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KEK Theory Meeting on Particle Physics Phenomenology (KEK-PH2026winter)

Feb 16 – 19, 2026
San-go-kan (Building #3)
Asia/Tokyo timezone

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Contribution List

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1. Quantum Machine Learning for High-Energy Physics
Michael Spannowsky
2/16/26, 10:10 AM
2. Light new physics and rare tau decays
Jure Zupan
2/16/26, 10:50 AM
3. Current Status and Future Prospects of Belle II
Yu Nakazawa
2/16/26, 1:00 PM
4. B physics: known and unknown
Zoltan Ligeti
2/16/26, 1:40 PM
5. The EIC and ePIC Experiments: Current Status and Synergies with High-Energy Physics
Kentaro Kawade
2/16/26, 2:40 PM
9. Higgs production in association with a Z boson at TeV-scale lepton colliders
Hiroyuki Furusato
2/16/26, 4:30 PM

We study the neutrino-associated Zh production process at lepton colliders, whose cross section exceeds that of Zh production in the multi-TeV energy regime.
The scattering amplitudes are classified into three main groups according to the topology of the corresponding Feynman diagrams, and their interference patterns are systematically analyzed.
We demonstrate that the delicate gauge...
6. Walking-Dilaton Hybrid Inflation in a Model with Dynamical Scalegenesis
HIROYUKI ISHIDA
2/16/26, 4:30 PM

We propose a hybrid inflationary scenario based on eight-flavor hidden QCD with the hidden colored fermions being in part gauged under B−L gauge 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...
10. Chasing Long-lived Scalars at the Future Lepton Colliders
Nivedita Ghosh
2/16/26, 4:50 PM

In this talk, I will discuss novel strategies to search for long-lived scalars at future lepton colliders in the context of the Type-II seesaw model. In the low-mass range, and for an appropriate choice of the triplet vev, these scalars can become long-lived, leading to displaced-vertex signatures. Depending on the proposed center-of-mass energy, we consider the pair production of these...
7. Emission of Nambu-Goldstone bosons from semilocal string networks
Yukihiro Kanda
2/16/26, 4:50 PM

Cosmic strings arise from the spontaneous breaking of a $U(1)$ symmetry, which can be either global or local, leading to distinct classes of string solutions. Their energy-loss mechanisms are known to differ significantly, which results in qualitatively different spectra of particles emitted from the string networks. Semilocal strings arise when global and local symmetries are simultaneously...
11. Impact of quark flavor violating SUSY on h(125) decays at future lepton colliders
Keisho Hidaka
2/16/26, 5:10 PM

We study the CP-even neutral Higgs boson decays $h^0 \to c \bar{c}, b\bar{b}, b \bar{s}, \gamma \gamma, g g$ in the Minimal Supersymmetric Standard Model (MSSM) with general quark flavor violation (QFV) due to squark generation mixings, identifying the $h^0$ as the Higgs boson with a mass of 125 GeV. We compute the widths of the $h^0$ decays to $c \bar c, b \bar b, b \bar s$ at full one-loop...
8. Relaxing Cosmological Constraints on the Minimal $U(1)_{L_\mu - L_\tau}$ Model with One-Loop Corrections
Jun Miyamoto
2/16/26, 5:10 PM

Recently, Ref.~\cite{...} showed that the minimal gauged $U(1)_{L_\mu - L_\tau}$ model is constrained by cosmological bounds on the sum of neutrino masses.
In this work, we compute the one-loop corrections to the neutrino mass matrix in this model and examine whether these cosmological constraints can be relaxed.
12. Searching for dark matter in the gamma-ray sky
Shunsaku Horiuchi
2/17/26, 9:00 AM
13. A brief overview of ACT DR6 results
Toshiya Namikawa
2/17/26, 9:40 AM
14. Analysis of Monopoles Associated with Multi-Step Spontaneous Breaking of Gauge Symmetries
Fukutaro MIYA
2/17/26, 10:40 AM

