Brownian coating thermal noise in detector test masses is limiting the
sensitivity of current gravitational-wave detectors on Earth. Therefore,
accurate numerical models can inform the ongoing effort to minimize Brownian
coating thermal noise in current and future gravitational-wave detectors. Such
numerical models typically require significant computational resources and
time, and often involve closed-source commercial codes. In contrast,
open-source codes give complete visibility and control of the simulated physics
and enable direct assessment of the numerical accuracy. In this article, we use
the open-source SpECTRE numerical-relativity code and adopt a novel
discontinuous Galerkin numerical method to model Brownian coating thermal
noise. We demonstrate that SpECTRE achieves significantly higher accuracy than
a previous approach at a fraction of the computational cost. Furthermore, we
numerically model Brownian coating thermal noise in multiple sub-wavelength
crystalline coating layers for the first time. Our new numerical method has the
potential to enable fast exploration of realistic mirror configurations, and
hence to guide the search for optimal mirror geometries, beam shapes and
coating materials for gravitational-wave detectors.Comment: 9 pages, 5 figures. Results are reproducible with the ancillary input
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