The 14th KIAS Workshop, jointly held with the 6th AEI Workshop

27 Sept 2026, 18:00 → 3 Oct 2026, 12:30 Asia/Seoul

KIAS

Jae Hyeok Chang (Seoul National University), Seung J. Lee (Korea Institute for Advanced Study), Taewook Youn (Harvard University and KIAS)

The 14th "KIAS Workshop on Particle Physics and Cosmology" will be held jointly with the 6th “Asian-European-Institutes Workshop for BSM”.

The aim of this meeting is to gather theorists from participating institutes together to share their current research related to particle physics and cosmology, with a particular focus on BSM. Additionally, a number of overview talks from invited speakers have been organised to outline, and provide updates to, some broad classes of theoretical models. This joint workshop will provide opportunities for collaboration between researchers from different institutes, and help young researchers better promote themselves in the community. 

 

Talks are limited to invited speakers.
Regular talks are 25 minutes + 5 minutes for discussion, while student talks are 12 minutes + 3 minutes for discussion.

 

Invited Speakers

Wenyuan Ai (SJTU/TDLI)

Rodrigo Alonso (Durham)

Alfredo Aranda (Colima)

Hengameh Bagherian (Chicago)

Aritra Bal (KIT)

Ravneet Bedi (KAIST)

Zachary Bogorad (Fermilab)

Kierthika Chathirathas (KIT)

Arturo de Giorgi (Durham)

Melissa Diamond (McGill)

Shao-Feng Ge (TDLI/SJTU)

Yannis Georis (IPMU)

Jinn-Ouk Gong (Ewha)

Xiao-Gang He (TDLI)

Peisi Huang (Nebraska)

Joerg Jaeckel (Heidelberg)

Kiyoharu Kawana (KIAS)

Jörn Kersten (Bergen)

Valentin Khoze (Durham)

Kevin Langhoff (MIT)

Jiheon Lee (KIAS)

Junghwan Lee (SNU)

Sung Hak Lim (IBS CTPU-PTC)

Philip Lu (KIAS)

Peter Majcen (KIT)

Shigeki Matsumoto (IPMU)

Iwan Morton-Blake (TDLI)

Yushi Mura (KEK)

Daniel Naredo (KIT)

Mihoko Nojiri (KEK)

Seodong Shin (JBNU)

Satoshi Shirai (IPMU)

Oleg Titov (TDLI)

Keping Xie (TDLI/SJTU)

Chen Yang (KIAS)

 

Student Talks

Takafumi Aoki (Tokyo)

Subaru Fujisawa (IPMU)

Youngho Go (KAIST)

Ko Hirooka (Tokyo)

Shotaro Ieyasu (Tokyo)

Sungjung Kim (SNU)

Jaeyoung Park (SNU)

Tenta Tsuji (KEK)

Yaxuan Wen (Tokyo)

Heechan Yi (Yonsei)

Direction between Koreana Hotel to KIAS.pdf

KIAS_Wednesday_Excursion_Suggestions.pdf

Restaurant_Map_KIAS.pdf

Monday 28 September

08:30 → 09:20 Registration

09:20 → 09:30 Greetings

09:30 → 10:30 S1

Convener: Jae Hyeok Chang (Seoul National University)

09:30 Dark Matter During Phase Transitions

In this talk, I will discuss how a phase transition changes the dark matter properties and the related phenomenology.

Speaker: Peisi Huang

Huang KIAS workshop.pdf

10:00 The Sound of the QCD Phase Transition: Gravitational Waves from Newborn Neutron Stars

There is tentative evidence that the cores of the massive neutron stars consist of quark matter. I will discuss that the formation of such a quark-matter core during a galactic supernova could be accompanied by gravitational wave emission in the MHz band, sourced by the QCD phase transition. These signals constitute a new target for high-frequency gravitational wave detectors, suggesting they may offer a unique probe of QCD in an otherwise inaccessible regime.

Speaker: Jiheon Lee (KIAS)

KIAS_AEI.pdf

10:30 → 11:00 Coffee Break

11:00 → 12:00 S2

Convener: Prof. Jörn Andreas Kersten

11:00 Is Sterile Neutrino Dark Matter crying for GeV Heavy Neutral Leptons?

The ordinary and dark matter in the Universe may share a common origin in the framework of a minimal extension of the Standard Model by three right-handed neutrinos. A pair of such heavy neutral leptons (HNLs) can give masses to neutrinos, generate the baryon asymmetry at the electroweak scale and produce a large lepton asymmetry at the QCD scale, which is then resonantly transformed into an abundance of the third state that acts as sterile neutrino dark matter. The minimality of this setup, known as Neutrino Minimal Standard Model (νMSM), makes it highly predictive. Earlier attempts to pin down the properties of the HNLs based on the requirement to simultaneously explain the neutrino masses as well as the baryonic and dark matter abundances were hampered by an incomplete understanding of the quantum kinetic equations describing the HNLs throughout cosmic history. We perform the first parameter scan of the νMSM in which this shortcoming has been overcome. We find that the νMSM provides a common explanation for all aforementioned phenomena only within a well-defined parameter space that is limited in all directions, with HNL masses kinematically accessible by the SHiP experiment as well as searches at the LHC and future lepton colliders. Further predictions for the HNL decay branching ratios, CP-violation, and lepton number violation (LNV) make the model highly testable, bringing a discovery of the common origin of neutrino masses and all matter in the Universe within reach of existing and planned experiments.
Talk based on https://arxiv.org/abs/2609.28457