The ’t Hooft–Polyakov monopole is absent in the Standard Model, yet Cho and Maison revealed that the electroweak sector admits a spherically symmetric magnetic monopole solution. The resulting Cho–Maison monopole exhibits unresolved theoretical issues, most notably an energy divergence at the spatial origin. In this work, we analyze a scenario in which a ’t Hooft–Polyakov monopole arising in a...
17. Thermal precondensation in gauge-fermion theories and its cosmological implications
Alvaro Pastor Gutierrez
2/17/26, 10:40 AM
19. Screening Effects of Finite-Mass Fermions in Monopole Baryogenesis Scenario
Yukito Kato
2/17/26, 11:00 AM

To investigate the finite mass effects in recently proposed monopole baryogenesis scenario, this study analyzes screening effect for the electric monopole charge, induced by CP-violating theta term, within a 't Hooft-Polyakov monopole background. Utilizing partial wave expansion and bosonized effective field theory for the massive charged fermions, we demonstrate that fermion finite masses...
15. Supersymmetric Gauge Theories with Confining Phases
Riku Ishikawa
2/17/26, 11:00 AM

Confinement is one of the unresolved problems in modern physics. rgies. The analysis of confinement requires non-perturbative approaches due to asymptotic freedom. Supersymmetric gauge theories provide a powerful framework in which such non-perturbative analyses can be carried out. They are more tractable than their non-supersymmetric counterparts.In particular, the holomorphy of the...
20. Extended Higgs sectors and a scenario of electroweak baryogenesis
Shinya Kanemura
2/17/26, 1:00 PM
21. Testable leptogenesis with three right-handed neutrinos
Yannis Georis
2/17/26, 1:40 PM
22. Phenomenology of electroweakly interacting spin-1 dark matter with Sommerfeld enhancement
Tomohiro Abe
2/17/26, 2:50 PM

Weakly Interacting Massive Particles (WIMPs) are leading candidates for dark matter and have been widely studied. However, direct detection experiments have placed stringent constraints on many WIMP models. Some scenarios, such as Higgsino, Wino, and minimal dark matter, can evade these constraints. In these models, the dark sector contains an SU(2)_L multiplet, and the dark matter candidate...
26. Two Higgs doublet models with a new U(1) gauge symmetry
Takaaki Nomura
2/17/26, 2:50 PM

In this talk, we discuss two Higgs doublet models in which a new U(1) gauge symmetry is introduced. We investigate if these models are allowed by current phenomenological data without introducing a scalar field except for two Higgs doublet ones. We find they are excluded by constraints from scalar boson decays associated with new gauge boson Z'. Then a dark vector-like fermion is introduced to...
23. Minimal Dark Matter in the sky: updated Indirect Detection probes
Mohammad Aghaie
2/17/26, 3:10 PM

Minimal Dark Matter is among the simplest and most predictive Dark Matter frameworks, with the Majorana SU(2) 5-plet as its smallest accidentally stable real representation. We present a comprehensive reassessment of its indirect-detection signals. The γ-ray flux from both Sommerfeld-enhanced annihilations and bound-state formation is calculated, incorporating next-to-leading-order corrections...
27. Testing the Higgs triplet model via 125GeV Higgs boson decays with radiative corrections
Kodai Sakurai
2/17/26, 3:10 PM

The complex Higgs triplet model (CHTM) can explain the neutrino masses via the Type II seesaw mechanism. A feature of CHTM is that the electroweak rho parameter (\rho) deviates from unity at the tree-level. Thereby, how one renormalize electroweak sector is different from models with \rho=1. In this talk, we discuss imact of the radiative corrections to the 125 GeV Higgs boson decays in CHTM....
24. Dark matter explanations for the neutrino emission from the Seyfert galaxy NGC 1068
Kensuke Akita
2/17/26, 3:30 PM

We investigate the possibility that the high-energy neutrino flux observed from the Seyfert galaxy NGC 1068 originates from dark matter annihilations within the density spike surrounding the supermassive black hole at its center. The comparatively lower gamma-ray flux is attributed to a dark sector that couples predominantly to Standard Model neutrinos. To explain the absence of a...
29. Probing spontaneous CP-violation through precision Higgs observables
Kei Yagyu
2/17/26, 3:30 PM

