2026 CAU-IBS Beyond the Standard Model Workshop

7 Jun 2026, 12:00 → 11 Jun 2026, 18:00 Asia/Seoul

Chung-Ang University

The 2026 Chung-Ang University Beyond the Standard Model (CAU BSM) Workshop is the 7th international meeting on Physics Beyond the Standard Model (Higgs, Dark Matter, Neutrino, Axion, Flavor, Inflation, Gravitational Waves) in Chung-Ang University, Korea. The aim of the BSM Workshop is to discuss interesting current topics and initiate the collaboration between experts and participants working on BSM physics in the globe. The 7th workshop will be held as the joint efforts between CAU and Center for Theoretical Physics of the Universe (Particle Theory and Cosmology Group) in Institute for Basic Science. Registered participants are supposed to attend the workshop only in person. We hope that the CAU workshop is to keep the community moving with lively discussion and participation.

 

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Time Table

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Invited speakers

 

Kyu Jung Bae (Kyungpook National Univ)

Jae Hyeok Chang (Seoul National Univ)

Ki-Young Choi (Sungkyunkwan Univ)

Raymond Co (Indiana Univ)

Dumitru Ghilencea (Bucharest, IFIN-HH)

Jinn-Ouk Gong (Ewha Womans Univ)

Koichi Hamaguchi (Tokyo Univ)

Sungwoo Hong (KAIST)

Anson Hook (Maryland Univ)

Dong-hui Jeong (Penn State Univ)

Sunghoon Jung (Seoul National Univ)

Sin Kyu Kang (Seoultech)

Heejoo Kim (KIAS)

Hyung Do Kim (Seoul National Univ)

Yeongduk Kim (IBS CUP)

Youngjoon Kwon (Yonsei)

Shigeki Matsumoto (IPMU)

Chang Seong Moon (Kyungpook National Univ)

Hyung Mok Lee (Seoul National Univ)

Jong-Chul Park (Chungnam National Univ)

Myeonghun Park (Seoultech)

Seong Chan Park (Yonsei)

Misao Sasaki (IPMU & APCTP)

Ryosuke Sato (Osaka)

Kai Schmitz (Muenster Univ)

Chang Sub Shin (Chungnam National Univ)

Liang Sun (Wuhan Univ)

Wen Yin (Tokyo Metropolitan Univ)

SungWoo Youn (IBS DAG)

Gyunho Yoo (IBS CUP)

Seokhoon Yun (Kyungpook National Univ)

Jure Zupan (Cincinnati Univ)

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Workshop Avenue

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Banquet @ Hwangtojeong, 18:30-20:30 on 10 June.

Lunch @ UC Club (11th floor in Building 102), 12:30-14:00 on 8-11 June.

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Information

The sixth series: 2026 CAU BSM Focus Workshop (Theory)

The fifth series: 2025 CAU-IBS BSM Workshop

The fourth series: 2024 CAU-PNU BSM Workshop

The third series: 2023 CAU BSM Workshop

The second series: 2022 CAU BSM Workshop

The first series: 2021 CAU BSM Workshop

CAU Department of Physics: http://physics.cau.ac.kr

CAU THEP Group: https://sites.google.com/site/cautheplab

CAU HEP Center: https://hep.cau.ac.kr

CAU-IBS 2026 poster2.png

Sunday 7 June

13:30 → 14:00 Registration

14:00 → 15:15 Dark matter

14:00 Probing low reheating temperature with dark age 21cm signal

Speaker: Ki-Young Choi (Sungkyunkwan University (KR))

14:30 Scalar portal verifiable light dark matter and correlated gravitational wave signatures

Light DM candidates, motivated by the absence of WIMP signals in direct detection experiments, can yield observable direct detection signals if they interact through light mediators with sizeable couplings. However, such interactions generally lead to an under-abundant relic density due to efficient annihilation into the light mediators. This tension can be naturally resolved if DM freezes out during a non-standard cosmological epoch, such as a stiff-fluid dominated era, which enhances the expansion rate. These modified thermal histories leave characteristic imprints on the stochastic GW background, providing a unique probe of pre-BBN dynamics through deviations in the high-frequency spectrum.

