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. In some cases the scalar power spectrum can significantly exceed the ns=5 limit in single-field inflation and grow as fast as ns=9.1. 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 construct 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.

Scalar Induced Gravitational Waves Review

“…These are for example, the low frequency tail [74,78,79], the UV tail [80,81] and the log-normal peak in the primordial spectrum [82]. Furthermore, the primordial spectrum may also present oscillatory features which are captured into the induced GW spectrum [83][84][85][86][87]. On top of that, large primordial non-Gaussianities may have a non-trivial impact on the induced GW spectrum [81,[88][89][90][91][92][93].…”

“…If the frequency is linear in k, the oscillations resulted from sharp dynamics during inflation. For example, a step in the potential in single field inflation [260][261][262][263][264][265][266][267] or a sharp turn in field space [84,86,254,255,[268][269][270]. This case is also known as a sharp feature.…”

“…The main difficulty is to derive analytical approximations to the induced GW spectrum. In this respect, Fumagalli, Renaux-Petel and Witkowski [84,87] and also Braglia, Chen and Hazra [86] did a detailed numerical analysis of the induced GW spectrum and derived motivated semi-analytical templates. Perhaps the most interesting case is when the oscillations in the primordial spectrum are O(1).…”

CMB μT cross correlations as a probe of primordial black hole scenarios

“…Finally, extending the ideas we presented in this work to the multiple field case appear as another interesting venue to be explored, in particular to make a comparison with single-field results. Then a pronounced dip feature in the power spectrum might be missing [61][62][63] (but see [64]). Similarly, in models that utilize axion gauge-field dynamics during inflation to enhance the curvature perturbation, such a future is not present (See e.g.…”

Double peaks of gravitational wave spectrum induced from inflection point inflation

“…Thus it is different from the models with only one peak, which can only be detected in one frequency range. So the double peak models can be distinguished from other single peak models [16][17][18][19][98][99][100].…”