Axions in Japan

10 Nov 2025, 08:00 → 14 Nov 2025, 18:00 Asia/Tokyo

Lecture Hall (Kavli IPMU)

Axions in Japan

Axions are among the most compelling candidates in particle physics, offering a potential solution to the mystery of dark matter and a window into the dark sector of the universe. Over the years, axions have emerged as one of the leading candidates for dark matter, driving ambitious theoretical, experimental, and observational efforts worldwide.

This workshop aims to bring together leading experts in axion physics, spanning fundamental theory, cosmology, numerical simulations, astrophysical observations, and experimental searches. By fostering collaboration and discussion among researchers from diverse disciplines, the workshop will address the most pressing questions in axion physics and explore innovative approaches to advance our understanding of these elusive particles.

Japan has long been at the forefront of axion research, making groundbreaking contributions across multiple areas of the field. Given this leadership and the vibrant axion research community in Japan, we believe it is the ideal location to host this workshop. The event will provide a unique opportunity for leading experts from Japan and abroad to share their insights, forge new collaborations, and chart the future of axion physics. We hope this will be the first in an annual conference series, Axions in Japan.

Dates

10-14 November, 2025

Venue

The on-site workshop will take place at the Lecture Hall of Kavli IPMU, The University of Tokyo, Kashiwa Campus (5-1-5, Kashiwanoha, Kashiwa-shi, Chiba, 277-8584, Japan).

If you would like to join via Zoom, use this link.

Invited speakers

• Atsushi Nishizawa

• Chanda Prescod-Weinstein

• Cora Uhlemann

• Federico Urban

• Francesca Chadha-Day

• Ippei Obata

• Jens Niemeyer

• Keir Rogers

• Luna Zagorac

• Masahiro Kawasaki

• Mustafa Amin

• Neal Dalal

• Philip Mocz

• Richard Easther

• Simon May

• Simona Vegetti

• Tomohiro Fujita

• Vera Gluscevic

• Victor Robles

• Yuko Urakawa

• Yuta Michimura

Organizers

• Andrew Eberhardt (chair)
• Elisa Ferreira
• Qiuyue Liang
• Baptiste Jost
• Shunichi Horigome
• Marta Monelli

Contact

axions.japan@ipmu.jp

 

 

 

Monday 10 November

08:30 → 09:10 Registration

09:10 → 09:25 Opening remarks

09:25 → 10:10 When Waves Collapse

Chair: Mustafa Amin

Convener: Jens Niemeyer

10:10 → 10:55 Plenary

Chair: Mustafa Amin

Convener: Richard Easther

10:55 → 11:15 Coffee Break

11:15 → 12:00 Quantum DM nature: Waves and Fuzzyness at galactic scales

Convener: Victor Robles

12:00 → 13:15 Lunch

13:15 → 14:00 Making dark matter waves - the cosmic web and wavelike dark matter

Despite the astonishing success of cosmological probes in constraining the LCDM model, the dark matter mass remains one of the least constrained physical parameters. Wavelike dark matter is an intriguing alternative to standard cold dark matter with key particle physics motivations and potentially distinct astrophysical signatures. With a simple dynamical model for the evolution of a dark matter wavefunction, I will demonstrate how to predict the large-scale evolution and formation of destructive and constructive wave interference leading to topological defects and granules dressing the cosmic web of large-scale structure. I will also discuss recent advancements in creating efficient numerical methods for wave dark matter evolution, utilising approximative techniques originally developed for cold dark matter, such as FastPM and Bullfrog. Beyond offering a fundamental framework for ultralight particles, a wave-based approach serves as a versatile tool for reducing the complex phase-space dynamics of cold dark matter to position space.

Convener: Cora Uhlemann

14:00 → 15:00 Parallel session - Cosmology I

Convener: Chair: Dan Kondo

14:00 Multi-Axion Bosenovae and Sequential Axion Emissions

Axion particles can form gravitationally bound condensates known as axion stars. In the presence of self-interactions their collapse can trigger axion bosenovae — transient events accompanied by bursts of relativistic particle emission. We investigate such phenomena in systems composed of multiple axion fields, which can arise in various extensions of the Standard Model. Using both variational and numerical methods, we analyze the collapse dynamics and develop a framework to estimate collapse times. We explore the possibility of multiple bosenovae, where successive collapse events lead to the depletion and emission of different axion species. Our results provide a self-contained treatment of multi-axion collapse and uncover novel phenomena - time-separated, multi-frequency transients that could distinguish multi-field configurations from single-species axion stars.

Speaker: Jason Arakawa

14:20 Core–Halo Relation in Self-Interacting Scalar Field Dark Matter

In this talk, I will explore the phenomenology of scalar field dark matter with both attractive and repulsive self-interactions. Using idealized simulations, I analyze the properties of halo cores across a wide range of interaction strengths, from the strongly attractive regime to the Thomas–Fermi limit. The numerical results are compared with analytical predictions for the core mass–size relation and with free-case scalings reported in the literature. I will also examine the core–halo connection across all interaction regimes and discuss how scaling relations vary with the total energy of the system. Finally, I will present the time evolution of the core mass, which exhibits a self-similar growth behavior.

Speaker: Jessica N. Lopez-Sanchez

14:40 Interfering and Interacting Fuzzy Dark Matter

In the standard Fuzzy Dark Matter (FDM) scenario, the dark matter is composed of an ultra-light scalar field with coherence length and wave interference on astrophysical scales. However, scalar fields generically have quartic self-interactions that modify their dispersion relation and the associated evolution of density perturbations. I will begin by presenting the first dedicated analysis of the relationship between wave interference and the evolution due to self-interactions. For warm FDM, density perturbations are unable to grow on the expected self-interaction time scale because of interference effects, instead saturating on the much shorter de Broglie crossing time, with a dependence on the sign of the interaction. I will then introduce the Fuzzy Dark Sector (FDS) as a model extension with multiple interacting fuzzy degrees of freedom that interfere with each other. Remarkably, the FDS can recover a single cutoff scale in cosmology while generating a great diversity of halos at late times. Finally, I will discuss how these interference effects might be observed across a range of astrophysical environments and shed further light on interacting FDM.

Speaker: Christian Capanelli

14:00 → 15:00 Parallel session - Gravity I

14:00 Strong backreaction of gauge quanta produced during inflation and the sourced GWs

In this report, I will introduce our recent studies about the axion-gauge system during inflation, mainly focusing on the strong backreaction region. With a linear axion potential, we found that a steeper slope can enhance the gauge quanta production, while a larger coupling cannot increase it. We then apply this result to a realistic model with cosine axion potential, finding the quantum fluctuation can limit the max GW spectrum.

