# Homework Help: Momentum conservation under a Gauge Parametrization in string theory

1. May 8, 2010

### benbenny

Second attempt here to get an answer, im really lost on this.
Im reading "A first course in String Theory" by Zwiebach and it says that when applying a general $$\tau$$ gauge parametrization in the form of $$n_\mu X^\mu = \lambda \tau$$ we can take the vector $$n_\mu$$ so that for open strings connected to branes (fixed end points) $$n^\mu \mathcal{P}^\tau _\mu$$, is conserved.

But in general momentum is not conserved over the string for dirchlet boundary conditions, without taking into consideration the dynamics of the D-brane, as I understand, so how does applying the general \tau gauge make it so that it is essentially conserved? How can we choose a gauge that will conserve momentum on the string. The string is still going to be connected to a brane after all. Im trying to understand the physical interpretation of this statement.

Thanks,

B
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