APEC Seminar (Astronomy - Particle Physics - Experimental Physics - Cosmology)

Speaker: Bruce Allen (Max Panck Institute for for Gravitational Physics, Albert Einstein Institute)
Title: Pulsar Timing Arrays and the Hellings-Downs curve
Date (JST): Tue, Sep 06, 2022, 16:00 - 17:30
Place: Zoom
Abstract: Pulsar timing arrays (PTA) are galactic scale gravitational-wave (GW) detectors. PTAs search for low-frequency (nanohertz) GWs via correlations that they induce in the arrival times of pulses from different pulsars. The mean correlation as a function of the sky separation angle between two pulsars was calculated in 1983 by Hellings and Downs, and is considered a "smoking gun" signature for the detection of GWs. While several PTAs are searching for it, there is currently little evidence for the Hellings-Downs angular dependence, which makes it difficult to claim that a GW background is responsible. Could this just be a statistical fluctuation? To help answer this question, I present results for the variance of the Hellings-Downs correlation, taken from arXiv:2205.05637 and arXiv:2208.07230. The most important is an analytic prediction for the cosmic variance in the Hellings-Downs correlation.