Re: How real are the "Virtual" partticles?

Igor Khavkine wrote:

>
>>If you want to convince me, please show me a formulation of QED where
>>Feynman diagrams do not have 3-legged vertices.
>
>
> I've learned not to seek anything so ambitious as changing your
> convictions. But it seems relevant to point out a therory reformulated
> in this was is Fermi's theory of beta decay. It is an effective
> approximation of the theory of weak interactions. Weak theory contains
> trilinear terms like in QED, but in Fermi's theory gauge bosons are
> eliminated and only 4-fermion terms remain.
>
> The step from weak theory to Fermi's theory is handled through
> effective field theory. Weinberg talks about that in his second volume
> on QFT. A similar technique is applied to QED but to eliminated the
> elctrons instead of photons. The result is the Heisenberg-Euler
> Lagrangian describing non-linear effects in the electromagnetic field.


You are right that Fermi's theory and Heisenberg-Euler theory have
4-legged diagrams. But at this point the similarities with the dressed
particle approach end. Both these theories are approximations
in which some degrees of freedom of the general approach
(gauge bosons in the case of Fermi's theory; electrons in the
case of the Heisenberg-Euler theory) are "integrated out".

The dressed particle approach does not eliminate physical degrees of
freedom. All physical particles remain present in the theory,
and the S-matrix is exactly the same as in the renormalized QED.
The "only" significant difference between RQD and renormalized QED
is that the Hamiltonian of RQD does not contain trilinear and
other "bad" terms. S-matrix calculations in RQD do not require
regularization and renormalization.


Eugene Stefanovich.

.

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