引力波文獻周讀(11-15 Jan 2021)

每周搜集 arXiv（點擊文末「閱讀原文」訪問網站）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

[1/13] 標題：超大質量黑洞併合天體噴流作為引力波發射的電磁對應體 Title: Post-Merger Jets from Supermassive Black Hole Coalescences as Electromagnetic Counterparts of Gravitational Wave Emission Authors: Chengchao Yuan, Kohta Murase et al.https://arxiv.org/abs/2101.05788 Abstract:  As a powerful source of gravitational waves (GW), a supermassive black hole (SMBH) merger may be accompanied by a relativistic jet that leads to detectable electromagnetic emission (EM). We model the propagation of post-merger jets inside a pre-merger circumnuclear environment formed by disk winds, and calculate multi-wavelength EM spectra from the forward shock region. We show that the non-thermal EM signals from SMBH mergers are detectable up to the detection horizon of future GW facilities such as the Laser Interferometer Space Antenna (LISA). Calculations based on our model predict slowly fading transients with time delays from days to months after the coalescence, leading to implications for EM follow-up observations after the GW detection.       [2/13] 標題：雙黑洞併合和鈴宕階段引力波形的深度學習模型 Title: Deep Learning Model on Gravitational Waveforms in Merging and Ringdown Phases of Binary Black Hole Coalescences Authors: Joongoo Lee, Sang Hoon Oh et al.https://arxiv.org/abs/2101.05685 Abstract:  The waveform templates of the matched filtering-based gravitational-wave search ought to cover wide range of parameters for the prosperous detection. Numerical relativity (NR) has been widely accepted as the most accurate method for modeling the waveforms. Still, it is well-known that NR typically requires a tremendous amount of computational costs. In this paper, we demonstrate a proof-of-concept of a novel deterministic deep learning (DL) architecture that can generate gravitational waveforms from the merger and ringdown phases of the non-spinning binary black hole coalescence. Our model takes O(1) seconds for generating approximately 1500 waveforms with a 99.9% match on average to one of the state-of-the-art waveform approximants, the effective-one-body. We also perform matched filtering with the DL-waveforms and find that the waveforms can recover the event time of the injected gravitational-wave signals.       [3/13] 標題：GW190521的另一種可能性：來自大質量黑洞-盤系統的引力波 Title: Alternative possibility of GW190521: Gravitational waves from high-mass black hole-disk systems Authors: Masaru Shibata, Kenta Kiuchi, Sho Fujibayashi, Yuichiro Sekiguchi https://arxiv.org/abs/2101.05440 Abstract:  We evolve high-mass disks of mass 15-50M_\odot orbiting a 50M_\odot spinning black hole in the framework of numerical relativity. Such high-mass systems could be an outcome during the collapse of rapidly-rotating very-massive stars. The massive disks are dynamically unstable to the so-called one-armed spiral-shape deformation with the maximum fractional density-perturbation of \delta \rho/\rho \gtrsim 0.1, and hence, high-amplitude gravitational waves are emitted. The waveforms are characterized by an initial high-amplitude burst with the frequency of \sim 40-50 Hz and the maximum amplitude of (1-10)\times 10^{-22} at the hypothetical distance of 100 Mpc and by a subsequent low-amplitude quasi-periodic oscillation. We illustrate that the waveforms in our models with a wide range of the disk mass resemble that of GW190521. We also point out that gravitational waves from rapidly-rotating very-massive stars can be the source for 3rd-generation gravitational-wave detectors for exploring the formation process of rapidly-rotating high-mass black holes of mass \sim 50-100M_\odot in an early universe.       [4/13] 標題：NANOGrav11年數據集：500Mpc以內星系中超大質量黑洞雙星的限制 Title: The NANOGrav 11yr Data Set: Limits on Supermassive Black Hole Binaries in Galaxies within 500Mpc Authors: The NANOGrav Collaboration https://arxiv.org/abs/2101.02716 Abstract:  Supermassive black hole binaries (SMBHBs) should form frequently in galactic nuclei as a result of galaxy mergers. At sub-parsec separations, binaries become strong sources of low-frequency gravitational waves (GWs), targeted by Pulsar Timing Arrays (PTAs). We used recent upper limits on continuous GWs from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11yr dataset to place constraints on putative SMBHBs in nearby massive galaxies. We compiled