Detecting lensing-induced diffraction in astrophysical gravitational waves

Abstract

Gravitational waves emitted from compact binary coalescence can be subject to wave diffraction if they are gravitationally lensed by an intervening mass clump whose Schwarzschild timescale matches the wave period. Waves in the ground-based frequency band f ∼ 10-10 3 Hz are sensitive to clumps with masses ME ∼ 10 2 -10 3 M enclosed within the impact parameter. These can be the central parts of low mass ML ∼ 10 3 -10 6 M dark matter halos, which are predicted in Cold Dark Matter scenarios but are challenging to observe. Neglecting finely-tuned impact parameters, we focus on lenses aligned generally on the Einstein scale for which multiple lensed images may not form in the case of an extended lens. In this case, diffraction induces amplitude and phase modulations whose sizes ∼ 10%-20% are small enough so that standard matched filtering with unlensed waveforms do not degrade, but are still detectable for events with high signal-to-noise ratio. We develop and test an agnostic detection method based on dynamic programming, which does not require a detailed model of the lensed waveforms. For pseudo-Jaffe lenses aligned up to the Einstein radius, we demonstrate that a pair of fully upgraded aLIGO/Virgo detectors can extract diffraction imprints from binary black hole mergers out to zs ∼ 0.2-0.3. The prospect will improve dramatically for a third-generation detector for which binary black hole mergers out to zs ∼ 2-4 will all become valuable sources.

Observability of dark matter substructure with pulsar timing correlations

“…Halos below the dot-dashed-black line corresponding to ρ s = ρ DM cannot make up f = 1 . Also shown in dashed-gray are projections from photometric lensing [12,32], α and µ lensing from astrometric lensing in Gaia data [18][19][20] and diffraction of BH mergers observable in aLIGO [7,56].…”

Constraining the gravitational coupling of axion dark matter at LIGO

“…Since it has a well predicted waveform chirping in time and frequency domains in a particular way, even small perturbations to the chirping can be confidently detected. Example studies with dark matter perturbations are [9][10][11][12][13][14], one of which is probing coherently oscillating light dark matter around binary mergers [15].…”

LENSINGGW: a PYTHON package for lensing of gravitational waves

“…One example of such an avenue is gravitationally lensed GWs, the first of which may be possible to observe in the next few years (Ng et al 2018;Li et al 2018;Oguri 2018). It has been suggested that lensed GWs might offer interesting applications in fundamental physics, astrophysics, and cosmology (Sereno et al 2011;Liao et al 2017;Collett & Bacon 2017;Fan et al 2017;Baker & Trodden 2017;Lai et al 2018;Dai et al 2018;Mukherjee et al 2019;Oguri 2019;Pang et al 2020;Jung & Shin 2019;Cao et al 2019;Hou et al 2020;Sun & Fan 2019;Hannuksela et al 2020).…”