arXiv subjects

Asuka Ito

Publications and source records attributed to Asuka Ito.

At least 19 recordsLinked to original sources

arXiv2026

X-ray signals converted from high-frequency gravitational waves emitted by spinning light primordial black hole dark matter

We investigate the detectability of high-frequency gravitational waves from the superradiance of light primordial black hole dark matter through photons converted in the Galactic magnetic field. We find that the signal is significantly enhanced in the X-ray frequency range around $10^{18}$Hz. For clustered initial conditions, future X-ray observations may detect the converted photons from primordial black holes in the mass range $10^{-15}M_{\odot} \sim 10^{-13}M_{\odot}$. Our results indicate that future X-ray observations could provide a new probe of light primordial black hole dark matter through high-frequency gravitational waves.

astro-ph.CO↗

arXiv2026

Graviton Floor

It has been observed that the Universe is permeated by the cosmic photon background, ranging from radio waves to gamma rays. We investigate the conversion of the photon background into gravitons in the presence of background magnetic fields in the Milky Way Galaxy and in blazar jets. We find that the resulting graviton background is dominated by the contribution generated in blazar jets. Importantly, this graviton background constitutes a graviton floor for high-frequency gravitational wave detectors searching for new physics, analogous to the neutrino floor.

gr-qc↗

arXiv2026

Gravitational waves from gaps of neutron stars

The pulsar magnetosphere is a potential source of continuous gravitational waves due to the rapid charge-discharge process in short timescale, varying the electric-field energy density. We estimate the strain of the continuous gravitational waves, considering relativistic effects and different gap regions. We find that the strain from the polar cap is too small, in contrast to previous results. On the other hand, the strain from the outer gap is as large as $\sim2\times10^{-24}$, enough for future gravitational-wave detection such as the Einstein Telescope. Our result presents a new approach for the future detection of gravitational waves to probe the physics in the magnetosphere.

gr-qc↗

arXiv2025

Quantum sensing of high-frequency gravitational waves with ion crystals

A detection method for high-frequency gravitational waves using two-dimensional ion crystals is investigated. Gravitational waves can resonantly excite the drumhead modes of the ion crystal, particularly the parity-odd modes. In the optical dipole force protocol, entanglement between the drumhead modes and the collective spins transfers the excitation of the drumhead modes to the rotation of the total spin. Furthermore, gravitational wave detection beyond the standard quantum limit becomes possible as a squeezed spin state is generated through this entanglement. The sensitivity gets better with a larger ions crystals as well as a larger number of the ions. Future realization of large ion crystals can significantly improve the sensitivity to gravitational waves in the 10 kHz to 10 MHz region.

gr-qc↗

arXiv2025

Graviton-photon conversion in blazar jets as a probe of high-frequency gravitational waves

We study graviton-photon conversion in the magnetic fields of a blazar jet and explore the possibility of detecting high-frequency gravitational waves through blazar observations. We calculate the conversion rate using the magnetic field configurations of leptonic, lepto-hadronic, and hadronic one-zone synchrotron self-Compton models for the blazar jet of Mrk 501. By requiring that the photon flux produced within the blazar jet does not exceed the observed flux of Mrk 501, we derive conservative constraints on the abundance of stochastic gravitational waves. We find that, for all three models considered, the resulting limits can be more stringent than previous constraints in the frequency range from $10^8$ Hz to $10^{15}$ Hz.

gr-qc↗

arXiv2025

Warm multi natural inflation

Multi-natural inflation is studied in the context of warm inflation. We study the warm multi-natural inflation scenario with both linear and cubic temperature-dependent dissipation coefficients. The model is motivated by axion-like inflation models with coupling to non-Abelian gauge fields through a dimension-five coupling and dissipation originating from sphaleron decay in a thermal bath. Both cases of dissipation coefficients can be compatible with current observations. In the case of the cubic dissipation coefficient, we find that the curvature perturbation starts to grow suddenly when a transition from a weak dissipation to a strong dissipation regime occurs at the later stage of the inflation. We also show that such rapid growth of the curvature perturbation on small scales gives rise to abundant scalar induced gravitational waves, which may be detectable with future gravitational wave detectors such as DECIGO and ET. On the other hand, there are also other parameter regions of the model, in the warm inflation regime of weak to strong dissipation and with sub-Planckian axion decay constant, that can lead to overproduction of primordial black holes on small scales, which are constrained by nucleosynthesis bounds, thus ruling out the model in this region of parameters.

