Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session U09: Gravitational Wave Searches: Stochastic Gravitational Wave Background |
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Sponsoring Units: DGRAV Chair: Xavier Siemens Room: Conrad B/C - 2nd Floor |
Tuesday, April 18, 2023 1:30PM - 1:42PM |
U09.00001: An SZ-Like Effect on the Stochastic Gravitational Wave Background Marcell Howard The stochastic gravitational wave background is the conglomeration of unresolved gravitational waves signals from the early universe and astrophysical sources. By deriving the gravitational analog to the Kompaneets equation we establish that much like the cosmic microwave background, inverse Compton scattering will induce small distortions in the intensity spectrum of the stochastic background. We then show that when these spectral distortions can be attributed to the dark matter in the early universe, one can infer the spin of the dark matter particle. |
Tuesday, April 18, 2023 1:42PM - 1:54PM |
U09.00002: First Measurement of the Cross-Correlation Angular Power Spectrum Between the Stochastic Gravitational Wave Background and Galaxy Over-Density Kate Z Yang We study the cross-correlation between the Stochastic Gravitational-Wave Background (SGWB) and the distribution of galaxies across the sky: we use LIGO third run (O3) SGWB data, and galaxy over-density from the Sloan Digital Sky Survey (SDSS) spectroscopic catalog and we compute the angular power spectrum of the resulting cross-correlation. Instead of integrating the SGWB signal across frequencies, we analyze the cross-correlation in 10 Hz width SGWB frequency bands to study the frequency dependence of the angular power spectrum. Finally, we compare the observed cross-correlation to the spectrum predicted by astrophysical models. We apply parameter estimation based on maximum likelihood evaluation to explore the parameter space of the theoretical models, and we set constraints on a set of (effective) astrophysical parameters describing the galactic process of gravitational wave emission. |
Tuesday, April 18, 2023 1:54PM - 2:06PM |
U09.00003: Angular Resolution of the Spherical Harmonics Decomposition Search for the Stochastic Gravitational-Wave Background with Terrestrial Detectors Erik Floden We consider an anisotropic search for the stochastic gravitational-wave (GW) background using terrestrial detectors by decomposing the gravitational-wave sky into its spherical harmonics components. Previous analyses have used the diffraction limit to define the highest-order spherical harmonics components used in this search. We investigate whether the angular resolution of this search is indeed diffraction-limited by testing our ability to detect and localize simulated GW signals. We show that while using low-order spherical harmonics modes is optimal for initially detecting GW sources, those sources which are detectable are most effectively localized with higher-order spherical harmonics than what is suggested by the diffraction limit. Additionally, we discuss how our ability to recover simulated GW sources is affected by the number of detector baselines in our network, the frequency range over which we perform our search, and the method by which we regularize the covariance matrix of our GW skymap. Finally, we consider future analysis methods and parameter estimation schemes intended to avoid covariance matrix regularization and reduce assumptions regarding the statistical properties of the angular power spectra. |
Tuesday, April 18, 2023 2:06PM - 2:18PM |
U09.00004: Detecting cosmological gravitational waves background after removal of compact binary coalescences in future gravitational wave detectors Haowen Zhong, Rich Ormiston, Vuk Mandic The improved sensitivity of third-generation gravitational wave detectors(Cosmic Explorer, Einstein Telescope, etc.) opens the possibility of detecting the primordial cosmological stochastic gravitational wave background (SGWB). Detection of the cosmological SGWB is facing a novel challenge: it will very likely be masked by the foreground generated by a huge number of coalescences of compact binary systems consisting of black holes and/or neutron stars. We investigate the possibility of reducing this foreground by removing (notching) the individually resolved compact binary signals in time-frequency space. We establish that such an approach could be used to reach the SGWB sensitivity floor defined by the unresolved part of the compact binaries foreground, which we find to be between ΩGW~(9.1×10-12-8.6×10-11) for a frequency-independent energy density spectrum and depending on the rate of coalescing binary neutron star systems. Since third-generation gravitational wave detectors will not be able to resolve all compact binaries, the unresolvable component of the compact binaries foreground may limit the SGWB searches with these detectors. |
