Partial UV Completion of $P(X)$ from a Curved Field Space

Understand

The $k$-essence theory is a prototypical class of scalar-field models that already gives rich phenomenology and has been a target of extensive studies in cosmology.

• General forms of shift-symmetric $k$-essence are known to suffer from formation of caustics in a planar-symmetric configuration, with the only exceptions of canonical and DBI-/cuscuton-type kinetic terms.
• With this in mind, we seek for multi-field caustic-free completions of a general class of shift-symmetric $k$-essence models in this paper.
• The field space in UV theories is naturally curved, and we introduce the scale of the curvature as the parameter that controls the mass of the heavy field(s) that would be integrated out in the process of EFT reduction.