The treatment of gauge bosons assumes they are massless, which is accurate when partonic collisions occur at a scale much larger than the vector masses. However, for processes with relevant contributions at low τ, mass effects must be considered. The primary mechanism through which mass affects calculations is via the propagator. In the massless case, the virtual boson has a distinct virtuality compared to the propagator of a massive vector boson, altering the resulting splitting function and impacting the longitudinal PDF calculation.
In the massless case, the emitted vector boson has one type of virtuality, while for the massive vector boson, the off-shell propagator possesses a modified virtuality.
The dominant mass effect in calculations stems from the propagator, which can significantly impact the computation of the longitudinal parton distribution function (PDF) at lower scales.
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