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• Leading log approximation (LLA)

• different schemes exist

• to take into account

• subleading corrections

• (MLLA, NLLA,...)

• Moment, energy, color,¼, conservation imposed at each branching

• Stop the process when the mass of a final parton < mmin

• Many MC algorithms: different interpretations of t, Q2 and z

• e. g. z can be applied to

• E, E+ pz , E + ½p½

• This choice is not Lorentz-invariant

• Need to choose a gauge before evaluating the prob. of branching

• Branching rules do not depend on the nature of the hard interaction

• Coherence effects: Destructive interference in the emission prob. of

• a ``soft'' gluon

• Angular ordering: Decreasing opening angles

• This effect is important at high orders of Perturbation Theory