Oscillations in the stochastic gravitational wave background from sharp features and particle production during inflation

Abstract

We identify a characteristic pattern in the scalar-induced stochastic gravitational wave background from particle production during inflation. If particle production is sufficiently efficient, the scalar power spectrum exhibits O(1) oscillations periodic in k, characteristic of a sharp feature, with an exponentially enhanced envelope. We systematically study the properties of the induced spectrum of gravitational waves sourced after inflation and find that this inherits the periodic structure in k, resulting in a peak in the gravitational wave energy density spectrum with O(10%) modulations. The frequency of the oscillation in the scalar power spectrum is determined by the scale of the feature during inflation and in turn sets the frequency of modulations in the gravitational wave signal. We present an explicit realisation of this phenomenon in the framework of multifield inflation, in the form of a strong sharp turn in the inflationary trajectory. The resulting stochastic background is potentially detectable in future gravitational wave observatories, and considerations of backreaction and perturbativity can be used to constrain the parameter space from the theoretical side. Our work motivates more extensive research linking primordial features to observable properties of the stochastic background of gravitational waves, and dedicated development in data analysis for their detection.

Reheating in Runaway Inflation Models via the Evaporation of Mini Primordial Black Holes

“…In single field models, the special feature that amplifies the power spectrum can be either an inflection point [104][105][106] or a step-like transition in the inflationary plateau [107,108] 4 . The presence of step-like, or generally sharp, features in the inflation potential results in amplification and, additionally, in oscillatory patterns in the curvature power spectrum [108,111]. The potential might feature more than one steps, so that the relevant enhancement in the power spectrum becomes strong enough.…”

Inflation with strongly non-geodesic motion: theoretical motivations and observational imprints

“…On smaller scales, a transient phase of strongly non-geodesic motion provides a natural mechanism to boost the amplitude of primordial fluctuations and hence generate primordial black holes [33,34]. Independently, if this phase is short enough, the primordial power spectrum exhibits order one oscillations characteristic of sharp features, that are transferred to visible oscillations in the frequency profile of the scalar-induced stochastic gravitational wave background [35].…”

Constant-rate inflation: primordial black holes from conformal weight transitions

“…That enhanced primordial density fluctuations from inflationary models with large curvature perturbations on small scales is the mainstream scenario for PBH formation. PBHs from models of inflation, with targeting masses spanning in the range of 10 −17 -10 9 M , can be realized either in the single-field [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] or multi-field [22][23][24][25][26][27][28][29][30][31][32][33][34][35] framework.…”

“…35) and(2.36) are scale-dependent functions of τ * = k/k * . Since δ 3 > 0 implies an enhancement of 3 , we find that end = (η end ) = * x −2δ 2…”

“…A growth of the power spectrum faster than k 4 scaling (namely with a spectral index ns − 1 > 4) can be realized in the multi-field inflationary models[30,35,48] or with an intermediate δ = −1/2 phase between the primary slow-roll and the ultra-slow-roll phases in the single-field inflation[47].…”