Summer Institute 2025 (Aug 17 - 22, 2025)

17 Aug 2025, 11:00 → 22 Aug 2025, 18:00 Asia/Seoul

Utop Marina Hotel & Resort, Yeosu, Korea

Seodong Shin (Jeonbuk National University), Jong-Chul Park (Chungnam National University)

29th International Summer Institute on Phenomenology of Elementary Particle Physics and Cosmology (SI 2025)

 

 

The purpose of the Summer Institute, which began in 1995 in Japan, is to educate graduate students and junior postdocs in Eastern Asian Institutions in the field of high energy physics and cosmology. The SI also aims to promote communications and discussions on research among the participants, rather than to give pedagogical lectures for students.

Registration is open through June 30, 2025 in Korean Standard Time (KST).

Abstract submission for the posters (only) is open through June 30, 2025 in KST.

Important notification: From Aug 1st in KST, it is impossible to cancel your registration due to the accommodation issue.

 

 

Invited Lecturers

Kohei Fujikura (Yukawa Institute, Kyoto): Cosmological phase transition and gravitational wave

KC Kong (University of Kansas): AI in HEP/COSMO/ASTRO

Zhen Liu (University of Minnesota): Future colliders

Seokhoon Yun (IBS-CTPU): Light BSM particles from the astrophysical objects

 

Invited Speakers of Special Seminars

Koun Choi (IBS-CUP): Super-Kamiokande Physics

Jeong Han Kim (Chungbuk National University): AI in cosmology

Hyun Su Lee (IBS-CUP): Yemilab Physics

Meng-Ru Wu (Academia Sinica): Neutrino in astrophysics

Masahide Yamaguchi (IBS-CTPU-CGA): Cosmological collider physics and activities in IBS-CTPU-CGA

Runze Zhao (Institute of High Energy Physics, Beijing): JUNO Physics

 

Organizing Committee

Sanghyeon Chang (IBS-CTPU)
Ki Young Choi (Sungkyunkwan University) 
Eung Jin Chun (KIAS) 
Kwang Sik Jeong (Pusan National University) 
Hyung Do Kim (Seoul National University) 
Chan Beom Park (Chonnam National University) 
Jong-Chul Park (Chungnam National University, co-chair) 
Seong Chan Park (Yonsei University) 
Seodong Shin (Jeonbuk National University, chair) 
Masahide Yamaguchi (IBS-CTPU)

 

International Advisory Committee

K. Cheung (NTHU) 
C.-R. Chen (NTNU) 
K. Choi (IBS-CTPU) 
C.-S. Chu (NTHU) 
G. Hou (NTU) 
J.E. Kim (Seoul National University) 
P. Ko (KIAS) 
O. Kong (NCU) 
T. Kurimoto (University of Toyama) 
J.S. Lee (Chonnam National University) 
C.-D. Lu (LUCD) 
S.C. Park (Yonsei University) 
M. Spinrath (NTHU) 
M. Tanimoto (Niigata University) 
Q. Wang (Tsinghua University) 
T.C. Yuan (Academia Sinica) 
 

 

Best poster presentation awards (students)

• Yuki Honda (Yokohama National University): Mass spectrum and symmetry breaking in Non-Abelian gauge theory with extra dimensions of two-dimensional sphere
   
• Jinyoung Jhun (Rikkyo University): Gravitational Waves from Superconducting Cosmic Strings 
   
• Jiheon Lee (KAIST): Dark gauge-mediated supersymmetry breaking

 

 

Sunday, 17 August

16:00 → 20:30 Hotel check-in: Grand Ballroom in the 1st floor

20:30 → 22:30 Discussion

Monday, 18 August

08:00 → 08:50 Registration

08:50 → 09:00 Opening remarks

Convener: Prof. Seodong Shin (Jeonbuk National University)

08:50 Opening remarks

Speaker: Prof. Seodong Shin (Jeonbuk National University)

SI2025-opening.pdf

09:00 → 10:00 Lecture 1

Convener: Prof. Seodong Shin (Jeonbuk National University)

09:00 Light BSM particles from the astrophysical objects I

Speaker: Seokhoon Yun (IBS-CTPU)

SI2025_Preliminary_S.Yun.pdf

10:00 → 10:30 Coffee & Discussion

10:30 → 11:30 Lecture 2

Convener: Hyung Do Kim (Seoul National University)

10:30 Cosmological phase transition and gravitational wave I

Speaker: Kohei Fujikura (The University of Tokyo)

Yeosu.pdf

11:30 → 12:30 Lecture 3

Convener: Hyung Do Kim (Seoul National University)

11:30 Light BSM particles from the astrophysical objects II

Speaker: Seokhoon Yun (IBS-CTPU)

SI2025_Sun&StellarEvolution_S.Yun.pdf

12:30 → 14:00 Lunch

14:00 → 15:00 Special seminar 1

Convener: Ki-Young Choi (Sungkyunkwan University)

14:00 Super-Kamiokande Physics

Speaker: Koun Choi (IBS)

SI2025_sk_physics.pdf

15:00 → 16:00 Special seminar 2

Convener: Ki-Young Choi (Sungkyunkwan University)

15:00 JUNO Physics

Speaker: Runze Zhao (Institute of High Energy Physics, Chinese Academy of Science)

JUNO_Phyiscs_SI2025_v1.pdf

16:00 → 16:30 Coffee & Discussion

16:30 → 17:30 Special seminar 3

Convener: Prof. Seodong Shin (Jeonbuk National University)

16:30 Yemilab Physics

Speaker: Dr Hyunsu Lee (IBS)

Yemilab.pdf

17:30 → 18:30 Special seminar 4

Convener: Prof. Seodong Shin (Jeonbuk National University)

17:30 Neutrino in astrophysics

Speaker: Meng-Ru Wu (Institute of Physics, Academia Sinica)

250818_SI_MRW.pdf

18:30 → 20:30 Dinner

Tuesday, 19 August

09:00 → 10:00 Lecture 4

Convener: Masahide Yamaguchi

09:00 Cosmological phase transition and gravitational wave II

Speaker: Kohei Fujikura (The University of Tokyo)

kohei_fujikura_2.pdf

10:00 → 10:10 Conference Photo

10:10 → 10:40 Coffee & Discussion

10:40 → 11:40 Lecture 5

Convener: Seong Chan Park (Yonsei University)

10:40 Light BSM particles from the astrophysical objects III

Speaker: Seokhoon Yun (IBS-CTPU)

SI2025_SN&NS_S.Yun.pdf

11:40 → 12:40 Lecture 6

Convener: Seong Chan Park (Yonsei University)

11:40 Cosmological phase transition and gravitational wave III

Speaker: Kohei Fujikura (The University of Tokyo)

12:40 → 14:00 Lunch

14:00 → 16:00 Parallel session 1

Convener: Prof. Kwang Sik Jeong (Pusan National University)

14:00 A Quantum Description of Wave Dark Matter

In this talk, I will outline a fundamentally quantum description of bosonic dark matter. Following a quantum optics-inspired approach, I will show the density matrix of dark matter, which takes a mixed Gaussian form over a coherent state basis. This formalism also allows a precise description of quantities related to dark matter coherence. I will further give a continuous description of dark matter through the wave-particle transition, where the density fluctuation in various scales evolves between the two limits, showing a unique behavior near the boundary of these descriptions.

Speaker: Dhong Yeon Cheong (Yonsei University)

SI_Cheong.pdf

14:20 Indirect detection of dark matter annihilation using gamma-ray data of Fermi-LAT

Dark matter (DM) plays an important role in modern high-energy physics and indirect signals can provide evidence of DM interactions with Standard model (SM) particles. Among various of SM channels, gamma-rays are one of the most prominent channel because they head directly to the Earth unlike other charged cosmic-ray particles. Using gamma-ray data of Fermi-LAT, a space telescope that is cable of gamma-rays from 0.1 GeV to above 500 GeV. In this talk, we will discuss about analysis of Galactic Center Excess (GCE) which is known to be well explained by DM annihilation, and strong bounds on $\langle \sigma v \rangle$ from dwarf spheroidal galaxies (dSphs). And combining the results, we will investigate possibility of hadronic/leptonic annihilation channel of DM into SM.

