Beating the Lyth Bound by Parametric Resonance during Inflation

Area of Science:

• Cosmology
• Theoretical Physics
• Gravitational Waves

Background:

• Primordial gravitational waves are crucial for understanding the early universe.
• The Lyth bound suggests a minimum field excursion for detectable gravitational waves during inflation.
• Current models face challenges in detecting these waves with low-scale inflation.

Purpose of the Study:

• To propose a novel mechanism for enhancing primordial gravitational waves.
• To challenge the existing Lyth bound.
• To enable the detection of inflationary tensor modes in low-scale inflation scenarios.

Main Methods:

• Utilizing nonlinear sourcing of resonantly amplified scalar field fluctuations.
• Developing a scale-dependent counterexample to the Lyth bound.
• Simulating the effects on curvature perturbations during inflation.

Main Results:

• A novel mechanism enhancing primordial gravitational waves without affecting curvature perturbations.
• An explicit scale-dependent counterexample to the Lyth bound.
• Demonstrated potential for detectable inflationary tensor modes with sub-Planckian field excursion.

Conclusions:

• The proposed mechanism offers a new pathway for detecting primordial gravitational waves.
• This work opens up possibilities for low-scale inflation models to produce observable gravitational wave signals.
• The mechanism's testability with upcoming cosmic microwave background B-mode observations is confirmed.