arXiv subjects

Sachiko Kuroyanagi

Publications and source records attributed to Sachiko Kuroyanagi.

At least 37 records · Page 2Linked to original sources

arXiv2024

Gravitational Waves in the Circular Restricted Three Body Problem

The prospect of unprecedented high-quality data of gravitational waves in the upcoming decades demands a theoretical effort to optimally study and analyze the signals that next generation detectors will provide. Here we study the gravitational wave emission and related dynamics during the inspiralling phase of the Circular Restricted Three Body Problem, a modification of the conventional binary scenario in which a small third object co-rotates with the parent binary system. Specifically, we obtain analytic expressions for the emitted power, frequency variation and other dynamical variables that describe the evolution of the system. As a key highlight, we find that the presence of the third body actually slows down the coalescence of the binary, which can be partially interpreted as an effective rescaling of the binary's chirp-mass. Our analysis assumes semi-Keplerian orbits for the particles and a highly mass asymmetric parent binary needed for the stability of orbits.

gr-qc↗

arXiv2024

Effects of orbital precession on hyperbolic encounters

The hyperbolic encounters of two massive objects are characterized by the emission of a gravitational wave burst, with most of the energy released during the closest approach (near the periastron). The detection of such events, different from the well-known inspiral emission, would be an interesting discovery and provide complementary information to observations of binary mergers of black holes and neutron stars in the observable Universe, shedding light, for instance, on the clustering properties of black holes and providing valuable hints on their formation scenario. Here, we analyze the dynamics of such phenomena in the simplest case where two compact objects follow unbound/hyperbolic orbits. Moreover, we explore the effects of orbital precession on the gravitational wave emission, since the precession encodes certain general relativistic effects between two bodies. We also provide templates for the strain of gravitational waves and the power spectrum for the emission, and analytical expressions for the memory effect associated with such signals.

gr-qc↗

arXiv2023

Log-periodic gravitational-wave background beyond Einstein gravity

Periodic patterns of logarithmic oscillations can arise in primordial curvature perturbation spectra and in the associated gravitational-wave background via different mechanisms. We show that, in the presence of log oscillations, the spectral shape of the stochastic background has a unique parametrization independent of its physical origin. We also show that this log-periodic modulation can be generated in any scenario beyond Einstein gravity endowed with an approximate discrete scale invariance, a symmetry typical of deterministic fractal spacetimes that could emerge in quantum gravity under certain conditions. We discuss how a log-oscillatory spectral shape arises from concrete inflationary models beyond Einstein gravity and the prospects for detection in Einstein Telescope and other next-generation gravitational-wave observatories. We find that these instruments will be sensitive to log-periodic features if the detection is made with a high signal-to-noise ratio (SNR) and that the error scales as $1/{\rm SNR}$.

gr-qc↗

arXiv2023

Primordial black holes and their gravitational-wave signatures

In the recent years, primordial black holes (PBHs) have emerged as one of the most interesting and hotly debated topics in cosmology. Among other possibilities, PBHs could explain both some of the signals from binary black hole mergers observed in gravitational wave detectors and an important component of the dark matter in the Universe. Significant progress has been achieved both on the theory side and from the point of view of observations, including new models and more accurate calculations of PBH formation, evolution, clustering, merger rates, as well as new astrophysical and cosmological probes. In this work, we review, analyse and combine the latest developments in order to perform end-to-end calculations of the various gravitational wave signatures of PBHs. Different ways to distinguish PBHs from stellar black holes are emphasized. Finally, we discuss their detectability with LISA, the first planned gravitational-wave observatory in space.

