The diagonal terms are E ph (θ) (red parabolic curves in Figure ) and E M (cyan straight-line in Figure 4b-d), and the coupling term ℏ √ N g c (θ) causes the "band bending" when the matter and photon dispersion branches intercept. Note that g c (θ) picks up a θ dependence from the cavity dispersion relation of ω k (Eq. 87).