Speaker: Yannis Georis

main.pdf

11:30 Strongly Coupled Sectors in Inflation

Understanding the microscopic origin of primordial fluctuations remains a central challenge in inflationary cosmology. In this talk, I will explore a scenario where curvature perturbations interact with a strongly coupled sector known as unparticles. This setup allows for analytic control of cosmological correlators and reveals novel bispectrum shapes with distinctive phenomenological signatures. I will then discuss how we try to search for unparticles in the CMB. If time permits, I will also comment on a possible model realization called the Dark Walker.

Speaker: Dr Chen Yang

Slides_pheno_KIAS2610.pdf

12:00 → 14:00 Lunch

14:00 → 15:30 S3

Convener: Rodrigo Alonso De Pablo

14:00 Stochastic Tsunamis: Diffuse Scalar Background from Black Hole Formation

Massive astrophysical objects can support large, quasi-static scalar-field configurations. When such an object collapses into a black hole, for example in a core-collapse supernova, the field abruptly loses its source and is released as a propagating burst, a "scalar tsunami". Previous studies showed that individual bursts could be detectable on Earth, but only for sufficiently nearby sources and extremely light scalar fields. We take this idea further by considering their cumulative contribution throughout cosmic history. Their superposition produces a relic stochastic scalar background peaking in the $1\!-\!10^3\,\mathrm{Hz}$ range. I will present this mechanism, its predicted spectrum, and prospects for detection in future experiments. This background extends the experimental reach to scalar masses $m_\phi \lesssim 10^{-13}\,\mathrm{eV}$, roughly ten orders of magnitude above the range accessible through individual transient events.

Speaker: Dr ARTURO DE GIORGI

2026_deGiorgi_ AEI.pdf

14:30 Instanton processes at colliders

Speaker: VALENTIN,V KHOZE

Khoze-Instantons_AEI_2026.pdf

15:00 How a gravitational wave background affects particle processes

In one of his final papers, Steven Weinberg, together with Raphael Flauger, asked whether gravitational waves can be attenuated through their interactions with matter. They argued that no attenuation occurs, owing to a cancellation between graviton absorption and stimulated emission, as inferred from leading-order soft-graviton arguments. In this talk, I revisit this reasoning and show that it fails for the converse problem: the influence of a gravitational-wave background on matter. For unstable particles, real graviton emission and absorption appear to enhance decay rates. However, these apparent effects are a mirage, arising from an overreliance on leading-order perturbation theory. To resolve this issue, we formulate a new version of Weinberg’s soft graviton theorem that properly accounts for the presence of a graviton medium. We find that the mutual transparency of matter and gravitational radiation is preserved in general cases.

Speaker: Wenyuan Ai

15:30 → 16:00 Coffee Break

16:00 → 17:30 S4

Convener: VALENTIN,V KHOZE

16:00 Revisiting wormhole-induced global symmetry breaking

It is widely believed that exact global symmetries cannot exist in a consistent theory of quantum gravity. Euclidean wormholes, in particular, are generally thought to generate local symmetry-violating operators in the low-energy effective action, potentially leading to a serious axion quality problem. In this talk, I carefully revisit this argument and show that, when the wormhole-induced effective theory is treated consistently, these operators do not give rise to an axion quality problem.

Speaker: Dr Kiyoharu Kawana (KIAS)

KIAS_kawana.pdf

16:30 Amnesia in the Axion Misalignment Landscape

Pre-inflationary axion cosmologies admit a broad range of initial velocities and angles that generate a landscape of misalignment histories, whose nonlinear fate and small-scale structure remain uncertain. We use lattice simulations to follow the QCD axion in the kinetic misalignment scenario through the QCD crossover into the non-relativistic regime, towards matter-radiation equality. In the meV mass range, this landscape contains a continuum of ''summit-landing" solutions sensitive to both the initial angle and velocity. Nonlinear fragmentation reduces the comoving axion number and modifies the relation between the misalignment history and present relic abundance. For sufficiently large axion masses, strong self-interactions drive the small-scale spectrum towards the attractor found for post-inflationary axions, so that distinct early histories can lead to similar late-time structures.

