174 research outputs found

    Sample Variance of the Higher-Order Cumulants of Cosmic Density and Velocity Fields

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    If primordial fluctuation is Gaussian distributed, higher-order cumulants of the cosmic fields reflect nonlinear mode coupling and provide useful information of gravitational instability picture of structure formation. We show that their expected deviation (sample variance) from the universal values is nonvanishing even in linear theory in the case where observed volume is finite. As a result, we find that the relative sample variance of the skewness of the smoothed velocity divergence field remains as large as 30\sim 30% even if the survey depth is as deep as 150h1Mpc\sim 150h^{1}Mpc.Comment: 8 pages including 1 figure, aas.te

    Search for an emission line of a gravitational wave background

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    In the light of the history of researches on electromagnetic wave spectrum, a sharp emission line of gravitational-wave background (GWB) would be an interesting observational target. Here we study an efficient method to detect a line GWB by correlating data of multiple ground-based detectors. We find that the width of frequency bin for coarse graining is a critical parameter, and the commonly-used value 0.25 Hz is far from optimal, decreasing the signal-to-noise ratio by up to a factor of seven. By reanalyzing the existing data with a smaller bin width, we might detect a precious line signal from the early universe.Comment: 5 pages, 3 figure