arXiv subjects

Yoshiaki Himemoto

Publications and source records attributed to Yoshiaki Himemoto.

At least 19 recordsLinked to original sources

arXiv2026

Signature of axion dark matter in low-frequency terrestrial electromagnetic fields: formulation and predictions

We develop a theoretical framework for axion dark matter (DM) searches using terrestrial electromagnetic (EM) fields, enabling a global and quantitative characterization of the signal across the Earth. Axions couple to the geomagnetic field and generate a monochromatic EM signal at a frequency set by the axion mass. Incorporating a realistic atmospheric conductivity, we describe the axion-induced EM waves confined in the Earth-ionosphere cavity, avoiding the divergences present in idealized treatments. Our semi-analytical method yields quantitative predictions for the axion-induced magnetic field near the Earth's surface, and we found that (i) at $m_{\rm a}\gtrsim10^{-14}$ eV, the signal exhibits resonance structures aligned with Schumann resonances, and the magnetic field amplitude is especially enhanced at $m_{\rm a}\sim3\times10^{-14}$ eV. (ii) The signal amplitude and orientation also vary with geographic location, with Southeast Asia offering the strongest sensitivity. These predictions are insensitive to uncertainties in conductivity models and boundary conditions. Those distinctive features provide a reliable template to distinguish axion-induced signals from natural or anthropogenic EM backgrounds, and the formalism can be extended to other DM candidates such as dark photons.

hep-ph↗

arXiv2026

Searching for dark photon dark matter from terrestrial magnetic fields

We present a novel search for dark photon dark matter (DM) using terrestrial magnetic field measurements at frequencies below 100 Hz. Coherently oscillating dark photon DM can induce a monochromatic magnetic field via kinetic mixing with ordinary photons. Notably, for dark photon masses $m_{A'}$ around $3 \times 10^{-14}$ eV, the signal can be resonantly amplified within a cavity formed by the Earth's surface and the ionosphere. We compute the expected signal incorporating the effect of atmospheric conductivity, and derive new upper limits on the kinetic mixing parameter $\varepsilon$ from long-term geomagnetic data. These limits improve upon previous ground-based constraints in the mass range of $1 \times 10^{-15}$ eV $\lesssim m_{A'} \lesssim 2 \times 10^{-13}$ eV.

hep-ph↗

arXiv2025

Hunting axion dark matter signatures in low-frequency terrestrial magnetic fields

We show that Earth's natural environment can serve as a powerful probe for ultralight axion dark matter. In the presence of global geomagnetic fields, the axions with masses ranging from $10^{-15}\,{\rm eV}-10^{-13}\,{\rm eV}$ induce electromagnetic waves in the (sub-) extremely low-frequency band ($0.3-30\,{\rm Hz}$) through the axion-photon coupling. We predict the amplitude of induced magnetic fields in the Earth-ionosphere cavity, taking the finite conductivity of the atmosphere into account. This allows us to constrain the axion-photon coupling parameter, $g_{\rm aγ}$, from the long-term monitoring data of the low-frequency magnetic fields, resulting in a significant improvement from the previous constraints down to $g_{\rm aγ} \lesssim 4\times10^{-13}\,{\rm GeV}^{-1}$ for axion mass $\sim 3 \times 10^{-14}\,{\rm eV}$.

hep-ph↗

arXiv2025

Axion dark matter search from terrestrial magnetic fields at extremely low frequencies

The natural environment of the Earth can act as a sensitive detector for dark matter in ultralight axions. When axions with masses between $1\times10^{-15}\,{\rm eV}$ and $1\times10^{-13}\,{\rm eV}$ pass through the Earth, they interact with the global geomagnetic field, generating electromagnetic (EM) waves in the extremely low-frequency range ($0.3$--$30\,{\rm Hz}$) through axion-photon coupling. This paper is one of a series of companion papers for~\cite{Taruya:2025zql}, focusing on the data analysis method and search results for an axion signal. Utilizing the theoretical predictions of axion-induced EM spectra from a companion study, we analyzed long-term observational data of terrestrial magnetic fields in this frequency band to search for axion-induced signals. Our analysis identified 65 persistent signal candidates with a signal-to-noise ratio (SNR) greater than 3. Aside from these candidates, we placed a new upper bound on the axion-photon coupling parameter, significantly refining the previous constraint from CAST by at most two orders of magnitude down to $g_{aγ} \lesssim 4\times10^{-13} \,{\rm GeV}^{-1}$ for the axion mass around $3 \times 10^{-14}\,{\rm eV}$.

hep-ph↗

arXiv2023

Distinguishing a stochastic gravitational-wave signal from correlated noise with joint parameter estimation: Fisher analysis for ground-based detectors

