引力波文獻周讀(31 Aug-4 Sep 2020)

 

每周搜集 arXiv 上 Astrophysics（天體物理） 和 General Relativity（廣義相對論）部分與 Gravitational Wave（引力波）相關的文章，方便快速了解學術前言動態。

Astrophysics

[1/30] 標題：150倍太陽質量雙黑洞合併GW190521的性質和天體物理意義 
Title: Properties and astrophysical implications of the 150 Msun binary black hole merger GW190521 Authors: The LIGO Scientific Collaboration, the Virgo Collaborationhttps://arxiv.org/abs/2009.01190 Abstract:  The gravitational-wave signal GW190521 is consistent with a binary black hole merger source at redshift 0.8 with unusually high component masses, 85^{+21}_{-14} M_{\odot} and 66^{+17}_{-18} M_{\odot}, compared to previously reported events, and shows mild evidence for spin-induced orbital precession. The primary falls in the mass gap predicted by (pulsational) pair-instability supernova theory, in the approximate range 65 - 120 M_{\odot}. The probability that at least one of the black holes in GW190521 is in that range is 99.0%. The final mass of the merger (142^{+28}_{-16} M_{\odot}) classifies it as an intermediate-mass black hole. Under the assumption of a quasi-circular binary black hole coalescence, we detail the physical properties of GW190521's source binary and its post-merger remnant, including component masses and spin vectors. Three different waveform models, as well as direct comparison to numerical solutions of general relativity, yield consistent estimates of these properties. Tests of strong-field general relativity targeting the merger-ringdown stages of coalescence indicate consistency of the observed signal with theoretical predictions. We estimate the merger rate of similar systems to be 0.13^{+0.30}_{-0.11}{Gpc}^{-3}{yr}^{-1}. We discuss the astrophysical implications of GW190521 for stellar collapse, and for the possible formation of black holes in the pair-instability mass gap through various channels: via (multiple) stellar coalescence, or via hierarchical merger of lower-mass black holes in star clusters or in active galactic nuclei. We find it to be unlikely that GW190521 is a strongly lensed signal of a lower-mass black hole binary merger. We also discuss more exotic possible sources for GW190521, including a highly eccentric black hole binary, or a primordial black hole binary.   [2/30] 標題：鑑於GW170817的短時伽馬射線暴及其外流 Title: Short duration gamma-ray bursts and their outflows in light of GW170817 https://arxiv.org/abs/2009.01773 Abstract:  The detection of GW170817, it's extensive multi-wavelength follow-up campaign, and the large amount of theoretical development and interpretation that followed, have resulted in a significant step forward in the understanding of the binary neutron star merger phenomenon as a whole. One of its aspects is seeing the merger as a progenitor of short gamma-ray bursts (SGRB), which will be the subject of this review. On the one hand, GW170817 observations have confirmed some theoretical expectations, exemplified by the confirmation that binary neutron star mergers are the progenitors of SGRBs. In addition, the multimessenger nature of GW170817 has allowed for gathering of unprecedented data, such as the trigger time of the merger, the delay with which the gamma-ray photons were detected, and the brightening afterglow of an off-axis event. All together, the incomparable richness of the data from GW170817 has allowed us to paint a fairly detailed picture of at least one SGRB. I will detail what we learned, what new questions have arisen, and the perspectives for answering them when a sample of GW170817-comparable events have been studied.       [3/30] 標題：GW190521質量間隙事件和原初黑洞方案 Title: The GW190521 Mass Gap Event and the Primordial Black Hole Scenario Authors: V. De Luca, V. Desjacques et al.https://arxiv.org/abs/2009.01728 Abstract:  The LIGO/Virgo Collaboration has recently observed GW190521, the first binary black hole merger with at least the primary component mass in the mass gap predicted by the pair-instability supernova theory. This observation disfavors the standard stellar-origin formation scenario for the heavier black hole, motivating alternative hypotheses. We show that GW190521 cannot be explained within the Primordial Black Hole (PBH) scenario if PBHs do not accrete during their cosmological evolution, since this would require an abundance which is already in tension with current constraints. On the other hand, GW190521 may have a primordial origin if PBHs accrete efficiently before the reionization epoch.       [4/30] 標題：隨機引力波背景和偏心恆星緊緻雙星 Title: Stochastic Gravitational Wave Background and Eccentric Stellar Compact Binaries Authors: Yuetong Zhao, Youjun Luhttps://arxiv.org/abs/2009.01436 Abstract:  Gravitational wave (GW) radiations from numerous cosmic stellar-compact-binaries form a stochastic GW background (GWB), which is expected to be detected by ground and space GW detectors in future. Theoretical predictions of this GWB were mostly obtained by assuming either circular binaries and/or a specific channel for binary formation, which may have some uncertainties. In this paper, we estimate the GWB and its spectrum by using simple models for the formation of both stellar mass binary black holes (sBBHs) and binary neutron stars (BNSs). We consider that the dynamically originated sBBHs have relatively larger masses and higher eccentricities compared with those from field binary stars and its possible effect on the GWB spectrum. We find that the GWB spectrum may have a turnover in the low-frequency (LISA) band and may be better described by a broken double power-law than a single power-law with the unique index 2/3, and the low-frequency slope depends on the significance of the dynamically originated sBBHs with high eccentricities. We further generate mock samples of sBBHs and BNSs, and simulate the mock GWB strain in the time domain. We find that GWB can be detected with signal-to-noise ratio (SNR) \gtrsim274/255/21 by LISA/Taiji/TianQin over 5-years' observation and \gtrsim3 by LIGO over 2-years' observation. Furthermore, we estimate that the number of sBBHs that may be detected by LISA/Taiji/TianQin individually with SNR \gtrsim8 is \sim5-221/7-365/3-223 over 5-years' observation.[5/30] 標題：結合電磁波和引力波對中子星質量和半徑的約束 Title: Combining Electromagnetic and Gravitational-Wave Constraints on Neutron-Star Masses and Radii Authors: Mohammad Al-Mamun, Andrew W. Steiner et al.https://arxiv.org/abs/2008.12817 Abstract:  We perform a joint Bayesian inference of neutron-star mass and radius constraints based on GW170817, observations of quiescent low-mass X-ray binaries (QLMXBs), photospheric radius expansion X-ray bursts (PREs), and X-ray timing observations of J0030+0451. With this data set, the form of the prior distribution still has an impact on the posterior mass-radius (MR) curves and equation of state (EOS), but this impact is smaller than recently obtained when considering QLMXBs alone. We analyze the consistency of the electromagnetic data by including an "intrinsic scattering" contribution to the uncertainties, and find only a slight broadening of the posteriors. This suggests that the gravitational-wave and electromagnetic observations of neutron-star structure are providing a consistent picture of the neutron-star mass-radius curve and the EOS.       [6/30] 標題：從雙中子星的隨機背景限制其稜鏡效應 Title: Constraining the lensing of binary neutron stars from their stochastic background Authors: Riccardo Buscicchio, Christopher J. Moore et al.https://arxiv.org/abs/2008.12621 Abstract:  Gravitational wave (GW) transients from binary neutron star (BNS) coalescences can, in principle, be subject to gravitational lensing thereby increasing the amplitude and signal-to-noise ratio. We estimate the rate of lensed BNS events resolvable by LIGO and Virgo and find that it is constrained by the current non-detection of a stochastic GW background. Following closely the formalism we developed previously (arXiv:2006.04516v2) in the context of binary black hole lensing, we show that at current sensitivities the fraction of BNS coalescences with lensing magnifications \mu> 1.02 is less than \sim 7\times 10^{-8} and therefore such events should not be expected in the near future. We also make predictions for projected future sensitivities.[7/30] 標題：GW190814：上下夸克星的間接證據 Title: GW190814: Circumstantial Evidence for Up-Down Quark Star Authors: Zheng Cao, Lie-Wen Chen, Peng-Cheng Chu, Ying Zhou https://arxiv.org/abs/2009.00942 Abstract:  Within a confining quark matter model which considers phenomenologically the quark confinement and asymptotic freedom as well as the chiral symmetry restoration and quark deconfinement at high baryon density, we find that if the up-down quark matter (udQM) is more stable than nuclear matter and strange quark matter (SQM), the maximum mass of static quark stars with udQM is 2.77 M_{\odot} under agreement with both the constraints on star tidal deformability from gravitational wave signal GW170817 and the mass-radius of PSR J0030+045 measured simultaneously by NICER. In contrast, the conventional strange quark star with SQM has a maximum static mass of only 2.05 M_{\odot} and its radius significantly deviates from NICER's constraint. Our results thus provide circumstantial evidence suggesting the recently reported GW190814's secondary component with a mass of 2.59^{+0.08}_{-0.09} M_\odot could be an up-down quark star.   [8/30] 標題：小尺度結構對宇宙弦引力波隨機背景的影響 Title: Impact of the small-scale structure on the Stochastic Background of Gravitational Waves from cosmic strings Author: Pierre G. Auclair https://arxiv.org/abs/2009.00334 Abstract:  Numerical simulations and analytical models suggest that infinite cosmic strings produce cosmic string loops of all sizes with a given power-law. Precise estimations of the power-law exponent are still matter of debate while numerical simulations do not incorporate all the radiation and back-reaction effects expected to affect the network at small scales. Previously it has been shown, using a Boltzmann approach, that depending on the steepness of the loop production function and the gravitational back-reaction scale, a so-called Extra Population of Small Loops (EPSL) can be generated in the loop number density. We propose a framework to study the influence of this extra population of small loops on the Stochastic Background of Gravitational Waves (SBGW). We show that this extra population can have a significant signature at frequencies higher than H_0(\Gamma G\mu)^{-1} where \Gamma is of order 50 and H_0 is the Hubble constant. We propose a complete classification of the gravitational wave power spectra expected from cosmic strings into four classes, including the model of Blanco-Pillado, Olum and Shlaer and the model of Lorenz, Ringeval and Sakellariadou. Finally we show that given the uncertainties on the Polchinski-Rocha exponents, two hybrid classes of gravitational wave power spectrum can be considered giving very different predictions for the SBGW.       [9/30] 標題：LIGO-Virgo合併的貝葉斯分析：原初與天體物理黑洞群 Title: Bayesian analysis of LIGO-Virgo mergers: Primordial vs. astrophysical black hole populations Authors: Alex Hall, Andrew D. Gow, Christian T. Byrnes https://arxiv.org/abs/2008.13704 Abstract:  We conduct a thorough Bayesian analysis of the possibility that the black hole merger events seen in gravitational waves are primordial black hole (PBH) mergers. Using the latest merger rate models for PBH binaries drawn from a lognormal mass function we compute posterior parameter constraints and Bayesian evidences using data from the first two observing runs of LIGO-Virgo. We account for theoretical uncertainty due to possible disruption of the binary by surrounding PBHs, which can suppress the merger rate significantly. We also consider simple astrophysically motivated models and find that these are favoured decisively over the PBH scenario, quantified by the Bayesian evidence ratio. Paying careful attention to the influence of the parameter priors and the quality of the model fits, we show that the evidence ratios can be understood by comparing the predicted chirp mass distribution to that of the data. We identify the posterior predictive distribution of chirp mass as a vital tool for discriminating between models. A model in which all mergers are PBH binaries is strongly disfavoured compared with astrophysical models, in part due to the over-prediction of heavy systems having {M}_{chirp} \gtrsim 40 M_\odot and positive skewness over the range of observed masses which does not match the observations. We find that the fit is not significantly improved by adding a maximum mass cut-off, a bimodal mass function, or imposing that PBH binaries form at late times. We argue that a successful PBH model must either modify the lognormal shape of the initial mass function significantly or abandon the hypothesis that all observed merging binaries are primordial. We develop and apply techniques for analysing PBH models with gravitational wave data which will be necessary for robust statistical inference as the gravitational wave source sample size increases.       [10/30] 標題：CMB-S4：原初引力波的預測約束 Title: CMB-S4: Forecasting Constraints on Primordial Gravitational Waves Authors: The CMB-S4 Collaborationhttps://arxiv.org/abs/2008.12619 Abstract:  CMB-S4---the next-generation ground-based cosmic microwave background (CMB) experiment---is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the Universe, from the highest energies at the dawn of time through the growth of structure to the present day. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semi-analytic projection tool, targeted explicitly towards optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2--3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments given a desired scientific goal. To form a closed-loop process, we couple this semi-analytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5\sigma, or, in the absence of a detection, of reaching an upper limit of r < 0.001 at 95\% CL.       [11/30] 標題：用於未來幹涉式空間引力波天線的雙通差分Fabry-Perot幹涉儀的演示Title: Demonstration of a dual-pass differential Fabry-Perot interferometer for future interferometric space gravitational wave antennas Authors: Koji Nagano, Hiroki Takeda et al.https://arxiv.org/abs/2008.12462 Abstract:  A dual-pass differential Fabry-Perot interferometer (DPDFPI) is one candidate of the interferometer configurations utilized in future Fabry-Perot type space gravitational wave antennas, such as Deci-hertz Interferometer Gravitational Wave Observatory. In this paper, the working principle of the DPDFPI has been investigated and necessity to adjust the absolute length of the cavity for the operation of the DPDFPI has been found. In addition, using the 55-cm-long prototype, the operation of the DPDFPI has been demonstrated for the first time and it has been confirmed that the adjustment of the absolute arm length reduces the cavity detuning as expected. This work provides the proof of concept of the DPDFPI for application to the future Fabry-Perot type space gravitational wave antennas.       [12/30] 標題：LIGO-Virgo參數估計中先驗的重要性：原初黑洞的情況 Title: The Importance of Priors on LIGO-Virgo Parameter Estimation: the Case of Primordial Black Holes Authors: S. Bhagwat, V. De Luca et al.https://arxiv.org/abs/2008.12320 Abstract:  The black holes detected by current and future interferometers can have diverse origins. Their expected mass and spin distributions depend on the specifics of the formation mechanisms. When a physically motivated prior distribution is used in a Bayesian inference, the parameters estimated from the gravitational-wave data can change significantly, potentially affecting the physical interpretation of certain gravitational-wave events and their implications on theoretical models. As a case study we analyze primordial black holes, which might be formed in the early universe and could comprise at least a fraction of the dark matter. If accretion is not efficient during their cosmic history, primordial black holes are expected to be almost non-spinning. If accretion is efficient, massive binaries tend to be symmetrical and highly spinning. We show that incorporating these priors can significantly change the inferred mass ratio and effective spin of some binary black hole events, especially those identified as high-mass, asymmetrical, or spinning by a standard analysis using agnostic priors. The Bayes factors are only mildly affected by the new priors, implying that it is hard to distinguish whether merger events detected so far are of primordial or astrophysical origin. In particular, if binaries identified by LIGO/Virgo as asymmetrical (including GW190412) are of primordial origin, their mass ratio inferred from the data can be compatible with unity.       [13/30] 標題：來自暗區，振蕩暴脹子和質量增強暗物質的引力波 Title: Gravitational Waves From Dark Sectors, Oscillating Inflatons, and Mass Boosted Dark Matter Authors: Amit Bhoonah, Joseph Bramante, Simran Nerval, Ningqiang Song https://arxiv.org/abs/2008.12306 Abstract:  Gravitational waves signatures from dynamical scalar field configurations provide a compelling observational window on the early universe. Here we identify intriguing connections between dark matter and scalars fields that emit gravitational waves, either through a first order phase transition or oscillating after inflation. To study gravitational waves from first order phase transitions, we investigate a simplified model consisting of a heavy scalar coupled to a vector and fermion field. We then compute gravitational wave spectra sourced by inflaton field configurations oscillating after E-Model and T-Model inflation. Some of these gravitational wave signatures can be uncovered by the future Big Bang Observatory, although in general we find that MHz-GHz frequency gravitational wave sensitivity will be critical for discovering the heaviest dark sectors. Intriguingly, we find that scalars undergoing phase transitions, along with E-Model and T-Model potentials, can impel a late-time dark matter mass boost and generate up to Planck mass dark matter. For phase transitions and oscillating inflatons, the largest dark matter mass boosts correspond to higher amplitude stochastic gravitational wave backgrounds.       [14/30] 標題：從周雙星吸積變化中發現周期性類星體中的候選超大質量雙黑洞 Title: Discovery of a Candidate Binary Supermassive Black Hole in a Periodic Quasar from Circumbinary Accretion Variability Authors: Wei-Ting Liao, Yu-Ching Chen et al.https://arxiv.org/abs/2008.12317 Abstract:  Binary supermassive black holes are expected to be a generic byproduct from hierarchical galaxy formation. The final coalescence of BSBHs is thought to be the loudest gravitational wave siren in the universe, yet no confirmed BSBH is known in the GW-dominated regime. While periodic quasars have been proposed as BSBH candidates, the physical origin of the periodicity has been largely uncertain. Here we report discovery of a periodicity (P~1607 days) at 99.95% significance in the optical light curves of a quasar at z=1.53, SDSS J025214.67-002813.7. Combining archival Sloan Digital Sky Survey data with new, high signal to noise imaging from the Dark Energy Survey, the total ~20yr time baseline spans ~4.6 cycles of the observed 4.4-yr (restframe 1.7-yr) periodicity. The light curves are best characterized by a bursty model predicted by hydrodynamic simulations of circumbinary accretion disks. The periodicity is likely caused by accretion rate variability periodically modulated by a milli-parsec BSBH emitting gravitational waves while still being dynamically coupled to the circumbinary accretion disk. A characteristic bursty hydrodynamic variability model is statistically preferred over a smooth, sinusoidal model expected from relativistic Doppler boost, a kinematic effect proposed for PG1302-102. Furthermore, the frequency dependence of the variability amplitudes disfavors Doppler boost as the dominant mechanism, lending independent support to the circumbinary accretion variability hypothesis. Given our detection rate of one BSBH candidate from circumbinary accretion variability out of 625 quasars, it suggests that future large, sensitive synoptic surveys such as the Legacy Survey of Space and Time at Vera C. Rubin Observatory may be able to detect hundreds to thousands of candidate BSBHs from circumbinary accretion variability with direct implications for Laser Interferometer Space Antenna.       