Speaker: Kierthika Chathirathas

Kinetic_Misalignment.pdf

17:00 Revisiting Instanton Effects in the Broken Phase

Instanton effects in gauge theories with spontaneously broken gauge symmetries are relevant to several phenomenological settings, including electroweak baryon-number violating processes and nonperturbative contributions to axion physics. In such theories, the relevant configurations are not exact classical minima of the action, so evaluating their effects requires some care. Earlier work pointed out a subtle difficulty in this analysis. In this talk, we revisit semiclassical instanton calculus in broken gauge theories and show how this issue can be resolved in a controlled way. This talk is based on our recent paper, 2604.02987 [hep-th].

Speaker: Takafumi Aoki (ICRR, The University of Tokyo)

Aoki_KIAS2026.pdf

17:15 Yukawa Unification in Renormalizable SU(5) GUT with Froggatt-Nielsen Mechanism

Grand Unified Theories (GUTs) predict the unification of Yukawa couplings at high energies, but reproducing the observed flavor structure of the Standard Model (SM) remains challenging.

In this talk, we propose a renormalizable SU(5) GUT with the Froggatt–Nielsen (FN) mechanism, in which the SM Yukawa couplings are naturally explained by introducing heavy FN fermions. We further show that the presence of these FN fermions can simultaneously account for gauge coupling unification and the suppression of proton decay.

Speaker: Ko Hirooka (ICRR, the University of Tokyo)

Ko_Hirooka_KIAS.pdf

Tuesday 29 September

08:30 → 09:30 Coffee

09:30 → 10:30 S5

Convener: Peisi Huang

09:30 A Natural Dark Matter–Dark Energy Interaction from Axion–Monopole Dynamics

We propose a natural framework for interacting dark matter and dark energy based on axion–monopole dynamics in a dark gauge sector. Dark matter is composed of dark ’t Hooft–Polyakov monopoles, while dark energy is an ultralight axion whose coupling to the dark gauge field induces an axion-dependent dyon mass through the Witten effect. This generates a direct dark matter–dark energy interaction. We show that generic models with a significant dark matter–dark energy coupling suffer from a naturalness problem: the Coleman–Weinberg potential induced by the interaction is typically much larger than the dark-energy scale. In our model, the corrections arise from a monodromy tower of dyon states, allowing them to be exponentially suppressed. In the minimal setup, the interaction strength is predicted to be $\sim 0.1\%$, below the sensitivity of current observations. We discuss scenarios in which cosmological population of higher-charge dyons can enhance the interaction to the percent level, producing an apparent phantom dark-energy equation of state.

Speaker: Hengameh Bagherian (University of Chicago)

KIAS_30min.pdf

10:00 Physics Informed Machine Learning: Dark Matter and Galactic Dynamics

Machine learning (ML) has become a powerful tool for scientific research, and its effectiveness can be further enhanced by incorporating physical knowledge directly into the learning process. Physics-informed machine learning is a broad class of ML methods in which such knowledge is embedded in the choice of inputs, model architecture, or learning objective. In this talk, I will present examples of studying dark matter distribution in the Milky Way. I will show how dynamical equations can be incorporated into the learning objective through physics-informed neural networks, using the estimation of local dark matter density in galaxies as an example. Extensions of these methods can also address incomplete observations, such as dust obscuration in the Milky Way and the limited phase-space information available for dwarf galaxies. Together, these examples demonstrate how combining flexible ML models with physical symmetries, constraints, and dynamical equations enables data-driven studies of fundamental physics, from galaxies.

Speaker: Sung Hak Lim (IBS CTPU-PTC)

KIAS_no_backup.pdf

10:30 → 11:00 Coffee

11:00 → 12:00 S6

Convener: Sung Hak Lim (IBS CTPU-PTC)

11:00 "Effectively" Limiting Light Dark Matter with Loops

Dark matter searches often focus on a single interaction between dark matter and the Standard Model.  However, any tree level interaction between the dark sector and any Standard Model particle  can lead to many additional loop level interactions with many other Standard Model particles.  In this talk, I will show how dark matter which interacts with nuclei automatically gains interactions with electrons, photons, and light mesons.  Despite their loop level suppression, these additional effective interactions can lead to new observables and limits for nucleophillic dark matter.  In particular, many sub-GeV dark matter models which are difficult to observe or constrain via direct detection experiments are strongly limited by their effective interactions with photons, electrons and mesons.

Speaker: Melissa Diamond

loops.pdf

loops.pdf

11:30 Cavendish Searches for Millicharged Particles

A terrestrial population of millicharged particles can arise if they constitute a subcomponent of dark matter, or if sufficiently light millicharged particles are produced in cosmic-ray air showers. Through repeated scattering with ordinary matter, these particles thermalize to terrestrial temperatures in Earth’s environment. I will show that a simple electrified shell, such as a Van de Graaff generator, acts as an efficient accumulator of these room-temperature particles and can enhance their local density by up to twelve orders of magnitude. A millicharge detector placed inside the shell can therefore gain a dramatic boost in sensitivity. In particular, Cavendish tests of Coulomb’s law act naturally as both accumulators and detectors of this overdensity. Reinterpreting past Cavendish experiments already yields some of the strongest bounds on terrestrial millicharged-particle populations. I will also discuss a modified setup in which the Cavendish apparatus is surrounded by an additional charged shell, substantially improving the reach and potentially enabling detection of the minimum density generated by cosmic rays. With established electrostatic technology, such experiments can surpass the projected sensitivity of future accelerator searches for sub-GeV masses.

