Detecting primordial features with LISA

Oscillations in the frequency profile of the stochastic gravitational wave back-ground are a characteristic prediction of small-scale features during inflation. In this paper we present a first investigation of the detection prospects of such oscillations with the upcoming space-based gravitational wave observatory LISA. As a proof of principle, we show for a selection of feature signals that the oscillations can be reconstructed with LISA, employing a method based on principal component analysis. We then perform a Fisher forecast for the parameters describing the oscillatory signal. For a sharp feature we distinguish between the contributions to the stochastic gravitational wave background induced during inflation and in the post-inflationary period, which peak at different frequencies. We find that for the latter case the amplitude of the oscillation is expected to be measurable with < 10% accuracy if the corresponding peak satisfies h(2)omega(GW) >= 10(-12)-10(-11), while for inflationary-era gravitational waves a detection of the oscillations requires a higher peak amplitude of h(2)omega(GW), as the oscillations only appear on the UV tail of the spectrum. For a resonant feature the detection prospects with LISA are maximised if the frequency of the oscillation falls into the range omega(log) = 4 to 10. Our results confirm that oscillations in the frequency profile of the stochastic gravitational wave background are a worthwhile target for future detection efforts and offer a key for experimentally testing inflation at small scales.

Automated summary

In this study, the detection prospects of oscillations in the frequency profile of the stochastic gravitational wave background are investigated using the upcoming space-based gravitational wave observatory LISA. It is found that the oscillations can be reconstructed with LISA, and it is confirmed that they are a worthwhile target for future detection efforts and offer a key for experimentally testing inflation at small scales.