hep-ph↗

arXiv2025

Challenges and Opportunities of Gravitational Wave Searches above 10 kHz

The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band. The scarcity of possible astrophysical sources in most of this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising of these sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of a series of workshops on the topic of high-frequency gravitational wave detection, held in 2019 (ICTP, Trieste, Italy), 2021 (online) and 2023 (CERN, Geneva, Switzerland).

gr-qc↗

arXiv2024

Macroscopic Quantum Response to Gravitational Waves

We study the excitation of a one-electron quantum cyclotron by gravitational waves. The electron in such as a penning trap is prepared to be at the lowest Landau level, which has an infinite degeneracy parameterized by the size of the wave function. We find that the excitation rate from the ground state to the first excited state is enhanced by the size of the electron wave function: an electron with a larger wave function feels gravitational waves more. As a consequence, we derive a good sensitivity to gravitational waves at a macroscopic one-electron quantum cyclotron.

gr-qc↗

arXiv2024

Quantum entanglement of ions for light dark matter detection

A detection scheme is explored for light dark matter, such as axion dark matter or dark photon dark matter, using a Paul ion trap system. We first demonstrate that a qubit, constructed from the ground and first excited states of vibrational modes of ions in a Paul trap, can serve as an effective sensor for weak electric fields due to its resonant excitation. As a consequence, a Paul ion trap allows us to search for weak electric fields induced by light dark matter with masses around the neV range. Furthermore, we illustrate that an entangled qubit system involving $N$ ions can enhance the excitation rate by a factor of $N^2$. The sensitivities of the Paul ion trap system to axion-photon coupling and gauge kinetic mixing can reach previously unexplored parameter space.

hep-ph↗

arXiv2024

Gravitational wave search through electromagnetic telescopes

We study the graviton-photon conversion in the magnetic fields of the Earth, the Milky Way Galaxy, and intergalactic regions. Requiring that the photon flux converted from gravitons does not exceed the observed photon flux with telescopes, we derive upper limits on the stochastic gravitational waves in frequency ranges from $10^{7}$Hz to $10^{35}$Hz. Remarkably, the upper limits on $h^2 Ω_{\rm GW}$ could be less than unity in the frequency range of $10^{18}$-$10^{23}$ Hz in a specific case. The detection of gravitational waves using telescopes would open up a new avenue for high frequency gravitational wave observations.

gr-qc↗

arXiv2024

Effects of Finite Material Size On Axion-magnon Conversion

Magnetic materials are particularly favorable targets for detecting axions interacting with electrons because the collective excitation of electron spins, the magnon, can be excited through the axion-magnon conversion process. It is often assumed that only the zero-momentum uniformly precessing magnetostatic (Kittel) mode of the magnon is excited. This is justified if the de Broglie wavelength of the axion is much longer than the size of the target magnetic material. However, if the de Broglie wavelength is shorter, finite-momentum magnon modes can also be excited. We systematically analyze the target material size dependence of the axion-magnon conversion rate. We discuss the importance of these effects in the detection of relativistic axions as well as in the detection of axion dark matter of relatively heavy mass with large material size.

hep-ph↗

arXiv2023

Exploring High Frequency Gravitational Waves with Magnons

Detecting gravitational waves with frequencies higher than 10 kHz requires new strategies. In previous papers, we proposed magnon gravitational wave detectors and gave the first limit on GHz gravitational waves by reinterpreting the existing data from axion dark matter experiments. In this paper, we show that the sensitivity can be improved by constructing the detector specific to gravitational waves. In particular, we employ an infinite sum of terms in the expansion of Fermi normal coordinates to probe gravitational waves with a wavelength comparable to the detector size. As a consequence, we obtain sensitivity of around $h_c \sim 10^{-20}$.

gr-qc↗

arXiv2023

Probing high frequency gravitational waves with pulsars

We study graviton-photon conversion in magnetosphere of a pulsar and explore the possibility of detecting high frequency gravitational waves with pulsar observations. It is shown that conversion of one polarization mode of photons can be enhanced significantly due to strong magnetic fields around a pulsar. We also constrain stochastic gravitational waves in frequency range of $10^{8}-10^{9}\,$Hz and $10^{13}-10^{27}\,$Hz by using data of observations of the Crab pulsar and the Geminga pulsar. Our method widely fills the gap among existing high frequency gravitational wave experiments and boosts the frequency frontier in gravitational wave observations.