Speaker: Zachary Bogorad (Fermilab)

CavendishSlides - KIAS.pdf

12:00 → 14:00 Lunch

14:00 → 15:30 S7

Convener: Prof. Shao-Feng Ge (TDLI-SJTU)

14:00 MeV-Scale Dark Matter Candidates in the Seesaw Scenario

MeV gamma-ray astronomy is entering a new era, with several future missions opening a largely unexplored window for dark matter searches. In this talk, I will discuss well-motivated dark matter candidates associated with seesaw scenarios for neutrino mass generation and leptogenesis. I will first review sterile-neutrino dark matter in the Standard Model extended by right-handed neutrinos, where the conventional scenario typically points to masses of order 10–100 keV. I will then show how a gauged U(1){B-L} extension opens a much wider mass range through additional gauge interactions, allowing MeV-scale sterile-neutrino dark matter that can be probed by future MeV gamma-ray observations. The U(1){B-L} gauge boson itself can also constitute dark matter when the gauge coupling is sufficiently small. Finally, I will discuss Majoron dark matter realized through a gauged discrete Z_N　\subset U(1)_{B-L} symmetry. In particular, the Z_7 model naturally predicts a Majoron mass in the MeV range, providing a concrete target for future experiments such as COSI.

Speaker: Dr Shigeki Matsumoto (Kavli IPMU)

ShigekiMATSUMOTO.pptx

14:30 The Majoron Cosmological Window

The majoron is the Nambu-Goldstone boson associated with the spontaneous breaking of a global $B-L$ symmetry. Remarkably, the minimal majoron framework can simultaneously address three key empirical indications of physics beyond the Standard Model: neutrino masses, the matter-antimatter asymmetry, and dark matter. In this work, we identify the cosmologically viable region in which majoron dark matter and high-scale thermal leptogenesis can be realised simultaneously. We show that successful leptogenesis plays a central role in making this scenario predictive: by constraining the right-handed-neutrino mass scale, it determines the irreducible freeze-in contribution to the majoron abundance and fixes the size of the couplings relevant for visible dark matter decays. Combining the irreducible dark matter production mechanisms with warm dark matter limits and indirect searches for decaying dark matter, we map the resulting majoron cosmological window and show that future X- and gamma-ray telescopes can probe part of the surviving parameter space.

Speaker: Daniel Naredo (KIT)

Naredo_KIAS.pdf

15:00 Baryogenesis via the CKM Matrix with Minimal Flavor Violation

It is often claimed Standard Model CP violation is insufficient for baryogenesis. We present a counterexample using minimal flavor violation (MFV) in which all CP-violating effects arise from the
Cabibbo-Kobayashi-Maskawa (CKM) matrix. Our scenario involves a leptoquark field with MFVpreserving interactions whose decays to Standard Model particles yield the observed baryon asymmetry in the early universe. Unlike previous efforts to realize baryogenesis through the CP violation
of the CKM matrix, our scenario does not require any time-variation of model parameters.

Speaker: Kevin Langhoff

15:30 → 16:00 Coffee

16:00 → 17:30 S8

Convener: Dr Shigeki Matsumoto (Kavli IPMU)

16:00 Neutrino RG Running vs CP Phases in Oscillation Experiments

The neutrino oscillation involves two charged-current interaction vertices for the neutrino production and detection processes, each with a PMNS matrix element. Assuming these two PMNS mixing matrices to be the same, which is the usual case in the SM at the tree level, the oscillation probability is unitary. However, these two PMNS matrices can be different in the presence of RG running due to radiative corrections induced by new physics at the loop levels. A direct consequence is that effective non-unitarity can arise, although each PMNS matrix at the two vertices is still unitary. This affects not just the CP measurement at the accelerator experiments, but can also introduce CP effect in the reactor experiments and even allow JUNO to have the capability of disentagling the Dirac vs Majorana natures.

Speaker: Prof. Shao-Feng Ge (TDLI-SJTU)

260929_6thAEI.pdf

16:30 Testing new — reasonable as well as crazy — forces with atoms, ions and astrophysics

This talk will discuss a few tests of new physics beyond the Standard Model, with precision probes (e.g. atoms and ions) but also exploit the power of astrophysics for the same purpose.