Speaker: Jian-Feng He

14:20 Gravitational waves from self-interacting axion clouds around rotating black holes

Black hole superradiance can lead to the formation of clouds of ultralight bosons such as axions. These clouds are expected to be detected through gravitational wave observations, but reliable predictions require a detailed understanding of their evolution. We investigate the dynamics of axion clouds including the effects of self-interaction, with particular emphasis on the role of mode couplings with multiple levels. We present the resulting phenomena and discuss their potential impact on gravitational wave signals.

Speaker: Takuya Takahashi

15:00 → 15:30 Tea time

15:30 → 16:50 Parallel session - Pheno I

15:30 Background-Enhanced Axion Force by Axion Dark Matter

In this talk, I will discuss the impact of axion dark matter on spin-independent forces between nucleons. Our study shows that when the axion dark matter background is taken into account, the axion-mediated force changes its distance dependence from 1/r^3 to 1/r, and its magnitude is significantly enhanced proportionally to the axion number density. This amplification allows fifth-force experiments—such as Casimir-less setups and torsion balance tests—to place constraints on the axion decay constant several orders of magnitude stronger than previously estimated, across a wide range of axion masses. These results suggest that such experiments are even more sensitive to axion detection than previously understood.

Speaker: Yu Cheng

15:50 Electric Dipole Moments From Missed Dark Matter Scattering

Axion-like particles are a well-motivated candidate for ultralight dark matter. Because dark
matter must be non-relativistic, the effects of its scattering with Standard Model particles are
negligible and generally go unnoticed. However, due to the large occupation number of ultralight
dark matter, the sum of all scatterings leads to a classical field-like interaction with Standard Model
particles. In the case of an axion-like particle, this scattering imparts a parity violating effect. If this
collective scattering with axion-like particles is inserted into the one-loop quantum electrodynamics
diagram, the parity violation imparted by this scattering will convert the anomalous magnetic
moment contribution into an electric dipole moment. This contribution is quite large and leads
to a prediction inconsistent with precision measurements of the proton and electron electric dipole
moments, unless their couplings to the axion-like particles are very weak. As a result, the constraints
on the couplings of axion-like particle dark matter to the electron and proton are improved by as
much as eleven and six orders of magnitude, respectively."

Speaker: Jason L. Evans

16:10 Constraints on MeV Axion Models from Kaon Decays with KTeV Data

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
\gtrsim10^9 GeV). However, recent work has pointed out that viable axion models may also exist
for (f_a\sim1 GeV). In our research, we derive stringent constraints on this axion scenario from kaon
decay measurements.

Speaker: Takaya Iwai

16:30 Search for sub-eV ALP via quasi-parallel stimulated resonant photon collision with “coronagraphy” to mitigate background photon based on spatial distribution characteristics

The identity of dark matter (DM) remains one of the major mysteries of modern physics.
The QCD axion, arising from the Peccei-Quinn mechanism that solves the strong CP
problem, is a well-motivated low-mass DM candidate.
The SAPPHIRES collaboration searches for the QCD axion and axion-like particles
(ALPs) using two-color, high-intensity, short-pulse lasers [1]. Our approach targets signal
photons from stimulated resonant photon-photon scattering via ALP exchange. The
dominant background photons, originating from nonlinear photon-atom interactions in
optical elements, have been verified to be spatially concentrated near the beam axis, in
contrast to the expected distribution of signal photons. Exploiting this spatial distinction, we
developed a “coronagraphy” method that introduces an eclipse filter to effectively mitigate
background photons while maintaining sensitivity to signal photons. We further acquired
data with deliberately degraded spatial overlap of the two beams at the focus and found no
statistically significant excess. With this technique, we have achieved the highest laboratory
sensitivity to date in the sub-eV mass range. In this presentation, we report the results of
this search.
[1] Y. Kirita, A. Kodama, K. Homma, C. Chiochiu, M. Cuciuc, G. Giubega, T. Hasada, M.
Hashida, S. Masuno, Y. Nakamiya, L. Neagu, V. Phung, V. Rodrigues, M. Rosu, S. Sakabe,
S. Tazlauanu, O, Tesileanu, and S. Tokita, [SAPPHIRES collaboration], “Search for sub-eV
axion-like particles in a quasi-parallel stimulated resonant photon-photon collider with
“coronagraphy””, JHEP, 06(2025)138"

Speaker: Airi Kodama

15:30 → 16:30 Parallel session - Theory I

Convener: Chair: Qiuyue Liang

15:30 Resolving the QCD Axion Domain Wall Problem with a Light Axion

We propose two novel solutions to the domain wall problem of the QCD axion by introducing a massless or light axion that also couples to gluons. The first solution applies when the new axion forms strings after inflation. Due to its mixing with the QCD axion, domain walls of the QCD axion are bounded by these strings and confined into cosmologically safe string bundles. This scenario predicts the existence of such string bundles, which may survive until today and leave observable signatures, such as gravitational waves, cosmic birefringence, and CMB anisotropies. The simultaneous detection of the QCD axion and any of these cosmological signatures would serve as a smoking-gun signal. The second solution assumes a homogeneous initial condition for the new axion. If it is sufficiently light, its potential temporarily induces a bias in the QCD axion potential before the onset of oscillations, rendering the domain walls unstable. In both scenarios, the Peccei-Quinn mechanism remains effective, and the strong CP problem is not reintroduced. We identify the viable parameter regions and discuss the resulting dark matter abundance.

Speaker: Kai Murai

15:50 A Step in Flux to Suppress Axion Isocurvature

The QCD axion is one of the most compelling dark matter candidates, but faces a stringent isocurvature constraint, which requires a relatively low Hubble scale during inflation. If the axion was heavier than the Hubble scale during inflation, its isocurvature is suppressed and the constraint significantly relaxes. We point out a novel mechanism for achieving this, relying on the topological nature of a monodromy mass for the axion. Such a mass term has an integer coefficient, so it could naturally have been very large during inflation and exactly zero by the time of the QCD phase transition. This integer can be viewed as a quantized flux, which is discharged in a first-order phase transition that proceeds by the nucleation of charged branes. We provide a detailed case study of the scenario in which the tunneling event occurs during inflation.

