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Axions in Japan

10–14 Nov 2025
Kavli IPMU
Asia/Tokyo timezone

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3. Multi-Axion Bosenovae and Sequential Axion Emissions
Jason Arakawa
10/11/2025, 14:00

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...
2. Strong backreaction of gauge quanta produced during inflation and the sourced GWs
Jian-Feng He
10/11/2025, 14:00

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...
4. Core–Halo Relation in Self-Interacting Scalar Field Dark Matter
Jessica N. Lopez-Sanchez
10/11/2025, 14:20

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...
1. Gravitational waves from self-interacting axion clouds around rotating black holes
Takuya Takahashi
10/11/2025, 14:20

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...
5. Interfering and Interacting Fuzzy Dark Matter
Christian Capanelli
10/11/2025, 14:40

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...
9. Background-Enhanced Axion Force by Axion Dark Matter
Yu Cheng
10/11/2025, 15:30

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...
13. Resolving the QCD Axion Domain Wall Problem with a Light Axion
Kai Murai
10/11/2025, 15:30

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...
14. A Step in Flux to Suppress Axion Isocurvature
Priyesh Chakraborty
10/11/2025, 15:50

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...
10. Electric Dipole Moments From Missed Dark Matter Scattering
Jason L. Evans
10/11/2025, 15:50

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...
11. Constraints on MeV Axion Models from Kaon Decays with KTeV Data
Takaya Iwai
10/11/2025, 16:10

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.
12. Search for sub-eV ALP via quasi-parallel stimulated resonant photon collision with “coronagraphy” to mitigate background photon based on spatial distribution characteristics
Airi Kodama
10/11/2025, 16:30

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...
6. Toward remote sensing of backward reflection from stimulated axion decay
Kensuke Homma
11/11/2025, 14:00

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...
15. What can solve the strong CP problem?
Tom Melia
11/11/2025, 14:00
7. A Way of Axion Detection with Mass 10^(−4)eV ∼ 10^(−3)eV using Cylinder with Low Electric Conductivity
Aiichi Iwazaki
11/11/2025, 14:20

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 =...
16. High-quality QCD Axion in the Standard Model---- Blue Bird Scenario of the Axion
Tsutomu Yanagida
11/11/2025, 14:20
17. All axion dark matter from supersymmetric models
Kairui Zhang
11/11/2025, 14:40

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...
8. Axion dark matter search using quantum sensing of magnons: Estimation of sensitivity for Kittel mode – superconducting qubit hybrid
Yaman Singh Shrestha
11/11/2025, 14:40

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...
18. Massive black hole binaries in ultralight dark matter solitons
Russell Boey
11/11/2025, 15:30

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...
21. Probing Axion-like Dark Matter via Time-Variable Polarization in Protoplanetary Disks
Kanako Narita
11/11/2025, 15:30

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...
22. Dynamical heating in Dwarf Spheroidal Galaxies in spin-s Ultra-light Dark Matter models
Erick Munive Villa
11/11/2025, 15:50

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...
20. Measurable Effects from Unresolvable Perturbations of Axion Dark Matter in the Critical Region of Gravitational Lenses
Leo W.H. Fung
11/11/2025, 15:50

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...
23. Revisiting Fuzzy Dark Matter Constraints: Accounting for Core–Halo Mass Relation Diversity
Dafa Wardana
11/11/2025, 16:10

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...
26. Axion/ ALP scenario with high scale inflation
Dan Kondo
12/11/2025, 14:00

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...
24. Domain walls induced by domain walls in a two axion system
Junseok Lee
12/11/2025, 14:00

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...
27. Circularly polarized radiation from Axion-Photon conversion and CMB V-mode measurements
Ashu Kushwaha
12/11/2025, 14:20

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...
25. The Gravitational-Wave Symphony of Axion-like Particles
Pankaj Saha
12/11/2025, 14:20

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...
44. Constraints on extended axion structures from the lensing of fast radio bursts
Kuan-Yen Chou
12/11/2025, 14:40

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...
28. Improved cosmological constraints on axion-lepton interactions
Adam Gomułka
12/11/2025, 14:40

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,...
31. Aspects of non-minimal couplings
Anamaria Hell
13/11/2025, 14:00

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...
29. Baryogenesis in the Axiverse
David Cyncynates
13/11/2025, 14:00

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...
30. Multimodal axion emissions from Abelian-Higgs cosmic strings
Naoya Kitajima
13/11/2025, 14:20

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...
32. Reheating after Axion Inflation and its implications (CANCELLED)
Tenta Tsuji
13/11/2025, 14:20

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...
41. Beyond Qubits: Multilevel Quantum Sensing for Axion Dark Matter
Xiaolin Ma
13/11/2025, 14:40

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...
33. Examining Mass Enhancement in a High-Quality Composite Axion Model
Takafumi Aoki
13/11/2025, 14:40

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...
45. Diverse dark matter haloes in Two-field Fuzzy Dark Matter
Hoang Nhan Luu
14/11/2025, 13:40

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...
37. 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
Takumi Hasada
14/11/2025, 13:40

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...
38. Precision Atomic Response Functions for Probing Dark Matter–Electron Scattering in Xenon and Germanium Detectors
Mukesh Kumar Pandey
14/11/2025, 14:00

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...
34. SPINN: Advancing Cosmological Simulations of Fuzzy Dark Matter with Physics Informed Neural Networks
Ashutosh Kumar Mishra
14/11/2025, 14:00

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...
39. Axion searches at Belle/Belle II
Tomoyuki Shimasaki
14/11/2025, 14:20

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...
36. Cosmology-informed constraints on the fuzzy dark matter mass from dwarf-spheroidal stellar kinematics
Shunichi Horigome
14/11/2025, 14:20

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...
35. Cosmological Zoom-in simulations of Fuzzy Dark Matter dwarf halos in the field
Victor H. Robles
14/11/2025, 14:40

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...
40. Search for dark-matter axions beyond the quantum limit: the Cosmological Axion Sarov Haloscope (CASH) proposal and status
Petr Satunin
14/11/2025, 14:40

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...
47. Axion dark matter searches with KAGRA and DANCE
Yuta Michimura

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...
46. Plenary
Neal Dalal
42. Spinoptics in the presence of axion-like particles
Tomoki Takeuchi

In curved spacetime, the trajectory of a light ray is described by a geodesic under the geometric optics approximation.However, this approximation is valid only locally and is not justified int the all spacetime regions.If it breaks down, the polarization of light can affect its propagation.In this presentation, we consider light propagating through an axion field in spinoptics...
43. Spinoptics in the presence of axion-like particles (cancelled)
Tomoki Takeuchi

In curved spacetime, the trajectory of a light ray is described by a geodesic under the geometric optics approximation.However, this approximation is valid only locally and is not justified int the all spacetime regions.If it breaks down, the polarization of light can affect its propagation.In this presentation, we consider light propagating through an axion field in spinoptics...
19. Ultra-light dark matter and gravitational wave interferometers
Federico Urban

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...
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