Speaker: Joerg Jaeckel (Institut fuer theoretische Physik, Heidelberg University)

JJ.pdf

17:00 MeV Majoron Dark Matter from a Discrete Z_N Gauge Symmetry and Prospects for COSI

Majoron dark matter models are well motivated since they can provide a framework for explaining tiny neutrino masses and the baryon asymmetry of the Universe through leptogenesis. Conventional majoron models are based on a global U(1){B-L} symmetry. However, global symmetries are generally expected to be explicitly broken by quantum-gravity effects, making it difficult to theoretically control the majoron mass induced by such effects. Motivated by this issue, we consider a majoron dark matter model based on a discrete Z_N gauge symmetry, in which U(1){B-L} emerges only as an accidental symmetry at low energies. In particular, for Z_7, the majoron naturally acquires a mass in the MeV range, making it an interesting target for future MeV gamma-ray observations. As an example, we focus on the Compton Spectrometer and Imager (COSI) and estimate its sensitivity to MeV-scale majoron dark matter.

Speaker: Subaru Fujisawa (Kavli IPMU)

SubaruFujisawa_KIAS.pdf

17:15 Global Structures in Spontaneously Broken Gauge Theories

To date, most of the observables of particle physics have been only sensitive to the local Lie algebra of its gauge group. Recently, the importance of global aspects of gauge groups has begun to be widely appreciated, and the demand for their systematic study is emerging. The global structure ambiguity of the Standard Model gauge group is a good example. This strongly motivates a comprehensive analysis of the global structure and discrete factors (topological sectors) appearing in Grand Unified Theories. In this work, we initiate a systematic analysis of these global aspects. In particular, we show how methods of group theory and representation theory can be utilized to determine the global structure and topological sector structures emerging below the spontaneous symmetry breaking scale. In general, it is expected that these global aspects, while insensitive to local observables, are encoded in the physics of topological defects, which potentially contain invaluable information on the short distance physics.

Speaker: Youngho Go (KAIST)

Global Structures in Spontaneously Broken Gauge Theories.pdf

Wednesday 30 September

08:30 → 09:30 Coffee

09:30 → 10:30 S9

Convener: Dr Taewook Youn (Harvard University)

09:30 The theta angles of the Standard Model

We use generalised symmetries to study the shape and size of the CP violating theta parameter space. This study is then used to look at axion couplings and their dependence on the global structure of the SM group.

Speaker: Rodrigo Alonso De Pablo

AEIAlonso.pdf

10:00 Solving the strong CP problem with massless grand-color quarks

We propose a solution to the strong CP problem that specifically relies on massless quarks and has no light axion. The QCD color group $SU(3)_c$ is embedded into a larger, simple gauge group (grand-color) where one of the massless, colored fermions enjoys an anomalous chiral symmetry, rendering the strong CP phase unphysical. The grand-color gauge group $G_{\rm GC}$ is Higgsed down to $SU(3)_c\times G_{c'}$, after which $G_{c'}$ eventually confines at a lower scale, spontaneously breaking the chiral symmetry and generating a real, positive mass to the massless, colored fermion. Since the chiral symmetry has a $G_{c'}$ anomaly, there is no corresponding light Nambu-Goldstone boson.

Speaker: Dr Ravneet Bedi (KAIST)

Bedi_AEI.pdf

10:30 → 11:00 Coffee

11:00 → 12:00 S10

Convener: Hualin Mei (Tsung-Dao Lee Institute (CN))

11:00 LIGO-Virgo-KAGRA Constraints on Cosmological Phase Transitions

We use the latest LIGO-Virgo-KAGRA data to search for a stochastic
gravitational wave background from a first-order phase transition in the early Universe. We discuss the prior dependence in Bayesian inference approaches. We apply the results to constrain the parameters of a dark sector Abelian Higgs model.

Speaker: Prof. Jörn Andreas Kersten

LVKConstraints.pdf

11:30 Effects of Non-Instantaneous Thermalization on Gravitational Waves during Reheating

Gravitational waves provide a unique probe of the Universe before the CMB. Two generic gravitational-wave sources are expected in the formation of the hot Big Bang. First, a thermal plasma inevitably emits gravitational waves because gravity couples universally to the energy-momentum tensor, providing a gravitational counterpart of thermal radiation such as the CMB. Second, if inflation precedes the hot Big Bang, the inflaton must reheat the Universe by decaying into relativistic particles. Gravitons are then inevitably emitted through graviton bremsstrahlung.

Conventional calculations of these two gravitational-wave sources, however, rely on opposite assumptions. Thermal gravitational waves are calculated assuming that the inflaton decay products thermalize instantaneously through interactions with the surrounding plasma, whereas graviton bremsstrahlung is usually evaluated neglecting these interactions. In realistic case, however, thermalization occurs over a finite timescale, so the physical situation lies between these two limiting cases.

In this talk, I will show how the gravitational-wave spectrum is modified by the finite-time thermalization of the inflaton decay products.

