# A Extra terms in the Action in Zee chapter 1.3?

#### looseleaf

Hi, could someone please explain where the tau and sigma terms come from in this expression:

I see the kinetic energy and quadratic "mattress" potential terms, but the tau and sigma kinda come out of nowhere. Where are they from?

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#### Hans de Vries

Gold Member
These are just arbitrary coupling constants. They originate from the self interaction energy V of the field $\varphi$ with itself in equation (2). It is a way of expressing the self interaction part of the arbitrary function V in a series of $\varphi$.

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#### looseleaf

These are just arbitrary coupling constants. They originate from the self interaction energy V of the field $\varphi$ with itself in equation (2). It is a way of expressing the self interaction part of the arbitrary function V in a series of $\varphi$.
Thanks that makes sense.

$e^{i P . x}\alpha(p)e^{-i P . x} = e^{-i p . x}\alpha(p)$