Equation of State and Duration to Radiation Domination after Inflation

Area of Science:

• Cosmology
• Particle Physics

Background:

• Cosmic inflation is a key theory explaining the early universe's rapid expansion.
• The equation of state describes the universe's energy density and pressure after inflation, crucial for understanding its evolution.
• Inflationary models often involve a scalar field (inflaton) whose potential dictates the universe's behavior.

Purpose of the Study:

• To calculate the equation of state after inflation.
• To establish an upper bound on the duration before radiation domination.
• To analyze the impact of inflaton field dynamics on post-inflationary evolution.

Main Methods:

• Incorporating nonlinear dynamics of the fragmented inflaton field.
• Analyzing a broad class of single-field inflationary models with specific potential shapes (V(ϕ)∝|ϕ|^{2n}).
• Utilizing linear instability analysis, scaling arguments, and 3+1-dimensional lattice simulations.

Main Results:

• The equation of state parameter (w) approaches 0 for n=1 and 1/3 for n≳1.
• The duration to radiation domination depends significantly on the potential's flattening scale (M) relative to the Planck mass (m_{Pl}).
• A negligible duration to radiation domination is found when M ≪ m_{Pl}.

Conclusions:

• The upper bound on postinflationary duration reduces uncertainty in inflationary observables.
• Results hold even with perturbative decay into additional light fields.
• The study provides a more refined understanding of the universe's evolution immediately following inflation.