Speaker: Tenta Tsuji (KEK Theory Center)

Rehating_GW_KIAS.pdf

11:45 High Frequency Gravitational Wave Detection with Superconducting Qubit

High-frequency gravitational waves (HFGWs) provide a unique window into high-energy and early-universe physics, yet they evade traditional macroscopic interferometry.
To bridge this detection gap, we propose a novel quantum-sensing paradigm utilizing superconducting transmon qubits embedded in resonant microwave cavities.
Through the inverse Gertsenshtein effect, HFGWs propagating in a static magnetic field resonantly excite a cavity mode.
By leveraging the characteristic spin-2 quadrupolar pattern of the induced electromagnetic field, we position qubits directly at the electric-field hot spots of the $\mathrm{TE}_{212}$ mode to act as localized sensors.
Crucially, configuring this array as an entangled quantum register via symmetric Dicke states unlocks a fundamental scaling advantage: the signal probability scales quadratically with the qubit number, translating to a $h_{\min} \propto n_q^{-3/4}$ strain sensitivity scaling.
Within the idealized benchmark considered here, the collective-qubit readout reaches beyond the conventional excess-power cavity benchmark.
Benchmarked against representative axion-haloscope parameters, this collective quantum enhancement decisively mitigates the profound Planck-scale suppression inherent to gravitational interactions, establishing a transformative framework for next-generation HFGW searches in the GHz band.

Speaker: Heechan Yi (Yonsei University)

Thursday 1 October

08:30 → 09:30 Coffee

09:30 → 10:30 S11

Convener: Jinn-Ouk Gong

09:30 Quantum and Quantum-informed Machine Learning for Jet Physics at the LHC

Speaker: Mr Aritra Bal (Karlsruhe Institute of Technology)

KIAS Workshop 2026.pdf

10:00 Dark Matter Inelastic Scattering with Nuclei

The talk is devoted to the role of excited final nuclear states in WIMP-nucleus scattering. We generalize the formalism of non-relativistic effective field theory to inelastic scattering and apply the state-of-the-art Relativistic Configuration-interaction Density functional theory to evaluate the event rates in direct detection experiments. We show that for certain interaction operators, the expected signal is significantly enhanced, by 1-3 orders of magnitude, if one takes the contribution of inelastic channel into account.

Speaker: Oleg Titov (TDLI)

Titov_KIAS_Workshop_2026_Slides.pdf

10:30 → 11:00 Coffee

11:00 → 12:00 S12

Convener: Wenyuan Ai

11:00 JUNO Recent Results

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20-kton liquid scintillator detector located in southern China. Its primary goal is the determination of the neutrino mass ordering through precision measurements of reactor antineutrino oscillations at a baseline of 52.5 km. In addition, JUNO will deliver world-leading measurements of neutrino oscillation parameters while pursuing a broad scientific programme including solar, atmospheric, geoneutrino and supernova neutrinos, as well as searches for rare processes beyond the Standard Model. Following the start of physics operations in 2025, JUNO has continued stable data taking and is steadily expanding its scientific reach. In this seminar, I will present the latest results from the experiment, including reactor antineutrino oscillation measurements and highlights from JUNO's broader physics programme. I will also discuss the implications of these measurements and the prospects for future discoveries as JUNO accumulates additional exposure.

Speaker: Iwan Morton-Blake (Tsung-Dao Lee Institute / Shanghai Jiao Tong University)

JUNO_2026Results_KIAS14th_IwanMortonBlake.pdf

JUNO_2026Results_KIAS14th_IwanMortonBlake.pptx

11:30 Probe of Solar Neutrino Magnetic Moments through Spin–Flavor Precession: Resonance Structure and Antineutrino Appearance

We investigate solar-neutrino spin–flavor precession (SFP) induced by magnetic moments
in the three-active-flavor framework. For Majorana neutrinos, SFP can convert solar neu-
trinos into antineutrinos of different active flavors. In the Dirac case, SFP instead produces
sterile right-handed states and can lead to the disappearance of active neutrinos. Using
the full 6 × 6 Hamiltonians and GS98 and AGSS09 solar profiles, we examine propagation-
eigenvalue crossings at B⊥ = 0 and the projected magnetic couplings between the corre-
sponding states. For normal mass ordering and 1 ≤ Eν /MeV ≤ 20, we confirm the absence
of finite-density Majorana crossings. A magnetically coupled Dirac crossing emerges above
approximately 12 MeV but involves only a subdominant electron-flavor component, limiting
resonant disappearance. Nonresonant Majorana conversion nevertheless offers a distinctive
lepton-number-violating solar ¯ νe signal, motivating our sensitivity study for the Jinping
Neutrino Experiment. For a proposed 3 kt detector operating for five to ten years, we
project a 90% C.L. sensitivity of P (νe →¯
νe) ≃ (0.85− 1.3) × 10−5. In the µ12-only bench-
mark, optimistic solar-core transverse magnetic fields of B⊥ = 7− 10 MG imply a reach
of |µ12| ≃ (2.3− 4.1) × 10−13 µB , numerically below existing direct-scattering limits and
commonly quoted stellar-cooling bounds. This could enable Jinping to provide one of the
most stringent projected terrestrial sensitivities to Majorana transition magnetic moments.

