# Infinite number of conserved charges for the Sine-Gordon Lagrangian

I recently came across a paper of Witten that talks about the S-matrix of the supersymmetric non-linear sigma model. In the beginning part of the paper, he mentions that theories like the non-linear sigma model or the sine-gordon theory have an infinite number of conserved charges which come from locally conserved currents. Also, that the sine-gordon theory which is given by

$${L=\frac{1}{2}\partial_{\mu}\varphi \partial^{\mu}\varphi+\frac{m^2}{\beta^2}cos(\beta \varphi)}$$ supposedly has a conserved charge in every representation of the Lorentz group.

I don't understand how this comes about. It would be great if someone could help me with figuring out how to construct higher spin conserved charges.

This is the paper: https://doi.org/10.1103/PhysRevD.17.2134