Speaker: SangHwan Kim (Department of Physics, Yonsei University)

Dark matter indirect detection using Fermi-LAT gamma-ray data_SI.pdf

14:40 Quantum entanglement of ions for light dark matter detection

A detection scheme is explored for light dark matter, such as axion dark matter or
dark photon dark matter, using a Paul ion trap system. We first demonstrate that
a qubit, constructed from the ground and first excited states of vibrational modes
of ions in a Paul trap, can serve as an effective sensor for weak electric fields due
to its resonant excitation. As a consequence, a Paul ion trap allows us to search
for weak electric fields induced by light dark matter with masses around the neV
range. Furthermore, we illustrate that an entangled qubit system involving $N$
ions can enhance the excitation rate by a factor of $N^2$. The sensitivities of the
Paul ion trap system to axion-photon coupling and gauge kinetic mixing can reach
previously unexplored parameter space.

Speaker: Wakutaka Nakano (YITP)

nakano.pdf

15:00 Evading the Current Direct Detection Bound through Metastable Particle-Assisted Freeze-Out

In this work, we have explored the conversion-driven freeze-out scenario, where the next-to-lightest stable particle (NLSP) sets the dark matter (DM) abundance through
the process ``NLSP SM $\leftrightarrow$ DM SM". Although DM is produced via
freeze-out mechanism, its interaction strength with the visible sector can
range from weak-scale to feeble-scale couplings. This leads to a vast,
largely unexplored parameter space that remains beyond the reach of current
direct, indirect, and collider searches with possibility of detection
in near future.
We have studied this mechanism in the context of an alternative $U(1)_{B-L}$ model, where four chiral fermions are required to cancel gauge anomalies, in contrast to the usual case with three right-handed neutrinos. The observed relic abundance,
as measured by Planck, is successfully reproduced within this framework. The viable parameter space can be probed by future direct detection experiments,
while remaining inaccessible to indirect searches in near future.
Our results show that the DM relic density is highly sensitive to both the NLSP's interaction strength with the visible sector and the mass difference between the NLSP and DM but not on the DM interaction strength with the visible sector.
When the NLSP decays to DM via a two-body process involving an extra gauge boson,
the decay can be long-lived, outside the CMS or ATLAS detector at LHC.
In contrast, if the NLSP decays via a CP-odd Higgs, it decays promptly inside the detector.
We have investigated the prospects for detecting such long-lived NLSP signatures
at the proposed MATHUSLA detector, with similar conclusions applying to the ongoing FASER experiment. Finally, we find that choosing arbitrarily small values for the
gauge coupling and the BSM fermionic mixing angle can violate successful BBN predictions.

Speaker: Sarif Khan (Chung-Ang University, Seoul)

SI-2025.pdf

15:20 Neutrino masses and mixed dark matter from doublet and singlet scalars

We consider the extension of the Standard Model with an inert scalar doublet, three right-handed neutrinos, and singlet scalar fields, φ and S. In this model, neutrino masses are zero in the limit of the unbroken Z4 discrete symmetry. We show that when the singlet scalar field φ gets a VEV, the Z4 symmetry is broken to Z2, and neutrino masses are generated at one-loops due to the mixings between the neutral components of the inert scalar doublet and the singlet scalar field S. There is a dark matter candidate from the lightest neutral scalar field, which is a mixture of the inert scalar doublet and the singlet scalar field S, in general. The Z4 breaking mass terms are constrained by electroweak precision data and direct detection (DD) bounds for dark matter, favoring small mixings or almost degenerate masses for the DM scalars. We discuss the implications of the results for small neutrino masses and DD-safe dark matter.

Speaker: Seongsik KIm (Chung-Ang University)

2025 Aug SI_SSK_v2.pdf

14:00 → 16:00 Parallel session 2

Convener: Chan Beom Park (Chonnam National University)

14:00 Impact of the electroweak Weinberg operator on the electric dipole moment of electron

Recent progress in the electric dipole moment (EDM) measurements of the electron using the paramagnetic atom or molecule is remarkable. In this paper, we calculate a contribution to the electron EDM at three-loop level, introducing the CP-violating Yukawa couplings of new SU(2)$_L$ multiplets. At two-loop level, the Yukawa interactions generate a CP-violating dimension-six operator, composed of three SU(2)$_L$ field strengths, called the electroweak-Weinberg operator. Another one-loop diagram with this operator inserted induces the electron EDM. We derive the matching condition and find that even if new SU(2)$_L$ particles have masses around the TeV scale, the electron EDM may be larger than the Standard Model (SM) contribution to the paramagnetic atom or molecule EDMs.

Speaker: Kiyoto Ogawa (Nagoya University)

SI_2025_Ogawa.pdf

14:20 A triple Z’ signal via light scalar interaction in Z-factories

We discuss triple $Z'$ boson signatures via the decay chain of $Z \to Z' \phi \to Z' Z' Z'$, with a new light scalar $\phi$, at future Z factories such as CEPC and FCC-ee. These new bosons $\phi$ and $Z'$ naturally appear in models with a new $U(1)$ gauge symmetry which is spontaneously broken and introduced in various new physics scenarios. The branching ratio of $Z \to Z' \phi \to Z' Z' Z'$ can be larger than $10^{-12}$, which gives $O(1)$ events at Tera-Z experiments, when a product of $g_X$ (new gauge coupling) and $\zeta$ ($Z$-$Z'$ mixing) is larger than around $10^{-6}$. We find that the search for $Z \to Z'Z'Z'$ can significantly improve the current bound on a kinetic mixing parameter $\epsilon$ in the dark photon case, where $e \epsilon \gtrsim \mathcal{O}(10^{-5})$ with $g_X={\cal O}(1)$ can be explored at Tera-Z experiments. We also show that a sufficiently large number of events with multi-lepton plus hadronic jets can be obtained in benchmark points, which cannot be realized by the usual decay of Z in the standard model.

Speaker: Takaaki Nomura (Sichuan University)

Nomura0819.pdf

14:40 Pseudo NG bosons from finite modular symmetry

Pseudo Nambu-Goldstone (pNG) bosons can play important roles in particle physics, such as being a light dark matter (DM), the QCD axion to solve the strong CP problem, and so on. I point out that such a pNG boson is naturally realized by the finite modular symmetry, which may originate from the geometry of extra dimensions in the superstring models. An accidental global U(1) symmetry arises due to the residual $Z_N$ symmetry, when the modulus is stabilized near a fixed point of the finite modular symmetry. To illustrate, I will show the realization of the KSVZ axion model to solve the strong CP problem, where the modulus is stabilized by the radiative potential generated by the vector-like quarks, based on arXiv:2402.02071 (JHEP) and 2405.03996 (JHEP). Since the finite modular symmetries were originally used to explain the flavor structure of the quarks and leptons, this observation suggests that there are non-trivial connections between the pNG mode, which may be the DM, and flavor physics. If time permits, I will discuss the existence of such pNG mode in other stabilization mechanisms and possible applications to particle physics based on 2409.19261 (JHEP) and 2412.18435 (JHEP).

Speaker: Junichiro Kawamura (IBS-CTPU)

slide_JKawamura_SI2025.pdf

15:00 Explosive production of Higgs particles and implications for heavy dark matter

In this talk, we propose a new Higgs-portal dark matter scenario considering the Higgsplosion effect, which is a hypothesis of the significant production rate of high multiplicity of Higgs particles at high $\sqrt{s}$. Our scenario allows heavy Higgs-portal dark matter of $m_\chi\gtrsim{\cal O}(1)$ TeV, while the typical scenario indicates the order of ${\cal O}(10-100)$ GeV. We show that the multiplicity can be as large as ${\cal O}(200)$ for the parameters of the Standard Model Higgs, independently of the kinematics of the particle production process. Our result is applicable to a wider class of models with other scalar fields, opening a new window for heavy DM.