Speaker: Prof. Seodong Shin (Jeonbuk National University)

KIAS-AEI2026.pdf

12:00 → 14:00 Lunch

14:00 → 15:30 S13

Convener: Prof. Seodong Shin (Jeonbuk National University)

14:00 Primordial Black Hole Formation and Reformation

Primordial black holes (PBHs) can arise in a wide range of early Universe scenarios, from inflation to first-order phase transitions (FOPTs). In the first part of this talk, I will discuss PBH formation in FOPTs, where dark sector particles trapped in the old phase form compact remnants called thermal balls that can evolve into Fermi balls and collapse into PBHs. Slow cooling of these remnants can delay this collapse beyond the CMB era, evading bounds on their density fraction from recombination and opening the intermediate mass black hole range to PBH binary merger and supermassive black hole seed populations. Alternatively, light PBHs formed from dark matter (DM) particles can subsequently Hawking evaporate, regurgitating the same types of particles and allowing viable DM production in parameter space excluded to thermal freeze-out. In the second part, I will discuss PBH reformation, which involves light PBHs with $M \lesssim 10^{9}\,\mathrm{g}$ that evaporate before BBN and can induce an early matter-dominated era given a moderate initial abundance. During this era, the growth of PBH density perturbations along with a lowered collapse threshold can trigger re-collapse into much heavier reformed PBHs. These reformed PBHs survive far longer than the original population and can potentially emit Hawking radiation in the present day, detectable by next-generation gamma-ray and cosmic-ray experiments. The rapid reheating from the initial PBH evaporation generates a coincident stochastic gravitational wave background potentially within reach of CMB-S4.

Speaker: Mr Philip Lu (KIAS)

PBH Formation and Reformation KIAS 2026.pdf

14:30 Quantum Clausius Relation in an Inflationary Universe

In this talk, I will present a quantum Clausius relation for conformal fields inside the apparent horizon of a quasi de Sitter spacetime. We calculate the net horizon heat flow from the renormalized stress-energy tensor from trace anomaly of Weyl symmetry and independently evaluate the evolution of the renormalized von Neumann entropy using the replica method. At leading order in the Hubble-flow expansion $\epsilon$, the two results agree exactly, without invoking gravitational equations of motion. I will then discuss how local curvature contributions extend this result to a scheme-independent entropy balance that includes the corresponding Wald entropy from the non-equilibrium by the higher curvature term $R^2$. These findings provide a quantum field theoretic account of dynamical horizon thermodynamics beyond exact de Sitter equilibrium.

Speaker: JungHwan Lee (Seoul National University)

KIAS_Quantum_Eq_qdS.pdf

15:00 Particle transport in electroweak baryogenesis: from field theory to Boltzmann

Electroweak baryogenesis, a scenario for explaining the matter-antimatter asymmetry of the Universe, requires a description of particle transport in a nonequilibrium plasma in the presence of a spacetime-dependent bubble-wall background. This transport is usually described by Boltzmann equations in the quasiparticle picture, where a CP-violating background modifies the quasiparticle distributions and generates particle-antiparticle asymmetries.

In this talk, I will review conventional approaches to deriving these Boltzmann equations from quantum field theory and discuss effects and theoretical issues that have not been adequately addressed in previous treatments. I will then introduce our recently proposed systematic approach, which provides a more transparent derivation and is applicable to a broad class of systems.

Speaker: Yushi Mura

AEIworkshop2026.pdf

15:30 → 16:00 Coffee

16:00 → 17:30 S14

Convener: Satoshi Shirai (Kavli IPMU)

16:00 Enhancing the Charged Higgs Decay to Bottom and Charm Quarks

A model with two Higgs SU(2) doublets and a Z3 flavor symmetry is shown to generate an enhancement of its charged Higgs coupling to c and b quarks. The enhancement allows the model to reproduce the ATLAS excess associated to the process H ±  → bc for a charged Higgs mass of 130 GeV, and considering a potential search at the future LHeC, the analysis suggests viability for its detection.

Speaker: Alfredo Aranda

Aranda_Charged_Talk_KIAS.pdf

16:30 Science with LLM -- Role of Small LLMs

Speaker: Prof. Mihoko Nojiri (Theory Center, IPNS, KEK)

KIAS2026.pdf

17:00 Cosmic Strings in Multi-Step Symmetry Breaking

We study the magnetic flux structure of metastable cosmic strings arising from multi-step symmetry breaking in an extended gauge theory. We show that the ordering of the final symmetry breaking and string decay determines whether the flux is confined within the string or not. We discuss the implications of these results for cosmic string dynamics and gravitational-wave signatures.

Speaker: Yaxuan Wen

po.pdf

17:15 Variable stars as a dark matter detector

There are many astrophysical environments in the Universe where the local dark matter density may be significantly enhanced. Variable stars located in such environments may provide a probe of high-density dark matter. In this work, the resonant conversion of meV-scale dark photon dark matter into photons inside stars is studied. The resulting additional energy injection can affect the pulsation properties of variable stars. Future observations of variable stars across diverse astrophysical environments may therefore provide new insights into local dark matter density enhancements and their astrophysical implications.

