Gravitational wave signals of dark matter freeze-out

We study the stochastic background of gravitational waves which accompany the sudden freeze-out of dark matter triggered by a cosmological first order phase transition that endows dark matter with mass. We consider models that produce the measured dark matter relic abundance via (1) bubble filtering, and (2) inflation and reheating, and show that gravitational waves from these mechanisms are detectable at future interferometers.

Inferring the lensing rate of LIGO–Virgo sources from the stochastic gravitational wave background

ABSTRACT Strong lensing of gravitational waves (GWs) is more likely for distant sources but predicted event rates are highly uncertain with many astrophysical origins proposed. Here, we open a new avenue to estimate the event rate of strongly lensed systems by exploring the amplitude of the stochastic gravitational wave background (SGWB). This method can provide a direct upper bound on the high-redshift binary coalescing rates, which can be translated into an upper bound on the expected rate of strongly lensed systems. We show that from the ongoing analysis of the Laser Interferometer Gravitational-wave Observatory (LIGO)-Virgo and in the future from the LIGO–Virgo design sensitivity stringent bounds on the lensing event rate can be imposed using the SGWB signal. Combining measurements of loud GW events with an unresolved stochastic background detection will improve estimates of the numbers of lensed events at high redshift. The proposed method is going to play a crucial in understanding the population of lensed and unlensed systems from GW observations.

High-Q Spectral Peaks and Nonstationarity in the Geomagnetic Field Over the 400-4000 μHz Band

This paper analyzes three 60 d sections of geomagnetic data from Honolulu Observatory during 2001 − 2, showing the ubiquitous presence of narrowband, very statistically significant, high Q features in multitaper power spectra, along with pervasive nonstationarity as measured by the frequency offset coherence over 400 − 4000 µHz (or 2500 − 250 s period). This behavior is nearly identical in the H and Z components of the geomagnetic field, and more subdued in the much weaker D component. The peak frequencies correlate well with the optically − measured frequencies of solar p − modes, and the raw Qs are defined by the resolution bandwidths of the estimates, with values ranging from hundreds to thousands. Further, spectral peaks are consistently coherent across frequency due to nonstationarity, and frequently exhibit cyclostationarity at offset frequencies of ± 0.5 cycles per day. None of these characteristics are consistent with internal magnetospheric processes. A mixture central/noncentral chi square model was fit to raw spectral estimates in an attempt to model narrowband, high Q, quasi − deterministic modes embedded in a stochastic background. This model yielded noncentral fractions of 0.13 (1000 − 2000 µHz), 0.24 (1500 − 2500 µHz), 0.35 (2000 − 3000 µHz), 0.30 (2500 − 3500 µHz) and 0.17 (3000 − 4000 µHz). These values suggest that up to 35% of the power in the geomagnetic field in the 1000 − 4000 µHz band averaged over 60 days is forced by solar p − modes.