Speaker: Seishi Enomoto (Kyushu Sangyo University)

Seishi_Enomoto.pptx

Seishi_Enomoto_pdf_ver.pdf

15:20 Dynamical Up Quark Mass Generation in QCD-like Theories

The possibility that the up quark mass is generated entirely through nonperturbative dynamics offers an elegant solution to the strong CP problem. In this talk, I will present a controlled calculation of the dynamically generated up quark mass in a class of QCD-like theories, based on supersymmetric QCD deformed by anomaly mediated supersymmetry breaking (AMSB). By matching the low-energy chiral Lagrangian of these models to standard QCD chiral perturbation theory at next-to-leading order, we identify the contributions responsible for additive quark mass renormalization. Remarkably, we find that for three flavors and three colors ($F = N = 3$), the dynamical up-quark mass can be of order one in units of the strange quark mass, potentially accounting for the full observed mass. I will discuss the parameter dependence of this effect, its behavior at large N, and the implications for the strong CP problem.

Speaker: Taewook Youn (Cornell University / KIAS)

2025:08:19.pdf

15:40 Lepton number violation in future lepton colliders and neutrinoless double beta decay

We investigate the origin of neutrino masses, focusing on theoretical models in which neutrinos are massive Majorana fermions.
Such neutrinos naturally lead to processes that violate the lepton number which is strictly conserved in the Standard Model.
We discuss the current constraints on such models from lepton number violating processes, such as neutrinoless double beta decays.
Especially, we consider a model extended by right-handed neutrinos with the seesaw mechanism, and discuss the impacts on the lepton number violating search for right-handed neutrinos in future lepton collider experiments.
The lepton number violating processes provide crucial insight into the fundamental nature of neutrinos and offer potential signatures of physics beyond the Standard Model.

Speaker: Towa Takahashi (Niigata university)

slide_TTakahashi_SI2025.pdf

16:00 → 16:30 Coffee & Discussion

16:30 → 18:10 Parallel session 3

Convener: Shohei Okawa (YITP, Kyoto University)

16:30 The oscillation formula of Majorana neutrino in Quantum Field Theory

We derive the oscillation formula of Majorana neutrinos based on quantum field theory. Since the Hamiltonian under the Majorana mass term does not conserve lepton number, the eigenstates of lepton number change complexly over time. With the Bogoliubov transformation, we successfully relate the lepton number eigenstates at different times. This method enables us to understand the time evolution of lepton number induced by neutrino oscillations phenomena in terms of transition probabilities. We also present the physical picture that emerges through the Majorana mass term.

Speaker: Tomoharu Tahara (Hiroshima-university)

SI2025_Tahara.pdf

16:50 Phenomenology of Neutrino-Dark Matter Interaction in DSNB and AGN

We investigate a neutrino-scalar dark matter (DM) $\nu\phi$ interaction encountering distinctive neutrino sources, namely Diffuse Supernova Neutrino Background (DSNB) and Active Galactic Nuclei (AGN). The interaction is mediated by a fermionic particle $F$ , in which the $\nu\phi$ scattering cross section characterizes different energy dependent with respect to the kinematic regions, and manifests itself through the attenuation of neutrino fluxes from these sources. We model the unscattered neutrino flux from DSNB via core-collapse supernova (CCSN) and star-formation rate (SFR), then incorporate the present Super-Kamionkande and future DUNE/Hyper-Kamiokande experiments to set limits on DM-neutrino interaction. For AGNs, NGC 1068 and TXS 0506+056, where the neutrino carries energy above TeV, we select the kinematic region $m^2_F \gg E_\nu m_\phi \gg m^2_\phi $ such that the $\nu\phi$ scattering cross section features an enhancement at high energy. Furthermore, taking into account the DM spike profile at the center of AGN, we constrain on $m_\phi$ and scattering cross section via computing the neutrino flux at IceCube, where the $\phi\phi^*$ annihilation cross
section is implemented to determine the saturation density of the spikes.

Speaker: Po-Yen Tseng (National Tsing Hua University)

slide_PYTseng.pdf

17:10 Solar neutrinos and future experiments

In this talk, I will discuss future solar neutrino observatories and their role in measuring solar neutrino oscillation parameters. These observatories will also contribute to determining the structure of the Sun and the Earth through the study of day-night asymmetry. Solar neutrinos, produced via the pp-chain and CNO cycle, travel directly from the solar core to the Earth. Detecting these neutrinos provides crucial insights into the thermonuclear reactions occurring in the solar core, enhancing our understanding of both the Sun and the standard stellar model.

Speaker: Pouya Bakhti (JBNU)

presentation.pdf

17:30 IWCD-PRISM for Dark Matter Direct Detection

Dark matter (DM) is one of the main components of the universe and strongly related to the evolution of the universe. In order to understand the nature of DM, numerous direct and indirect search experiments are on-going or planned. The Intermediate Water Cherenkov Detector (IWCD), a near detector planned for Hyper-Kamiokande, is equipped with a vertically movable capability that enables the implementation of the PRISM technique. This feature, originally designed to provide off-axis measurements for neutrino studies, may also offer advantages for DM direct detection. We obtain DM direct detection sensitivity of IWCD-PRISM with optimized kinematic cuts and realistic detector effects. We find that the expected sensitivity of IWCD-PRISM is comparable to that of DUNE-PRISM.

Speaker: Seong ha Kim (Chungnam National University / IBS-CUP)

[250819] 2025 Summer Institute IWCD PRISM for Dark Matter Search.pdf

17:50 PQ quality and scale hierarchy of extra-dimensional axions

Axions provide a compelling solution to the strong CP problem and a viable candidate for dark matter. We explore their realization in a minimal five-dimensional $M_4 \times S^1/\mathbb{Z}_2$ orbifold framework. An explicit one-loop Casimir energy calculation reveals that the irreducible axion potential induced by worldline instantons is exponentially suppressed, thereby ensuring a high-quality Peccei–Quinn (PQ) symmetry. We further investigate how warped geometry, $\mathbb{Z}_2$-odd gauge couplings, and fixed-point interactions influence the PQ symmetry quality and determine the hierarchy of the axion decay constant.

Speaker: Chang Hyeon Lee (Chungnam National University)

SI.2025.08.19.V9.pdf

16:30 → 18:30 Parallel session 4

Convener: Jeong Han Kim (Chungbuk National University)

16:30 Exploring chirality structure in nucleon decay

proposal): The search for baryon number violation offers a promising path to uncovering new physics. In this talk, we examine how measurements of different nucleon decay channels can shed light on the underlying theory. We first investigate the chirality structure of baryon-number-violating interactions through lifetime measurements of strangeness-conserving nucleon decay modes. Using an effective field theory framework, we show that the ratio of partial decay widths—specifically, Γ(p→ηℓ+)/Γ(p→π0ℓ+), where ℓ+ denotes a positron or anti-muon—is sensitive to this chirality structure. Moreover, we find that in certain new physics scenarios, decay channels involving both anti-leptons and anti-neutrinos can provide complementary insights into their structures. These results underscore the importance of searching for various decay modes in future nucleon decay experiments.

Speaker: Hiroki Takahashi (Japan)

SI2025_HT.pdf

16:50 Future beam dump experiments constraint on light bosons with lepton flavor violating couplings

We consider charged lepton flavor violation (CLFV) via a light and weakly interacting boson and discuss the detectability by future proton and lepton beam dump experiments. We focus on three types of CLFV interactions, i.e., the scalar-, pseudoscalar-, and vector-type interactions, and calculate the sensitivities of beam dumps to each CLFV interaction. We show that a wide region of the parameter space can be explored. Particularly, it is found that future beam dump experiments have sensitivities to very small coupling regions in which the rare muon decays, such as $\mu \to e \gamma$, cannot place bounds, and that there is a possibility to detect CLFV decays of the new light bosons.

Speaker: Kento Asai (YITP, Kyoto University)

SI2025_KentoAsai.pdf

17:10 VBF for Higgs to BSM at the future Muon Collider

In this talk, we discuss the direct coupling of the Higgs boson to BSM particles at the future Muon Collider (MuC). At high-energy MuC, the processes we consider are naturally dominated by vector boson fusion (VBF), which emits high-rapidity muon pairs. Thus, by studying forward muon pairs, we can probe the coupling. Furthermore, due to the characteristics of VBF, we can determine whether the process is Higgs-mediated.