astro-ph.CO↗

arXiv2023

Stochastic gravitational wave background constraints from Gaia DR3 astrometry

Astrometric surveys can be used to constrain the stochastic gravitational wave background (SGWB) at very low frequencies. We use proper motion data provided by Gaia DR3 to fit a generic dipole+quadrupole field. We analyse several quasar-based datasets and discuss their purity and idoneity to set constraints on gravitational waves. For the cleanest dataset, we derive an upper bound on the (frequency-integrated) energy density of the SGWB $h_{70}^2Ω_{\rm GW}\lesssim 0.087$ for $4.2\times 10^{-18}~\mathrm{Hz}\lesssim f\lesssim 1.1\times 10^{-8}~\mathrm{Hz}$. We also reanalyse previous VLBI-based data to set the constraint $h_{70}^2Ω_{\rm GW}\lesssim 0.024$ for $5.8\times 10^{-18}~\mathrm{Hz}\lesssim f\lesssim 1.4\times 10^{-9}~\mathrm{Hz}$ under the same formalism, standing as the best astrometric constraint on GWs. Based on our results, we discuss the potential of future Gaia data releases to impose tighter constraints.

astro-ph.CO↗

arXiv2023

Tracking the origin of black holes with the stochastic gravitational wave background popcorn signal

Unresolved sources of gravitational waves (GWs) produced by the merger of a binary of black holes at cosmological distances combine into a stochastic background. Such a background is in the continuous or popcorn regime, depending on whether the GW rate is high enough so that two or more events overlap in the same frequency band. These two regimes respectively correspond to large and small values of the so-called {\it duty cycle}. We study the detection regime of the background in models of Primordial Black Holes (PBHs) and compare it to the one produced by black holes of stellar origin. Focusing on ground-based detectors, we show that the duty cycle of the PBH-origin background is larger than that of astrophysical black holes because of differences in their mass function and the merger rate. Our study opens up the possibility to learn about the primordial or astrophysical nature of black hole populations by examining the statistical properties of the stochastic background.

astro-ph.CO↗

arXiv2023

Deep learning for intermittent gravitational wave signals

The ensemble of unresolved compact binary coalescences is a promising source of the stochastic gravitational wave (GW) background. For stellar-mass black hole binaries, the astrophysical stochastic GW background is expected to exhibit non-Gaussianity due to their intermittent features. We investigate the application of deep learning to detect such non-Gaussian stochastic GW background and demonstrate it with the toy model employed in Drasco \& Flanagan (2003), in which each burst is described by a single peak concentrated at a time bin. For the detection problem, we compare three neural networks with different structures: a shallower convolutional neural network (CNN), a deeper CNN, and a residual network. We show that the residual network can achieve comparable sensitivity as the conventional non-Gaussian statistic for signals with the astrophysical duty cycle of $\log_{10}ξ\in [-3,-1]$. Furthermore, we apply deep learning for parameter estimation with two approaches, in which the neural network (1) directly provides the duty cycle and the signal-to-noise ratio (SNR) and (2) classifies the data into four classes depending on the duty cycle value. This is the first step of a deep learning application for detecting a non-Gaussian stochastic GW background and extracting information on the astrophysical duty cycle.

gr-qc↗

arXiv2022

Probing pre-Recombination Physics by the Cross-Correlation of Stochastic Gravitational Waves and CMB Anisotropies

We study the effects of pre-recombination physics on the Stochastic Gravitational Wave Background (SGWB) anisotropies induced by the propagation of gravitons through the large-scale density perturbations and their cross-correlation with Cosmic Microwave Background (CMB) temperature and E-mode polarization ones. As examples of Early Universe extensions to the $Λ$CDM model, we consider popular models featuring extra relativistic degrees of freedom, a massless non-minimally coupled scalar field, and an Early Dark Energy component. Assuming the detection of a SGWB, we perform a Fisher analysis to assess in a quantitative way the capability of future gravitational wave interferometers (GWIs) in conjunction with a future large-scale CMB polarization experiment to constrain such variations. Our results show that the cross-correlation of CMB and SGWB anisotropies will help tighten the constraints obtained with CMB alone, with an improvement that significantly depends on the specific model as well as the maximum angular resolution $\ell_{\rm max}^{\rm GW}$ of the GWIs, their designed sensitivity, and the amplitude $A_*$ of the monopole of the SGWB.

astro-ph.CO↗

arXiv2022

Gravitational wave matched filtering by quantum Monte Carlo integration and quantum amplitude amplification

