feynlag.pheno.particles

Physical (post-EWSB) Dirac particles for the decay calculator.

A Dirac fermion is not a declarable input field in feynlag — the SM is chiral, so b_L (an SU(2) doublet, $Y=+1/6$) and b_R (a singlet, $Y=-1/3$) carry different reps and no 4-component field can hold both invariantly; DiracFermion raises on construction for exactly this reason. After electroweak symmetry breaking, however, the physical b is one Dirac particle built from those two Weyl legs, and a decay calculation needs to treat it as one.

DiracParticle is that post-EWSB view. It bundles the two Weyl leg bases, the particle/antiparticle symbols, the mass, and the colour multiplicity $N_c$ into a single object, so the three things the calculator otherwise tracks in separate, separately-keyed dicts (particle_map/masses/color_factors) travel together and cannot fall out of sync. The bar legs are derived automatically from the bar_partner() registry — they are not passed in.

Functions

expand_particles(particles)

Merge a list of DiracParticle into the calculator's dicts.

Classes

DiracParticle(particle, left, right, mass[, ...])	One physical Dirac fermion, assembled from its two Weyl legs.
ExternalState(name, mass, spin[, color])	One external particle of a 2→2 scattering process.