Speaker: Yongik Jang (Kyungpook National University)

SI_2025_Jang.pdf

17:30 Quantum entanglement in top quark pair production at a photon collider

We explore quantum entanglement in top quark pair production at a photon collider realized via laser backscattering at an electron linear collider. By analyzing the $\gamma\gamma \to t\bar{t}$ process within the density matrix formalism, we quantify spin correlations and entanglement using concurrence and entropy-based measures. The high degree of control over photon polarization in this setup enables precise tests of quantum coherence and sensitivity to possible new physics effects. Our results demonstrate that such photon colliders provide a promising platform for probing fundamental aspects of quantum information in high-energy processes.

Speaker: Dong Woo Kang (Jeonbuk National University)

SI2025_DWK.pdf

17:50 Constraints on MeV Axions from Kaon Decays

The QCD axion is a compelling mechanism for solving the strong CP problem. Most studies have focused on axion models with a large decay constant, $(f_{a}\gtrsim 10^{9}\,\mathrm{GeV})$. However, recent work has pointed out that viable axion models may also exist for $(f_{a}\sim1\,\mathrm{GeV}$). In our research, we derive stringent constraints on this axion scenario from kaon decay measurements.

Speaker: Takaya Iwai (University of Osaka)

SI スライド.pdf

18:10 Trilinear Higgs Coupling as a Probe for Extended Higgs Sectors

Although the Higgs boson has been discovered, its couplings to Standard Model (SM) particles may deviate from SM predictions. Such deviations can arise in extensions of the SM, including those that modify the Higgs sector. In particular, extended Higgs models often exhibit different shapes of the Higgs potential depending on their structure. In this work, we focus on near-aligned extended Higgs models, which can be well described as a classical field. The shape of the Higgs potential in these models can be characterized by the trilinear Higgs boson coupling, providing a powerful classification tool. Precise measurements of this coupling at future collider experiments could serve as an efficient way to discriminate between different extended Higgs scenarios. In this talk, we calculate the trilinear Higgs coupling, including one-loop corrections from top quarks and new particles, for several representative nearly-aligned Higgs models. We also discuss the potential to constrain model-dependent parameters based on expected sensitivities at future colliders. This work is a work in progress.

Speaker: Shuhei Ohzawa (University of Toyama)

SI2025_ohzawa.pdf

18:10 → 19:30 Dinner

19:30 → 21:05 Poster session

19:30 Probing PBH dark matter scenarios with IceCube diffuse neutrino data

We study the signature of the final stage of the evaporation of primordial black holes (PBH), focusing on high energy neutrinos and gamma-rays. For distributions of PBH with finite widths in mass spectrum, we derive a new upper limits $f_{\rm PBH} \lesssim 10^{-4} - 1$ for $M_{\rm PBH} = 10^{15-20}$ g by utilizing the IceCube latest data set of diffuse neutrinos for $E_\nu \geq 30$ TeV. We note that a transient signature involving high-energy neutrinos at the final stage of primordial black hole (PBH) evaporation could offer a potential explanation for the recently reported ultra-high-energy (UHE) neutrino event by the KM3NeT collaboration. We also examine the sensitivity limit for detecting a single PBH burst as the origin of KM3NeT UHE event.

Speaker: Jeonghwan Park (Yonsei University)

19:35 General Pseudo Scalar Dark Matter and Direct Detection

n the WIMP framework, the Higgs portal has a relatively small Higgs–nucleon interaction compared to other mechanisms, and, since the mediator is the Higgs boson, it is subject to fewer theoretical constraints. However, recent improvements in the precision of direct detection experiments have placed increasing pressure on Higgs-portal dark matter models. In simple models, the preferred DM mass is typically pushed into the TeV range. O. Lebedev et al. propose a simple Higgs-portal model with softly broken symmetry (S^2+h.c.) in which the direct-detection amplitude is automatically canceled. This mechanism demonstrates that an electroweak-scale WIMP can satisfy all constraints without fine-tuning. However, in Cartesian coordinates, the cancellation mechanism is not apparent. We therefore formulate the theory in polar coordinates to make the mechanism explicit. Extending their setup, we consider a more general breaking term of the form (S^n+h.c.) and investigate the cancellation condition in this broader context.

Speaker: Mr Junho Kang (Chung-Ang university)

19:40 Higgs pole inflation in light of ACT results

Cosmic inflation was introduced to address several shortcomings of the standard Big Bang cosmology. The observed red tilt of the CMB power spectrum and potential future detection of primordial gravitational waves could provide valuable clues to reconstructing the inflaton potential. Recent small scale CMB measurements from the Atacama Cosmology Telescope (ACT), combined with Planck data, suggest an increased spectral index, creating tension with predictions of some well-studied inflationary models.

In this work, we investigate pole inflation in the presence of one-loop Coleman–Weinberg corrections arising from Standard Model or additional fields, focusing on both Higgs pole inflation and PQ pole inflation. We parametrize these loop effects as a running quartic coupling for the inflaton and study how the inflationary predictions change with different two-loop beta function coefficients of the running coupling.

Speaker: Jeonghak Han (Chungang university)

19:45 Gravitational Waves from Superconducting Cosmic Strings

Cosmic strings are one-dimensional topological defects that arise from the spontaneous symmetry breaking in the early universe. In particular, superconducting cosmic strings, which have attracted attention from an astrophysical perspective, are characterized by their interactions with matter fields and are thought to have formed during the grand unification epoch. Cosmic strings have been proposed as a potential source of primordial gravitational waves and may provide insights into new physics associated with grand unified theories. In this workshop, we will present research findings on gravitational waves induced by superconducting cosmic strings, based on numerical simulations of field dynamics.

Speaker: JINYOUNG JHUN (Rikkyo University)

19:50 OSPREY(Operator learning for Secondary Primordial black hole Radiation Emission Yield)

BlackHawk is a widely used tool for computing the secondary spectra of particles emitted via Hawking radiation from evaporating black holes. In order to account for particle hadronization and decay processes, it employs different computational backends—such as Hazma, PYTHIA, and HDMSpectra—depending on the energy scale of the initial emission. While effective in separate regimes, this hybrid approach introduces inconsistencies and interpolation ambiguities in the overlapping energy regions where the validity of multiple methods overlaps. To address this limitation, we develop a unified framework based on operator learning techniques, OSPREY(Operator learning for Secondary Primordial black hole Radiation Emission Yield). By training a neural operator on the combined datasets, we construct a surrogate model that consistently captures the secondary spectrum over the entire energy range. Our approach improves the continuity and accuracy of the spectrum, making it suitable for precision studies in both astrophysical and phenomenological applications involving Hawking radiation.

Speaker: Mingi Park (Yonsei University)

19:55 Vector Dark Matter From Hidden Gauge Symmetry : U(1)_D and SU(2)_D

We present a unified study of vector dark matter (VDM) from hidden gauge symmetries U(1)D or SU(2)D. Starting from the renormalizable Higgs-portal UV theory for VDM with a dark Higgs field, we integrate out the radial mode of the dark Higgs to derive the leading low-energy interactions for Higgs-portal VDM, which are constrained into the validity domain in the UV theory. We also make the VDM stability realized: for U(1)D, a dark charge-conjugation (residual Z2) forbids VDM from decaying; for SU(2)D, a residual/custodial symmetry similarly stabilizes the lightest state of VDM. While the Higgs-portal EFT for VDM looks similar in both cases, non-abelian self-interactions of SU(2)D qualitatively modify the thermal history relative to U(1)D. Finally, we show how the isospin representation of the dark Higgs that breaks SU(2) controls the VDM mass spectrum and the VDM–dark-Higgs interactions, and how this feeds into the relic density and phenomenology, highlighting the representation-dependent signatures.