The speedup of heavy numerical tasks by quantum computing is now actively investigated in various fields including data analysis in physics and astronomy. In this paper, we propose a new quantum algorithm for matched filtering in gravitational wave (GW) data analysis based on the previous work by Gao et al., Phys. Rev. Research 4, 023006 (2022) [arXiv:2109.01535]. Our approach uses the quantum algorithm for Monte Carlo integration for the signal-to-noise ratio (SNR) calculation instead of the fast Fourier transform used in Gao et al. and searches signal templates with high SNR by quantum amplitude amplification. In this way, we achieve an exponential reduction of the qubit number compared with Gao et al.'s algorithm, keeping a quadratic speedup over classical GW matched filtering with respect to the template number.

astro-ph.IM↗

arXiv2022

The stochastic gravitational wave background from close hyperbolic encounters of primordial black holes in dense clusters

The inner part of dense clusters of primordial black holes is an active environment where multiple scattering processes take place. Some of them give rise from time to time to bounded pairs, and the rest ends up with a single scattering event. The former eventually evolves to a binary black hole (BBH) emitting periodic gravitational waves (GWs), while the latter with a short distance, called close hyperbolic encounters (CHE), emits a strong GW burst. We make the first calculation of the stochastic GW background originating from unresolved CHE sources. Unlike the case for BBH, the low-frequency tail of the SGWB from CHE is sensitive to the redshift dependence of the event rate, which could help distinguish the astrophysical from the primordial black hole contributions. We find that there is a chance that CHE can be tested by third-generation ground-based GW detectors such as Einstein Telescope and Cosmic Explorer.

gr-qc↗

arXiv2022

Cosmology with the Laser Interferometer Space Antenna

The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational wave observations by LISA to probe the universe.

astro-ph.CO↗

arXiv2022

Probing Anisotropies of the Stochastic Gravitational Wave Background with LISA

We investigate the sensitivity of the Laser Interferometer Space Antenna (LISA) to the anisotropies of the Stochastic Gravitational Wave Background (SGWB). We first discuss the main astrophysical and cosmological sources of SGWB which are characterized by anisotropies in the GW energy density, and we build a Signal-to-Noise estimator to quantify the sensitivity of LISA to different multipoles. We then perform a Fisher matrix analysis of the prospects of detectability of anisotropic features with LISA for individual multipoles, focusing on a SGWB with a power-law frequency profile. We compute the noise angular spectrum taking into account the specific scan strategy of the LISA detector. We analyze the case of the kinematic dipole and quadrupole generated by Doppler boosting an isotropic SGWB. We find that $β\, Ω_{\rm GW}\sim 2\times 10^{-11}$ is required to observe a dipolar signal with LISA. The detector response to the quadrupole has a factor $\sim 10^3 \,β$ relative to that of the dipole. The characterization of the anisotropies, both from a theoretical perspective and from a map-making point of view, allows us to extract information that can be used to understand the origin of the SGWB, and to discriminate among distinct superimposed SGWB sources.

astro-ph.CO↗

arXiv2021

Testing Primordial Black Holes with multi-band observations of the stochastic gravitational wave background

The mass distribution of Primordial Black Holes (PBHs) is affected by drops in the pressure of the early Universe plasma. For example, events in the standard model of particle physics, such as the $W^\pm/Z^0$ decoupling, the quark-hadron transition, the muon and pion becoming non-relativistic, and the annihilation of electrons and positrons, cause a suppression in the Equation of State parameter and leave peaks in the PBH mass function around $10^{-6},\,2,\,60$, and $10^6\, M_\odot$, respectively, in the case of a nearly scale-invariant primordial power spectrum. The superposition of unresolved mergers of such PBHs results in a stochastic gravitational-wave background (SGWB) that covers a wide range of frequencies and can be tested with future gravitational wave (GW) detectors. In this paper, we discuss how its spectral shape can be used to infer properties about inflation, the thermal history of the Universe, and the dynamics of binary formation in dense halos encoded in their merger rate formula. Although many of these physical effects are degenerate within the sensitivity of a single detector, they can be disentangled by the simultaneous observation of the SGWB at different frequencies, highlighting the importance of multi-frequency observations of GWs to characterize the physics of PBHs from the early to the late time Universe.

