# Current of Complex scalar field

1. Nov 1, 2014

### PhyAmateur

I was trying to derive current for Complex Scalar Field and I ran into the following:

So we know that the Lagrangian is:

$$L = (\partial_\mu \phi)(\partial^\mu \phi^*) - m^2 \phi^* \phi$$
The Lagrangian is invariant under the transformation:
$$\phi \rightarrow e^{-i\Lambda} \phi$$ and $$\phi^* \rightarrow e^{i\Lambda} \phi^*$$

Infinitesimal Transformation:
$$\delta \phi = -i\Lambda \phi$$ and $$\delta \phi^* = i\Lambda \phi^*$$

So, applying Noether's Theorem and using the Lagrangian above,

I get

$$J^{\mu} = \frac{\partial L}{\partial (\partial_\mu \phi} (-i\Lambda \phi) + \frac{\partial L}{\partial (\partial_\mu \phi^*} (i\Lambda \phi^*) =$$
$$\partial ^\mu \phi^* (-i\Lambda \phi) + \partial _\mu \phi (i\Lambda \phi) =$$
$$i(\Lambda \phi^* \partial _\mu \phi - \Lambda \phi \partial ^\mu \phi^*)$$

but as I googled it there is no $$\Lambda$$ in the final equation of the current. What did I do wrong?

2. Nov 1, 2014

### vanhees71

You did nothing wrong. The current is simply defined as the expression proportional to the infinitesimal group parameter.

3. Nov 1, 2014

### PhyAmateur

Ah phew! Thanks!!