Speaker: Sanghun Lee (Chungang University)

20:00 Mass spectrum and symmetry breaking in Non-Abelian gauge theory with extra dimensions of two-dimensional sphere

In the standard model, the mechanism for gauge symmetry breaking and the theoretical origin of the Higgs boson remains unclear.
Non-Abelian gauge theories in higher dimensions are good candidates to address this issue.
We have constructed a Non-Abelian gauge theory with extra dimensions of two-dimensional sphere. In this model, compared to conventional models such as those with $S^1$ and $T^2$, curvature of the extra dimensions and the non-commutative nature of the gauge group result in different features in gauge symmetry breaking process and the origin of scalar fields.
We will report the gauge symmetry breaking observed in the Kaluza-Klein expansion of four-dimensional gauge fields, as well as the mass spectrum obtained from the Kaluza-Klein expansion of the extra-dimensional gauge fields, which appear as scalar fields in our four-dimensional spacetime.

Speaker: Yuki Honda (Yokohama National University)

20:05 Surface Treatment of NaI(Tl) Crystals for Reducing Surface Contamination

COSINE-100 is an experiment designed to search for dark matter interactions using an array of scintillating NaI(Tl) crystals, which serve as both the WIMP interaction target and detector. We have found that contamination on the crystal surface affects the energy range of the dark matter signal. To improve the performance of detectors, we have developed cleaning methods using organic solvents to reduce surface contamination for the next-phase experiment, COSINE-200. In this poster, we present a new method for minimizing crystal surface contamination and discuss the corresponding results.

Speaker: Minki Son (Chungnam National University)

20:10 Reconciling Cosmological Tensions with Inelastic Dark Matter and Dark Radiation in a U(1)D Framework

We propose a novel and comprehensive particle physics framework that addresses multiple cosmological tensions observed in recent measurements of the Hubble parameter, S8, and Lyman-α forest data. Our model, termed `{\bf SIDR+zt}' (Self Interacting Dark Radiation with transition redshift), is based on an inelastic dark matter (IDM) scenario coupled with dark radiation, governed by a U(1)D gauge symmetry. This framework naturally incorporates cold dark matter (DM), strongly interacting dark radiation (SIDR), and the interactions between these components. The fluid-like behavior of the dark radiation component which originates from the self-quartic coupling of the U(1)D breaking scalar can suppress the free-streaming effects. Simultaneously, the interacting DM-DR system can attenuate the matter power spectrum at small scales. The inelastic nature of DM provides a distinct temperature dependence for the DM-DR interaction rate determined by the mass-splitting between the inelastic dark fermions which is crucial for resolving the Ly-α discrepancies. We present a cosmologically consistent analysis of the model by solving the relevant Boltzmann equations to obtain the energy density and number density evolution of different species of the model. The DR undergoes two ``steps" of increased energy density when the heavier dark species freeze out and become non-relativistic, transferring their entropy to the dark radiation and enhancing ΔNeff. The analysis showcases the model's potential to uphold the Big Bang Nucleosynthesis (BBN) prediction of ΔNeff but dominantly producing additional contributions prior to recombination, while simultaneously achieving correct relic density of DM though an hybrid of freeze-in and non-thermal production.

Speaker: Wonsub Cho (SungKyunKwan University)

20:15 Echoes of Self-Interacting Dark Matter from Binary Black Hole Mergers

Dark matter (DM) environments around black holes (BHs) can influence their mergers through dynamical friction, causing gravitational wave (GW) dephasing during the inspiral phase. While this effect is well studied for collisionless dark matter (CDM), it remains unexplored for self-interacting dark matter (SIDM) due to the typically low DM density in SIDM halo cores. In this work, we show that SIDM models with a massive force mediator can support dense enough DM spikes, significantly affecting BH mergers and producing a distinct GW dephasing. To incorporate the feedback of the BH orbital motion that can significantly modify the DM profiles, we use $N$-body simulations to analyze GW dephasing in binary BH inspirals within CDM and SIDM spikes. By tracking the binary's motion in different SIDM environments, we show that the Laser Interferometer Space Antenna (LISA) can distinguish DM profiles shaped by varying DM interaction strengths, revealing detailed properties of SIDM.

Speaker: Junseung Pi (Chungbuk National University)

20:20 Dark gauge-mediated supersymmetry breaking

We investigate dark gauge-mediated supersymmetry breaking with an unbroken U(1) gauge symmetry and a massless dark photon. Messengers charged under both Standard Model and dark gauge groups generate new soft SUSY-breaking terms via gauge kinetic mixing. Large mixing significantly alters superpartner spectra compared to standard GMSB, reduces the μ parameter, and predicts a relatively light Higgsino detectable at the LHC. Simple messenger scenarios yield a very light bino-dark photino state observable in exotic Higgs decays at future colliders. The cosmological and phenomenological effects of stable, fractionally charged messenger states are also explored.

Speaker: Jiheon Lee (KAIST)

20:25 Exploring the Degree of Freedom Beyond Standard Model via Primordial Black Hole Evaporation with Memory Burden Effect

Primordial black holes (PBHs) formed during the early universe provide a unique probe of physics beyond the Standard Model. In this study, we investigate the impact of additional degrees of freedom from supersymmetry (SUSY) particles and the memory burden effect (MBE) on the evaporation process of PBHs formed via first-order phase transitions. By analyzing how these factors influence the PBH lifetime, we aim to provide insights into potential new physics and constraints on early universe phase transitions. Our findings may offer indirect evidence supporting the existence of first-order phase transitions, contributing to a deeper understanding of high-energy physics and cosmology.

Speaker: Leah Ya-Ling Lin (National Tsing Hua University)

20:30 Leptogenesis from magnetic helicity of gauged U(1)_{B − L}

If the B – L symmetry is gauged with the addition of right-handed neutrinos, the standard model B – L current is anomalous with respect to the B – L gauge field itself. Then, the anomaly relation implies that the magnetic helicity of the B – L gauge field is related to the standard model B – L charges, although the whole universe is B – L neutral with right-handed neutrinos. Based on this, we propose a new leptogenesis scenario with the gauged B – L symmetry as follows. First, the magnetic helicity of the B – L gauge field is generated, e.g., by the axion inflation, together with the standard model and right-handed neutrino B – L charges, with the net B – L charge kept zero. The B – L charges in the standard model and right-handed neutrino sectors are then subject to washout effects from the interactions between them. After the washout effects decouple, the B – L gauge symmetry is Higgsed and the magnetic helicity of the B – L gauge field decays and generates B – L charges in the both sector; thanks to the washout effects, we obtain a non-zero B – L asymmetry. We show that the baryon asymmetry of the universe can be generated in this scenario, discussing the decay of the magnetic helicity of the B – L gauge field and the interactions between the right-handed neutrinos and the standard model particles. [JHEP 02 (2025) 192]

Speaker: Thanaporn Sichanugrist (The University of Tokyo)

20:35 Walking-dilaton hybrid inflation in dynamical scalegenesis

We propose a hybrid inflationary scenario based on eight-flavor hidden QCD with the hidden colored fermions being in part gauged under U(1) B-L symmetry. This hidden QCD is almost scale-invariant, so-called walking, and predicts the light scalar meson (the walking dilaton) associated with the spontaneous scale breaking, which develops the Coleman-Weinberg (CW) type potential as the consequence of the nonperturbative scale anomaly, hence plays the role of an inflaton of the small-field inflation. The B-L Higgs is coupled to the walking dilaton inflaton, which is dynamically induced from the so-called bosonic seesaw mechanism. We explore the hybrid inflation system involving the walking dilaton inflaton and the B-L Higgs as a waterfall field. We find that observed inflation parameters tightly constrain the B-L breaking scale as well as the walking dynamical scale to be $10^9$ GeV and $10^{14}$ GeV, respectively, so as to make the waterfall mechanism worked. The lightest walking pion mass is then predicted to be around 500 GeV. Phenomenological perspectives including embedding of the dynamical electroweak scalegenesis and possible impacts on the thermal leptogenesis are also addressed.

Speaker: HIROYUKI ISHIDA (Toyama Prefectural University)

20:40 Changing 21cm Signal History of Boosted Dark Matter

We consider the boosted dark matter(BDM) model that consists of two-component dark matter with the boost effect from the annihilation of heavier DM into lighter one and the self-heating effect from the self-interaction of lighter DM. These effects suppress the formation of small-scale structures, and this suppression affects 21cm signal. We expect that BDM model will change 21cm signal and reionization history, and that these change may detectable in Square Kilometer Array (SKA), a future 21cm hydrogen line observatory.