Speaker: Jaeyoung Park (Seoul National University)

202609_KIAS_JYP.pdf

17:30 → 20:00 Banquet

Friday 2 October

08:30 → 09:30 Coffee

09:30 → 10:30 S15

Convener: Eung Jin Chun

09:30 Leptogenesis Determined By Low Energy Parameters

We study thermal leptogenesis in three predictive type-I seesaw models in which the neutrino Dirac mass matrix is equal to the mass matrix of up-type quarks, Model A, or down-type quarks, Model B, or charged leptons, Model C. In this framework, the seesaw relation permits a full reconstruction of the heavy right-handed neutrino mass matrix from low-energy neutrino parameters, which greatly reduces the parameter freedom. In these cases, viable solutions are found in model B, and model C. Both point to a close-mass pair of heavy neutrinos satisfying |Mi −Mj|/Mi < 10−3, while remaining outside the conventional quasi-degenerate resonant regime. Neutrinoless double beta decay is further studied for all parameter points that can generate an acceptable baryon asymmetry ηB = (6.12 ± 0.20) × 10−10. The predicted effective Majorana mass for certain cases can be probed by next generation experiments with sub-10 meV sensitivity. This framework therefore provides clear targets for future searches.

Speaker: Xiao-Gang He

AEI6th-Leptogenesis.pdf

10:00 Chart of dynamics in single-field inflation

Speaker: Jinn-Ouk Gong

10:30 → 11:00 Coffee

11:00 → 12:30 S16

Convener: Seung J. Lee (Korea Institute for Advanced Study)

11:00 Tensor-Network Simulations of Hamiltonian Lattice Gauge Theories: Truncation and Scattering

Tensor-network methods provide a powerful framework for studying equilibrium and nonequilibrium properties of low-dimensional quantum many-body systems. In this talk, I will discuss the application of tensor-network methods to Hamiltonian lattice gauge theories, focusing first on the dressed-site formalism, the algorithmic construction of its local gauge-invariant basis, and systematic and optimized approaches to truncating that basis. I will then turn to scattering dynamics. Using creation operators that generate dressed, localized excitations above the interacting vacuum, we selectively prepare and detect quasiparticle wave packets. We test this approach with matrix product states in pure hard-core Hamiltonian QCD on a ladder lattice and show how the resulting dynamics can resolve scattering outcomes.

Speaker: Peter Roland Majcen (Karlsruhe Institute of Technology)

kias_workshop_seoul_Peter_Majcen.pdf

11:30 Do Cosmic String Segments Emit Gravitational Waves?

Recent pulsar timing array (PTA) observations have provided indications of a stochastic gravitational-wave (GW) background in the nanohertz frequency band, stimulating intense interest in its possible origin. Among proposed beyond-the-Standard-Model explanations, models based on metastable cosmic strings have been found to fit current PTA data relatively well. When these strings decay, they fragment into finite segments with monopoles and antimonopoles at their endpoints. Strongly accelerated by the string tension, the endpoints have been expected to undergo violent oscillations. GW emission from these segments has therefore been thought to make a significant contribution to the nanohertz background, alongside emission from string loops. In this talk, I will revisit this picture by taking thermal fluctuations on the segments into account. We show that monopoles frequently collide with these fluctuations, generating an effective resistance that suppresses or even prevents oscillation. Under realistic cosmological conditions, the resulting GW contribution from string segments is negligible. I will discuss the physical origin of this suppression and its implications for interpreting PTA signals in metastable cosmic-string scenarios.

Speaker: Satoshi Shirai (Kavli IPMU)

cosmic_string.pdf

12:00 Assessing the Naturalness of the Reheating Temperature Based on Leptogenesis

Explaining the baryon asymmetry through leptogenesis requires a sufficiently high reheating temperature. Conventional analyses have obtained a lower bound of $10^{10}\,\mathrm{GeV}$ within specific regions of parameter space fixed by hand. However, the lower bound in the general parameter space remains unclear. In particular, it may be possible to lower the reheating temperature arbitrarily through parameter tuning. We therefore use Bayesian inference to investigate the range of reheating temperatures consistent with natural leptogenesis.

Speaker: Shotaro Ieyasu

The14th_KIAS_Shotaro_Ieyasu.pdf

12:15 False Learning in Sparse Parity: From Reversed Updates to Resonant Barriers

In this talk, I will study training failure of neural networks on sparse parity, a standard minimal model in machine learning theory. Trainability on this task turns out not to be monotone in problem size. This happens because parts of the data push training away from the correct solution, a phenomenon we call false learning. When these reversed updates resonate, they build a barrier in the loss landscape that can be predicted before training. This shows that learning can fail not only because signals are weak, but also because strong signals line up in the wrong direction.

Speaker: Sungjung Kim

Kias-False-Learning.pdf

12:30 → 12:40 Closing

Saturday 3 October

09:30 → 12:30 Discussion