Speaker: Erdenebulgan Lkhagvadorj (Sungkyunkwan University (KR))

14:45 Primordial Black Hole Hotspots Beyond Flat Spacetime

Evaporating primordial black holes heat the surrounding plasma via Hawking radiation, forming localized hotspots whose temperature may far exceed that of the cosmological background. Previous studies of hotspot formation and cooling have treated the subsequent energy transport in flat spacetime, thereby neglecting the expansion of the Universe. We formulate the diffusion equation governing the hotspot evolution in an expanding universe, and clarify the regime in which the formalism is valid. We find that hotspot formation is robust against cosmological expansion, and the critical distance scale where Hubble expansion overtakes diffusion coincides with the decoupling radius introduced in earlier work. However, the cooling stage is substantially modified: the plateau temperature decreases more steeply than in the flat-spacetime treatment, and this scaling cannot be obtained by simply redshifting the flat-spacetime solution because expansion also suppresses diffusive transport. As a consequence, all hotspots disappear within a finite time, as opposed to the flat-spacetime prediction of everlasting hotspots in part of the parameter space.

Speaker: Jong-Hyun Yoon (Chungnam National University)

15:00 B-Modes Beyond Inflation: Causal Tensor Sources in the Early Universe

Primordial B-mode polarization is often viewed as a smoking-gun signature of inflationary gravitational waves. However, as experiments such as LiteBIRD, the Simons Observatory, and CMB-S4 push toward sensitivities near r ~ 0.001, non-inflationary tensor sources may become observationally relevant. In this talk, I will introduce early causal tensor sources (ECTs), including dark-sector first-order phase transitions and topological defects (cosmic strings, domain walls), and explain how causality gives rise to a characteristic B-mode signal distinct from inflation. I will also present current state-of-the-art constraints on the ECT amplitude from South Pole Telescope B-mode measurements.

Speaker: Kylar Greene (University of New Mexico)

15:15 → 15:45 Coffee break

15:45 → 17:15 Dark matter

15:45 Circumstellar Medium of Supernovae as New Probes for Feebly-Interacting Particles

Speaker: Seokhoon Yun (Kyungpook National University)

16:15 Neutron Portal and Dark Matter-Baryon Coincidence: from UV Completion to Phenomenology

Speaker: Sudhakantha Girmohanta

16:30 On the Low-Energy Behavior of Dynamical Gauge Couplings

Speaker: Michael Shamma (Korea Institute for Advanced Study)

16:45 Peccei Quinn genesis

Speaker: Jun-Ho Song (Chung-Ang University)

Monday 8 June

09:30 → 10:30 Cosmo

09:30 Predicting the dark matter - baryon abundance ratio

We discuss relaxation solutions to the dark matter - baryon coincidence problem in the context of QCD axion dark matter. In relaxation solutions, a moduli dynamically adjusts the mass of dark matter and baryons until their energy densities are O(1) the same. Because the QCD axion is heavily connected to QCD, scanning the QCD axion mass inherently also scans the proton mass. In the context of relaxation solutions, this implies that the ratio of dark matter to baryon abundances (ΩDM/ΩB) is a ratio of beta functions showing that these models can only accommodate discrete values of ΩDM/ΩB thereby “predicting” the ratio of the dark matter to baryon abundances. The original composite axion model has only a single integer degree of freedom N, the size of the gauge group, and we show that when N = 8 the observed value of ΩDM/ΩB = 5.36 is reproduced to within its percent level error bars. Novel tests of this model include more precise measurements of ΩDM/ΩB, a better lattice determination of the dependence of the proton mass on the high energy QCD gauge coupling, as well as more traditional tests such as fifth force experiments.

Speaker: Anson Hook (University of Maryland)

10:30 → 11:00 Coffee break

11:00 → 12:00 Cosmo

11:00 Cepheid as a dark matter detector

Speaker: Prof. Hyung Do Kim (Seoul National University)

11:30 Can pre-inflationary axions form miniclusters?

The pre-inflationary axion dark matter scenario, with its uniform initial misalignment angle, is conventionally expected to yield smooth dark matter without substructure. We explore scenarios of pre-inflationary axion cosmology, where adiabatic temperature perturbations from inflation can source non-trivial axion density fluctuations through both the temperature-dependent QCD axion mass and anharmonic resonance with close-to-hilltop misalignment angles.

