Evaluating Cosmic Inflation: New Insights from Bayesian Analysis

Recent research titled "Cosmic Inflation at the Crossroads" evaluates the ability of cosmic inflation theories to explain current observational data, particularly from the Cosmic Microwave Background (CMB) and Baryonic Acoustic Oscillation (BAO). The study, authored by Jerome Martin, Christophe Ringeval, and Vincent Vennin, employs Bayesian model comparison across nearly 300 models of single-field slow-roll inflation.

Key findings include:

• The analysis presents the first Bayesian data evaluation based on third-order slow-roll primordial power spectra.
• The fourth Hubble-flow function, denoted as (\epsilon_4), remains unbounded, while the third function (\epsilon_{3}) is found to be compatible with slow-roll predictions, lying within the range of [-0.4, 0.5] at a two-sigma confidence level.
• There is a noted residual excess of (B)-modes in the BICEP/Keck data, suggesting the presence of non-vanishing primordial tensor modes, with a logarithmic value of (\log(\epsilon_{1}) > -3.9) at a 68% confidence level.
• The study computes Bayesian evidence and dimensionality for 283 models, revealing that over 40% of the scenarios are strongly disfavored, indicating that cosmological data is effectively constraining the number of viable models.
• The average information gain on the reheating parameter (R_{reh}) is reported as 1.3 ± 0.18 bits, marking a significant improvement compared to earlier Planck data releases.

This research underscores the importance of refining inflationary models to align with observational data, particularly regarding the reheating phase of the universe. The implications of these findings could influence future theoretical developments in cosmology and our understanding of the early universe.

For further details, the full paper can be accessed at arXiv:2404.10647.