師走に素粒子若手が新しいことを考える会

Monday Dec 22, 2025, 1:00 PM → 5:00 PM Asia/Tokyo

K206 (YITP)

素粒子大学院生を中心に、興味を持っていることを自由に語ってもらう会。そして老人を教育する会。

以前の若手会:
https://indico.yukawa.kyoto-u.ac.jp/event/69/ (皐月会)
https://indico.yukawa.kyoto-u.ac.jp/event/67/ (卯月会）

世話人：
浅井健人（YITP）
井黒就平（名古屋大/KEK）
北野龍一郎（YITP）
 

1:00 PM → 1:40 PM Some Phenomenological Implications from the hep-th Side

In this talk, I will present two works that we have carried out on the hep-th side.

The first part concerns the SU(2) adjoint Higgs model, which can be regarded as a toy model of grand unified theories (GUTs). The phase structure of this model has not attracted much attention since the 1980s. However, our recent study suggests that it actually exhibits a nontrivial phase structure, which we refer to as deconfinement–Higgs continuity. I will explain this result and its implications.

The second part focuses on type IIB superstring theory. Type IIB string theory is particularly attractive because it accommodates both GUT-like structures, such as F-theory GUTs, and inflationary scenarios. On the other hand, analyzing its vacua typically requires sophisticated tools from algebraic geometry, making the theory technically challenging, and many aspects remain to be fully understood. In our work, we showed that a generalized symmetry necessarily emerges, largely independent of the detailed choice of vacuum. Moreover, this symmetry is scale invariant and can potentially influence infrared physics.

Due to time constraints, I may not be able to cover all details. Nevertheless, I hope that this talk will provide some useful insights for the hep-ph community.

Speaker: Masashi Kawahira (Kobe U.)

1:40 PM → 2:20 PM break

2:20 PM → 3:00 PM Enhanced particle emission from wide cosmic strings

Cosmic strings are linear topological defects produced during a U(1) symmetry-breaking phase transition. Recent results from Pulsar Timing Array (PTA) collaborations can be interpreted as evidence for gravitational waves sourced by heavy metastable string networks. However, such string networks are strongly constrained by observations from LIGO-Virgo-KAGRA (LVK). In this talk, we propose a scenario that reconciles this tension by focusing on particle emission from cosmic strings. When the fields constituting a cosmic string are coupled to light particles, the string can emit them, providing an additional energy loss channel. We develop a systematic method to derive effective interactions between cosmic strings and light particles. Applying this framework to the Abelian-Higgs model coupled to the Standard Model via gauge kinetic mixing, we identify a novel particle emission channel that is significantly enhanced for strings with a large width. We evaluate the impact of this channel on the gravitational wave spectrum and show that it can suppress the gravitational wave amplitude at LVK frequencies. As a result, heavy string networks favored by PTA observations can remain consistent with current LVK constraints in this scenario.

Speaker: Yukihiro Kanda (ICRR)

3:00 PM → 3:40 PM break

3:40 PM → 4:20 PM Thermal Lepton Oscillations in Leptogenesis

Abstract: Oscillation phenomena occur in both active and sterile neutrinos, where the oscillation phases are triggered by vacuum mass difference. Before the electroweak gauge symmetry breaking, leptons are massless, and cannot oscillate in the conventional way. However, they can still oscillate in the background plasma. Using the flavor-covariant nonequilibrium quantum field theory, I will discuss how oscillations appear from thermal leptons at finite temperatures, and present new ideas that may have significant impacts on leptogenesis.

Speaker: Shaoping Li (Osaka U.)

4:20 PM → 5:00 PM discussion