The former permits minicluster formation only in a narrow window; the latter produces O(0.1) density contrast at scales below the quantum Jeans momentum at matter–radiation equality, providing a clean initial condition for Schrodinger-Poisson simulations.

Speaker: Heejoo Kim (KIAS)

12:00 → 14:00 Lunch

14:00 → 15:30 Cosmo

14:00 Micro Black Holes may be Dark Matter of the Universe

Speaker: Misao Sasaki

14:30 TBA

Speaker: Jinn-Ouk Gong

15:00 Kinetic Isocurvature Perturbation

We formulate a new class of primordial perturbations called \textit{kinetic isocurvature perturbations}, where the mass density of dark matter is constant relative to the photon number density while the kinetic energy of dark matter fluctuates in space. Such perturbations naturally arise in scenarios where a nonrelativistic heavy field decays into relativistic dark matter particles with a spatially modulated rate. As dark matter cools and becomes nonrelativistic, these fluctuations in kinetic energy leave large-scale density perturbations essentially unaffected and therefore evade the Cosmic Microwave Background bounds on isocurvature perturbations, yet survive as spatial variations in the free-streaming scale, resulting in patch-by-patch variation of the matter power spectrum.

Speaker: Chang Sub SHIN (Chungnam National University)

15:30 → 16:00 Coffee break

16:00 → 17:30 Neutrino / Dark matter

16:00 Overview of matter creation double beta decay experiments

I would like to review future double beta decay experiments in terms of background, exposure, schedule, and sensitivities.

Speaker: Prof. Yeongduk Kim (Institute for Basic Science (IBS), South Korea)

16:30 Semi-visible Jets as a Hidden-Sector Signature at the LHC

Hidden-sector models provide a well-motivated framework for physics beyond the Standard Model, offering potential explanations for dark matter and other unresolved questions in particle physics. In a broad class of these models, particles produced at the Large Hadron Collider (LHC) may undergo complex showering and hadronization processes within a hidden strongly interacting sector. The resulting final states can contain a mixture of visible Standard Model particles and invisible dark-sector states, giving rise to a distinctive experimental signature known as semi-visible jets. Unlike conventional jets, semi-visible jets are characterized by a significant fraction of missing transverse momentum aligned with the jet direction, making them challenging to identify using standard search strategies. This talk reviews the theoretical motivation for semi-visible jets, their phenomenological properties, and the experimental techniques developed to distinguish them from Standard Model backgrounds. Recent results and future prospects for semi-visible jet searches at the LHC, including implications for dark-sector physics and upcoming analyses in the High-Luminosity LHC era, will also be discussed.

Speaker: Chang-Seong Moon (Kyungpook National University (KR))

17:00 Exploring Light Scalars in Type-I 2HDM with Boosted Double-$b$ Tagging at the LHC

In this talk, I will discuss the prospects of probing a light scalar state in the Type-I Two-Higgs Doublet Model (2HDM) at the LHC. In this framework, one of the additional scalar states can be as light as $\lesssim 100$ GeV while remaining consistent with current collider and flavour constraints, yet it can evade conventional search strategies due to its suppressed couplings to the SM Higgs and fermions. I will focus on electroweak production channels where the light scalar $h$ is produced in association with heavier states such as a pseudoscalar $A$ or a charged scalar $H^\pm$, followed by cascade decays yielding multiple $h$ in the final state. Owing to the mass hierarchy, the light scalar is typically boosted, allowing its decay $h \to b\bar{b}$ to be reconstructed as a fat-jet with two $b$-subjets. I will show that such ``multi double-$b$'' fat-jet signatures provide a promising probe of this scenario, particularly in regions with large mass splittings, and can extend the LHC sensitivity beyond the reach of conventional resolved analyses.