Tuesday, April 18, 2023 2:18PM - 2:30PM |
U09.00005: Stess testing pulsar timing array models Patrick Meyers, Michele Vallisneri, Katerina Chatziioannou The recent common process that has been observed by many pulsar timing arrays could presage a gravitational wave background detection. Such a detection would require carefully testing and checking that the models used for PTAs are appropriate, and we should highlight where mismodelling might occur and whether it can cause a "false" detection. Most pulsar timing array experiments use a power law to model the power spectral density of the gravitational wave background and intrinsic pulsar red noise. These assumptions can be relaxed using so-called "free spectral" Bayesian runs that model the power in each frequency bin individually, but they are time consuming. In this talk, I'll present a fast and efficient method to test the power law assumption in the GWB and intrinsic red noise. I'll show how we can perform fast, repeated simulations using this method to estimate the "significance" of deviations from a power law. I'll close by showing how we can use the formalism to test whether correlations between pulsars follow the Hellings and Downs curve. |
Tuesday, April 18, 2023 2:30PM - 2:42PM |
U09.00006: Don’t wait, reweight: Accurate characterization of the stochastic gravitational-wave background with pulsar timing arrays by likelihood reweighting Sophie R Hourihane, Patrick Meyers, Aaron Johnson, Katerina Chatziioannou, Michele Vallisneri The nanohertz gravitational-wave background modifies pulsar pulse arrival times stochastically, generating excess power in pulsar-timing-array datasets with characteristic inter-pulsar correlations that follow the Hellings-Downs function. These correlations appear as non-diagonal terms in the noise-covariance matrix which is inverted to evaluate the pulsar-timing-array likelihood. Gravitational-wave background searches, which require many such likelihood calculations, therefore become quite expensive. In this talk I present a more efficient method: first compute approximate posteriors by ignoring the inter-pulsar correlations and then obtain the exact posteriors via reweighting. I will show that this method is robust, unbiased, and able to estimate Bayes factors up to at least 106. |
Tuesday, April 18, 2023 2:42PM - 2:54PM |
U09.00007: Analytic distribution of the optimal cross-correlation statistic for pulsar timing arrays Jeffrey S Hazboun, Patrick Meyers, Joseph D Romano, Xavier Siemens We show via both analytical calculation and numerical simulation that the optimal cross-correlation statistic (OS) for stochastic gravitational-wave-background (GWB) searches using data from pulsar timing arrays follows a generalized chi-squared (GX2) distribution---i.e., a linear combination of chi-squared distributions with coefficients given by the eigenvalues of the quadratic form defining the statistic. This observation is particularly important for calculating the frequentist statistical significance of a possible GWB detection, which depends on the exact form of the distribution of the OS signal-to-noise ratio (S/N) in the absence of GW-induced cross correlations (i.e.,the null distribution). Previous discussions of the OS have incorrectly assumed that the analytic null distribution of the S/N is well-approximated by a zero-mean unit-variance Gaussian distribution. The "tails" of this simple distribution which differ significantly from those for the GX2distribution, which taken by itself would lead to an incorrect assessment of the statistical significance of a potential detection. |
Tuesday, April 18, 2023 2:54PM - 3:06PM |
U09.00008: Generalized Optimal Statistic for Multiple Cross Correlated Signals Shashwat C Sardesai, Sarah J Vigeland The Optimal Statistic is a frequentist approach within pulsar timing arrays (PTAs) to calculate the amplitude squared of our gravitational wave background (GWB). The expected cross correlations of this signal are quadrupolar and higher order. But monopole and dipole correlated noise may be present within our data. |
Tuesday, April 18, 2023 3:06PM - 3:18PM |
U09.00009: Estimating and Characterizing Gravitational Wave Backgrounds in Pulsar Timing Arrays with Frequentist Statistics Kyle Gersbach, Stephen R Taylor Three separate PTAs have all found evidence for a common-spectrum process hinting at the imminent detection of a Gravitational Wave Background (GWB) at low gravitational-wave frequencies. Such a detection will in turn pose many new questions, most of which may be answered through spectral characterization of the GWB. Current methods for spectral analyses require time-consuming Bayesian techniques and stochastic sampling in high dimensions. Our method expands on a frequentist estimation technique called the optimal statistic. |
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