Search sensitivity to a stochastic gravitational-wave background (SGWB) is enhanced by cross-correlating detector signals. However, one of the most serious concerns is the environmental noise correlated between detectors. The global electromagnetic fields on the Earth, known as Schumann resonances, produce the correlated noise through the instrumental magnetic couplings. In this paper, we study the detectability of a SGWB in the presence of the correlated magnetic noise, using the Fisher analysis based on the analytical model of the correlated magnetic noise. We find that there is no significant degeneracy between the SGWB and noise parameters. Marginalizing over the correlated noise parameters degrades the constraint on each SGWB parameter by a factor of $\sim2$ at most in the four-detector case, irrespective of the strength of the magnetic coupling. We also confirm that the forecast results are robust against the variation of correlated noise parameters and can vary up to $40\%$ in the realistic range of the coupling parameters for the second-generation detectors. However, ignoring the correlated noise in parameter estimation generally leads to a biased constraint on the SGWB parameters. If the coupling strength is twice as large as expected, this could result in a serious bias.

gr-qc↗

arXiv2021

Impacts of overlapping gravitational-wave signals on the parameter estimation: Toward the search for cosmological backgrounds

Third-generation gravitational wave detectors, such as the Einstein Telescope and Cosmic Explorer, will detect a bunch of gravitational-wave (GW) signals originating from the coalescence of binary neutron star (BNS) and binary black hole (BBH) systems out to the higher redshifts, $z\sim 5-10$. There is a potential concern that some of the GW signals detected at a high statistical significance eventually overlap with each other, and the parameter estimation of such an overlapping system can differ from the one expected from a single event. Also, there are certainly overlapping systems in which one of the overlapping events has a low signal-to-noise ratio $\lesssim 4$, and is thus unable to be clearly detected. Those system will potentially be misidentified with a single GW event, and the estimated parameters of binary GWs can be biased. We estimate the occurrence rate of those overlapping events. We find that the numbers of overlapping events are $\sim 200$ per day for BNSs and a few per hour for BBHs. Then we study the statistical impacts of these overlapping GWs on a parameter estimation based on the Fisher matrix analysis. Our finding is that the overlapping signals produce neither large statistical errors nor serious systematic biases on the parameters of binary systems, unless the coalescence time and the redshifted chirp masses of the two overlapping GWs are very close to each other, i.e., $|\mathcal{M}_{z1}-\mathcal{M}_{z2}|\lesssim10^{-4} \,(10^{-1})\,M_\odot$ and $|t_{\rm c1}-t_{\rm c2}|\lesssim10^{-2}\,(10^{-1})$\,s for BNSs (BBHs). The occurrence rate of such a closely overlapping event is shown to be much smaller than one per year with the third-generation detectors.

gr-qc↗

arXiv2020

Current status of space gravitational wave antenna DECIGO and B-DECIGO

Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is the future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection of primordial gravitational waves, which could be produced during the inflationary period right after the birth of the universe. There are many other scientific objectives of DECIGO, including the direct measurement of the acceleration of the expansion of the universe, and reliable and accurate predictions of the timing and locations of neutron star/black hole binary coalescences. DECIGO consists of four clusters of observatories placed in the heliocentric orbit. Each cluster consists of three spacecraft, which form three Fabry-Perot Michelson interferometers with an arm length of 1,000 km. Three clusters of DECIGO will be placed far from each other, and the fourth cluster will be placed in the same position as one of the three clusters to obtain the correlation signals for the detection of the primordial gravitational waves. We plan to launch B-DECIGO, which is a scientific pathfinder of DECIGO, before DECIGO in the 2030s to demonstrate the technologies required for DECIGO, as well as to obtain fruitful scientific results to further expand the multi-messenger astronomy.

gr-qc↗

arXiv2019

Correlated magnetic noise from anisotropic lightning sources and the detection of stochastic gravitational waves

Direct detection of gravitational waves (GWs) from compact binary systems suggests that the merger rate of such events is large, and the sum of their GWs can be viewed as stochastic signals. Because of its random nature, cross-correlating the signals from multiple detectors is essential to disentangle the GWs from instrumental noise. However, the global magnetic fields in the Earth-ionosphere cavity produce the environmental disturbances at low-frequency bands, known as Schumann resonances, and coupled with GW detectors, they potentially contaminate the stochastic GW signal as a correlated noise. Previously, we have presented a simple analytical model to estimate its impact on the detection of stochastic GWs. Here, extending the analysis to further take account of the effects of anisotropic lightning source distributions, we present a comprehensive study of the impact of correlated magnetic noise at low-frequency bands, including non-tensor-type GWs, as well as circularly polarized tensor-type GWs. We find that as opposed to a naive expectation, the impact of correlated magnetic noise does not always increase with anisotropies in the lighting source distribution. Even in the presence of large anisotropies, there is a robust detector pair for which the amplitude of correlated magnetic noise becomes comparable to or well below detectable amplitude of stochastic GWs. The results indicate that the properties of the correlated magnetic noise depend crucially on both the geometrical and geographical setup of the detector's pair, and Virgo and KAGRA would be potentially the most insensitive detector pair against the correlated magnetic for both tensor- and non-tensor-type stochastic GWs.