Speaker: CHANDRIMA SEN

17:15 Long-Lived Heavy Neutrinos from Neutrinophilic Charged Higgs at the HL-LHC

In this talk, I will discuss an alternative production mechanism for long-lived heavy neutrinos within the framework of neutrinophilic Higgs doublet models, where an additional Higgs doublet couples exclusively to the Standard Model (SM) lepton doublets and right-handed neutrinos (RHNs). This structure allows the vacuum expectation value (VEV) of the extra Higgs doublet to be much smaller than that of the SM Higgs, thereby generating naturally small Dirac neutrino masses without requiring extremely small Yukawa couplings.A distinctive feature of this framework is the presence of neutrinophilic charged Higgs bosons, which, once produced at the LHC through the Drell--Yan process, decay dominantly into heavy neutrinos and charged leptons. If the heavy neutrinos are sufficiently long-lived, their subsequent decays can give rise to displaced signatures at the LHC. Within the type-I seesaw framework with three RHNs, one of the heavy neutrinos can be long-lived even when it decays through on-shell gauge bosons. In this case, its lifetime is inversely proportional to the lightest neutrino mass while remaining consistent with neutrino oscillation data. I will discuss the displaced-vertex signatures of these long-lived heavy neutrinos produced from neutrinophilic charged Higgs decays at the High-Luminosity LHC.

The talk is based on arXiv:2604.00866.

Speaker: Prasenjit Sanyal (Asia Pacific Center for Theoretical Physics)

Tuesday 9 June

09:30 → 10:30 Flavor / Dark matter

09:30 Searching for new physics using rare lepton transitions

I will review how rare tau and muon transitions can be used to search for new physics. Of special interest are decays into light new physics states, that still lead to visible exotic signatures.

Speaker: Jure Zupan (University of Cincinnati)

10:30 → 11:00 Coffee break

11:00 → 12:00 Flavor / Dark matter

11:00 New Physics Searches at BESIII

The BESIII experiment is a symmetric e+e- collider operating at c.m.
energy from 2.0 to 4.95 GeV. With the world’s largest threshold
production data set of J/ψ (10 billion), ψ(3686) (2.6 billion), and
millions of D(s) meson pairs, we are able to search for various BSM
particles (dark sector, Z', X(17), etc) produced in e+e- annihilation
and meson decay processes, as well as searching for (very) rare decays
of charm mesons. This talk is to highlight recent BESIII searches for
FCNC decays, very rare decays, and decays into invisible final states,
of charm and light hadrons.

Speaker: Dr Liang Sun (Wuhan University (CN))

11:30 Search for dark sector particles and other highlights from Belle II

In this talk, we present recent results on dark sector search at Belle II experiment. In particular, we will report the searches for dark Higgs in inelastic dark matter scenario, axion-like particle searches both in ISR continuum and in B decays, and feebly-interacting particles in B decays. In addition, we will also report a few recent highlights including updates of R[D(*)] and B+ -> mu+ nu.

Speaker: Prof. Youngjoon Kwon (Yonsei University)

12:00 → 14:00 Lunch

14:00 → 15:15 Axion / dark matter / GW

14:00 Global Structure, Non-Invertible PQ Symmetry, and the DFSZ Domain Wall Problem

In this talk, I will introduce the notion of global aspects in the physics of particles and topological defects by taking a concrete example of DFSZ axion model. In particular, I will describe how various global structures play important roles in the domain wall problem of the DFSZ axion model. A precise identification of the axion string–domain wall network—and hence the true nature of the domain wall problem—becomes possible by recognizing a discrete overlap between the Peccei-Quinn symmetry and the SM gauge group.

An elegant solution to the domain wall problem can also be realized by introducing another global structure shared between the color and family gauge groups, which gives rise to discrete non-invertible Peccei-Quinn symmetries. This discrete non-invertible symmetry can then be slightly broken by small instanton effects in a UV completion in the form of an SU(9) color–flavor unification. In this part of talk, if time is permitted, I will discuss construction of non-invertible symmetry defect operator and its action on both local and line operators in the language of "partial gauging".

Speaker: Sungwoo Hong

14:30 A particle on a ring or: how I learned to stop worrying and love theta-vacua

Although the QCD Lagrangian allows CP violation by the theta-term, no such effect has been observed yet. This puzzle is called the strong CP problem. In this talk, I will review a recent debate on the order of limit in the path integral formulation of strong CP violation, and discuss the validity of the formulation by focusing on quantum mechanics on a circle.

