Consider a Lagrangian L(ϕ,Aμ) with ϕ being some scalar field and Aμ some dynamical U(1) gauge field that minimally couples to ϕ. Under a global U(1) symmetry the field ϕ transforms as δϕ=iϵqϕ.
In a Higgs phase we have that |ϕ(x,t)|≠0. In particular we can fix a gauge so that |ϕ(x,t)|=Φ(x,t) is real. Then we consider small fluctuations Φ(x,t)=Φ0+δΦ and integrate them out to obtain an effective theory in which the gauge field A is massive.
My question: It seems to me as though the requirement that ϕ is charged enters when integrating out the small flunctuations, because if ϕ were neutral (i.e. q=0) there wouldn't be any flucutations that one can integrate out and hence one wouldn't obtain a massive term for the gauge field in the Lagrangian. Is this correct? If not where does the requirement for ϕ to be charged enter in the argument? And: Does the requirement for the matter field to be charged with respect to the corresponding gauge field carry over without difficulties to the non-abelian case?
I am looking forward to your responses!
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