Projection effects on the observed angular spectrum of the astrophysical stochastic gravitational wave background

Abstract

The detection and characterization of the stochastic gravitational wave background (SGWB) is one of the main goals of gravitational wave (GW) experiments. The observed SGWB will be the combination of GWs from cosmological (as predicted by many models describing the physics of the early universe) and astrophysical origins, which will arise from the superposition of GWs from unresolved sources whose signal is too faint to be detected. Therefore, it is important to have a proper modeling of the astrophysical SGWB (ASGWB) in order to disentangle the two signals; moreover, this will provide additional information on astrophysical properties of compact objects. Applying the cosmic rulers formalism, we compute the observed ASGWB angular power spectrum, hence using gauge-invariant quantities, accounting for all effects intervening between the source and the observer. These are the so-called projection effects, which include Kaiser, Doppler, and gravitational potentials effect. Our results show that these projection effects are the most important at the largest scales, and they contribute to up to tens of percent of the angular power spectrum amplitude, with the Kaiser term being the largest at all scales. While the exact impact of these results will depend on instrumental and astrophysical details, a precise theoretical modeling of the ASGWB will necessarily need to include all these projection effects.

Search for anisotropic gravitational-wave backgrounds using data from Advanced LIGO and Advanced Virgo’s first three observing runs

“…The background may also include signals of cosmological origin, i.e., produced in the early Universe during an inflationary epoch [19][20][21][22][23][24][25][26][27], or as a direct result of phase transitions [28][29][30], primordial black hole mergers [31][32][33][34], or other associated phenomena [35]. Different models could, in principle, be distinguished by characteristic features in the angular distribution [36][37][38][39][40][41][42][43][44][45][46][47]. For example, cosmic strings have an angular power spectrum which is sharply peaked at small multipoles [48,49], while neutron stars in our Galaxy would trace out the Galactic plane [50,51].…”

Cross-correlation of the astrophysical gravitational-wave background with galaxy clustering

“…Note also that in Eq. ( 5) we neglect relativistic corrections, as they are generally found to be below cosmic variance [45].…”

Characterizing the cosmological gravitational wave background: Anisotropies and non-Gaussianity

“…However, future detectors will allow for a better angular resolution of anisotropies of the astrophysical background. Therefore, another tool could be the directionality dependence of the SGWB [14][15][16][17][18][19] and, as we explore here, its statistics.…”