Speaker: Priyesh Chakraborty

Tuesday 11 November

09:25 → 10:10 Effective field theory for chiral gravitational waves in axion inflation

Axions are well-motivated inflaton candidates that naturally couple to gauge fields via the Chern–Simons interaction. When the gauge field is non-Abelian, an isotropic background can form during inflation, producing strongly chiral gravitational waves—a phenomenon studied in chromo-natural inflation and related models. We develop an effective field theory (EFT) that generalizes these scenarios, showing that chiral gravitational waves arise generically from axion–gauge field dynamics. The framework also clarifies stability conditions and provides a unified basis for studying signals potentially detectable in forthcoming CMB experiments such as the Simons Observatory.

Convener: Tomohiro Fujita

10:10 → 10:55 Cosmic birefringence and its implications for axion cosmology

In this talk, we will present recent updates on the measurements of isotropic cosmic birefringence in CMB polarization data and discuss implications of new physics beyond the Standard Model, focusing on axion-like particles.

Convener: Ippei Obata

10:55 → 11:15 Coffee break

11:15 → 12:00 Cosmological tests of ultra-light axions

The fundamental nature of dark matter and dark energy so far eludes direct detection experiments, but it has left its imprint in the cosmic large-scale structure. Ultra-light axions (ULAs; masses m < 10^-17 eV) are motivated by axiverse considerations. Searching for ULAs requires accurate modelling of axion structure formation including wave effects, careful handling of astrophysical uncertainties and consistent observations in independent cosmological probes. I will review a multi-scale, multi-epoch test of ULAs combining state-of-the-art modelling with observations of the cosmic microwave background, galaxy clustering (redshift z < 2), the Lyman-alpha forest (2 < z < 5) and the high-redshift (z > 5) galaxy UV luminosity function from the Hubble and Webb Space Telescopes. I will discuss the extent to which cosmological data are more consistent in the presence of ULAs. I will further discuss prospects for adjudicating the viability of axion models in observations of the galaxy and Milky Way sub-structure distributions in the transformative Vera C. Rubin Observatory.

Conveners: Keir Rogers, (Chair: Andrew Eberhardt)

12:00 → 13:15 Lunch

13:15 → 14:00 Not Really Quantum Cosmology: How far can we get by treating a dark matter halo like an atom?

In this talk, I will focus on the fuzzy region of ultralight dark matter (FDM/ULDM): an axion-like candidate which keeps the successes of cold dark matter on large scales but alleviates tensions on small scales. This small-scale behavior is due to characteristic observable cores in ULDM called solitons, which also correspond to the ground state of the equations governing ULDM. Thus, one promising avenue for studying ULDM dynamics is by treating individual halos as hydrogen atoms and calculating the full spectrum of their eigenstates, which are then linked to the qualitative behavior of the halo. In this talk, I will outline how and why this approach is useful, demonstrate some of its application, and describe first steps towards this approach from a single axion field into two species of axions on our way to exploring the axiverse.

Conveners: Luna Zagorac, (Chair: Yuko Urakawa)

14:00 → 15:00 Parallel session - Experiments II

14:00 Toward remote sensing of backward reflection from stimulated axion decay

We propose a method for remotely detecting backward reflection via induced decay of cold dark matter such as axion in the background of a propagating coherent photon field. This method can be particularly useful for probing concentrated dark matter streams by Earth’s gravitational lensing effect. Formulae for the stimulated reflection process and the expected sensitivities in local and remote experimental approaches are provided for testing eV scale axion models using broad band lasers. The generic axion-photon coupling is expected to be explorable up to O(10^-11 ) GeV and O(10^-22 ) GeV for the idealized local and remote setups, respectively [1]. We report on the recent developments toward the pilot search.

[1] K. Homma, JHEP 09 (2024) 034 • e-Print: 2312.02005 [hep-ph]"

Speaker: Kensuke Homma

14:20 A Way of Axion Detection with Mass 10^(−4)eV ∼ 10^(−3)eV using Cylinder with Low Electric Conductivity

A dark matter axion with mass ma induces an oscillating electric field in a cylindrical sample placed under a magnetic field B parallel to the cylinder axis. When the cylinder is made of a highly conductive material, the induced oscillating current primarily dissipates the axion energy at the surface. In contrast, if the cylinder is composed of a material with low conductivity, e.g. σ = 10^(−3)eV, the axion energy is dissipated mainly inside the bulk of the cylinder. Within the QCD axion model, the dissipated power P is estimated as P ≃2.8×10^(-28)W g^2 (L/100cm) (10^(−4)eV/ma )(B/10T)^2
(ρa/0.3GeV cm^(−3))(yx^2/(ϵ^2 +y^2)), with parameters y ≡ σ/ma = 10, x ≡ maR ≃ 10, axion mass ma, radius R = 2cm, length L = 100cm, electric permittivity ϵ = 10 and axion energy density ρa. For the coupling constants, we take g(KSVZ) = −0.96 and g(DFSZ) = 0.37. Using an LC circuit tuned to a quality factor Q = 10^6, the signal-to-noise ratio is given by P(Q sqrt(δω tob/2π)/Pt ≃ 10 g^2(ma/10^(−4)eV)^(−3/2) (T/100mK)^(−1)sqrt(tob/60s), where Pt is the thermal noise power at temperature T = 100mK and bandwidth δω = 10^(−6)ma. By choosing appropriate values of conductivity and cylinder radius for example, σ/ma = 10 and ma R ≥ 10, the detection of dark matter axions is feasible in the mass range ma = 10^(−4)eV ∼ 10^(−3)eV

Speaker: Aiichi Iwazaki

14:40 Axion dark matter search using quantum sensing of magnons: Estimation of sensitivity for Kittel mode – superconducting qubit hybrid

Axions can be probed through the interaction between axions and electron spins. By detecting magnons (quantum of collective spin excitation) induced by axions inside a ferromagnetic crystal such as YIG, we can explore the parameter space of axions in the GHz regime. To improve the sensitivity of axion detectors, we must (1) increase the signal (magnons) excited by axions and (2) suppress detector noise. Using a dilution refrigerator, thermal noise can be suppressed to below 50 mK. The noise of conventional axion detectors is limited by the Standard Quantum Limit. ThisStandard Quantum Limit can be overcome by quantum sensing of magnons using superconducting qubits. I will present the sensitivity evaluation along with our R&D toward an axion dark matter detector using a superconducting qubit-Kittel mode hybrid system.

Speaker: Yaman Singh Shrestha

14:00 → 15:00 Parallel session - Theory II

Convener: Chair: Qiuyue Liang

14:00 What can solve the strong CP problem?