General Relativity

[15/30] 標題：GW190521：總質量為150倍太陽質量的雙黑洞合併 Title: GW190521: A Binary Black Hole Merger with a Total Mass of 150 M_{\odot} Authors: The LIGO Scientific Collaboration, the Virgo Collaborationhttps://arxiv.org/abs/2009.01075 Abstract:  On May 21, 2019 at 03:02:29 UTC Advanced LIGO and Advanced Virgo observed a short duration gravitational-wave signal, GW190521, with a three-detector network signal-to-noise ratio of 14.7, and an estimated false-alarm rate of 1 in 4900 yr using a search sensitive to generic transients. If GW190521 is from a quasicircular binary inspiral, then the detected signal is consistent with the merger of two black holes with masses of 85^{+21}_{-14} M_{\odot} and 66^{+17}_{-18} M_{\odot} (90 % credible intervals). We infer that the primary black hole mass lies within the gap produced by (pulsational) pair-instability supernova processes, and has only a 0.32 % probability of being below 65 M_{\odot}. We calculate the mass of the remnant to be 142^{+28}_{-16} M_{\odot}, which can be considered an intermediate mass black hole (IMBH). The luminosity distance of the source is 5.3^{+2.4}_{-2.6} Gpc, corresponding to a redshift of 0.82^{+0.28}_{-0.34}. The inferred rate of mergers similar to GW190521 is 0.13^{+0.30}_{-0.11}{Gpc}^{-3}{yr}^{-1}.     [16/30] 標題：超越GW190521的標準模型解釋 Title: Beyond the Standard Model Explanations of GW190521 Authors: Jeremy Sakstein, Djuna Croon et al.https://arxiv.org/abs/2009.01213 Abstract:  The LIGO/Virgo collaboration has recently announced the detection of a heavy binary black hole merger, with component masses that cannot be explained by standard stellar structure theory. In this letter we propose several explanations based on models of new physics, including new light particle losses, modified gravity, large extra dimensions, and a small magnetic moment of the neutrino. Each of these affect the physics of the pair-instability differently, leading to novel mechanisms for forming black holes inside the black hole mass gap.       Title: Time-Frequency Analysis of Gravitational Wave Data https://arxiv.org/abs/2009.00043 Abstract:  Data from gravitational wave detectors are recorded as time series that include contributions from myriad noise sources in addition to any gravitational wave signals. When regularly sampled data are available, such as for ground based and future space based interferometers, analyses are typically performed in the frequency domain, where stationary (time invariant) noise processes can be modeled very efficiently. In reality, detector noise is not stationary due to a combination of short duration noise transients and longer duration drifts in the power spectrum. This non-stationarity produces correlations across samples at different frequencies, obviating the main advantage of a frequency domain analysis. Here an alternative time-frequency approach to gravitational wave data analysis is proposed that uses discrete, orthogonal wavelet wavepackets. The time domain data is mapped onto a uniform grid of time-frequency pixels. For locally stationary noise - that is, noise with an adiabatically varying spectrum - the time-frequency pixels are uncorrelated, which greatly simplifies the calculation of quantities such as the likelihood. Moreover, the gravitational wave signals from binary systems can be compactly represented as a collection of lines in time-frequency space, resulting in a computational cost for computing waveforms and likelihoods that scales as the square root of the number of time samples, as opposed to the linear scaling for time or frequency based analyses. Key to this approach is having fast methods for computing binary signals directly in the wavelet domain. Multiple fast transform methods are developed in detail.       [18/30] 標題：引力波的強引力透鏡產生的相位效應 Title: Phase effects from strong gravitational lensing of gravitational waves Authors: Jose María Ezquiaga, Daniel E. Holz et al.https://arxiv.org/abs/2008.12814 Abstract:  Assessing the probability that two or more gravitational wave (GW) events are lensed images of the same source requires an understanding of the properties of the lensed images. For short enough wavelengths where wave effects can be neglected, lensed images will generically have a fixed relative phase shift that needs to be taken into account in the lensing hypothesis. For non-precessing, circular binaries dominated by quadrupole radiation these lensing phase shifts are degenerate with either a shift in the coalescence phase or a detector and inclination dependent shift in the orientation angle. This degeneracy is broken by the presence of higher harmonic modes with |m|\ne 2 in the former and |m| \ne l in the latter. The presence of precession or eccentricity will also break this degeneracy. This implies that a lensed GW image will not necessarily be consistent with (unlensed) predictions from general relativity (GR). Therefore, unlike the conventional scenario of electromagnetic waves, strong lensing of GWs can lead to images with a modified phase evolution that can be observed. However, we find that templates with a shifted orientation angle remain a good approximation, with signal-to-noise ratio differences of less than 1% for mass ratios up to 1/18, and less than 5% for precession parameters up to 0.5 and eccentricities up to 0.4. We conclude that an optimal strong lensing search strategy would incorporate phase information in all stages of the identification of strong-lensing, with an exact treatment in the final assessment of the probability of multiple lensed events. This work clarifies the role that strong lensing plays in the phase evolution of GWs: how it can lead to apparent deviations from GR, how it can affect the detectability of GW events, and how it can be exploited to help identify cases of strong gravitational lensing of gravitational wave sources.       [19/30] 標題：修正的廣義相對論中所有可能的引力波極化的脈衝計時陣列信號的脈衝紅移 Title: Pulse redshift of pulsar timing array signals for all possible gravitational wave polarizations in modified general relativity Authors: Adrian Boîtier, Shubhanshu Tiwari, Lionel Philippoz, Philippe Jetzer https://arxiv.org/abs/2008.13520 Abstract:  Pulsar timing arrays (PTA) have the promise to detect gravitational waves (GWs) from sources which are in a unique frequency range of 10^-9 - 10^-6 Hz. This in turn also provides an opportunity to test the theory of general relativity in the low frequency regime. The central concept of the detection of GWs with PTA lies in measuring the time of arrival difference of the pulsar signal due to the passing of GWs i.e. the pulses get red-shifted. In this paper we provide a complete derivation of the redshift computation for all six possible polarizations of GW which arise due to the modifcations to general relativity. We discuss the smoothness of the redshift and related properties at the critical point, where the GW source lies directly behind the pulsar. From our mathematical discussion we conclude that the redshift has to be split differently into polarization part (pattern functions) and interference part, to avoid discontinuities and singularities in the pattern functions. This choice of pattern functions agrees with the formula one uses for interferometers with a single detector arm. Finally, we provide a general expression which can in principle be used for pulsars and GW of any frequency without invoking the low frequency assumption and using said assumption we develop the expression up to first order in the strain and find correction terms to the canonical redshift formula.       [20/30] 標題：相互作用的玻色-愛因斯坦氣體模型中的原初引力波譜 Title: Primordial gravitational waves spectrum in the interacting Bose-Einstein gas model Authors: German Izquierdo, Gildardo Alonzo, Jaime Besprosvany https://arxiv.org/abs/2008.12701 Abstract:  We study the evolution and power spectrum of primordial gravitational waves in the interactive Bose-Einstein gas model for dark energy, relevant, as it addresses the coincidence problem. The model is applied in the radiation, matter and dark-energy domination stages. The model introduces a scale factor associated with the radiation-matter transition which influences the gravitational spectrum. We focus on the impact of the free parameters on both the gravitational waves amplitude and its power-spectrum slope. For sets of parameters fitting Hubble's law, we show that the model's parameter for today's dark-matter energy density has a noticeable impact on such waves, while the others produce an indistinguishable effect. The feasibility of detecting such waves under present and future measurements is discussed.     [21/30] 標題：前四個雙黑洞合併中的Pearson互相關 Title: Pearson cross-correlation in the first four black hole binary mergers Authors: Paolo Marcoccia, Felicia Fredriksson, Alex B. Nielsen, Germano Nardini https://arxiv.org/abs/2008.12663 Abstract:  We adopt the Pearson cross-correlation measure to analyze the LIGO Hanford and LIGO Livingston detector data streams around the events GW150914, GW151012,GW151226 and GW170104. We find that the Pearson cross-correlation method is sensitive to these signals, with correlations peaking when the black hole binaries reconstructed by the LIGO Scientific and Virgo Collaborations, are merging. We compare the obtained cross-correlations with the statistical correlation fluctuations arising in simulated Gaussian noise data and in LIGO data at times when no event is claimed. Our results for the significance of the observed cross-correlations are broadly consistent with those announced by the LIGO Scientific and Virgo Collaborations based on matched-filter analysis. In the same data, if we subtract the maximum likelihood waveforms corresponding to the announced signals, no residual cross-correlations persists at a statistically significant level.       [22/30] 標題：TDI-infinity：無延遲的時延幹涉測量 Title: TDI-infinity: time-delay interferometry without delays Authors: Michele Vallisneri, Jean-Baptiste Bayle, Stanislav Babak, Antoine Petiteau https://arxiv.org/abs/2008.12343 Abstract:  The space-based gravitational-wave observatory LISA relies on a form of synthetic interferometry (time-delay interferometry, or TDI) where the otherwise overwhelming laser phase noise is canceled by linear combinations of appropriately delayed phase measurements. These observables grow in length and complexity as the realistic features of the LISA orbits are taken into account. In this paper we outline an implicit formulation of TDI where we write the LISA likelihood directly in terms of the basic phase measurements, and we marginalize over the laser phase noises in the limit of infinite laser-noise variance. Equivalently, we rely on TDI observables that are defined numerically (rather than algebraically) from a discrete-filter representation of the laser propagation delays. Our method generalizes to any time dependence of the armlengths; it simplifies the modeling of gravitational-wave signals; and it allows a straightforward treatment of data gaps and missing measurements.       [23/30] 標題：偏心軌道極端質量比旋進輻射IITitle: Eccentric-orbit extreme-mass-ratio-inspiral radiation II: 1PN correction to leading-logarithm and subleading-logarithm flux sequences and the entire perturbative 4PN flux Authors: Christopher Munna, Charles R. Evans https://arxiv.org/abs/2009.01254 Abstract:  In a recent paper we showed that for eccentric-orbit extreme-mass-ratio inspirals the analytic forms of the leading-logarithm energy and angular momentum post-Newtonian (PN) flux terms (radiated to infinity) can, to arbitrary PN order, be determined by sums over the Fourier spectrum of the Newtonian quadrupole moment. We further showed that an essential part of the eccentricity dependence of the related subleading-logarithm PN sequences, at lowest order in the symmetric mass ratio \nu, stems as well from the Newtonian quadrupole moment. Once that part is factored out, the remaining eccentricity dependence is more easily determined by black hole perturbation theory. In this paper we show how the sequences that are the 1PN corrections to the entire leading-logarithm series, namely terms that appear at PN orders x^{3k+1} \log^k(x) and x^{3k+5/2} \log^k(x) (for PN compactness parameter x and integers k\ge 0), at lowest order in \nu, are determined by the Fourier spectra of the Newtonian mass octupole, Newtonian current quadrupole, and 1PN part of the mass quadrupole moments. We also develop a conjectured (but plausible) form for 1PN correction to the leading logs at second order in \nu. Further, in analogy to the first paper, we show that these same source multipole moments also yield nontrivial parts of the 1PN correction to the subleading-logarithm series, and that the remaining eccentricity dependence (at lowest order in \nu) can then more easily be determined using black hole perturbation theory. We use this method to determine the entire analytic eccentricity dependence of the perturbative (i.e., lowest order in \nu) 4PN non-log terms, {R}_4(e_t) and {Z}_4(e_t), for energy and angular momentum respectively.       [24/30] 標題：混淆正面和進動的中間質量雙黑洞合併 Title: Confusing head-on and precessing intermediate-mass binary black hole mergers Authors: Juan Calderón Bustillo, Nicolas Sanchis-Gual, Alejandro Torres-Forné, José A. Font https://arxiv.org/abs/2009.01066 Abstract:  We report a degeneracy between the gravitational-wave signals from quasi-circular precessing black-hole mergers and those from extremely eccentric mergers, namely head-on collisions. Performing model selection on numerically simulated signals of head-on collisions using models for quasi-circular binaries we find that, for signal-to-noise ratios consistent with Advanced LIGO observations, head-on mergers with total mass M \in (130,310) M_\odot would be identified as a precessing quasi-circular intermediate-mass black hole binary, located at a much larger distance. Ruling out the head-on scenario would require to perform model selection using currently nonexistent waveform models for head-on collisions, together with the application of astrophysically motivated priors on the (rare) occurrence of those events. We show that in situations where standard parameter inference of compact binaries may report component masses inside (outside) the pair-instability supernova gap, the true object may be a head-on merger with masses outside (inside) this gap. We briefly discuss the potential implications of these findings for the recent gravitational-wave detection GW190521.       [25/30] 標題：通過極端質量比旋進的引力波檢測時空對稱性 Title: Testing spacetime symmetry through gravitational waves from extreme-mass-ratio inspirals Authors: Kyriakos Destounis, Arthur G. Suvorov, Kostas D. Kokkotas https://arxiv.org/abs/2009.00028 Abstract:  One of the primary aims of upcoming space-borne gravitational wave detectors is to measure radiation in the mHz range from extreme-mass-ratio inspirals. Such a detection would place strong constraints on hypothetical departures from a Kerr description for astrophysically stable black holes. The Kerr geometry, which is unique in general relativity, admits a higher-order symmetry in the form of a Carter constant, which implies that the equations of motion describing test particle motion in a Kerr background are Liouville-integrable. In this article, we investigate whether the Carter symmetry itself is discernible from a generic deformation of the Kerr metric in the gravitational waveforms for such inspirals. We build on previous studies by constructing a new metric which respects current observational constraints, describes a black hole, and contains two non-Kerr parameters, one of which controls the presence or absence of the Carter symmetry, thereby controlling the existence of chaotic orbits, and another which serves as a generic deformation parameter. We find that these two parameters introduce fundamentally distinct features into the orbital dynamics, and evince themselves in the gravitational waveforms through a significant dephasing. Although only explored in the quadrupole approximation, this, together with a Fisher metric analysis, suggests that gravitational wave data analysis may be able to test, in addition to the governing theory of gravity, the underlying symmetries of spacetime.       [26/30] 標題：KAGRA引力波探測器隔振系統中的爆裂噪聲研究 Title: Investigation of crackling noise in the vibration isolation systems of the KAGRA gravitational wave detector Authors: Shin Kirii, Yingtao Liu et al. https://arxiv.org/abs/2009.00400 Abstract:  It is essential to investigate various types of noise in gravitational-wave telescopes such as KAGRA. A crackling noise is an intermittent noise, which can occur when a material experiences stress. KAGRA could be prevented from reaching the target sensitivity if the crackling noise appears in the geometric anti-spring filter (GAS) of the vibration isolation system. Therefore it is necessary to investigate the effect of crackling noise in the GAS. For this research, a crackling noise measurement system with a miniature GAS was built, and the noise was measured when stress was intentionally added to the GAS. The scaling law of crackling noise was also investigated using a GAS of a different design. Then the upper limit of the crackling noise in KAGRA was estimated, from the results of the experiment and the derived scaling law, to be less than the target sensitivity of KAGRA at frequencies above 55 Hz.       [27/30] 標題：絕熱階下在赤道面上的極端質量比旋進 Title: Extreme mass ratio inspirals on the equatorial plane in the adiabatic order Authors: Ryuichi Fujita, Masaru Shibata https://arxiv.org/abs/2008.13554 Abstract:  We compute gravitational waves from inspiraling stellar-mass compact objects on the equatorial plane of a massive spinning black hole (BH). Our inspiral orbits are computed by taking into account the adiabatic change of orbital parameters due to gravitational radiation in the lowest order in mass ratio. We employ an interpolation method to compute the adiabatic change at arbitrary points inside the region of orbital parameter space computed in advance. Using the obtained inspiral orbits and associated gravitational waves, we compute power spectra of gravitational waves and the signal-to-noise ratio (SNR) for several values of the BH spin, the masses of the binary, and the initial orbital eccentricity during a hypothetical three-yrs LISA observation before final plunge. We find that (i) the SNR increases as the BH spin and the mass of the compact object increase for the BH mass M \agt 10^6M_\odot, (ii) the SNR has a maximum for M \approx 10^6M_\odot, and (iii) the SNR increases as the initial eccentricity increases for M=10^6M_\odot. We also show that incorporating the contribution from the higher multipole modes of gravitational waves is crucial for enhancing the detection rate.Title: On the waveform of the scalar induced gravitational waves Authors: Fengge Zhang, Arshad Ali et al.https://arxiv.org/abs/2008.12961 Abstract:  The scalar induced gravitational waves (SIGWs) is a useful tool to probe the physics in the early universe. To study inflationary models with this tool, we need to know how the waveform of SIGWs is related to the shape of the scalar power spectrum. We propose two parameterizations to approximate the scalar power spectrum with either a sharp or a broad spike at small scales, and then use these two parameterizations to study the relation between the shapes of \Omega_{GW} and the scalar power spectrum. We find that the waveform of SIGWs has a similar shape to the power spectrum. Away from the peak of the spike, the frequency relation \Omega_{GW}(k)\sim {P}_\zeta^2(k) holds independent of the functional form of the scalar power spectrum. We also give a physical explanation for this general relationship. The general relation is useful for determining the scalar power spectrum and probing inflationary physics with the waveform of SIGWs.  [29/30] 標題：由人工神經網絡驅動的引力波替代模型：用于波形生成的ANN-SurTitle: Gravitational-wave surrogate models powered by artificial neural networks: The ANN-Sur for waveform generation Authors: Sebastian Khan, Rhys Green https://arxiv.org/abs/2008.12932 Abstract:  Inferring the properties of black holes and neutron stars is a key science goal of gravitational-wave (GW) astronomy. To extract as much information as possible from GW observations we must develop methods to reduce the cost of Bayesian inference. In this paper, we use artificial neural networks (ANNs) and the parallelisation power of graphics processing units (GPUs) to improve the surrogate modelling method, which can produce accelerated versions of existing models. As a first application of our method, ANN-Sur, we build a time-domain surrogate model of the spin-aligned binary black hole (BBH) waveform model SEOBNRv4. We achieve median mismatches of 2e-5 and mismatches no worse than 2e-3. For a typical BBH waveform generated from 12 Hz with a total mass of 60 M_\odot the original SEOBNRv4 model takes 1812 ms. Existing bespoke code optimisations (SEOBNRv4opt) reduced this to 91.6 ms and the interpolation based, frequency-domain surrogate SEOBNRv4ROM can generate this waveform in 6.9 ms. Our ANN-Sur model, when run on a CPU takes 2.7 ms and just 0.4 ms when run on a GPU. ANN-Sur can also generate large batches of waveforms simultaneously. We find that batches of up to 10^4 waveforms can be evaluated on a GPU in just 163 ms, corresponding to a time per waveform of 0.016 ms. This method is a promising way to utilise the parallelisation power of GPUs to drastically increase the computational efficiency of Bayesian parameter estimation.       [30/30] 標題：測定Virgo輸入模式清潔器端鏡的新型儀表擋板的光電二極體上的曝光量 Title: Determination of the light exposure on the photodiodes of a new instrumented baffle for the Virgo input mode cleaner end-mirror Authors: A. Romero, A. Allocca et al.https://arxiv.org/abs/2008.13740 Abstract:  As part of the upgrade program of the Advanced Virgo interferometer, the installation of new instrumented baffles surrounding the main test masses is foreseen. As a demonstrator, and to validate the technology, the existing baffle in the area of the input mode cleaner end-mirror will be first replaced by a baffle equipped with photodiodes. This paper presents detailed simulations of the light distribution on the input mode cleaner baffle, with the aim to determine the light exposure of the photodiodes under different scenarios of the interferometer operation.       

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