Small field models with gravitational wave signature supported by CMB data

Area of Science:

• Cosmology
• Theoretical Physics

Background:

• Cosmic Microwave Background (CMB) power spectrum analysis is crucial for understanding early universe cosmology.
• Single-field inflation models are key theoretical frameworks, but their predictions require precise validation.

Purpose of the Study:

• To investigate the scale dependence of the CMB power spectrum in specific single-field inflation models.
• To accurately calculate cosmological parameters like scalar spectral index (ns), its running (nrun), and the tensor-to-scalar ratio (r).

Main Methods:

• Utilizing degree 5 polynomial inflaton potentials for precise power spectrum calculations.
• Extracting key cosmological parameters (ns, nrun, r) from the calculated power spectrum.
• Scanning potential parameter values to align with observational constraints.

Main Results:

• Precisely calculated ns and nrun values deviate significantly from standard analytic predictions, even for small tensor-to-scalar ratios (r = 0.001) when nrun is non-vanishing.
• The 5-parameter model class successfully reproduces allowed ns and nrun values for r up to 0.001.
• Identified probable reasons for deviations from standard analytic treatments.

Conclusions:

• Previously used analytical approximations (Stewart-Lyth term) are inaccurate for these models.
• The study validates small-field inflation models by demonstrating they can yield appreciable r while matching CMB observables.
• Refutes prior models based on inaccurate assumptions regarding inflationary potentials.