astro-ph.CO↗

arXiv2021

Stochastic gravitational-wave background in quantum gravity

Among all cosmological quantum-gravity or quantum-gravity-inspired scenarios, only very few predict a blue-tilted primordial tensor spectrum. We explore five of them and check whether they can generate a stochastic gravitational-wave background detectable by present and future interferometers: non-local quantum gravity, string-gas cosmology, new ekpyrotic scenario, Brandenberger-Ho non-commutative inflation and multi-fractional spacetimes. We show that non-local quantum gravity is unobservable, while all the other models can reach the strain sensitivity of DECIGO but not that of LIGO-Virgo-KAGRA, LISA or Einstein Telescope. Other quantum-gravity models with red-tilted spectra (most loop quantum cosmologies) or with exceptionally tiny quantum corrections (Wheeler-DeWitt quantum cosmology) are found to be non-detectable.

gr-qc↗

arXiv2021

Blue-tilted inflationary tensor spectrum and reheating in the light of NANOGrav results

We discuss the possibility of explaining the recent NANOGrav results by inflationary gravitational waves (IGWs) with a blue-tilted primordial spectrum. Although such IGWs can account for the NANOGrav signal without contradicting the upper bound on the tensor-to-scalar ratio at the cosmic microwave background scale, the predicted spectrum is in strong tension with the upper bound on the amplitude of the stochastic gravitational wave background by big-bang nucleosynthesis (BBN) and the second LIGO-Virgo observation run. However, the thermal history of the Universe, such as reheating and late-time entropy production, affects the spectral shape of IGWs at high frequencies and permits evading the upper bounds. We show that, for the standard reheating scenario, when the reheating temperature is relatively low, a blue tensor spectrum can explain the recent NANOGrav signal without contradicting the BBN and the LIGO-Virgo constraints. We further find that, when one considers a late-time entropy production, the NANOGrav signal can be explained even for an instant reheating scenario.

astro-ph.CO↗

arXiv2020

Optimization of quantum noise by completing the square of multiple interferometer outputs in quantum locking for gravitational wave detectors

The quantum locking technique, which uses additional short low-loss sub-cavities, is effective in reducing quantum noise in space gravitational wave antenna DECIGO. However, the quantum noise of the main interferometer depends on the control systems in the sub-cavities. Here we demonstrate a new method to optimize the quantum noise independently of the feedback gain by completing the square in the quantum locking system. We successfully demonstrate in simulations that this method is effective in optimizing the homodyne angle to the best quantum-noise-limited sensitivity.

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↗

arXiv2020

Gravitational wave spectrum from kinks on infinite cosmic superstrings with Y-junctions

We calculate the gravitational wave (GW) background spectra from kink propagation and kink-kink collisions on infinite cosmic superstrings. We take into account two characteristics of the cosmic superstring network: a small reconnection probability and Y-junctions. First, a small reconnection probability increases the number of infinite strings inside the horizon and enhances the kink production, which leads a larger amplitude of the GW background. Second, a kink going through a Y-junction transforms into three daughter kinks. In this way, the existence of Y-junctions also increases the number of kinks on cosmic superstrings. However, at the same time, it smooths out the sharpness of kinks rapidly and reduces the number of sharp kinks, which are responsible for the emissions of strong GW bursts. We compute the number distribution of kinks as a function of the sharpness by taking into account the above two effects, and translate it to the amplitude of the GW background spectra. We first investigate the case of the string network with equal string tensions, and find that the effect of Y-junctions to smooth out kink sharpness dominates that of the enhancement of the kink number by a small reconnection probability, and the GW amplitude turns out to be smaller than the ordinary cosmic string case. On the other hand, for non-equal string tensions, we find that there is a parameter space where the GW amplitude is slightly enhanced by the effect of a small reconnection probability.

astro-ph.CO↗