Spontaneous CP-violation (SCPV) is one of the interesting possibilities for explaining observed CP-violation. As a simple realization of SCPV, we consider 2 Higgs doublet models (2HDMs), where complex phases of the Higgs doublets can be a source of SCPV. We discuss two important phenomenological consequences of the SCPV 2HDMs,
i.e., non-decoupling nature of extra Higgs bosons and constrained...
25. Light neutrinophilic thermal dark matter
Tatsuya Aonashi
2/17/26, 3:50 PM

No signal of the electroweak (EW) scale WIMP has been observed so far, and the lighter WIMP, whose mass is much lighter than the EW scale, attracts attention. However, light WIMP receives severe constraints from cosmological (CMB and BBN) observation when the WIMP couples mainly to electromagnetically interacting particles. We constructed a model where the light WIMP interacts mainly with...
31. Forbidden Dark Matter with Sommerfeld Enhancement
Takumu Yamanaka
2/17/26, 4:40 PM

We discuss the Sommefeld enhancement of the annihilation cross section of dark matter into heavier unstable particles which have long-range interaction with each other. Since annihilation products become non-relativistic near kinematical threshold, the wave function is modified from the plain wave, and significant enhancement of the annihilation cross section can be induced. In this talk, we...
33. Possible scenarios for baryogenesis in the presence of a lepton number violating operator in the rare meson decays
Yushi Mura
2/17/26, 4:40 PM

We discuss lepton number violating operators motivated by the flavor-changing rare meson decays, B -> Kvv and K ->πvv.
They can erase a pre-existing baryon asymmetry via electroweak sphaleron, and we analyze their impacts on baryon number washout in the early Universe,
We also discuss other topics related to the lepton number violation, the Majorana masses of the active neutrinos and the...
32. Asymmetric Dark Matter from Low-Scale Spontaneous Leptogenesis
Hiroki Takahashi
2/17/26, 5:00 PM

"We investigate a novel type of asymmetric dark matter (ADM) model in which the dark matter asymmetry and the baryon asymmetry in our universe (BAU) are produced simultaneously via low-scale spontaneous leptogenesis, where the mass scale of right-handed neutrino is much lower than the Davidson-Ibarra bound $M_1 \ll 10^{9}~\mr{GeV}$.
In our scenario, both asymmetries are predominantly sourced...
34. Rare meson decay constraints on dark photon and the like
Osamu Seto
2/17/26, 5:00 PM

We evaluate constraints from flavor changing rare meson decays to a light vector boson X, followed by the decay of the on-shell X into the SM fermions. Our theoretical evaluation of the branching ratio of charged B meson decay and charged kaon decay is compared to experimental results, and we derive new constraints for dark photon, U(1)B−L​ and U(1)R​ models.
35. Radiative Corrections to $D_s \to \ell \nu$ and CKM Unitarity Test
Kota Sasaki
2/17/26, 5:20 PM

Recently, a violation of the CKM unitarity condition has been reported in the latest charm-meson data and the latest lattice results, once the universal electroweak correction is taken into account. In this talk, we analytically derive for the first time the complete one-loop electroweak (EW) and QED corrections to the $D_{s}^+ \to \ell^+ \nu_\ell$ decays for $\ell = \mu, \tau$. Our analysis...
36. Advancing Standards in Early Universe Physics: The Impact of Bound States & Thermal Effects
Julia Harz
2/18/26, 9:00 AM
37. Cutting rule for cosmological correlators and its applications
Yohei Ema
2/18/26, 9:40 AM
41. Quintessence with a sudden transitional feature and its late-time cosmological signals
Takahiro Terada
2/18/26, 10:40 AM

Combinations of recent cosmological observations, including Dark Energy Spectroscopic Instrument, show hints of a dynamical nature for dark energy. While the data suggest the possibility of the phantom crossing, it is worth exploring thoroughly quintessence models. As phenomenological parametrizations of the equation-of-state parameter $w(a)$ with a sharp transitional feature fit the data...
38. Sommerfeld Enhancement in the light of Halo gamma-ray excess
Yongsoo Jho
2/18/26, 10:40 AM

