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General Relativity and Quantum Cosmology, gr-qc, Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
Abstract:
Current searches for gravitational waves from coalescing binary black holes
(BBH) use templates that only include the dominant harmonic. In this study we
use effective-one-body multipolar waveforms calibrated to numerical-relativity
simulations to quantify the effect of neglecting sub-dominant harmonics on the
sensitivity of searches. We consider both signal-to-noise ratio (SNR) and the
signal-based vetoes that are used to re-weight SNR. We find that neglecting
sub-dominant modes when searching for non-spinning BBHs with component masses
$3\,M_{\odot} \leq m_1, m_2 \leq 200\,M_{\odot}$ and total mass $M <
360\,M_{\odot}$ in advanced LIGO results in a negligible reduction of the
re-weighted SNR at detection thresholds. Sub-dominant modes therefore have no
effect on the detection rates predicted for advanced LIGO. Furthermore, we find
that if sub-dominant modes are included in templates the sensitivity of the
search becomes worse if we use current search priors, due to an increase in
false alarm probability. Templates would need to be weighted differently than
what is currently done to compensate for the increase in false alarms. If we
split the template bank such that sub-dominant modes are only used when $M
\gtrsim 100\,M_{\odot}$ and mass ratio $q \gtrsim 4$, we find that the
sensitivity does improve for these intermediate mass-ratio BBHs, but the
sensitive volume associated with these systems is still small compared to
equal-mass systems. Using sub-dominant modes is therefore unlikely to
substantially increase the probability of detecting gravitational waves from
non-spinning BBH signals unless there is a relatively large population of
intermediate mass-ratio BBHs in the universe.
