non-resonant VBS channels provide powerful and complementary probes of ALP-gauge boson interactions. Tau spin correlations at the Z pole probe CP violation with a sensitivity that depends strongly on the spin projection. For a fixed Z sample, transverse...
The two-Higgs-doublet model with a light pseudoscalar singlet (2HDM + a) provides a wellmotivated dark matter (DM) framework, but hadron colliders face severe background ceilings
in the light-scalar (mh1) and light-mediator (ma) windows, while non-relativistic directdetection bounds are momentum-suppressed. To address these experimental bottlenecks, this study investigates the potential of...
Future high-luminosity $e^+e^-$ colliders such as CEPC and FCCee will measure the Higgsstrahlung cross section $e^+e^- \to Zh$ with sub-percent precision, offering a unique window into probing extended scalar sectors. We present a complete one-loop electroweak calculation of this process in the real triplet Higgs model with a non--zero triplet vev, using a fully automated renormalisation...
Photon pairs have provided an ideal laboratory for exploring entanglement and Bell inequality violation in low-energy experiments. Extending such studies to high-energy colliders is of great interest but has yet to be explored. Exploiting the photon conversion process for nearly on-shell photons, we formulate a factorization framework and an effective two-qubit description, which enable access...
We investigate the sensitivity of proposed CEPC and FCC-ee with a center-of-mass energy of 240 GeV to long-lived dark photons heavier than 2 GeV that are pair-produced via the prompt decays of a light scalar mixed with the Standard-Model Higgs boson. We compute the production and decay rates of both the light scalar and the dark photon, and develop two search strategies targeting displaced...
Future lepton colliders such as CEPC and FCC-ee are capable of producing trillions of Z-bosons. Such Tera-Z factories can discover new elementary particles with couplings to the Z-boson several orders of magnitude smaller than current bounds, and could also measure the new particles' properties in detail. Using simple analytic estimates, we quantify how the discovery reach and measurement...
We explore quantum entanglement and Bell-inequality violation in Higgs decays at the CEPC, using simulated e+e−→ZH events at $\sqrt{s} = $ 250 GeV with 50 $\mathrm{ab}^−1$. From lepton angular distributions in $H\to ZZ^*\to$ 4ℓ, we reconstruct the ZZ spin-density matrix and test the CGLMP inequality for a two-qutrit system. Considering semileptonic and pure-leptonic associated-Z channels, we...
