Probing Primordial Features with the Stochastic Gravitational Wave Background

Abstract

The stochastic gravitational wave background (SGWB) offers a new opportunity to observe signals of primordial features from inflationary models. We study their detectability with future space-based gravitational waves experiments, focusing our analysis on the frequency range of the LISA mission. We compute gravitational wave spectra from primordial features by exploring the parameter space of a two-field inflation model capable of generating different classes of features. Fine-tuning in scales and amplitudes is necessary for these signals to fall in the observational windows. Once they show up, several classes of frequency-dependent oscillatory signals, characteristic of different underlying inflationary physics, may be distinguished and the SGWB provides a window on dynamics of the primordial universe independent of cosmic microwave background and large-scale structure. To connect with future experimental data, we discuss two approaches of how the results may be applied to data analyses. First, we discuss the possibility of reconstructing the signal with LISA, which requires a high signal-to-noise ratio. The second more sensitive approach is to apply templates representing the spectra as estimators. For the latter purpose, we derive templates that can accurately capture the spectral features of several classes of feature signals and compare them with the SGWB produced by other physical mechanisms.

String Cosmology: from the Early Universe to Today

“…This originates from transient violations of slow-roll, η 1, caused by the modulations in the scalar potential. (ii) The non-trivial dynamics lead to a large enhancement of the adiabatic power spectrum at small scales, providing the first concrete realisation of resonant features studied recently in the literature [645,646,647,648]. These can lead to considerable production of light PBHs and a large and wide spectrum of induced GWs.…”

Sharp turns in axion monodromy: primordial black holes and gravitational waves

“…However, models where the scalar fluctuations are significantly enhanced at scales smaller than those probed by the CMB can lead to large induced GW spectra. Thus, multifield inflation scenarios that highly enhance the scalar power spectrum at short scales as mentioned above, may give rise to potentially detectable induced GWs with interesting features [32][33][34][35] Due to their phenomenological richness, and potential detectability in future experiments, developing explicit models in fundamental theories such as supergravity and string theory, realising strong non-geodesic trajectories, transient sharp turns and double inflation, opens the path to test these theories at the highest energies through their predictions for the scalar perturbations at short scales and their associated source of GWs.…”

New Horizons for Fundamental Physics with LISA

“…ζ (f ). PBH formation from multi-field inflationary models (Fumagalli et al, 2020a;Palma et al, 2020), and more generally large particle production mechanisms involving a sharp feature, lead to oscillatory power spectra that result in a 10% oscillatory modulation in the peak of the frequency profile of the SGWB (Braglia et al, 2020;Fumagalli et al, 2020b), thus representing a potentially observable characteristic of these models.…”