We examine Sommerfeld enhancement in dark matter annihilation as a potential origin of the halo-like gamma-ray excess near E ~ 20 GeV reported by Totani. A minimal model with a light CP-even scalar mediator naturally produces a velocity-dependent annihilation cross section consistent with thermal freeze-out, the Milky Way excess, and limits from dwarf spheroidal galaxies. We discuss future...
39. Composite Asymmetric Dark Matter from Primordial Black Holes
Takumi Kuwahara
2/18/26, 11:00 AM

We investigate a cogenesis scenario for composite asymmetric dark matter framework: a dark sector has a similar strong dynamics to quantum chromodynamics in the standard model, and the dark-sector counterpart of baryons is the dark matter candidate. The Hawking evaporation of primordial black holes plays the role of a source of heavy scalar particles whose CP-violating decay into quarks and...
42. Gravitational Wave signatures of Reheating after Warm Axion Inflation
Tenta Tsuji
2/18/26, 11:00 AM

Before the Big Bang, the Universe experienced an era of accelerated expansion known as inflation.
Reheating is the process that bridges this inflationary phase to the hot Big Bang, and it also provides one of the few opportunities for information from the inflaton sector to survive into the later Universe. Although many details of the inflaton’s interactions are erased as the Universe...
43. Quantum sensing of high-frequency gravitational waves with ion traps
Ryoto Takai
2/18/26, 11:20 AM
44. Selected highlights from the LHC-ATLAS experiment
Yu Nakahama
2/18/26, 1:00 PM
45. The recent progress from FASER, focusing on the Axion-Like Particle search and Dark Photon search
Daichi Yoshikawa
2/18/26, 1:40 PM

FASER (the ForwArd Search ExpeRiment) is an experiment at the CERN Large Hadron Collider (LHC) designed to measure Standard Model neutrinos and to search for light, weakly interacting Beyond the Standard Model (BSM) particles. These particles are produced at the ATLAS interaction point in the forward direction and subsequently decay inside the FASER detector.
In this talk, we present the...
55. Exploring Lepton Flavor Structures with a Latent Diffusion Model
Haruto Kitagawa
2/18/26, 2:50 PM

In this talk, we present a model-independent analysis based on a latent diffusion model to address the flavor structure of leptons. The latent diffusion model combines a diffusion model with a variational autoencoder as a generative AI framework. By generating a wide variety of parameter sets consistent with experimental observations, we find non-trivial features characterizing lepton flavor...
46. Three-body entanglement and nonlocality in particle decays
Kazuki Sakurai
2/18/26, 2:50 PM

The investigation and collider measurement of quantum information generated in elementary particle interactions have attracted growing interest in recent years. To date, most studies have focused on bipartite systems, for example, spin correlations in top-quark pair production, while the rich structure of multipartite quantum correlations remains largely unexplored in high-energy physics.
In...
47. An Analytic Prescription for t-channel Singularities
Ryusei Sato
2/18/26, 3:10 PM

The t-channel singularity is a divergence in the scattering amplitude which occurs when a stable particle propagating in t-channel scattering process becomes an on-shell state. Such situations appear either in the system of collider experiments or in the context of the cosmological particle production. No scheme which is generally applicable is known. In this work, we propose a new formulation...
50. Machine learning the likelihoods
Rafal Maselek
2/18/26, 3:10 PM

Searches for BSM Physics have produced many theoretical ideas, but only a few can be directly tested at the LHC. Reinterpreting existing results is therefore essential for constraining a wider range of models. Independent of the specific reinterpretation method, the final step always involves statistical analysis and hypothesis testing. Accurate tests require detailed information on...
48. Searching for Leptoquarks at Future Circular Colliders
Christian Heiderijk
2/18/26, 3:30 PM

We study the sensitivities of the Future Circular Collider (FCC) under electron-positron collision and hadron-hadron collision scenarios for the search of Leptoquarks. In particular, we focus on the Z-factory mode and the high-pT mode. For the Z-factory mode, we summarize past analytical works on Z-boson decays introducing Leptoquarks at loop-level. For the high-pT mode, we update the current...
51. Systematic mapping of $U(1)_{L_{e}-L_{mu}-L_{tau}}$ flavor model via reinforcement learning
Satsuki Nishimura
2/18/26, 3:30 PM

