Equation Icon  ∫ ′ μναβ ′ π-- 2 μνα β -d4p-----eip(x−x)-θ(− p2)--- 𝒢 (x,x ) = 45 G ℱx (2π)4|| 2 &tidle; 2 ||2, (144 ) |1 + 4π Gp H (p; ¯μ )|