New Insights into Aligned Axion Inflation Models

Recent research by Federico Greco and Marco Peloso, titled "Analytic results in aligned axion inflation," presents significant findings in the field of cosmology. The paper, available on arXiv, discusses a model of aligned axion inflation, which addresses limitations of the original axion natural inflation model that produced a tensor-to-scalar ratio exceeding experimental limits.

The authors explain that aligned axion inflation allows for inflationary trajectories that begin near a saddle point of a two-field potential. These trajectories terminate due to the instability of the orthogonal direction. The solutions provided in the paper are consistent with current experimental constraints, and the authors suggest that a range of parameters will be examined in upcoming cosmic microwave background (CMB) experiments.

One of the key contributions of this research is the provision of analytic solutions for these trajectories, along with compact expressions for the associated phenomenology. Notably, the inflationary trajectory's extension is described as sub-Planckian for parameters leading to the observed scalar spectral tilt. However, the research also identifies that one eigenvalue of the axion kinetic matrix is trans-Planckian.

Furthermore, the authors discuss the post-inflationary evolution following the instability, indicating that in some scenarios, the fields may reach a second inflationary valley connected to a minimum. This suggests that multiple stages of inflation could be a common occurrence in multi-field inflationary models that start near critical points.

The findings have implications for future research and experiments, particularly in understanding the dynamics of inflation and the potential for multiple inflationary phases in the universe's early development. The paper can be cited as Greco, F., & Peloso, M. (2024). Analytic results in aligned axion inflation. arXiv:2409.01126.