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Дата изменения: Wed Aug 9 20:40:47 2000
Дата индексирования: Mon Oct 1 22:52:10 2012
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Unitary gauge

The unitary gauge may be considered as a limit of $\xi \rightarrow \infty$ of the following gauge fixing Lagrangian:

$$-\frac{1}{2} (\partial^\mu A_\mu)^2 -\frac{M_Z^2}{2\xi} (Z_f)^2 -\frac{M_W^2}{\xi} (W^+_f W^-_f)\;.$$

In this limit one gets $Z_f=0$ and $W_f=0$, what decreases a number of vertices. Under these constraints the Faddeev-Popov Lagrangian (3) takes the form:

$$\begin{eqnarray*} -A_{\bar{c}} \partial^\mu (-i\,g_2 \sin{\Theta_w}(W^+_\mu W^-... ...^+_c -W^+_{\bar{c}} M_W ( M_W + \frac{g_2}{2} H ) W^-_c \;. && \end{eqnarray*}$$

Integration over $A_c$ and $A_{\bar{c}}$ can be performed explicitly and gives a result which does not depend on other fields. So $A_c$ and $A_{\bar{c}}$ ghosts may be omitted.

In the unitary gauge only physical polarization states of the incoming and outgoing $W^\pm$ and $Z$ bosons are considered. So $W^\pm_c$ and $Z_c$ are not needed in the external lines of Feynman diagrams and may be omitted also in tree level calculations. Consequently, in the unitary gauge all ghost and Goldstone fields may be omitted.