astro-ph.IM↗

arXiv2017

Impact of correlated magnetic noise on the detection of stochastic gravitational waves: Estimation based on a simple analytical model

After the first direct detection of gravitational waves (GW), detection of stochastic background of GWs is an important next step, and the first GW event suggests that it is within the reach of the second-generation ground-based GW detectors. Such a GW signal is typically tiny, and can be detected by cross-correlating the data from two spatially separated detectors if the detector noise is uncorrelated. It has been advocated, however, that the global magnetic fields in the Earth-ionosphere cavity produce the environmental disturbances at low-frequency bands, known as Schumann resonances, which potentially couple with GW detectors. In this paper, we present a simple analytical model to estimate its impact on the detection of stochastic GWs. The model crucially depends on the geometry of the detector pair through the directional coupling, and we investigate the basic properties of the correlated magnetic noise based on the analytic expressions. The model reproduces the major trend of the recently measured global correlation between the GW detectors via magnetometer. The estimated values of the impact of correlated noise also match those obtained from the measurement. Finally, we give an implication to the detection of stochastic GWs including upcoming detectors, KAGRA and LIGO India. The model suggests that LIGO Hanford-Virgo and Virgo-KAGRA pairs are possibly less sensitive to the correlated noise, and can achieve a better sensitivity to the stochastic GW signal in the most pessimistic case.

astro-ph.IM↗

arXiv2007

Effective Search Templates for a Primordial Stochastic Gravitational Wave Background

We calculate the signal-to-noise ratio (SNR) of the stochastic gravitational-wave background in an extreme case that its spectrum has a sharp falloff with its amplitude close to the detection threshold. Such a spectral feature is a characteristic imprint of the change in the number of relativistic degrees of freedom on the stochastic background generated during inflation in the early Universe. We find that, although SNR is maximal with the correct template which is proportional to the assumed real spectrum, its sensitivity to the shape of template is fairly weak indicating that a simple power-law template is sufficient to detect the signature.

gr-qc↗

arXiv2007

Detecting a stochastic background of gravitational waves in the presence of non-Gaussian noise: A performance of generalized cross-correlation statistic

We discuss a robust data analysis method to detect a stochastic background of gravitational waves in the presence of non-Gaussian noise. In contrast to the standard cross-correlation (SCC) statistic frequently used in the stochastic background searches, we consider a {\it generalized cross-correlation} (GCC) statistic, which is nearly optimal even in the presence of non-Gaussian noise. The detection efficiency of the GCC statistic is investigated analytically, particularly focusing on the statistical relation between the false-alarm and the false-dismissal probabilities, and the minimum detectable amplitude of gravitational-wave signals. We derive simple analytic formulae for these statistical quantities. The robustness of the GCC statistic is clarified based on these formulae, and one finds that the detection efficiency of the GCC statistic roughly corresponds to the one of the SCC statistic neglecting the contribution of non-Gaussian tails. This remarkable property is checked by performing the Monte Carlo simulations and successful agreement between analytic and simulation results was found.

gr-qc↗

arXiv2005

Detecting a gravitational-wave background with next-generation space interferometers

Future missions of gravitational-wave astronomy will be operated by space-based interferometers, covering very wide range of frequency. Search for stochastic gravitational-wave backgrounds (GWBs) is one of the main targets for such missions, and we here discuss the prospects for direct measurement of isotropic and anisotropic components of (primordial) GWBs around the frequency 0.1-10 Hz. After extending the theoretical basis for correlation analysis, we evaluate the sensitivity and the signal-to-noise ratio for the proposed future space interferometer missions, like Big-Bang Observer (BBO), Deci-Hertz Interferometer Gravitational-wave Observer (DECIGO) and recently proposed Fabry-Perot type DECIGO. The astrophysical foregrounds which are expected at low frequency may be a big obstacle and significantly reduce the signal-to-noise ratio of GWBs. As a result, minimum detectable amplitude may reach h^2 \ogw = 10^{-15} \sim 10^{-16}, as long as foreground point sources are properly subtracted. Based on correlation analysis, we also discuss measurement of anisotropies of GWBs. As an example, the sensitivity level required for detecting the dipole moment of GWB induced by the proper motion of our local system is closely examined.

