Particle production during inflation and gravitational waves detectable by ground-based interferometers (1109.0022v3)

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.

• The paper demonstrates that particle production during inflation can generate chiral gravitational waves, providing an alternative observational signature.
• It employs a robust mathematical framework to model gravitational wave amplification through axion-like inflaton coupling using gauge-invariant Lagrangians.
• The study identifies a finite parameter space where axion-induced tensor modes may be measurable by detectors such as Advanced LIGO and Advanced Virgo.

Particle Production During Inflation and Its Impact on Gravitational Waves: A Synopsis

This paper investigates the role of particle production during the inflationary phase of the universe on the spectrum of gravitational waves. Predominantly, inflation is predicted to yield a quasi scale-invariant spectrum of gravitational waves, with slow-roll inflation models suggesting a background too subtle for detection by any instrument other than those space-based, such as the proposed Big Bang Observer (BBO) or DECIGO. This research explores the alternative pathway of particle production during inflation potentially generating detectable features within the primordial gravitational wave spectrum that could be accessible to ground-based interferometers like Advanced LIGO and Advanced Virgo.

Key Findings

1. Gravitational Waves from Scalar and Vector Particle Production:
   • Nonperturbative, explosive particle production, whether through scalar or vector particles during inflation, does not significantly impact the primordial tensor spectrum. The amplitude of gravitational waves induced by scalars or vectors remains notably small when following particle production events.
2. Chiral Gravitational Waves:
   • A unique scenario involves chiral gravitational waves emanating from electromagnetic fields amplified by an axion-like inflaton. These waves may present detectable signals within the advanced capabilities of LIGO and Virgo through their sensitivity at certain scales, particularly when considering a rolling pseudoscalar inflaton field.
3. Mathematical Framework:
   • The work explores the mathematical modeling of how perturbations in the Friedmann-Robertson-Walker Universe can amplify gravitational waves, applying a range of gauge-invariant Lagrangians and operator algebra. The detailed computations weigh the amplitude of gravitational waves as sourced by particles against the inflationary background.
4. Parametric Constraints and Observational Opportunities:
   • Tensor modes produced through axion-like inflation are explored, revealing that while constraints exist—particularly from non-gaussianities—there is a finite parameter space offering detectable signatures for advanced interferometric detectors. This provides not just a potential empirical verification of inflationary dynamics but also a test for axion-inflation mechanisms.

Implications for Research and Observation

This research underscores the importance of alternative inflationary scenarios, suggesting that particle production can leave detectable imprints on gravitational wave backgrounds. It beckons ground-based detector enhancements aiming to bridge the sensitivity gap with space mission capabilities. It further refines our theoretical understanding of inflation, adding dimensions that could manifest in terms of observable gravitational wave signatures.

Future Prospects and Developments

The paper's implications are twofold. Firstly, on the theoretical front, it invites refinements in inflationary models, particularly those integrating complex couplings like axion-field interactions. Secondly, it affirms the need for advancing interferometer precision to fully harness the potential of these models. With technology catching up, these explorations could substantiate the predicted textures of the early universe, unraveling inflation's nuances and possibly redefining our comprehension of cosmic genesis.

While current capabilities might limit immediate detection, the trajectory of these investigative pathways suggests inevitable breakthroughs as observational technologies evolve. The work harmonizes theoretical advances with the technical roadmap for upcoming observational missions.