Large tensor-to-scalar ratio in small-field inflation

Area of Science:

• Cosmology
• Particle Physics
• General Relativity

Background:

• Density perturbations are crucial for structure formation.
• Standard inflationary cosmology predicts specific relationships between perturbation properties and the inflaton field's behavior.
• The Lyth bound relates the inflaton field excursion to the amplitude of primordial gravitational waves.

Purpose of the Study:

• To investigate the impact of additional light degrees of freedom on density perturbations during inflation.
• To explore mechanisms for generating large gravitational waves from small-field inflation.
• To generalize the Lyth bound in the presence of light scalar fields.

Main Methods:

• Theoretical analysis of inflaton fluctuations in the presence of light scalar fields.
• Investigating the dynamics of density perturbations during and after inflation.
• Deriving a generalized Lyth bound and examining consistency relations.

Main Results:

• Density perturbations from inflaton can be suppressed by light fields.
• Inflaton fluctuations modulate light field dynamics, creating post-inflationary perturbations that can cancel primordial ones.
• Production of large gravitational waves from small-field inflation becomes possible.
• A generalized Lyth bound is derived, considering the total field space.
• Violation of the standard consistency relation r ≤ -8n(T) is demonstrated.

Conclusions:

• The presence of light degrees of freedom offers a novel mechanism to reconcile large gravitational wave production with small-field inflation.
• The generalized Lyth bound provides a more comprehensive constraint on inflationary models.
• This work opens new avenues for testing inflationary models through gravitational wave observations.