Speaker: Ryosuke Sato

15:00 Holographic Origins of the QCD Vacuum Angle and Axion

We present a holographic construction of the QCD axion based on a warped 5D model. A key ingredient of our setup is the introduction of a bulk scalar field $\theta$ which is holographically dual to the topological operator of QCD. We identify the bulk modes corresponding to the $\eta'$ and axion states, and show that an adjustment analogous to that of the usual 4D axion takes place.
We trace the origin of the axion quality problem within this framework and demonstrate that its resolution requires significant axion compositeness, a limit where the physical state resides predominantly in the bulk gauge field.

Speaker: Dr Taewook Youn (Cornell University)

15:15 → 15:45 Coffee break

15:45 → 17:30 Axion / dark matter / GW

15:45 Probing the QCD Axion: Current Limits and Future Directions

The QCD axion is a well-motivated dark matter candidate arising from both the strong CP problem and cosmology. Recent advances in haloscope experiments and quantum-limited microwave detection have substantially expanded the search sensitivity toward the QCD axion parameter space. In this talk, I will review the current status of axion dark matter searches and present recent experimental results. I will also discuss future directions beyond conventional haloscopes, including challenges in the high-frequency regime, emerging quantum-enabled detection concepts, and opportunities to probe unexplored parameter space.

Speaker: Dr SungWoo Youn (Institute for Basic Science)

16:15 New Physics at the Pulsar Timing Array Frontier

I will review the 2023 pulsar timing array (PTA) evidence for a
stochastic gravitational-wave background at nanohertz frequencies and
discuss how PTA observations allow us to search for new particle and
gravitational physics, including: (1) physics beyond the Standard Model
in the early Universe, (2) dark matter in our galaxy and in the vicinity
of supermassive black-hole binaries, and (3) scenarios of modified
gravity. Along the way, I will present new gravitational-wave templates
for certain signal hypotheses and recommend best practices for the
analysis of future PTA data sets.

Speaker: Kai Schmitz

16:45 Status of GLIMPSE and Dark-Matter Mass from Angular Scanning

We propose a novel detection strategy for super-light dark matter (DM), m_DM ~ O(keV), using a detector based on Graphene Josephson Junctions (GJJ). By intimately integrating the π-bond electrons of graphene as the target material into a Josephson junction, we create a sensor capable of detecting energy deposits as small as O(meV). We evaluate the scattering rates between DM and free electrons in the two-dimensional graphene, incorporating Pauli-blocking factors and in-medium screening effects. Our analysis of pg- to µg-scale detectors demonstrates that this setup achieves superior experimental sensitivity due to its extremely low energy threshold. Furthermore, we demonstrate that this 2D direct detection framework allows for the determination of the DM mass scale through directionality observables. Due to the relative motion of the Earth through the Galactic DM halo, the event rates depend non-trivially on the orientation of the graphene plane relative to the DM flux. We show that the curvature of this resulting angular spectrum encodes critical information about the particle mass. By validating these theoretical expectations through numerical analysis of the GJJ detector, we establish that this platform serves not only as a highly sensitive probe for the discovery of super-light DM but also as a precision instrument for measuring its fundamental properties.

Speaker: Prof. Jong-Chul Park (Chungnam National University (KR))

17:15 Self-Resonant Dark Matter and its Z4 realization

Speaker: Seong-Sik Kim (Chungnam National University)

Wednesday 10 June

09:30 → 10:30 Axion / dark matter / GW

09:30 Axiogenesis and Kinetic Misalignment with Dissipation from Dark Magnetic Monopoles

We propose a framework in which the QCD axion simultaneously accounts for the baryon asymmetry and contributes to dark matter through its early-universe rotation. A Peccei–Quinn (PQ) field rotation corresponds to a conserved PQ charge, which can be transferred to baryon number via sphaleron processes (axiogenesis) and to the axion abundance through its kinetic energy (the kinetic misalignment mechanism). However, a rotating axion field that generates the observed baryon asymmetry via axiogenesis typically overproduces axion dark matter via kinetic misalignment. We present a model in which this excess abundance is reduced by interactions with dark magnetic monopoles. We show that monopole-axion couplings induce transitions between dyonic levels that efficiently dissipate the axion’s kinetic energy into dark fermions. The resulting cosmology features a multi-component dark matter sector consisting of axions, monopoles, and dark fermions with comparable energy densities. The viable parameter space requires an axion decay constant below ~10^9 GeV.