Speaker: Minsub Lee (Chungbuk National University)

20:45 Realizing Non-Singular Cosmologies within Horndeski Gravity

We present a minimal setup within the framework of Horndeski gravity that describes a nonpathological Genesis scenario. Our setup allows for a fully stable transition to the kination epoch, during which General Relativity (GR) is restored. This Genesis scenario circumvents the no-go theorem, albeit at the cost of encountering the risk of strong coupling in the past. Interestingly, our scenario admits two distinct regimes for the background evolution of the Hubble parameter during the Genesis phase: one with power-law behavior and one with manifestly non-power-law behavior. We explicitly show that, in both regimes, our model remains within unitarity bounds. However, in most cases, the resulting tensor spectrum is blue-tilted. We then investigate an alternative model in which the Genesis phase is followed by Starobinsky inflation. We find that corrections from the Genesis phase to Starobinsky inflation can account for the ACT data.

Speaker: Pavel Petrov (IBS, CTPU CGA)

20:50 Exploring Electroweak Phase Transition and Collider Signatures in Two-Higgs-Doublet Models

We investigate the electroweak phase transition (EWPT) and collider phenomenology in the Two-Higgs-Doublet Models (2HDM). The interplay between the thermal properties of the scalar potential and experimental constraints offers a promising framework to explore beyond the Standard Model physics. We analyze scenarios that may realize a strong first-order phase transition (SFOPT), which is essential for electroweak baryogenesis, and examine their possible signatures at current and future colliders.

Speaker: Soojin Lee (Konkuk University)

20:55 More is Different: Multi-Axion Dynamics Changes Topological Defect Evolution

We study topological defects in multi-axion models arising from multiple Peccei-Quinn (PQ) scalars. Using a simplified two-axion system, we reveal fundamental differences in the evolution of these defects compared to single-axion scenarios. This finding is particularly significant because, despite the fact that integrating out heavier axions reduces these models to an effective single PQ scalar theory at low energies, the actual physical behavior of topological defects differs markedly from single-axion predictions. Unlike single-axion models where conventional cosmic strings form, multi-axion scenarios with post-inflationary or mixed initial conditions generically produce networks of strings interconnected by high-tension domain walls. This results in a severe cosmological domain wall problem. We determine string-wall network instability conditions and discuss cosmological implications including the application to the QCD axion and gravitational wave generation. Our findings highlight that multi-axion dynamics can lead to qualitatively different outcomes for topological defects, challenging the conventional picture of cosmic evolution of topological defects based on single-axion models.

Speaker: Junseok Lee (Tohoku U.)

21:00 Emerging Photon Jets in the Hadronic Calorimeter: A Novel Signature of Neutral Long-Lived Particles at the LHC

We propose a new collider signature for neutral long-lived particles (LLPs): an emerging photon jet in the hadronic calorimeter (HCAL), from LLP decays to photons with no ECAL activity or tracks. Using the ultralight fermiophobic Higgs $h_f$ in the Type-I 2HDM as a benchmark, we study

$pp \to H^\pm h_f \to W^\pm h_f h_f$

where one $h_f$ decays in the ECAL and the other in the HCAL. Fast simulation shows this signature enables discovery-level sensitivity at the HL-LHC and opens a new direction in LLP searches.

Speaker: dongjoo Kim (Konkuk University)

Wednesday, 20 August

09:00 → 10:00 Lecture 7

Convener: Myeonghun Park (Seoul National University of Science and Technology)

09:00 AI in HEP/COSMO/ASTRO I

Speaker: KC Kong (University of Kansas)

L1.pdf

10:00 → 10:30 Coffee & Discussion

10:30 → 11:30 Special seminar 5

Convener: Hyun Min Lee (Chung-Ang University)

10:30 Cosmological collider physics and activities in IBS-CTPU-CGA

Speaker: Prof. Masahide Yamaguchi

11:30 → 18:30 Free discussion

Thursday, 21 August

09:00 → 10:00 Lecture 8

Convener: Jong-Chul Park (Chungnam National University)

09:00 AI in HEP/COSMO/ASTRO II

Speaker: KC Kong (University of Kansas)

L2.pdf

10:00 → 10:30 Coffee & Discussion

10:30 → 11:30 Lecture 9

Convener: Kyu Jung Bae (IBS)

10:30 Future colliders I

Speaker: Zhen Liu (University of Minnesota)

FutureColliders_Pheno_ZhenLiu_Yeosu_Korea_SI_2025_PartI.pptx

11:30 → 12:30 Lecture 10

Convener: Kyu Jung Bae (IBS)

11:30 AI in HEP/COSMO/ASTRO III

Speaker: KC Kong (University of Kansas)

L3.pdf

12:30 → 12:40 Conference Photo

12:40 → 14:00 Lunch

14:00 → 16:00 Parallel session 5

Convener: Chan Beom Park (Chonnam National University)

14:00 Searching for ways to probe pseudo-Nambu-Goldstone-Boson dark matter

This study explores a dark matter model in which a pseudo-Nambu-Goldstone boson arises as a viable dark matter candidate from the spontaneous and soft breaking of global $U(1)$ symmetries and stabilized by a residual $\mathbb{Z}_3$ discrete symmetry. The model introduces three complex scalar fields, singlets under the Standard Model gauge group, and charged under a dark $U(1)_V$ gauge symmetry together with a permutative exchange symmetry among three scalars. These features naturally suppress the dark matter--nucleon scattering cross section by its Nambu-Goldstone boson nature. In addition to conventional annihilation channels, the $\mathbb{Z}_3$ structure allows semi-annihilation processes, potentially leading to new phenomenological signatures. We analyze theoretical and experimental constraints, including relic abundance, Higgs invisible decays, and perturbative unitarity, and evaluate the elastic scattering cross section for boosted dark matter.

Speaker: Riasat Sheikh (Elementary Particle Theory Lab, Kyushu University, Japan)

RSheikh_SI2025_0821.pdf

14:20 Multi-component dark matter from Minimal Flavor Violation

Minimal Flavor Violation (MFV) offers an appealing framework for exploring physics beyond the Standard Model. Interestingly, within the MFV framework, a new colorless field that transforms non-trivially under a global ${\rm SU}(3)^3$ quark flavor group can naturally be stable. Such a new field is thus a promising dark matter candidate, provided it is electrically neutral. We extend the MFV framework for dark matter and demonstrate that dark matter can naturally be multi-component across a broad parameter space. For illustration, we consider a gauge singlet, flavor triplet scalar field and identify parameter spaces for multi-component dark matter, where only the lightest flavor component is absolutely stable and heavy flavor components are decaying with lifetimes sufficiently longer than the age of the universe. Phenomenological, cosmological and astrophysical aspects of multi-component flavored dark matter are briefly discussed.

Speaker: Shohei Okawa (YITP, Kyoto University)

SI2025_Okawa.pdf

14:40 A Z4 symmetric model for self-resonant dark matter

Models of multi-component dark matter can explain small-scale problems through the presence of self-interaction. We propose a model where DM consists of two scalar fields stabilized by a Z4 symmetry and which can take part in annihilation or semi-annihilation processes. Some of these scatterings can be Sommerfeld enhanced through the u-channel without the need of a light mediator. The semi-annihilation, in particular, can produce boosted DM particles that can be detected by neutrino or direct detection experiments, as well as dark photons or dark Higgs that can give signals in indirect detection searches. In this work, we analyze the standard limits for this model and also the consequences of the u-channel resonance in small-scale data, the calculation of relic abundance, and the signals relevant for direct and indirect detection experiments.

Speaker: Lucca Justino (Chung-Ang University)

SI-Yeosu-2025-2.pdf

15:00 Composite Dark Matter with Forbidden Annihilation

A dark matter model with QCD-like SU(N) gauge symmetry and electroweakly interacting dark quarks is discussed. In this model, the lightest G-parity odd dark pion is a main component of dark matter. I will discuss the relation between the mass spectrum of dark pions and annihilation channels which mainly contribute to the relic abundance. When the masses of dark matter and heavier dark pions are degenerate, dark matter mainly annihilates into the heavier dark pions and realizes heavy dark matter whose mass is ${\cal O}(1$-$10)$ TeV. I will also discuss the Sommerfeld effect of the annihilation channels.

