feynlag.pheno.kinematics.TwoBodyKinematics

class feynlag.pheno.kinematics.TwoBodyKinematics(M, m1, m2, name1='p1', name2='p2')

On-shell kinematics of parent(P) → 1(p₁) + 2(p₂).

Holds the momentum tensor heads the trace engine contracts over, and the on-shell dot products they reduce to:

p₁·p₁ = m₁²,  p₂·p₂ = m₂²,  p₁·p₂ = (M² − m₁² − m₂²)/2

the last from M² = (p₁+p₂)² = m₁² + m₂² + 2 p₁·p₂.

Parameters:

• M (Expr)

• m1 (Expr)

• m2 (Expr)

• name1 (str)

• name2 (str)

__init__(M, m1, m2, name1='p1', name2='p2')

Parameters:

• M (Expr)

• m1 (Expr)

• m2 (Expr)

• name1 (str)

• name2 (str)

Return type:

None

Methods

__init__(M, m1, m2[, name1, name2])
allowed()	M ≥ m1 + m2 (None if undecidable symbolically).
dot(head_a, head_b)	p_a·p_b for two momentum heads.
phase_space()	The √λ/(16πM³) factor for this configuration.

Attributes

beta	β = √λ/M² — the two-body velocity factor.
name1
name2
p1
p2
M
m1
m2