Speaker: Raymond Co (Indiana University)

10:30 → 11:00 Coffee break

11:00 → 12:00 Cosmo

11:00 Shock Waves from Single-Field Low-Scale Inflation

Low-scale inflation is increasingly motivated by current observational constraints. In this talk, I will discuss a generic dynamical feature that arises after inflation in a broad class of single-field models. A tachyonic instability can develop immediately after the end of inflation, leading to the rapid growth of field fluctuations and highly nonlinear dynamics. This process results in the formation of Hubble scale shock-like structures, whose subsequent collisions produce particles and a stochastic gravitational-wave background. These signals provide a new and potentially observable prediction of low-scale inflation, offering a novel probe over a wide range of energy scales. I will also show that a simple coupling of the ALP inflaton to the Higgs field may explain the baryon asymmetry through the induced wall dynamics and spontaneous baryogenesis.

Speaker: ＷＥＮ ＹＩＮ

11:30 de Sitter information paradox: Random state models and CMB probes

Speaker: Sung Hoon Jung (Seoul National University)

12:00 → 14:00 Lunch

14:00 → 15:30 GW / Dark energy / PBH

14:00 What have we learned from 10 years of GW observations?

The year 2025 marks ten years since the landmark detection of GW150914, which inaugurated gravitational-wave astronomy. Across four observing runs of the LIGO–Virgo–KAGRA (LVK) network, more than 300 events — primarily binary black hole mergers — have been detected, enabled by steady improvements in detector sensitivity and a rapidly expanding observable volume. These discoveries have reshaped our understanding of compact-object populations, binary evolution, and the astrophysics of strong-field gravity, while providing new tools for cosmology and fundamental physics. Yet, major questions remain regarding formation channels, population evolution, and the broader role of gravitational waves in multi-messenger astronomy. This talk will synthesize the key lessons from the first decade of observations and outline the scientific frontier for the next generation of gravitational-wave detectors.

Speaker: Hyung Mok Lee (Korea Astronomy and Space Science Institute)

14:30 PowerFull: fully relativistic full-shape galaxy two-point statistics for primordial non-Gaussianity and dark energy

Speaker: Dr Donghui Jeong (The Pennsylvania State University)

15:00 PBH DM and signals

Speaker: Prof. Seong Chan Park (Yonsei University)

15:30 → 16:00 Coffee break

16:00 → 17:15 GW / Dark energy / PBH

16:00 Quantum Gravity from Weyl conformal geometry

Speaker: Dumitru Ghilencea (Horia Hulubei National Institute of Physics and Nuclear Engineering (RO))

16:30 Weyl gauge symmetry at LIGO

Speaker: Vlad-Mihai Mandric (IFIN-HH)

16:45 Relativistic-like behavior of ALPs with non-relativistic momenta

Axion-like particles (ALPs) are among the leading dark-matter candidates. In the minimal cosine potential, cosmology imposes a robust requirement: by the epoch when ALPs behave as matter, the potential height needs to exceed the ALP energy density. This translates into a lower bound on the decay constant. A plausible loophole is to store most of the energy in nonzero-momentum modes while keeping the momenta non-relativistic. Using lattice simulations, we show that this does not evade the bound. When the condition is violated, the system behaves effectively as relativistic radiation rather than matter. For sufficiently small typical momentum, it also undergoes a nonlinear transition accompanied by the formation of “Baumkuchen-like” domain walls.

Speaker: Yuma Narita (Tohoku Univ.)

17:00 Electromagnetic Signatures of Dark Matter in the Terrestrial Environment

We present a novel framework to search for dark matter (DM) through its electromagnetic (EM) signatures in the terrestrial environment. Ultralight DM candidates, such as axions and dark photons, can induce nearly monochromatic EM fields via their coupling to ordinary photons. In the presence of the geomagnetic field, axion DM induces extremely low-frequency EM signals in the Earth–ionosphere cavity, with spectral features shaped by atmospheric conductivity and resonances. We develop a semi-analytical framework to predict these signals and compare them with geoscience data sets to place new constraints. We further extend this approach to dark photon DM, highlighting both similarities and key differences. These results establish terrestrial EM fields as a powerful and complementary probe of ultralight DM.