Speaker: Tom Melia

14:20 High-quality QCD Axion in the Standard Model---- Blue Bird Scenario of the Axion

Speaker: Tsutomu Yanagida

14:40 All axion dark matter from supersymmetric models

Supersymmetric models accompanied by certain anomaly-free discrete R-symmetries Z_n^R are attractive in that 1. the R-symmetry (which can arise from compactified string theory as a remnant of the broken 10-d Lorentz symmetry) forbids unwanted superpotential terms while allowing for the generation of an accidental, approximate global U(1){PQ} symmetry needed to solve the strong CP problem and 2. they provide a raison d'etre for an otherwise ad-hoc R-parity conservation. We augment the minimal supersymmetric Standard Model (MSSM) by two additional Z_n^R- and PQ-charged fields X and Y wherein SUSY breaking at an intermediate scale m{hidden} leads to PQ breaking at a scale f_a\sim 10^{11} GeV leading to a SUSY DFSZ axion. The same SUSY breaking can trigger R-parity breaking via higher-dimensional operators leading to tiny R-violating couplings of order (f_a/m_P)^N and a WIMP quality problem. For Z_4^R and Z_8^R, we find only an N=1 suppression. Then the lightest SUSY particle (LSP) of the MSSM becomes unstable with a lifetime of order ~ 10^{-3}-10 seconds so the LSPs all decay away before the present epoch. That leaves a universe with all axion cold dark matter and no WIMPs in accord with recent LZ-2024 WIMP search results.

Speaker: Kairui Zhang

15:00 → 15:30 Tea time

15:30 → 16:30 Parallel session - Cosmology II

Convener: Chair: Shunichi Horigome

15:30 Probing Axion-like Dark Matter via Time-Variable Polarization in Protoplanetary Disks

Among the various dark matter candidates, axion-like dark matter—particularly in the ultralight regime around 10^−22 eV—has attracted significant attention in recent years, as it has been proposed as a potential solution to the small-scale structure problems in the standard cosmological model.
In this talk, we present a new observational constraint on ALP dark matter based on archival data from the Very Large Telescope (VLT). Specifically, we analyze time-series polarimetric data of HD 163296 and place limits on the coupling between ALP dark matter and photons. Furthermore, we show that if the uncertainty in the polarization angle can be reduced to 0.1° and high-cadence monitoring is achieved, the existing upper bounds can be significantly improved. This demonstrates the potential of time-domain polarimetry of nearby young stellar objects as a novel probe of ultralight dark matter.

Speaker: Kanako Narita

15:50 Dynamical heating in Dwarf Spheroidal Galaxies in spin-s Ultra-light Dark Matter models

Ultralight dark matter (ULDM), characterized by particles with masses log(m/eV) ~ -22 and de Broglie wavelengths on kiloparsec scales, behaves as a coherent quantum field at galactic scales. This wave-like nature drives time-dependent gravitational potential fluctuations that can dynamically heat stellar systems. In this talk, I will present the results of a numerical study of ULDM fluctuation-induced dynamical heating in dwarf spheroidal galaxies. We will analyze how this effect affects stellar velocity dispersion and the long-term stability of cold substructures. Our simulations explore a range of ULDM particle masses and initial stellar configurations, and we discuss the implications for current observational constraints. In particular, we investigate how the nature of the ULDM assuming spin-0 (scalar), spin-1 (vector), and spin-2 (tensor) configurations modifies the characteristics of the induced fluctuations and how these differences affect the heating rates of stellar systems.

Speaker: Erick Munive Villa

16:10 Revisiting Fuzzy Dark Matter Constraints: Accounting for Core–Halo Mass Relation Diversity

The estimation of the fuzzy dark matter (FDM) particle mass from the Milky Way’s dwarf satellite galaxies relies critically on the core–halo mass relation. Previous studies have generally assumed a one-to-one core–halo mass relation, despite growing evidence that this relation exhibits considerable intrinsic scatter. Neglecting this diversity could lead to artificially tight constraints and potentially false exclusions within the allowed FDM particle mass range inferred from stellar kinematics of the Milky Way’s dwarf galaxies. Using eight Milky Way dwarf spheroidal galaxies, we re-estimate the allowed range of the FDM particle mass while incorporating the observed diversity in the core–halo mass relation. To further mitigate the degeneracy with the stellar velocity anisotropy—which remains unobservable—we adopt a flexible line-of-sight velocity distribution (LOSVD) by including the fourth-order stellar velocity moments, rather than assuming a conventional, fixed LOSVD form.

Speaker: Dafa Wardana

15:30 → 16:10 Parallel session - Gravity II

Convener: Chair: Xinpeng Wang

15:30 Massive black hole binaries in ultralight dark matter solitons

Ultralight dark matter (ULDM) is a dark matter candidate composed of light axion-like particles, and is a promising alternative to cold dark matter. A unique feature of ULDM is the formation of solitonic cores at the centre of collapsed halos, which may increase the drag experienced by black hole binaries orbiting within the soliton. We present high-resolution numerical simulations of the dynamics of SMBH binaries in the soliton of a massive halo, finding that higher ULDM particle masses can potentially alleviate the final parsec problem. We show that dynamical friction from ULDM can suppress gravitational wave power in the PTA band. Through fits to our simulations, we develop a semi-analytic model for orbital decay due to ULDM with the aim of constraining ULDM particle masses through PTA data.

Speaker: Russell Boey

15:50 Measurable Effects from Unresolvable Perturbations of Axion Dark Matter in the Critical Region of Gravitational Lenses

Successful dark matter (DM) models have to predict the condensation of dark matter into haloes, reproducing the observed mass of galaxies and clusters in the Universe. Axionic DM, predicts an over-concentrated core 'soliton' residing within each of the haloes, which is a generic feature from models that effectively include interaction among the DM particles. This has been the major way to constrain axion parameter space from gravitational lens, and this aspect of axionic DM is not distinguishable with gravothermally collapsed self-interacting DM.

In this talk however, I would discuss utilising some exotic gravitational lenses to measure another prediction unique to axionic DM: the density modulations in the halo outskirt analogous to the excited states of hydrogen wavefunction. These density modulations are small and operate on a spatial scale below the resolution limit of the existing telescopes. Yet, they can be sustantially amplified in the 'near-critical region' of gravtational lens, thus resembling a cosmological 'transition-edge detector; Specifically, I would quantify the effect of axionic DM at the umbilic point of gravtational lens, revealing their unique imprint in terms of observable lens-magnified flux.
A recently executed proposal on JWST have observed such a special gravitational lens, the measurements of the fluxes distribution therein would soon give a stringent constraint, eventually narrowing down the axion parameter space."

