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{\bf Homework 4}
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1) By using the Infinite Momentum Frame (IMF) technique discussed in class, 
demonstrate that the matrix element modulus squared for
radiation of a gluon by a quark is:

\[ \mid M_{l \rightarrow k l^\prime} \mid^2 = 
\frac{1}{2} g^2 C_F 4 \left[\frac{l_\perp^2}{z} + 
\frac{2 l_\perp^2}{l_\perp^2 + (1-z)^2} \right] \] 

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2) What approximation is needed in the equation above in order to
obtain the {\em splitting function}:

\[ P_{qq} = C_F \frac{1+z^2}{1-z} \]

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3) Draw all the (distinct) radiation processes that can occur at leading order 
in the DIS reaction, besides the gluon radiation discussed in class.  

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