Detecting primordial features with LISA

Abstract

Oscillations in the frequency profile of the stochastic gravitational wave background 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 Ω GW 10 −12 -10 −11 , while for inflationary-era gravitational waves a detection of the oscillations requires a higher peak amplitude of h 2 Ω 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 ω 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.

Primordial Black Holes and Gravitational Waves in Multi-Axion-Chern-Simons Inflation

“…The oscillations of the field appear effectively as many tiny "step"-like patterns, however we stress here that the evolution is smooth, and there are no discontinuities neither in the field nor in its first derivative. We expect this behaviour to be reflected in the background of GWs [43,45,46].…”

“…Fig. 3), which may lead to resonant peaks in the GWs spectra [45], that can lead to in principle detectable effects in future interferometers [46].…”

“…Thus, this smooth enhancement is reflected to the GWs energy density spectrum. Consequently, future observations in the GWs spectra, like those form LISA [59], can in principle distinguish between these two classes of inflationary models, depending, of course, on the sensitivity of the corresponding observations [46].…”

Gravitational waves from dark matter isocurvature

“…At second order in cosmological perturbation theory, this appears as a scalar squared source to the equation of motion for tensor modes. These induced GWs have been shown to be a promising and unique tool to probe new physics during [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69] and after inflation [40][41][42][70][71][72][73][74][75][76][77][78][79][80][81] and to map the primordial curvature spectrum on small scales [36,37,[82][83][84][85][86].…”

"Stairway to Heaven" -- Spectroscopy of Particle Couplings with Gravitational Waves

“…We review next the basics of the PCA technique of [120] (see also [146]). For simplicity we restrict ourselves to a single data channel per experiment [147] and proceed to build a Gaussian likelihood to describe the data:…”