Speaker: Leo W.H. Fung

Wednesday 12 November

09:25 → 10:10 Plenary

Convener: Masahiro Kawasaki

10:10 → 10:55 The Devil is in the (Axion) Details

In this talk, I focus on why it matters that we continue to pay attention to challenge our back of the envelope notions about axions in the context of structure formation. Axions continue to surprise us, and we continue to have a need to think carefully about definitions. I will highlight results from my research group that indicate: the devil is in the details. I will also talk about prospects for multi-field scenarios as we move into exploring the axiverse.

Convener: Chanda Prescod-Weinstein

10:55 → 11:15 Coffee break

11:15 → 12:00 Hunting axion dark matter signatures in terrestrial magnetic fields

Axions are one of the candidates for the unknown dark matter. Ultralight axions form a huge number of clouds in galactic halos. When such an axion cloud passes through the Earth, it interacts electromagnetically with the geomagnetic field and generates a monochromatic electromagnetic wave whose frequency corresponding to the axion mass. Recently we modeled the axion-induced electromagnetic wave signals by solving Maxwell's equations under the appropriate boundary conditions of the ionosphere for geomagnetic fields and showed that Earth's natural environment can serve as a powerful probe for ultralight axion dark matter with masses ranging from 10^{-15} eV -- 10^{-13} eV. Based on the derived theoretical model, we searched for axion-induced magnetic field signals within the observational data of global geomagnetic field variations (Eskdalemuir Observatory, 2012–2022). In this talk, I report on the idea of the search, the data analysis method, the results of the search having several tens of axion signal candidates.

Convener: Atsushi Nishizawa

12:00 → 12:10 Group photo

12:10 → 13:15 Lunch

13:15 → 14:00 Axion Structure Formation: Self-Interactions, Multi-Field Dynamics, and Observational Signatures

Ultra-light axions remain a plausible candidate for the dark matter, with wave-like dynamics that can leave distinctive imprints on structure formation across a wide range of scales. I will present results from high-resolution simulations exploring extensions to the canonical fuzzy dark matter (FDM) model motivated by axion theory: attractive self-interactions from a finite decay constant and multi-field "axiverse" scenarios. Attractive self-interactions drive a phase transition from dilute to dense solitons and boost small-scale structure formation. Multi-field FDM yields diverse halo structures and alleviates tensions with dwarf galaxy populations. At high redshift, the observed abundance of prolate galaxies in JWST surveys matches axion predictions, and stellar core–halo structures can trace underlying solitons. Together, these results illustrate how axion-inspired extensions to fuzzy dark matter offer a coherent and testable framework linking particle physics to astrophysical data. I will also introduce Jaxion: a new open-source high-performance Python/JAX code for simulating FDM.

Conveners: Philip Mocz, (Chair: Andrew Eberhardt)

14:00 → 15:00 Parallel session - CMB

14:00 Axion/ ALP scenario with high scale inflation

Considering that next generation CMB experiments like LiteBIRD and CMBS4 will probe the gravitational wave from high scale inflation via the observation of B-mode. We study the DFSZ-like GUT scenario where QCD axion and ALP exist in the evolution of the universe. In the conventional DFSZ scenario, since the domain wall number is larger than one, axion DM with PQ scale lower than inflation scale is not allowed, while PQ scale larger than inflation scale suffers from isocurvature problem. In other words, high scale inflation is not in good terms with this scenario. In this study, we consider the case where the existence of ALP can decay the domain wall of axion. Therefore, there is no domain wall problem and DFSZ axion DM with high scale inflation can be allowed, which can be a target of the next generation measurements like CMB or further investigation like PTA.

Speaker: Dan Kondo

14:20 Circularly polarized radiation from Axion-Photon conversion and CMB V-mode measurements

In the presence of a background magnetic field, axions or axion-like particles (ALPs) can be resonantly converted to photons when their mass is nearly equal to the effective photon mass. In this paper, we propose a novel method to constrain the parameter space of ALPs by investigating the resulting imprints of axion-photon conversion in the cosmic microwave background (CMB) observations. We show that a helical magnetic field existing prior to the CMB epoch can generate an excess population of photons carrying net circular polarization due to the axion-photon conversion mechanism.

Consequently, current measurements of the angular power spectrum of circular polarization (V-mode) in the CMB can be used to constrain the parameter space of ALP mass and its coupling to photons.

In the optimistic scenario of a maximally helical magnetic field with strength $\sim {\rm nG}$, we find that CLASS observations at $40 \, {\rm GHz}$ can probe the previously unconstrained regions of axion-photon coupling corresponding to ALP masses in the range $10^{-8}-10^{-10} \, {\rm eV}$.

Speaker: Ashu Kushwaha

14:40 Improved cosmological constraints on axion-lepton interactions

We present improved cosmological constraints on lepton couplings to thermally produced axion-like particles (ALPs). These interactions can affect the expansion history of the early Universe and leave distinctive signatures on the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAO). We compute precise ALP energy spectra by numerically solving the full Boltzmann equation, accounting for non-equilibrium production effects. Using Planck 2018 and the latest DESI data, we obtain the tightest cosmological limits to date on lepton–ALP couplings.

Speaker: Adam Gomułka

14:00 → 15:00 Parallel session - Gravity III

14:00 Domain walls induced by domain walls in a two axion system

We show that heavy axion domain walls induce domain walls of the QCD axion through a mixing between the heavy axion and the QCD axion, even when the pre-inflationary initial condition is assumed for the QCD axion. The induced domain walls arise because the effective θ parameter changes across the heavy axion domain walls, shifting the potential minimum of the QCD axion. When the heavy axion domain walls collapse, the induced QCD axion domain walls collapse as well. This novel mechanism for producing the QCD axions can explain dark matter even with the axion decay constant as small as ${\mathcal O}(10^9)$ GeV. In particular, this scenario requires domain wall collapse near the QCD crossover, potentially accounting for the stochastic gravitational wave background suggested by recent pulsar timing array observations, including NANOGrav. Using this mechanism, it is also possible to easily create induced domain walls for string axions or axions with a large decay constant, which would otherwise be challenging. We also comment on the implications for cosmic birefringence using induced axion domain walls.

