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Дата изменения: Wed Aug 9 20:40:48 2000 Дата индексирования: Mon Oct 1 22:53:07 2012 Кодировка: |
CompHEP uses the squared diagram technique with summation over
polarizations. Basically one squared diagram corresponds to the
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If we follow an idea of the previous section and take into account
the ghost incoming particles, a number of squared diagrams
increases significantly. For example, in the simplest case of
process one physical squared diagram
(the diagram (a) on the figure below)
is accompanied by three ghost diagrams (b,c,d) with
the similar topology.
e1 n1 ! n1 e1 e1 n1 ! n1 e1
==>==@==>====!==>===@==>== ==>==@==>====!==>===@==>=
| ! | | ! |
W+| ! W+| W+| ! W+|
| ! | | ! |
-----@--<----!--<---@----- -----@--<----!--<---@-----
A W- W- A A W-.f W-.f A
a) b)
e1 n1 ! n1 e1 e1 n1 ! n1 e1
==>==@==>====!==>===@==>== ==>==@==>====!==>===@==>==
| ! | | ! |
W+| ! W+| W+| ! W+|
| ! | | ! |
--<--@--<----!--<---@--<-- -->--@--<----!--<---@-->--
A.C W-.C W-.C A.C A.c W-.c W-.c A.c
c) d)
Let us note that all these diagrams of have the same
denominators. The numerators of these diagrams are
polynomials of scalar products of momenta. The powers of these polynomials
are the same for all diagrams, so one might expect that the symbolic
sum of all these diagrams has approximately the same size as one term.
Following this note CompHEP calculates the symbolic sum of all sets of diagrams which become identical after replacing the ghost particles by their parents.