Mismodeling in gravitational-wave astronomy: The trouble with templates

Abstract

Waveform templates are a powerful tool for extracting and characterizing gravitational wave signals, acting as highly restrictive priors on the signal morphologies that allow us to extract weak events buried deep in the instrumental noise. The templates map the waveform shapes to physical parameters, thus allowing us to produce posterior probability distributions for these parameters. However, there are attendant dangers in using highly restrictive signal priors. If strong field gravity is not accurately described by General Relativity (GR), then using GR templates may result in fundamental bias in the recovered parameters, or even worse, a complete failure to detect signals.Here we study such dangers, concentrating on three distinct possibilities. First, we show that there exist modified theories compatible with all existing observations that would fail to be detected by the LIGO/Virgo network using searches based on GR templates, but which would be detected using a one parameter post-Einsteinian extension. Second, we study modified theories that produce departures from GR that turn on suddenly at a critical frequency, producing waveforms that do not directly fit into the simplest parameterized post-Einsteinian (ppE) scheme. We show that even the simplest ppE templates are still capable of picking up these strange signals and diagnosing a departure from GR. Third, we study whether using inspiral-only ppE waveforms for signals that include merger and ringdown can lead to problems in misidentifying a GR departure. We present a simple technique that allows us to self-consistently identify the inspiral portion of the signal, and thus remove these potential biases, allowing GR tests to be performed on higher mass signals that merge within the detector band. We close by studying a parameterized waveform model that may allow us to test GR using the full inspiral-merger-ringdown signal.

Testing the no-hair theorem with black hole ringdowns using TIGER

“…An explicit demonstration is left for future work. On the other hand, if the signal waveform is not among any of the template models, then fundamental bias can make it difficult to reliably pinpoint the underlying nature of the violation [26,[59][60][61][62]. This remains an open problem for ringdown as well.…”

Quasiequilibrium sequences of binary neutron stars undergoing dynamical scalarization

“…Note that depending on the EOS those differences can be smaller than or comparable to what we have found in dynamical scalarization (see Table II). At SNR around 30-35, deviations from general relativity might also be observable even in cases in which the onset of dynamical scalarization happens at orbital frequencies above 50 Hz [28,61]. It will be interesting to investigate in the future the detectability of tidal effects in the presence of dynamical scalarization.…”

“…Recent studies carried out in Refs. [28,61], which use scalar-tensor templates in the frequency domain, rely on the scalar-charge evolution and numerical-relativity simulations of Refs. [9,11], which concluded that advanced detectors operating at a signal-to-noise ratio (SNR) of 10 will be able to constrain dynamical scalarization only if the system scalarizes at low enough orbital frequencies, e.g., ≤ 50 Hz, so that a sufficient number of GW cycles emitted during the dynamical-scalarization phase can contribute to the accumulated SNR.…”

Theory-Agnostic Constraints on Black-Hole Dipole Radiation with Multiband Gravitational-Wave Astrophysics

“…However, as shown explicitly in [63], at least in FJBD theory, these higherorder PN corrections only affect a Fisher analysis like ours by at most 10%. The addition of many terms in the GW phase at multiple PN orders is not only unnecessary, but actually counterproductive as it dilutes the ability to extract information from the signal (as pointed out in [75,76] and verified in [73]). …”