Speaker: Junseok Lee

14:20 The Gravitational-Wave Symphony of Axion-like Particles

The early Universe offers a unique window into fundamental physics far beyond the reach of terrestrial experiments. In this talk, I will discuss how ultra-light axionlike scalar fields—ubiquitous in extensions of the Standard Model---can leave observable imprints through stochastic gravitational waves (GWs) generated by parametric resonance in the post-inflationary era. Using lattice simulations across broad parameter ranges, we find that such dynamics can produce GW signals spanning from nanohertz to kilohertz frequencies, potentially explaining recent NANOGrav results while predicting signatures for ground-based detectors such as LIGO and Cosmic Explorer. Remarkably, the same mechanisms can also account for the genesis of dark matter or dark radiation, and even realize Affleck–Dine–type baryogenesis without invoking supersymmetry. The resulting picture connects cosmic evolution, particle physics, and gravitational-wave astronomy into a unified framework—where early-universe field dynamics may soon become experimentally testable across multiple frontiers.

Speaker: Pankaj Saha

14:40 Constraints on extended axion structures from the lensing of fast radio bursts

Axions are hypothetical pseudoscalar particles that have been regarded as promising dark matter (DM) candidates. On the other hand, extended compact objects such as axion stars, which are supported by gravity and axion self interactions, may have also been formed in the early Universe and comprise part of DM. In this work, we consider the lensing of electromagnetic signals from distant sources by axion stars, as a way to constrain the properties of axion stars and fundamental axion parameters. Accounting for the effect of the finite size of the axion star, we study the lensing effect induced by gravity, and by axion-photon interactions. The latter effect is frequency dependent, and is relevant in the low frequency band, which motivates the use of fast radio burst (FRB) signals as a probe. We calculate the predicted number of lensed FRB events by specifying the fundamental axion parameters, axion star radial profile, fraction of DM residing in axion stars, and imposing lensing criteria based on the flux ratio and time delay between the brightest images from lensing. Assuming an optimistic case of $10^4$ observed FRB events, and a timing resolution of $1\,\mu{\rm s}$, the lack of observed FRB lensing events in CHIME allows us to probe axion stars with mass $ \gtrsim 10^{-2} M_\odot$, corresponding to axion masses $\lesssim 10^{-10}\,{\rm eV}$ and for negligible axion-photon couplings. Even lighter axion stars up to $\sim 10^{-3} M_\odot$ can be probed, assuming axion-photon couplings of at least $10^{-6}\,{\rm GeV}^{-1}$. Our results indicate that while FRB lensing by axion stars lead to sensitivities that are competitive with conventional microlensing searches operating in the optical band, it remains a challenge to probe axion-photon induced lensing effects.

Speaker: Kuan-Yen Chou

15:00 → 15:30 Tea time

Thursday 13 November

09:25 → 10:10 Randomness and Warmth (and spin) in Wave Dark Matter: [APEC]

If wave dark matter density is dominated by subhorizon field modes in the early universe, then the field exhibits Poisson fluctuation related enhancement on small scales, as well as warmth. These lead to scale dependent growth of structure, which leaves free-streaming, Jeans and shot-noise related features in the linear matter power spectrum as well as halo mass function. They also lead to significant soliton formation after matter radiation equality. I will discuss a general analytical framework as well as numerical results for the growth of structure in such systems, including cases with different species having different amounts of warmth and Poisson fluctuations, as well as species with different spin.

Conveners: Mustafa Amin, (Chair: Luna Zagorac)

10:10 → 10:55 Early growth of structure with warm wave dark matter

I will present unique features in the growth of structure in wave dark
matter models with warm white noise, where the power spectrum is peaked
at sub-horizon wavenumbers, using results from numerical simulations.
The post-inflationary production of bosonic particles, such as axions or
axion-like particles, leads to an enhanced isocurvature density power
spectrum on small scales. Moreover, when dark matter is extremely light,
these inhomogeneities result in a non-negligible velocity dispersion and
hence free-streaming suppression of the adiabatic power spectrum.
Starting with the Schrödinger–Poisson system of equations as the
relevant equations of motion, I will present results from simulations of
cosmic structure formation and compare them to analytic predictions. In
particular, the simulations reveal the enhancement and evolution of the
small-scale power spectrum and the formation of non-linear collapsed
objects, including wave dark matter halos and “Bose stars” (solitons),
shortly after matter–radiation equality. Using hydrodynamical
simulations of warm wave dark matter with baryons, I will further show
first insights into how this affects the early clustering of baryonic
matter. Probes of the small-scale power spectrum (e.g. dynamical heating
of stars, Ly-α forest, gravitational lensing, 21cm line intensity
mapping) can be sensitive to these effects of warm white noise on
quasi-linear scales, making this broad class of dark matter models
accessible to observations.

Conveners: Simon May, (Chair: Luna Zagorac)

10:55 → 11:15 Coffee break

11:15 → 12:00 Dynamical heating: solitons, stellar self-potentials and tidal stripping

Convener: Andrew Eberhardt

12:00 → 13:15 Lunch

13:15 → 14:00 Ultra-light dark matter and gravitational wave interferometers

Ultra-light dark matter, a compelling candidate for the cosmological dark matter, is modelled as an oscillating classical field, existing as a superposition of nearly coherent waves of macroscopic wavelength. If ultra-light dark matter has spin 2 it would look like a (massive) continuous gravitational wave, and as such it would be detectable in gravitational wave interferometers. In this talk I review the theory behind spin 2 dark matter models and describe the analysis pipeline to detect it with LIGO/Virgo data. If time allows I will also discuss how levitated sensor detectors can test this type of dark matter.

Convener: Federico Urban

14:00 → 15:00 Parallel session - Phenomenology II

Convener: Chair: Andrew Eberhardt

14:00 Baryogenesis in the Axiverse

Axiogenesis links the baryon asymmetry and dark matter abundance through the dynamics of the QCD axion, but its minimal form overproduces dark matter and can exacerbate the QCD axion quality problem. In this talk, I’ll show how these issues are naturally resolved in an axiverse framework, where the QCD axion arises from multiple interacting axions. This setup generates large axion velocities without spoiling the Strong CP solution and introduces new friction channels that reduce the relic abundance. The resulting theory makes imminently testable predictions for haloscopes, colliders, and the CMB.

Speaker: David Cyncynates

14:20 Multimodal axion emissions from Abelian-Higgs cosmic strings

We show that axions can be produced from Abelian-Higgs cosmic strings due to the axion-gauge coupling. The strong magnetic field is confined in the string, and the electric field is induced around the moving string, allowing axion productions from the dynamics of cosmic strings. Our simulation on the string network shows multimodal axion emissions in the sense that axions are produced in both the low-energy and high-energy regimes. The former can contribute to the cold dark matter and the latter can be regarded as dark radiation. We found that the axion with sub-GeV mass can explain the current relic dark matter abundance and simultaneously predicts a sizable amount of dark radiation which can be probed by future observations.