Recent studies actively apply machine learning to the exploration of flavor physics. In analyzing the flavor structure of the lepton sector, we apply reinforcement learning to a $U(1)$ flavor model with $L_{e}-L_{mu}-L_{tau}$ charges. By testing multiple architectures to explore charge combinations, we develop a strategy to efficiently achieve high-precision solutions. It turns out that the...
57. A TeV-scale model for neutrino mass, dark matter and baryon asymmetry of the universe and its phenomenology
Sora Taniguchi
2/18/26, 4:20 PM

The Standard Model successfully describes particle physics but cannot explain neutrino oscillations, the baryon asymmetry of the universe (BAU), and dark matter. The Aoki-Kanemura-Seto (AKS) model is a new physics model that can explain these three phenomena simultaneously at TeV scale testable by future experiments. However, in the original model published in 2009, the baryon number was not...
52. The Electric Dipole Moment of electron induced by Electroweak Multiplets at full Three-loop
Kiyoto Ogawa
2/18/26, 4:20 PM

There has been remarkable progress in recent years in the electric dipole moment (EDM) measurements of electron using paramagnetic atom or molecule. In a previous study, we calculated the contribution to the electron EDM induced by the CP-violating Yukawa interaction of electroweak multiplets at the three-loop level in effective field theory. We found that this contribution might reach the...
53. Gradient-flowed operator product expansion without IR renormalons
Hiromasa Takaura
2/18/26, 4:40 PM

A long-standing problem concerns the question how to consistently combine perturbative expansions in QCD with power corrections in the context of the operator product expansion (OPE), since the former exhibit ambiguities due to infrared renormalons, which are of the same order as the power corrections. We propose to use the gradient flow time as a factorization scale and to express the OPE in...
56. Probing Scalar-Mediator Quark Couplings via CLFV Lepton-Nucleon Scattering
Masato Yamanaka
2/18/26, 4:40 PM

We investigate charged lepton flavor violating (CLFV) deep-inelastic scattering, focusing on the gluon-initiated subprocess $\ell_i g \to \ell_j g$ via the gluon effective operator $\phi\, G_{\mu \nu}^a G_a^{\mu \nu}$, and demonstrate how to probe the nature of the CLFV mediator $\phi$, specifically its mass and interaction with quarks.
We consider two benchmark scenarios for the...
54. Toponium at the LHC
Ya-Juan Zheng
2/18/26, 5:00 PM

We review the signature of toponium formation at the LHC. A color-singlet bound state effect at the threshold region is included in the MonteCarlo simulation. The top pair dileptonic decay final states distributions shows distinctive signature in the small dilepton correlation region. We also discuss the potential effects of P wave contribution.
58. New Axion Bounds from Big Bang Nucleosynthesis
Kohsaku Tobioka
2/19/26, 9:00 AM
59. Sweeping the pion chimney for axion-like particles with KOTO
Christiane Scherb
2/19/26, 9:40 AM
63. Constraints on MeV Axion Models from Kaon Decays with KTeV Data
Takaya Iwai
2/19/26, 10:40 AM

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 in the low-scale regime, $f_a \sim \mathcal{O}(1),\mathrm{GeV}$, corresponding to an axion mass in the MeV range.

In this mass range, the...
61. Diffuse Multi-messenger Signals of Dark Matter Powered Stars
Tom Schwemberger
2/19/26, 10:40 AM

Dark matter (DM) annihilation can power the first generation of stars as long lived dark stars (DSs) that grow to supermassive scales $M_{\rm DS}\gtrsim 10^{5} M_{\odot}$ and eventually collapse into heavy black holes that could seed the supermassive black holes observed at high redshifts. We compute the electromagnetic and neutrino emission from these objects and determine the diffuse...
62. MeV-Scale Sterile Neutrino Dark Matter and Future Detection
Subaru Fujisawa
2/19/26, 11:00 AM