gr-qc↗

arXiv2023

Superluminal propagation from IR physics

One may believe that front velocities of waves in a given theory coincide with the UV limit of phase velocities for any dispersion relations. This implies that IR physics is irrelevant to the discussion of propagation speed of waves. We first consider a theory that contains higher spatial derivatives in the wave equation and prove that front velocities coincide with the UV limit of phase velocities, at least, if parity is conserved. However, we also show that front velocities do not coincide with the UV limit of phase velocities in general dispersion relations. We explicitly give several examples in which front velocities are superluminal owing to an IR or intermediate energy scale property of dispersion relations even if the UV limit of phase velocities is luminal. Our finding conveys the important caution that not only UV physics but also IR physics can be significant to superluminality.

hep-th↗

arXiv2022

Gravitational Waves in Metastable Supersymmetry Breaking

If supersymmetry is broken in metastable vacua, it is not clear why we are now in there rather than supersymmetric vacua. Moreover, it is natural to expect that we were in supersymmetric vacua, which have higher symmetry than metastable vacua, in the early universe. In this paper, we reexamine and improve the previous analysis on the cosmological evolution of the vacuum structure in the ISS model of metastable supersymmetry breaking by taking into account constraints on the reheating temperature, which is needed to avoid the overproduction of gravitinos. It turns out that the desired phase transition from a supersymmetric vacuum to a metastable vacuum is allowed only in the light gravitino mass region $m_{3/2} < 4.7$ eV. This is achieved by either rolling down potential or tunneling processes depending on the reheating temperature. We show that when the tunneling processes are realized, abundant gravitational waves could be produced from collisions of runaway bubbles. The resulting gravitational waves are detectable with the future gravitational wave interferometers like LISA and DECIGO.

hep-th↗

arXiv2022

Tree-level unitarity in Higgs inflation in the metric and the Palatini formulation

We calculate the tree-level amplitudes for electrically neutral $2\to2$ scattering for the Standard Model Higgs doublet non-minimally coupled to the Ricci scalar. We consider both the metric and the Palatini formulation of gravity. We find the partial wave unitarity limit for a general background field value. Our results are in agreement with previous work. In the electroweak vacuum, tree-level unitarity is violated at $\sim M_\text{Planck}/ξ$ in the metric formulation, and at $\sim M_\text{Planck}/\sqrtξ$ in the Palatini formulation. In the inflationary large field background, the unitarity limit is at $\sim M_\text{Planck}/\sqrtξ$ in both formulations. We compare the unitarity violation energy to scales relevant during inflation. We also calculate a direct collider limit on $ξ$ in the Palatini formulation, $ξ<2.5\times10^{31}$.

astro-ph.CO↗

arXiv2022

Axion search with quantum nondemolition detection of magnons

The axion provides a solution for the strong CP problem and is one of the leading candidates for dark matter. This paper proposes an axion detection scheme based on quantum nondemolition detection of magnon, i.e., quanta of collective spin excitations in solid, which is expected to be excited by the axion-electron interaction predicted by the Dine-Fischer-Srednicki-Zhitnitsky (DFSZ) model. The prototype detector is composed of a ferrimagnetic sphere as an electronic spin target and a superconducting qubit. Both of these are embedded inside a microwave cavity, which leads to a coherent effective interaction between the uniform magnetostatic mode in the ferrimagnetic crystal and the qubit. An upper limit for the coupling constant between an axion and an electron is obtained as $g_{aee}<2.6\times10^{-6}$ at the 95% confidence level for the axion mass of $33.117$$μ$eV $<m_{a}<33.130$$μ$eV.

hep-ex↗

arXiv2022

Inertial and gravitational effects on a geonium atom

We reveal all linear order inertial and gravitational effects on a non-relativistic Dirac particle (mass $m$) on the Earth up to the order of $1/m$ in the Foldy-Wouthuysen-like expansion. Applying the result to Penning trap experiments where a Dirac particle experiences the cyclotron motion and the spin precession in a cavity, i.e., a geonium atom, we study modifications to the $g$-factor of such as the electron. It is shown that each correction from gravity has different dependence on the cyclotron frequency and the mass $m$. Therefore, their magnitude change depending on situations. In a particular case of an electron $g$-factor measurement, the dominant correction to the observed $g$-factor comes from effects of the Earth's rotation, which is $δg / 2 \simeq 5.2 \times 10^{-17}$. It may be detectable in the near future.

gr-qc↗