Speaker: Naoya Kitajima

14:40 Beyond Qubits: Multilevel Quantum Sensing for Axion Dark Matter

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 axion dark matter searches, spin-1 NV-center qutrits can
enhance the axion-electron coupling reach by an order of magnitude
beyond qubits. This principle applies broadly to multilevel quantum
systems including superconducting, neutral atom and trapped-ion qutrits,
establishing higher dimensional sensing as a powerful tool for probing
new physics.

Speaker: Xiaolin Ma

14:00 → 15:00 Parallel session - Theory II

Convener: Chair: Jianing Wang

14:00 Aspects of non-minimal couplings

Non-minimal couplings between vector fields, 3-forms, and scalars have emerged as intriguing candidates for dark matter and dark energy. At the same time, their theoretical study reveals unexpected features, including subtle issues with dynamics and consistency. In this talk, I will review recent developments in the study of non-minimal couplings, highlighting both their potential roles and some of the surprising properties that arise from their theoretical analysis.

Speaker: Anamaria Hell

14:20 Reheating after Axion Inflation and its implications (CANCELLED)

In modern cosmology, it is generally assumed that after inflation, the energy of the inflaton field is transferred to radiation through a process known as reheating.
Axion-like particles (ALPs) have recently attracted attention as potential inflaton candidates, since their shift symmetry naturally protects the flatness of the inflaton potential.

In this work, we study reheating in a model where the ALP couples to a non-Abelian gauge field via a Chern–Simons interaction. In this scenario, energy transfer proceeds resonantly, as familiar from preheating analyses, and is expected to be highly efficient. However, a significant challenge remains: even a small fraction of the inflaton may eventually come to dominate the energy density again.

In this talk, I will present how reheating is completed in this context and discuss its implications for observation."

Speaker: Tenta Tsuji

14:40 Examining Mass Enhancement in a High-Quality Composite Axion Model

The Peccei–Quinn (PQ) mechanism is a prominent solution to the strong CP problem. However, it faces the axion quality problem: higher-dimensional, Planck-suppressed operators which explicitly break PQ symmetry can reintroduce the effective QCD theta angle. In composite axion models, where strong dynamics at high energies dynamically break PQ symmetry, certain constructions address this quality problem. In some cases, hidden interactions distinct from QCD appear to contribute to the axion mass through instanton effects. I demonstrate that while these small instantons enhance the axion mass in a toy model, they do not contribute to the axion mass in an explicit model which addresses the quality problem.

Speaker: Takafumi Aoki

15:00 → 15:30 Tea time

Friday 14 November

09:25 → 10:10 Plenary (online)

Conveners: Neal Dalal, (Chair: Ippei Obata)

10:10 → 10:55 Axion dark matter searches with KAGRA and DANCE

Using laser interferometry, we search for ultralight axion dark matter through the polarization modulation induced by the axion-photon coupling. In particular, the tabletop-scale optical ring cavity experiment DANCE (Dark matter Axion riNg Cavity Experiment) aims for a broadband search and we carried out its first run in 2021 [1]. The experiment is now being upgraded with a wavelength-tunable laser to achieve higher sensitivity and a tunable frequency band [2]. In parallel, a dedicated polarization optics for axion detection has been installed at the gravitational wave telescope KAGRA in Kamioka, Gifu, making it possible to observe gravitational waves and axions simultaneously for the first time since June 2025 [3]. In this talk, I will report on the current status and future prospects of both experiments.
[1] Y. Oshima+, Phys. Rev. D 108, 072005 (2023)
[2] H. Takidera+, Phys. Rev. D 112, 063048 (2025)
[3] K. Nagano+, Phys. Rev. Lett. 123, 111301 (2019)

Conveners: Yuta Michimura, (Chair: Ippei Obata)

10:55 → 11:15 Coffee break

11:15 → 12:00 Generalization of delta N formalism beyond gradient expansion and potential application to axion inflation

Despite the astonishing success of cosmological probes in constraining the LCDM model, the dark matter mass remains one of the least constrained physical parameters. Wavelike dark matter is an intriguing alternative to standard cold dark matter with key particle physics motivations and potentially distinct astrophysical signatures. With a simple dynamical model for the evolution of a dark matter wavefunction, I will demonstrate how to predict the large-scale evolution and formation of destructive and constructive wave interference leading to topological defects and granules dressing the cosmic web of large-scale structure. I will also discuss recent advancements in creating efficient numerical methods for wave dark matter evolution, utilising approximative techniques originally developed for cold dark matter, such as FastPM and Bullfrog. Beyond offering a fundamental framework for ultralight particles, a wave-based approach serves as a versatile tool for reducing the complex phase-space dynamics of cold dark matter to position space.

Conveners: Yuko Urakawa, (Chair: Ippei Obata)

12:00 → 12:10 Closing remarks

12:10 → 13:40 Lunch

13:40 → 15:00 Parallel session - Cosmology III

Convener: Chair: Anamaria Hell

13:40 Diverse dark matter haloes in Two-field Fuzzy Dark Matter

Fuzzy dark matter (FDM) is a compelling candidate for dark matter, offering a natural explanation for the structure of diffuse low-mass haloes. However, the canonical FDM model with a mass of 10^{−22} eV encounters challenges in reproducing the observed diversity of dwarf galaxies, except for possibly scenarios where strong galactic feedback is invoked. The introduction of multiple-field FDM can provide a potential resolution to this diversity issue. The theoretical plausibility of this dark matter model is also enhanced by the fact that multiple axion species with logarithmically-distributed mass spectrum exist as a generic prediction of string theory. In this talk, I consider the axiverse hypothesis and investigate non-linear structure formation in the two-field fuzzy dark matter (2FDM) model.

Speaker: Hoang Nhan Luu

14:00 SPINN: Advancing Cosmological Simulations of Fuzzy Dark Matter with Physics Informed Neural Networks

Physics-informed neural networks (PINNs) have emerged as a powerful tool for solving differential equations by integrating physical laws into the learning process. This work leverages PINNs to simulate gravitational collapse, a critical phenomenon in astrophysics and cosmology. We introduce the Schrödinger–Poisson (SP) informed neural network which solves the nonlinear SP equations to simulate the gravitational collapse of fuzzy dark matter (FDM) in both 1D and 3D settings. The results demonstrate accurate predictions of key metrics such as mass conservation, density profiles, and structure suppression, validating against known analytical or numerical benchmarks. This work highlights the potential of PINNs for efficient, possibly scalable modeling of FDM and other astrophysical systems, overcoming the challenges faced by traditional numerical solvers due to the nonlinearity of the involved equations and the necessity to resolve multiscale phenomena, especially resolving the fine wave features of FDM on cosmological scales. Next steps include full cosmological FDM simulations using physics informed generative modeling.

