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Particle production during inflation and gravitational waves detectable by ground-based interferometers

Jessica L. Cook, Lorenzo Sorbo

TL;DR

This work investigates whether particle production during inflation can imprint observable features in the gravitational-wave background at ground-based detector scales. It shows that nonperturbative production of scalar quanta yields only tiny corrections to the standard inflationary tensor spectrum, whereas vector production behaves similarly but with a modest doubling of the effect. A key result is that axion-like inflaton couplings to gauge fields can generate a strongly chiral GW background with potentially detectable amplitudes for Advanced LIGO/Virgo, while remaining consistent with CMB non-Gaussianity constraints; LISA, by contrast, is unlikely to detect these signals. The findings highlight distinctive, testable signatures—scale-dependent bumps, parity violation, and potential multi-messenger correlations—that connect early-Universe particle production to upcoming GW observations. The work maps out viable parameter regions where ground-based detectors could probe inflationary physics beyond the standard quasi–de Sitter tensor background.

Abstract

Inflation typically predicts a quasi scale-invariant spectrum of gravitational waves. In models of slow-roll inflation, the amplitude of such a background is too small to allow direct detection without a dedicated space-based experiment such as the proposed BBO or DECIGO. In this paper we note that particle production during inflation can generate a feature in the spectrum of primordial gravitational waves. We discuss the possibility that such a feature might be detected by ground-based laser interferometers such as Advanced LIGO and Advanced Virgo, which will become operational in the next few years. We also discuss the prospects of detection by a space interferometer like LISA. We first study gravitational waves induced by nonperturbative, explosive particle production during inflation: while explosive production of scalar quanta does not generate a significant bump in the primordial tensor spectrum, production of vectors can. We also show that chiral gravitational waves produced by electromagnetic fields amplified by an axion-like inflaton could be detectable by Advanced LIGO.

Particle production during inflation and gravitational waves detectable by ground-based interferometers

TL;DR

This work investigates whether particle production during inflation can imprint observable features in the gravitational-wave background at ground-based detector scales. It shows that nonperturbative production of scalar quanta yields only tiny corrections to the standard inflationary tensor spectrum, whereas vector production behaves similarly but with a modest doubling of the effect. A key result is that axion-like inflaton couplings to gauge fields can generate a strongly chiral GW background with potentially detectable amplitudes for Advanced LIGO/Virgo, while remaining consistent with CMB non-Gaussianity constraints; LISA, by contrast, is unlikely to detect these signals. The findings highlight distinctive, testable signatures—scale-dependent bumps, parity violation, and potential multi-messenger correlations—that connect early-Universe particle production to upcoming GW observations. The work maps out viable parameter regions where ground-based detectors could probe inflationary physics beyond the standard quasi–de Sitter tensor background.

Abstract

Inflation typically predicts a quasi scale-invariant spectrum of gravitational waves. In models of slow-roll inflation, the amplitude of such a background is too small to allow direct detection without a dedicated space-based experiment such as the proposed BBO or DECIGO. In this paper we note that particle production during inflation can generate a feature in the spectrum of primordial gravitational waves. We discuss the possibility that such a feature might be detected by ground-based laser interferometers such as Advanced LIGO and Advanced Virgo, which will become operational in the next few years. We also discuss the prospects of detection by a space interferometer like LISA. We first study gravitational waves induced by nonperturbative, explosive particle production during inflation: while explosive production of scalar quanta does not generate a significant bump in the primordial tensor spectrum, production of vectors can. We also show that chiral gravitational waves produced by electromagnetic fields amplified by an axion-like inflaton could be detectable by Advanced LIGO.

Paper Structure

This paper contains 12 sections, 48 equations, 2 figures.

Table of Contents

  1. Introduction.
  2. Gravitational waves from sudden production of scalars during inflation.
  3. Tensor production during the adiabatic epoch.
  4. Evaluating $\beta$.
  5. The two point function.
  6. Tensor production during the nonadiabatic epoch.
  7. An application: tensor modes in trapped inflation.
  8. Production via vectors.
  9. Gravitational waves produced during axion inflation via helical photons.
  10. The amplitude of the tensor modes.
  11. Gravitational waves from natural chaotic inflation observable by Advanced LIGO.
  12. Constraints and detectability.

Figures (2)

  • Figure 1: Amplitude of gravitational waves as a function of frequency in the case ${\cal N}_c=55$, $\xi_C=2.1$. The star denotes the projected sensitivity of Advanced LIGO.
  • Figure 2: Values of $\xi_C$ corresponding to detectable tensor modes by Advanced LIGO, as a function of the total number of efoldings of inflation from the time COBE scales left the horizon. The shaded area on the top left corner corresponds to the region where backreaction cannot be neglected and our analysis cannot be trusted. The shaded area on the top part of the plot corresponds to the region where LSS nongaussianities are too large to be consistent with observations. The shaded area at the bottom corresponds to the region where the amplitude of tensor modes is below the Advanced LIGO detection threshold. Finally, the thinner dotted line corresponds to the lower limit of portion of parameter space accessible to an instrument such as the Einstein Telescope.