a comprehensive catalog of ~44,000 galaxies in the local universe (up to redshift ~0.05) and populated them with hypothetical binaries, assuming that the total mass of the binary is equal to the SMBH mass derived from global scaling relations. Assuming circular equal-mass binaries emitting at NANOGrav's most sensitive frequency of 8nHz, we found that 216 galaxies are within NANOGrav's sensitivity volume. We ranked the potential SMBHBs based on GW detectability by calculating the total signal-to-noise ratio (S/N) such binaries would induce within the NANOGrav array. We placed constraints on the chirp mass and mass ratio of the 216 hypothetical binaries. For 19 galaxies, only very unequal-mass binaries are allowed, with the mass of the secondary less than 10 percent that of the primary, roughly comparable to constraints on a SMBHB in the Milky Way. Additionally, we were able to exclude binaries delivered by major mergers (mass ratio of at least 1/4) for several of these galaxies. We also derived the first limit on the density of binaries delivered by major mergers purely based on GW data.       

General Relativity

[5/13] 標題：廣義不確定性原理與隨機引力波背景譜 Title: Generalized uncertainty principle and stochastic gravitational wave background spectrum Authors: Mohamed Moussa, Homa Shababi, Ahmed Farag Ali https://arxiv.org/abs/2101.04747 Abstract:  This paper concerned with the effect of generalized uncertainty principle (GUP) on the stochastic gravitational wave (SGW) background signal that produced during first order cosmological QCD phase transition in early universe. A modified formula of entropy is used to calculate the temporal evolution of temperature of the universe as a function of the Hubble parameter. The pressure that results from the recent lattice calculations, which provides parameterizations of the pressure due to u,~d,~s quarks and gluons, with trace anomaly is used to describe the equation of state around QCD epoch. A redshift in the peak frequency of SGW at current epoch is calculated. The results indicate an increase in the frequency peak due to GUP effect, which improves the ability to detect it. Taking into account bubble wall collisions (BWC) and turbulent magnetohydrodynamics (MHD) as a source of SGW, a fractional energy density is investigated. It is found that the GUP effect weakens the SGW signal generated during QCD phase transition in comparison to its counterpart in the absence of GUP. These results support understanding the cosmological QCD phase transition and test the effectiveness of the GUP theory.       [6/13] 標題：NNETFIX：基於人工神經網絡的引力波信號降噪引擎 Title: NNETFIX: An artificial neural network-based denoising engine for gravitational-wave signals Authors: Kentaro Mogushi, Ryan Quitzow-James et al.https://arxiv.org/abs/2101.04712 Abstract:  Instrumental and environmental transient noise bursts in gravitational-wave detectors, or glitches, may impair astrophysical observations by adversely affecting the sky localization and the parameter estimation of gravitational-wave signals. Denoising of detector data is especially relevant during low-latency operations because electromagnetic follow-up of candidate detections requires accurate, rapid sky localization and inference of astrophysical sources. NNETFIX is a machine learning-based algorithm designed to remove glitches detected in coincidence with transient gravitational-wave signals. NNETFIX uses artificial neural networks to estimate the portion of the data lost due to the presence of the glitch, which allows the recalculation of the sky localization of the astrophysical signal. The sky localization of the denoised data may be significantly more accurate than the sky localization obtained from the original data or by removing the portion of the data impacted by the glitch. We test NNETFIX in simulated scenarios of binary black hole coalescence signals and discuss the potential for its use in future low-latency LIGO-Virgo-KAGRA searches. In the majority of cases for signals with a high signal-to-noise ratio, we find that the overlap of the sky maps obtained with the denoised data and the original data is better than the overlap of the sky maps obtained with the original data and the data with the glitch removed.       [7/13] 標題：利用玻色-愛因斯坦凝聚的參數共振探測引力波 Title: Detection of Gravitational Waves using Parametric Resonance in Bose-Einstein Condensates Authors: Matthew P. G. Robbins, Niayesh Afshordi, Alan O. Jamison, Robert B. Mann https://arxiv.org/abs/2101.03691 Abstract:  An interesting proposal for detecting gravitational waves involves quantum metrology of Bose-Einstein condensates (BECs). We consider a forced modulation of the BEC trap, whose frequency matches that of an incoming continuous gravitational wave. The trap modulation induces parametric resonance in the BEC, which in turn enhances sensitivity of the BEC to gravitational waves. We find that such a BEC detector could potentially be used to detect gravitational waves across several orders of magnitude in frequency, with the sensitivity depending on the speed of sound, size of the condensate, and frequency of the phonons. We outline a possible BEC experiment and discuss the current technological limitations. We also comment on the potential noise sources as well as what is necessary for such a detector to become feasible.  [8/13] 標題：在存在其它隨機信號的情況下測量原初引力波背景 Title: Measuring the primordial gravitational wave background in the presence of other stochastic signals https://arxiv.org/abs/2101.02713 Abstract:  Standard methodologies for the extraction of the stochastic gravitational wave background (SGWB) from auto- or cross-correlation of interferometric signals often involve the use of a filter function. The standard optimal filter maximizes the signal-to-noise ratio (SNR) between the total SGWB and the noise. We derive expressions for the optimal filter and SNR in the presence of a target SGWB plus other unwanted components. We also generalize the methodology to the case of template-free reconstruction. The formalism allows to easily perform analyses and forecasts that marginalize over foreground signals, such as the typical \Omega_{GW} \propto f^{2/3} background arising from binary coalescence. We demonstrate the methodology with the LISA mission and discuss possible extensions and domains of application.       [9/13] 標題：玻色-愛因斯坦凝聚中的雙模聲子壓縮用於探測引力波 Title: Two-mode Phonon Squeezing in Bose-Einstein Condensates for Gravitational Wave Detection https://arxiv.org/abs/2101.05051 Abstract:  Squeezed, nonclassical states are an integral tool of quantum metrology due to their ability to push the sensitivity of a measurement apparatus beyond the limits of classical states. While their creation in light has become a standard technique, the production of squeezed states of the collective excitations in gases of ultracold atoms, the phonons of a Bose-Einstein condensate (BEC), is a comparably recent problem. This task is continuously gaining relevance with a growing number of proposals for BEC-based quantum metrological devices and the possibility to apply them in the detection of gravitational waves. The objective of this thesis is to find whether the recently described effect of an oscillating external potential on a uniform BEC can be exploited to generate two-mode squeezed phonon states, given present day technology. This question brings together elements of a range of fields beyond cold atoms, such as general relativity and Efimov physics. To answer it, the full transformation caused by the oscillating potential on an initially thermal phononic state is considered, allowing to find an upper bound for the magnitude of this perturbation as well as to quantify the quality of the final state with respect to its use in metrology. These findings are then applied to existing experiments to judge the feasibility of the squeezing scheme and while the results indicate that they are not well suited for it, a setup is proposed that allows for its efficient implementation and seems within experimental reach. In view of the vast parameter space leaving room for optimization, the considered mechanism could find applications not only in the gravitational wave detector that originally motivated this work, but more generally in the field of quantum metrology based on ultracold atoms.       [10/13] 標題：來自極端質量比旋近的引力波模板 Title: Gravitational wave templates from Extreme Mass Ratio Inspirals Authors: Viktor Skoupý, Georgios Lukes-Gerakopouloshttps://arxiv.org/abs/2101.04533 Abstract:  An extreme mass ratio inspiral takes place when a compact stellar object is inspiraling into a supermassive black hole due to gravitational radiation reaction. Gravitational waves (GWs) from this system can be calculated using the Teukolsky equation (TE). In our case, we compute the asymptotic GW fluxes of a spinning body orbiting a Kerr black hole by solving numerically the TE both in time and frequency domain. Our ultimate goal is to produce GW templates for space-based detectors such as LISA.       [11/13] 標題：GW150914和GW190521的GUP參數的限定 Title: Bounds on GUP parameters from GW150914 and GW190521 Authors: Ashmita Das, Saurya Das, Noor R. Mansour, Elias C. Vagenas https://arxiv.org/abs/2101.03746 Abstract:  We compute bounds on the GUP parameters for two versions of GUP using gravitational wave data from the events GW150914 and GW190521. The speed of the graviton and photon are calculated in a curved spacetime modified by GUP, assuming that these particles have a small mass. The observational bound on the difference in their speeds translates to bounds on the GUP parameters. These bounds are some of the best obtained so far in the context of quantum gravity phenomenology.       [12/13] 標題：帶宇宙常數的Brans-Dicke理論中的引力波 Title: Gravitational waves in Brans-Dicke Theory with a cosmological constant Authors: Hatice Özer, Özgür Delice https://arxiv.org/abs/2101.03594 Abstract:  Weak field gravitational wave solutions are investigated in Brans-Dicke (BD) theory in the presence of a cosmological constant. In this setting the background geometry is not flat but asymptotically de-Sitter. We investigate the linearised field equations, and their gravitational wave solutions in a certain gauge choice. We will show that this theory leads to massless scalar waves as in original BD theory and in contrast to massive BD theory. The effects of these waves on free particles and their polarization properties are studied extensively and effects of the cosmological constant is analyzed in these phenomena in detail. The energy flux of these waves are also discussed in this background. By analyzing this flux, we obtain a critical distance where the waves cannot propagate further, which extends Cosmic no Hair Conjecture (CNC) to BD theory with a cosmological constant.       [13/13] 標題：緻密雙星引力波搜索中的隨機投影II：LLOID框架內探測統計量的高效重建 Title: Random projections in gravitational wave searches from compact binaries II: efficient reconstruction of detection statistic within LLOID framework Authors: Amit Reza, Anirban Dasgupta, Anand S. Sengupta https://arxiv.org/abs/2101.03226 Abstract:  Low-latency gravitational wave search pipelines such as LLOID take advantage of low-rank factorization of the template matrix via singular value decomposition (SVD). With unprecedented improvements in detector bandwidth and sensitivity in advanced-LIGO and Virgo detectors, one expects several orders of magnitude increase in the size of template banks. This poses a formidable computational challenge in factorizing extremely large matrices. Previously, [in Kulkarni et al. [6]], we introduced the idea of random projection (RP)-based matrix factorization as a computationally viable alternative to SVD, for such large template banks. In this follow-up paper, we demonstrate the application of a block-wise randomized matrix factorization (RMF) scheme using which one can compute the desired low-rank factorization corresponding to a fixed average SNR loss (h{\delta}\r{ho}/\r{ho}i). Unlike the SVD approach, this new scheme affords a much more efficient way of matrix factorization especially in the context of LLOID search pipelines. It is a well-known fact that for very large template banks, the total computational cost is dominated by the cost of reconstruction of the detection statistic and that the cost of filtering the data is insignificant in comparison. We are unaware of any previous work in literature that has tried to squarely address this issue of optimizing the reconstruction cost. We provide a possible solution to reduce the reconstruction cost using the matching pursuit(MP) algorithm. We show that it is possible to approximately reconstruct the time-series of the detection statistic at a fraction of the total cost using our MP algorithm. The combination of RMF along with MP can handle large template banks more efficiently in comparison to the direct application of SVD. Results from several numerical simulations have been presented to demonstrate their efficacy.

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