Speaker: Ashutosh Kumar Mishra

14:20 Cosmology-informed constraints on the fuzzy dark matter mass from dwarf-spheroidal stellar kinematics

Fuzzy dark matter (FDM) predicts a solitonic core within halos, in contrast to the cuspy inner profiles expected in the standard cold dark matter (CDM) model.
We investigate differences in the inner structure of dark matter halos through the stellar kinematics of dwarf spheroidal galaxies, which place constraints on the FDM particle mass.
We analyze the parameter space using a statistical framework with cosmology-informed priors derived from the Semi-Analytical SubHalo Inference ModelIng (SASHIMI), which restrict the outer NFW-like halo parameters to cosmologically motivated regions.
Guided by recent FDM simulations, we further assume a smooth connection between the inner soliton and outer NFW-like profiles, enabling an efficient constraint on the FDM mass. As shown in the previous study, Segue 1 provides most stringent constraint $m_\mathrm{FDM}\gtrsim 10^{-21}\ \mathrm{eV}$ even when the cosmological priors are taken into account."

Speaker: Shunichi Horigome

14:40 Cosmological Zoom-in simulations of Fuzzy Dark Matter dwarf halos in the field

Ultra-light bosons are a promising candidate for the dark matter in the Universe. The quantum nature implies minimum halo mass scale below which structure formation is suppressed. The limited number of Self-consistent FDM simulations have reveal that non-linear collapse can yield soliton formation below the Jeans scale. In this talk, I will present a suite of FDM cosmological zoom-in simulations of dwarf mass halos in the field for various boson masses. I will show how these results can inform about the formation of the smallest scales and how that impacts the soliton core-halo mass relation.

Speaker: Victor H. Robles

13:40 → 15:00 Parallel session - Experiments II

Convener: Chair: Baptiste Jost

13:40 Search for ALPs with mass near 2.3 eV via stimulated resonant photon scattering in a three-laser collision at a large crossing angle eV-mass

Axion-like particles(ALPs) are attractive candidates that could explain reported excesses in the cosmic optical and infrared background. We aim to search for ALPs via stimulated resonant photon scattering by colliding three short-pulse lasers. By changing angle of incidence of the three beams, the center-of-mass-system collision energy can be varied and the eV mass range can be continuously searched for. In this talk, I will report initial point search performed with a large-crossing-angle setup.

Speaker: Takumi Hasada

14:00 Precision Atomic Response Functions for Probing Dark Matter–Electron Scattering in Xenon and Germanium Detectors

This work presents a comprehensive theoretical investigation of dark matter (DM)–electron interactions using atomic response functions (ARFs), with a focus on Germanium and Xenon—two widely employed detectors in direct detection experiments. Accurately modeling these interactions is essential for interpreting and guiding searches for light dark matter candidates, particularly in scenarios where DM particles interact with atomic electrons rather than nuclei.
Our goal is to develop a comprehensive set of ARFs at leading order (LO), derived using state-of-the-art atomic many-body methods. We show that the complex dynamics of DM-induced atomic ionization can be effectively described by four independent atomic response functions. These newly identified responses prove particularly significant in the context of light dark matter (LDM) scenarios, which we investigate using a model-independent effective field theory framework.
To achieve this, we employ the relativistic random-phase approximation (RRPA) and the relativistic frozen-core approximation (RFCA), enabling differential cross-section predictions with estimated accuracies of ~5% (RRPA) and ~20% (RFCA)[1,2, 3].
Using our computed ARFs, we set 90% confidence level exclusion limits on various DM-electron effective interaction operators by comparing with null results from current and ongoing experiments. In particular, our analysis is relevant to the CDEX and CDMSlite experiments, as well as xenon-based detectors such as XENONnT and other next-generation liquid xenon experiments. These detectors, with their increasing sensitivity to low-energy ionization signals, stand to benefit from the improved theoretical modeling provided by our atomic approach.
This study not only refines theoretical tools for interpreting DM-electron signals but also enhances the sensitivity of future searches. The results will be presented at an upcoming international conference.
[1] M. K. Pandey et al., Phys. Rev. D 102, 123025 (2020).
[2] C.-P. Liu et al., Phys. Rev. D 106, 063003 (2022).
[3] C.-P. Liu et al., arXiv:2501.04020."

Speaker: Mukesh Kumar Pandey

14:20 Axion searches at Belle/Belle II

The Belle and Belle II experiments have collected samples of e+e− collision data at and near the centre-of-mass energies near the Υ(nS) resonances. These data have constrained kinematics and low multiplicity, which allow searches for dark sector particles in the mass range from a few MeV to 10 GeV. Using samples of up to 711 fb−1 collected by Belle and 365 fb−1 collected by Belle II at the Y(4S), we have performed searches of ALPs decaying to two photons and tau leptons; long-lived ALPs in bottom to strange quark transitions; and ALPs produced in bottom mesons decaying to two photons or invisible final states. We will present recent highlights from several ALPs and dark matter searches at Belle and Belle II.

Speaker: Tomoyuki Shimasaki

14:40 Search for dark-matter axions beyond the quantum limit: the Cosmological Axion Sarov Haloscope (CASH) proposal and status

Firmly established in astrophysical observations, dark matter evades direct detection in experiments. Axions and axion-like particles are among the leading dark-matter candidates, and numerous attempts to detect them in laboratories have been performed. Here, we propose to advance these efforts substantially, extending the sensitivity for dark-matter axions in the mass range 38-54 mu-eV down to the axion-photon couplings g_{agg} ~ 10^{-14}-10^{-15} GeV^{-1}, motivated by generic models of Quantum Chromodynamics axion. Single-photon detectors based on Josephson junctions operating at ultra-low temperatures are key elements of the experiment. The projected sensitivity will be reached in one year of data taking with magnetic field of 7 T, making Cosmological Axion Sarov Haloscope (CASH) the most sensitive haloscope in this mass range (based on arXiv:2506.18595 [hep-ph]). In addition, we discuss the sensitivity of proposed CASH experiment to relativistic axion flux. We report the current status of the first pathfinder run of CASH experiment.

Speaker: Petr Satunin

15:00 → 15:30 Tea time