# Using Noether's Theorem find a continuity equation for KG

## Homework Statement

Consider the Klein-Gordon equation $(\partial_\mu \partial^{\mu}+m^2)\varphi(x)=0$. Using Noether's theorem, find a continuity equation of the form $\partial_\mu j^{\mu}=0$.

## Homework Equations

$(\partial_\mu \partial^{\mu}+m^2)\varphi(x)=0$

## The Attempt at a Solution

I really haven't been able to solve this problem because I don't understand why Noether's Theorem would be useful in this case. Any help would be greatly appreciated.

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Twigg
Gold Member
The Klein-Gordon equation, like any quantum wave equation, is invariant under a complex phase shift of the wave function. You can show that this is a 1-parameter continuous symmetry.

If I show that, does Noether's theorem immediately guarantee such a continuity equation?

Twigg
Gold Member
The conserved current you're looking for is the one predicted by Noether's theorem given that the Lagrangian is invariant under a phase shift of the wavefunction.