Speaker: Atsushi Taruya (Yukawa Institute for Theoretical Physics / Korea Institute for Advanced Study)

18:30 → 20:30 Banquet - Hwangtojeong

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Thursday 11 June

09:30 → 10:30 Dark matter

09:30 Revisiting Minimal Dark Matter Models

We revisit several minimal extensions of the Standard Model for dark matter. Depending on time, we discuss some or all of the following: (i) a scalar dark matter with higher-dimensional operators, where thermal misalignment provides a viable production mechanism; (ii) sterile neutrino dark matter in the presence of lepton flavor asymmetries; (iii) Majorana fermion dark matter with a coannihilating scalar, with the bino-slepton scenario in supersymmetry as a concrete benchmark; (iv) Majoron dark matter arising from a minimal extension of the seesaw mechanism. We present recent updates on each topic in light of current experimental constraints.

Speaker: Koichi Hamaguchi (University of Tokyo)

10:30 → 11:00 Coffee break

11:00 → 12:00 Dark matter

11:00 Direct detection of sub-eV dark matter with torsion balance experiments

Dark matter with sub-eV masses has an extremely high number density in our Galaxy, and its scattering with macroscopic objects can be significantly enhanced by coherence effects. Repeated scatterings with a target object can then induce a measurable acceleration. Torsion balance experiments with geometrically asymmetric test masses are, in principle, sensitive to such a signal. We show that existing torsion balance experiments originally designed to test the Equivalence Principle already provide the strongest constraints on dark-matter–nucleon scattering in the mass range 10^{-2}--1 eV.

Speaker: Dr Shigeki Matsumoto (Kavli IPMU)

11:30 Invisible Higgs interaction at the muon collider

Speaker: Dr Kyu Jung Bae (Institute for Basic Science)

12:00 → 14:00 Lunch

14:00 → 15:30 Dark matter / neutrino / collider

14:00 Quantum Sensing Radiative Decays of Neutrinos and Dark Matter Particles

Speaker: Prof. Myeonghun Park (Seoultech)

14:30 Infrared Freeze-In of Magnetic Dipole Dark Matter

We propose a novel mechanism for the cosmological production of keV - GeV mass dark matter that interacts with the Standard Model through a small effective magnetic dipole moment. Such an interaction can be radiatively generated if dark matter couples to heavier charged particles. Previous studies have focused on the case where these charged states are much heavier than the reheat temperature, such that freeze-in production of dark matter is sensitive to the ultraviolet details of reheating. Here, we instead consider the possibility that these heavy states have masses comparable to the dark matter mass and are charged under a new kinetically-mixed U(1)' . As a result, dark matter production is dominated by the infrared freeze-in of the heavy charged states that subsequently thermalize the rest of the dark sector to a temperature much below that of the visible bath. We delineate regions of parameter space consistent with cosmological and astrophysical constraints and identify benchmark scenarios that can guide the next generation of direct detection experiments searching for spin-dependent scattering of sub-GeV dark matter.

Speaker: Jae Hyeok Chang (Seoul National University)

15:00 Spontaneous CP violation in an axion model with seesaw mechanism

We study a sequestered realization of spontaneous CP violation in an extension of the DFSZ axion framework.

CP is imposed at the Lagrangian level, so that all couplings and mass parameters are real.

The only physical source of CP violation arises from a PQ-invariant relative alignment of the singlet vacuum expectation values.

Since this CP-odd vacuum parameter is orthogonal to the axion direction, it does not spoil the PQ solution
to the strong CP problem. Vector-like quarks generate effective quark Yukawa textures in which
the CKM phase originates from mass-matrix misalignment, while the electroweak scalar sector
remains CP conserving in the sequestered limit. In the lepton sector, a minimal seesaw realization
with two heavy Majorana neutrinos yields a characteristic column-phase structure in the Dirac
mass matrix, so that both low-energy leptonic CP violation and the leptogenesis CP invariant
are controlled by the same vacuum origin of CP violation. We present a representative CKM fit
and illustrate the correlated implications for the PMNS Dirac phase and the baryon asymmetry,
demonstrating the viability of a single CP-violating origin linking CKM, PMNS, and leptogenesis
within an axion framework.