Sterile neutrinos are well-motivated candidates for dark matter. In particular, sterile neutrino dark matter in the MeV mass range has recently attracted increasing attention due to the prospects of future indirect detection experiments. In this work, we focus on the Compton Spectrometer and Imager (COSI) as a next-generation gamma-ray detector and investigate the detectability of MeV-scale...
65. Thermal Lepton Oscillations in Leptogenesis
Shaoping Li
2/19/26, 11:00 AM

Oscillation phenomena occur in both active and sterile neutrinos, where the oscillation phases are triggered by vacuum mass difference. Before the electroweak gauge symmetry breaking, leptons are massless, and cannot oscillate in the conventional way. However, they can still oscillate in the background plasma. Using the flavor-covariant nonequilibrium quantum field theory, I will discuss how...
66. First-order phase transitions in the early Universe: Recent theoretical/experimental progress
Ryusuke Jinno
2/19/26, 1:00 PM
67. How LLM can help particle physicists
Mihoko Nojiri
2/19/26, 1:40 PM
18. Electromagnetic leptogenesis in an effective field theory
Rin Takada

We present a unified, gauge-invariant EFT analysis of low-scale electromagnetic leptogenesis sourced by CP-violating neutrino–gauge dipole interactions. We first match UV-complete models onto the dimension-six effective operator, and evaluate the decay widths, CP asymmetries, and the corresponding transport equations in the electroweak-broken phase. We then show that the suppression arising...
49. Enhancing dark matter search using multi-level system
Xiaolin Ma

Quantum sensing with qubits has advanced fundamental physics searches,
but higher dimensional systems offer untapped potential. We present a universal qutrit
framework that yields a sequence-independent fourfold increase in quantum Fisher information and a twofold gain in sensitivity. In ultralight dark matter searches, spin-1 NV-center qutrits can enhance the axion-electron coupling reach...
16. Generalized CP from non-invertible selection rules
Hajime Otsuka

In this talk, we propose a framework in which fields are labeled by basis elements of a fusion algebra with non-invertible fusion rules. In particular, we consider the case where fields are labeled by conjugacy classes of a finite group rather than its irreducible representations.
When the fusion rules possess a Z2 symmetry identified with charge conjugation, a CPinvariant system can be...
28. Probing Compressed Inert Scalars with Forward Muon Tagging at the Muon Collider
Chandrima Sen

The compressed mass spectrum of the electroweak inert scalar models pose a significant challenge for current collider experiments, as the soft visible decay products and suppressed production rates hinder conventional search strategies. In this talk, I will explore the discovery prospects of such a compressed electroweak sector at a future high energy Muon Collider operating at 10 TeV....
40. Probing Reheating through Dark Matter Freeze-Out at Lepton Colliders
Niloy Mondal

We explore the potential of future lepton colliders to shed light on the reheating era through the detection of dark matter (DM) that undergoes freeze-out during this phase of the Universe. In this framework, DM interacts with the Standard Model (SM) primarily via leptophilic effective operators, exhibiting highly suppressed couplings to quarks and gluons, consistent with the null results from...
64. Residual Flavor Symmetries at the Modular Self-Dual Point: Predictive Insights into Neutrino Masses and Mixing
Monal Kashav

"We explore the theoretical consequences of residual symmetries that persist at the modular self-dual point $\tau = i$ within modular-invariant frameworks. Assuming the three generations of lepton doublets form an irreducible representation of a finite modular group $\Gamma_N$, and that the light neutrino masses arise from the Weinberg operator constructed from modular forms, we demonstrate...
30. Revisiting Bino-slepton Coannihilation Dark Matter in Light of Recent Experimental Results
Alethea To

Despite being a simple and well-motivated thermal relic scenario, coannihilation dark matter (DM) has remained largely unexplored experimentally due to the difficulty of probing its nearly degenerate mass spectrum. Recent LHC searches, however, have improved sensitivity, enabling broader explorations of the parameter space. We revisit the Bino-slepton coannihilation scenario in...
60. Superheavy Supersymmetric Dark Matter
Seong Chan Park

We propose an explanation for the recently reported ultrahigh-energy neutrino signal at KM3NeT, which shows no clear association with known astrophysical sources. 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...
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