Accelerating TTL noise post-processing via combined coefficients and alternative TDI configuration

TL;DR

This paper introduces a method to significantly speed up TTL noise parameter estimation in space-based gravitational-wave detectors by using a transformed coefficient set and an alternative TDI configuration, improving calibration efficiency.

Contribution

It proposes a novel linear transformation of coupling coefficients and employs the PD4L TDI configuration to accelerate TTL noise parameter fitting.

Findings

Convergence speed improved by a factor of ~10 for linear models.

Convergence speed improved by a factor of ~18 for quadratic models.

Enhanced efficiency in TTL noise calibration for space-based detectors.

Abstract

Tilt-to-length (TTL) noise induced by angular jitter of spacecraft and test masses can affect the sensitivity of space-based gravitational-wave detectors such as LISA, Taiji, and TianQin. Such angular jitter can be measured using the differential wavefront sensing technique, enabling the modeling and subtraction of TTL noise from the data. However, owing to the multiple degrees of freedom of the detector constellation, a linear TTL model requires at least 24 parameters, while a higher-fidelity quadratic model involves up to 60 coefficients, rendering parameter estimation computationally expensive. To accelerate parameter determination, we propose a modified parameter set obtained via a linear transformation of the original angular coupling coefficients, which effectively reduces correlations among TTL noise components. In addition, we perform parameter fitting using an alternative second-generation time-delay interferometry configuration, PD4L, rather than the fiducial Michelson configuration. These two improvements enhance the convergence speed of the fitting procedure by a factor of approximately 10 for the linear model and approximately 18 for the quadratic model. The proposed approach can therefore substantially improve the efficiency of TTL noise calibration in space-based gravitational-wave detectors.