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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.