Speaker: Takumu Yamanaka (The University of Osaka)

si_yamanaka.pdf

15:20 Superheavy Supersymmetric Dark Matter for the origin of KM3NeT Ultra-High Energy signal

We propose an explanation for the recently reported ultra-high-energy neutrino signal at KM3NeT, which lacks an identifiable astrophysical source. While decaying dark matter in the Galactic Center is a natural candidate, the observed arrival direction strongly suggests an extragalactic origin. We introduce a multicomponent dark matter scenario in which the components are part of a supermultiplet, with supersymmetry ensuring a nearly degenerate mass spectrum among the fields. This setup allows a heavy component to decay into a lighter one, producing a boosted neutrino spectrum with energy $E_\nu \sim 100$ PeV, determined by the mass difference. The heavy-to-light decay occurs at a cosmological redshift of $z \sim$ a few or higher, leading to an isotropic directional distribution of the signal.

Speaker: Yongsoo Jho (Yonsei University)

SI2025.pdf

15:40 Effects of electroweak phase transition on dark matter relic abundance

The true identity of dark matter (DM) is an unsolved problem in physics. Among the various DM candidates, weakly interacting massive particles (WIMP) are attractive because their abundance can be explained thermally. The WIMP abundance can be estimated using the Boltzmann equation, and particle masses at zero temperature are usually adopted. In this study, we take into account the electroweak phase transition, i.e., the particle masses should change with temperature through a varying vacuum expectation value of Higgs. We compare the DM abundance obtained using the conventional calculation method with our results using the temperature-dependent particle masses.

Speaker: Chikako Idegawa (Sun Yat-sen University)

SI2025_ChikakoIdegawa.pdf

14:00 → 16:00 Parallel session 6

Convener: Jeong Han Kim (Chungbuk National University)

14:00 Gravitational wave signatures of dark sector portal leptogenesis

We study the possibility of probing leptogenesis via stochastic gravitational waves (GW) arising from a dark sector assisted first-order electroweak phase transition. The same dark sector, with non-trivial transformation under an unbroken $Z_2$ symmetry is also responsible for providing the only source of CP asymmetry via one-loop interference with the tree level decay of a heavy right-handed neutrino into lepton and Higgs doublets. The new Yukawa and scalar portal couplings enhance the CP asymmetry allowing TeV scale leptogenesis without any resonant enhancement. Light neutrino masses arise from a combination of type-I and one-loop contributions with vanishing lightest neutrino mass. While the new degrees of freedom in sub-TeV range keep the detection prospects at terrestrial experiments promising, the new scalars enhance the strength of the electroweak phase transition keeping the GW signals within reach of near future experiments like LISA.

Speaker: Indrajit Saha (Indian Institute of Technology Guwahati, Assam, India)

SI2025_Indrajit.pdf

14:20 Leptogenesis from a Phase Transition in a Dynamical Vacuum

We show that a phase transition may take place in the early Universe at a temperature $T_*$ resulting a temperature dependent mass for right handed neutrinos (RHN) which finally relaxes to a constant value after electroweak symmetry breaking (EWSB). As a result, a requisite amount of lepton asymmetry can be produced near $T_*$ satisfying the observed baryon asymmetry of the Universe via sphaleron process even when zero temperature masses of the RHNs fall below the electroweak scale enhancing the detection possibility of RHNs. Interestingly, the framework is also capable of predicting a primordial lepton asymmetry (generated after EWSB) as hinted by helium abundance measurements, indicating a correlation with early phase of leptogenesis.

Speaker: Dipendu Bhandari (IIT Guwahati)

Dipendu-SI2025-PPT.pdf

14:40 Thermal leptogenesis in SO(10)× U(1)_A GUT

In this study, we show that thermal leptogenesis can be realized within the framework of the $SO(10)\times U(1)_A$ grand unified theory(GUT). Furthermore, by including flavor effects, we have found that the second-lightest right-handed neutrino makes a significant contribution. As a result, the mass derived in this study is approximately six times larger than the mass predicted for the right-handed neutrino by the $SO(10)\times U(1)_A$ GUT. This also implies that the mass of the left-handed neutrino becomes approximately one-sixth of the value predicted by the same symmetry.

Speaker: Kei SHIBATA (Nagoya Univ.)

SI_SHIBATA_v2.pdf

15:00 Decoherence of primordial perturbations in the view of a local observer

We study quantum decoherence of curvature perturbations at superhorizon scales caused by the gravitational nonlinearities. We show that cubic gravitational couplings, constrained by the spatial diffeomorphism invariance, lead to infrared (IR) and ultraviolet (UV) divergences in the decoherence rate at one loop. These divergences arise from fluctuations of deep IR modes which look like a background mode for a local observer and violent zero-point fluctuations in the deep UV, respectively. We argue that these divergences are unobservable, as they vanish when considering proper observables. We consider correlators defined using the geodesic distance for IR divergences and time-averaged correlators for UV divergences. To account for these observer's perspectives, we propose to consider an effective quantum state, defined in terms of actual observables, as a more appropriate probe of the quantum coherence of the system measured by an observer. We then evaluate the finite decoherence rate induced by superhorizon environment during inflation and at late universe. This talk is based on the paper arXiv:2504.10472.

Speaker: Fumiya Sano (Tokyo Institute of Technology / Institute for Basic Science)

Fumiya Sano.pdf

15:20 Detectability of the phase transition gravitational waves in the DFSZ axion model

In recent years, an increasing number of studies have focused on using gravitational waves to explore axions and the dynamics of Peccei-Quinn symmetry breaking at high energy scales in the early universe. To accurately quantify the capability of specific gravitational wave experiments to probe the axion properties, it is crucial to perform precise calculations of gravitational wave signals based on given axion models and to conduct detailed detectability analysis tailored to the experimental configurations. Therefore, in this work, we consider the widely-studied DFSZ axion model and, for the first time, perform precise calculations of the phase transition dynamics parameters and associated gravitational wave signals. Our results demonstrate that the DFSZ model allows a strong first-order phase transition for the Peccei-Quinn symmetry-breaking process at high energy scales exceeding $10^9 ~\mathrm{GeV}$. Moreover, by calculating the signal-to-noise ratio of the gravitational waves and comparing it with the thresholds of the Cosmic Explorer detector, we find that these signals are observable by the Cosmic Explorer with the energy scale range from $10^9~ \mathrm{GeV}$ to $10^{12} ~\mathrm{GeV}$. Notably, through Fisher Matrix analysis, we find that if Cosmic Explorer detectors observe these gravitational waves, the bubble wall velocity will be the first parameter to be determined. This study demonstrates that gravitational wave detection offers a powerful approach to investigating axion dynamics complementary to other experiments.

Speaker: Ms AiDi Yang (Sun Yat-sen University)

DFSZaxion-08-21-yad.pdf

15:40 Refining Gravitational Wave and Collider Physics Dialogue via Singlet Scalar Extension

Employing effective field theory techniques, we advance computations of thermal parameters that enter predictions for the gravitational wave spectra from first-order electroweak phase transitions. Working with the real-singlet-extended Standard Model, we utilize recent lattice simulations to confirm the existence of first-order phase transitions across the free parameter space. For the first time, we account for several important two-loop corrections in the high-temperature expansion for determining thermal parameters, including the bubble wall velocity in the local thermal equilibrium approximation. We find that the requirement of completing bubble nucleation imposes stringent bounds on the new scalar boson mass. Moreover, the prospects for detection by LISA require first-order phase transitions in a two-step phase transition, which display strong sensitivity to the portal coupling between the Higgs and the singlet.
Interestingly, signals from di-Higgs boson production at the HL-LHC probe parameter regions that significantly overlap with the LISA-sensitive region, indicating the possibility of accounting for both signals if detected. Conversely, depending on the mixing angle, a null result for di-Higgs production at the HL-LHC could potentially rule out the model as an explanation for gravitational wave observations.

