Evidence for bouncing evolution before inflation after BICEP2.

Area of Science:

• Cosmology
• Astrophysics
• Particle Physics

Background:

• The BICEP2 experiment detected primordial cosmic microwave background (CMB) B modes, indicating a tensor-to-scalar ratio (r) of 0.20.
• This BICEP2 result conflicts with the Planck satellite's upper limit of r < 0.11, posing a challenge for standard inflation models.

Purpose of the Study:

• To investigate an inflationary cosmology model that includes a preceding nonsingular bounce.
• To explore how this bounce mechanism can resolve discrepancies between BICEP2 and Planck observations.
• To analyze the observable signatures on primordial perturbations predicted by the bounce inflation scenario.

Main Methods:

• A global analysis was performed using combined data from Planck+WP and BICEP2.
• The study focused on a modified inflationary model featuring a step feature in primordial scalar and tensor power spectra.
• Constraints were derived for key model parameters: the jump scale and the ratio of bounce to inflation spectrum amplitude.

Main Results:

• The bounce inflation model successfully reconciles the seemingly contradictory CMB data from BICEP2 and Planck.
• Key parameters were constrained: jump scale log(10)(k(B)/Mpc^-1) = -2.4 ± 0.2 and spectrum amplitude ratio r(B) = 0.71 ± 0.09.
• The model's predicted cancellation of tensor excess power in the CMB temperature power spectrum was highlighted.

Conclusions:

• The bounce inflation scenario offers a better explanation for combined Planck and BICEP2 observations compared to the standard Lambda-CDM model.
• This model provides a compelling alternative for understanding early universe cosmology.
• Future CMB polarization measurements are crucial for verifying the predictions of the bounce inflation model.