gr-qc↗

arXiv2004

Gravity in Randall-Sundrum two D-brane model

We analyse Randall-Sundrum two D-brane model by linear perturbation and then consider the linearised gravity on the D-brane. The qualitative contribution from the Kaluza-Klein modes of gauge fields to the coupling to the gravity on the brane will be addressed. As a consequence, the gauge fields localised on the brane are shown not to contribute to the gravity on the brane at large distances. Although the coupling between gauge fields and gravity appears in the next order, the ordinary coupling cannot be realised.

hep-th↗

arXiv2004

Randall-Sundrum two D-brane model

In Randall-Sundrum two D-brane system we derive the gravitational theory on the branes. It is turned out from the consistency that one D-brane has the negative tension brane under Randall-Sundrum tuning and both gauge fields on the brane are related by scale transformation through the bulk RR/NS-NS fields. As same with the single D-brane case, the gauge field which is supposed to be localised on the brane does not couple to the gravity on the branes.

hep-th↗

arXiv2003

Generation of dark radiation in the bulk inflaton model

We investigate the dynamics of a bulk scalar field with various decay channels in the Randall-Sundrum infinite braneworld scenario. A bulk scalar field in this scenario has a quasi-localized mode which dominates the late-time behavior near the brane. As for this mode, an interesting point is the presence of dissipation caused by the escape of the energy in the direction away from the brane, even if the bulk scalar field does not have the interaction with the other bulk fields in the bulk and fields on the brane. We can interpret that this lost energy is transfered to the dark radiation. We show that such an effective 4-dimensional description for a bulk scalar field is valid including the various processes of energy dissipation.

gr-qc↗

arXiv2003

Geometry and cosmological perturbations in the bulk inflaton model

We consider a braneworld inflation model driven by the dynamics of a scalar field living in the 5-dimensional bulk, the so-called ``bulk inflaton model'', and investigate the geometry in the bulk and large scale cosmological perturbations on the brane. The bulk gravitational effects on the brane are described by a projection of the 5-dimensional Weyl tensor, which we denote by $E_{μν}$. Focusing on a tachionic potential model, we take a perturbative approach in the anti-de Sitter (AdS$_5$) background with a single de Sitter brane. We first formulate the evolution equations for $E_{μν}$ in the bulk. Next, applying them to the case of a spatially homogeneous brane, we obtain two different integral expressions for $E_{μν}$. One of them reduces to the expression obtained previously when evaluated on the brane. The other is a new expression that may be useful for analyzing the bulk geometry. Then we consider superhorizon scale cosmological perturbations and evaluate the bulk effects onto the brane. In the limit $H^2\ell^2\ll1$, where $H$ is the Hubble parameter on the brane and $\ell$ is the bulk curvature radius, we find that the effective theory on the brane is identical to the 4-dimensional Einstein-scalar theory with a simple rescaling of the potential even under the presence of inhomogeneities. % atleast on super-Hubble horizon scales. In particular, it is found that the anticipated non-trivial bulk effect due to the spatially anisotropic part of $E_{μν}$ may appear only at %second order in the low energy expansion, i.e., at $O(H^4\ell^4)$.

gr-qc↗

arXiv2003

Braneworld reheating in the bulk inflaton model

In the context of the braneworld inflation driven by a bulk scalar field, we study the energy dissipation from the bulk scalar field into the matter on the brane in order to understand the reheating after inflation. Deriving the late-time behavior of the bulk field with dissipation by using the Green's function method, we give a rigorous justification of the statement that the standard reheating process is reproduced in this bulk inflaton model as long as the Hubble parameter on the brane and the mass of the bulk scalar field are much smaller than the 5-dimensional inverse curvature scale. Our result supports the idea that the brane inflation model caused by a bulk scalar field is expected to be a viable alternative scenario of the early universe.

gr-qc↗

arXiv2003

Braneworld inflation driven by dynamics of a bulk scalar field

We review a viable alternative scenario of the inflationary universe in the context of the Randall-Sundrum (RS) braneworld. In this scenario, the dynamics of a 5-dimensional scalar field, which we call a bulk scalar field, plays the central role. Focusing on the second (single-brane) RS model, we discuss braneworld inflation driven by a bulk scalar field without introducing an inflaton on the brane. As a toy model, for the bulk scalar field, we consider a minimally coupled massive scalar field in the 5-dimensional spacetime, and look for a perturbative solution of the field equation in the anti-de Sitter background with an inflating brane. For a suitable range of the model parameters, we find a solution that realizes slow-roll inflation on the brane. When the Hubble parameter on the brane and the mass of a bulk scalar field are much smaller than a typical 5-dimensional mass scale, it is found that this proposed inflation scenario reproduces the standard inflation scenario in the 4-dimensional theory.

gr-qc↗