Function visibility_j_mu

pub fn visibility_j_mu(z: f64) -> f64

μ-distortion branching ratio: fraction of energy going into μ-type distortion.

J_μ(z) = 1 − exp(−((1+z)/5.8×10⁴)^{1.88})

Chluba (2013), arXiv:1304.6120, Eq. 5. Approaches 0 for z ≪ 5.8×10⁴ (no μ) and 1 for z ≫ 5.8×10⁴ (pure μ). The transition scale is physically motivated by y_γ(z) ≈ 1, but the precise value and exponent are fit parameters.