Time-delay interferometry without delays

The space-based gravitational-wave observatory LISA relies on a form of synthetic interferometry (time-delay interferometry, or TDI) where the otherwise overwhelming laser phase noise is canceled by linear combinations appropriately delayed measurements. These observables grow in length and complexity as realistic features orbits are taken into account. In this paper we outline an implicit formulation TDI write likelihood directly terms basic measurements, marginalize over noises limit infinite laser-noise variance. Equivalently, rely that defined numerically (rather than algebraically) from discrete-filter representation propagation delays. Our method generalizes to any time dependence armlengths; it simplifies modeling signals; allows straightforward treatment data gaps missing