Impact of the noise knowledge uncertainty for the science exploitation of cosmological and astrophysical stochastic gravitational wave background with LISA

TL;DR

This study assesses how uncertainties in LISA's instrumental noise affect the detection and characterization of various stochastic gravitational wave backgrounds, revealing significant degradation in constraints if noise knowledge is insufficient.

Contribution

It introduces a spline-based method to model noise uncertainties and quantifies their impact on gravitational wave background constraints with LISA.

Findings

Noise uncertainty causes 10-100x degradation in background constraints.

Sub-percent noise knowledge is required to avoid significant degradation.

Detectability thresholds increase with noise uncertainty.

Abstract

This paper investigates the impact of a lack of knowledge of the instrumental noise on the characterisation of stochastic gravitational wave backgrounds with the Laser Interferometer Space Antenna (LISA). We focus on constraints on modelled backgrounds that represent the possible backgrounds from the mergers of binary black holes of stellar origin, from primordial black hole generation, from non-standard inflation, and from sound wave production during cosmic fluid phase transitions. We use splines to model generic, slowly varying, uncertainties in the auto and cross-spectral densities of the LISA time delay interferometry channels. We find that allowing for noise knowledge uncertainty in this way leads to one to two orders of magnitude degradation in our ability to constrain stochastic backgrounds, and a corresponding increase in the background energy density required for a confident detection. We also find that to avoid this degradation, the LISA noise would have to be known at the sub-percent level, which is unlikely to be achievable in practice.