Speaker: Van Que Tran (NCTS, National Taiwan University)

VQTran-GW-collider.pdf

16:00 → 16:30 Coffee & Break

16:30 → 18:30 Parallel session 7

Convener: Jong-Chul Park (Chungnam National University)

16:30 Stable dark matter from Pauli blocking in the degenerate fermion background with Quantum Field Theory

We study a mechanism to make dark matter stable based on the Pauli blocking in the fermion background. In the background where fermions occupy the states, the decay of dark matter to those final states is not allowed, as a result, DM becomes stable.
We derive the evolution equations of the distribution function in the quantum field theory and compare it with the Boltzmann equation.
We apply this mechanism to a realistic model of neutrino and dark matter.

Speaker: Junghoon Joh (SungKyunKwan University)

Summer Institute 2025_Junghoon_Joh.pdf

16:50 Cosmological Roles of Dark Photons in Axion-induced Electroweak Baryogenesis

An axion coupled to both the Higgs field and electroweak gauge fields can generate the observed matter-antimatter asymmetry via electroweak baryogenesis, if its decay constant lies between $10^5$ and $10^7$ GeV. However, the axion remains constrained by astrophysical and cosmological bounds. In this talk, we introduce the intriguing possibility that the axion is also coupled to dark photons. Depending on their roles, these dark photons can be categorized into three types: (i) alleviating constraints on the axion by suppressing its decay into Standard Model sector; (ii) serving as dark matter if sufficiently massive and stable; (iii) and contributing to dark radiation if ultralight. Building on this, we propose a model that simultaneously explains both the observed matter-antimatter asymmetry and dark matter.

Speaker: Ju Hyeong Kang (Pusan National University)

JHKang_SI2025.pdf

17:10 Can AI understand Hamiltonian mechanics?

With recent breakthroughs in deep learning, particularly in areas like natural language processing and image recognition, AI has shown remarkable abilities in understanding complex patterns. This raises a fundamental question: Can AI grasp the core concepts of physics that govern the natural world?
In this talk, as a first step towards addressing this question, we will discuss the possibility of AI understanding Hamiltonian mechanics. We will first introduce the concept of operator learning, a novel technique that allows AI to learn mappings between infinite-dimensional spaces, and its application to Hamiltonian mechanics by reformulating it within this framework. Then, we will test whether AI can derive trajectories in phase space given an arbitrary potential function, without relying on any equations or numerical solvers. We will then showcase our findings, demonstrating AI's capability to predict phase space trajectories under certain constraints. Finally, we will discuss the limitations, future research directions, and the potential for AI to contribute to scientific discovery.

Speaker: Tae-Geun Kim (Yonsei University)

TGKim_SI2025.pdf

16:30 → 18:30 Parallel session 8

Convener: Dong Woo Kang (Yonsei University)

16:30 Analysis of inflationary models in higher-dimensional uniform inflation

We consider higher-dimensional uniform inflation, in which the extra dimensions expand at the same rate as three-dimensional non-compact space during inflation. We compute the cosmological perturbation in $D+4$ dimensions and derive the spectral index $n_s$ and the tensor-scalar ratio $r$. We analyze five inflationary models: chaotic inflation, natural inflation, quartic hilltop inflation, inflation with spontaneously broken SUSY, and $R^2$ inflation. By combining the results from these models with the Planck 2018 constraints, we discuss that it is not desirable for the extra-dimensional space to expand at the same rate as the three-dimensional non-compact space, except for the case of one extra dimension.

Speaker: Takuya Hirose (Kyushu Sangyo Universitiy)

SI2025_Hirose.pdf

16:50 Leptogenesis in the PQ pole inflation

We propose a leptogenesis scenario where baryon asymmetry is generated from the rotation of the QCD axion in the PQ pole inflation scenario. The rotation originating from PQ explicitly breaking terms corresponds to the asymmetry of the PQ charge and is converted into the baryon asymmetry by the inverse decay of a right-handed neutrino. We show the correlation between the reheating temperature, mass of the right-handed neutrino, initial velocity of the axion, and the axion decay constant, realizing the axion kinetic misalignment for the correct relic density.

Speaker: Junho Song (Chung ang university)

2025 SI Junho Song.pdf

17:10 Dark photon-photon resonance conversion of GRB221009A through extra dimension

The recently observed very high energy (VHE) photons,GRB221009A, require a physics explanation beyond the standard model. Such energetic gamma ray bursts, originating from yet unknown very distance source at redshift z = 0.1505, would be directly scattered by extragalactic background lights (EBL) rendering its improbable detection at the earth. We show that dark photon which resides in extra dimension would be able to resolve this issue when it oscillates resonantly with the photon in similar fashion with neutrino oscillation.

Speaker: Qidir Maulana Binu Soesanto (Universitas Diponegoro)

Presentation_QMBS.pdf

17:30 Interaction between cosmic strings in higher-dimensional models

Many recent studies of cosmic strings highlight the importance of investigating them within the framework of field theory to better understand their properties. In this talk, we show how the shape of scalar potential influences the interaction between strings. Although many works of cosmic strings assume that the Mexica-hat potential to break $U(1)$ symmetry, various types of potentials are considered in models that aim to describe physics beyond the Standard Model. As one of the examples, we have investigated the interactions between strings in higher-dimensional models. We have found that they exhibit a novel distance dependence, which is absent in the case of the Mexican-hat potential. We also propose a conjecture to explain the emergence of this distance-dependent interaction. This presentation is based on https://inspirehep.net/literature/2835186.

Speaker: Yukihiro Kanda (ICRR, University of Tokyo)

SI2025_Kanda.pdf

17:50 Modern Computational Approaches to Post-Inflationary Reheating and Dark Matter Production

While analytical methods remain fundamental in physics, many phenomena require computational approaches to be fully understood. In early universe cosmology, this necessity becomes paramount: understanding post-inflationary dynamics—including resonant particle production, backreaction, and rescattering—demands numerical solutions beyond perturbative methods.
We employ lattice simulations on high-performance computing (HPC) systems to study non-linear inflaton dynamics and subsequent matter production. Recent advances in HPC accessibility enable us to explore previously intractable parameter spaces, particularly for models that connect inflation to dark matter production through mechanisms such as gravitational particle creation or inflaton decay chains.
However, fully simulating the thermal universe remains a significant challenge for future work. Current simulation tools are optimized for the very short timescales of initial particle production, making it computationally prohibitive to evolve the system through the entire thermalization process. Additionally, these lattice simulations, being semiclassical, struggle to capture quantum effects crucial for complete thermalization. Fortunately, strongly-interacting turbulent thermalization systems exhibit universal scaling behaviors during the energy redistribution phase. We are leveraging machine learning techniques to exploit this universality and develop predictive models for the thermalization process. By combining these learned patterns with subsequent Boltzmann calculations, we aim to develop a comprehensive framework that bridges the gap between early-time particle production and the eventual thermal equilibrium of the universe.

Speaker: Jong-Hyun Yoon (Chungnam National University)

20250821_SI2025_YOON.pdf

18:30 → 20:30 Banquet

Friday, 22 August

09:00 → 10:00 Lecture 11

Convener: Jae Sik Lee (Chonnam National University)

09:00 Future colliders II

Speaker: Zhen Liu (University of Minnesota)

FutureColliders_Pheno_ZhenLiu_Yeosu_Korea_SI_2025_PartII_III.pptx

10:00 → 10:30 Coffee & Discussion

10:30 → 11:30 Special seminar 6

Convener: Seokhoon Yun (IBS-CTPU)

10:30 AI in cosmology

Speaker: Jeong Han Kim (Chungbuk National University)

SI_2025_Jeong_Han_Kim.pdf

SI_2025_Jeong_Han_Kim_ppt.pptx

11:30 → 12:30 Lecture 12

Convener: Seokhoon Yun (IBS-CTPU)

11:30 Future colliders III

Speaker: Zhen Liu (University of Minnesota)

12:30 → 12:35 Closing remarks

Convener: Prof. Seodong Shin (Jeonbuk National University)

12:30 Closing remarks & Poster awards

Speaker: Jong-Chul Park (Chungnam National University)

25.08 설문 국문 QR 코드.jpg

25.08 설문 영문 QR 코드.jpg

12:35 → 14:00 Lunch

14:00 → 18:00 Discussion & collaboration