Speaker: Prof. Sin Kyu Kang (Seoul National University of Science and Technology)

15:30 → 16:00 Coffee break

16:00 → 17:00 Neutrino / Dark matter

16:00 Search for Beyond Standard Model Physics with Reactor-Based CEvNS Search in NEON experiment

The detection of coherent elastic neutrino–nucleus scattering (CEvNS) is one of the primary research goals in contemporary neutrino experiments. Its observation provides critical insights not only into the Standard Model but also into physics beyond it, such as non-standard neutrino interactions, and establishes the so-called neutrino floor relevant for dark matter searches. Consequently, extensive efforts to observe CEvNS are underway worldwide.

The NEON experiment is a reactor-based CEvNS search utilizing NaI(Tl) crystal detectors. The detector system consists of six NaI(Tl) crystals with a total mass of 16.5 kg. These crystals achieve an average light yield of 25.6 photoelectrons per keV, enabling low-energy analyses down to the sub-keV region. The detector is installed at a distance of 23.7 m from the Hanbit Unit-6 reactor core in Yeonggwang, Korea. Data taking began in April 2022, and to date, the experiment has accumulated 860 days of reactor-on data and 223 days of reactor-off data under stable operating conditions.

For CEvNS detection in the NEON experiment, effective discrimination of scintillation-only events from PMT-induced noise and phosphorescence-related events is essential to achieve a sufficiently low analysis threshold. To address this challenge, a deep-learning–based event selection strategy has been developed using waveform structure information and pulse shape discrimination (PSD) parameters. This approach enables an analysis threshold of 5 photoelectrons, providing sufficient sensitivity for the CEvNS search. In addition, the abundant photon environment near the reactor allows the NEON experiment to perform complementary analyses on axion-like particles and dark photons.

By comparing event rates between reactor-on and reactor-off data after event selection, the NEON experiment aims to identify CEvNS interactions on sodium nuclei. In this presentation, we report the details of our analysis from the CEvNS and many other BSM phenomena based on NEON experimental data.

Speaker: Gyunho Yu (Institute for Basic Science)

16:30 Charged lepton flavor violation with light dark matter and muonium invisible decay

In this talk, I will present the prospect of lepton-flavor-violating (LFV) interactions of dark matter (DM) within an effective field theory framework, going beyond the conventional flavor-conserving paradigm. Considering scalar, fermion, and vector DM candidates, I study the three-body decays of charged leptons into a lighter lepton and a pair of DM particles. The invariant-mass distributions are shown to provide a useful handle to distinguish operator structures and probe the DM mass. Using current experimental bounds on LFV processes and leptonic decay measurements, I derive constraints on the effective interaction scales. For the electron–muon sector, radiative four-body decays are also examined as complementary probes. Finally, I analyze invisible muonium decays and find that their rates can be significantly enhanced, offering a promising signature for flavored DM in future experiments.

Speaker: Mr Sahabub Jahedi (Indian Institute of Technology, Guwahati)

16:45 $A_4$ symmetry combined with a type-II seesaw mechanism for neutrino mass generation

In this talk, I will discuss a flavour model based on an $A_4$ symmetry combined with a type-II seesaw mechanism for neutrino mass generation. The resulting neutrino mass matrix obeys a sum rule that, together with the measured mass-squared differences, fully determines the absolute neutrino mass spectrum. The constrained flavour structure
yields correlated predictions for lepton mixing parameters, leads to inverted ordering after imposing mixing constraints, restricts the Majorana phases and implies a neutrinoless double beta decay rate close to its maximal value for inverted ordering.
In the charged lepton sector, an approximate triality symmetry arises in the seesaw limit, suppressing muon flavour-violating processes and allowing only specific $\tau$ decay channels. The model provides a tightly constrained and experimentally testable framework linking neutrino masses, lepton mixing, and lepton-number-violating observables.

Speaker: Ranjeet Kumar (Seoul National University of Science and Technology)