# Zwiebach page 178

1. Oct 12, 2007

### ehrenfest

1. The problem statement, all variables and given/known data
Below equation 10.77, Zwiebach claims that the gauge epsilon = i A^+/p^+ makes the vector potential component A^+ vanish.

However, I thought epsilon was supposed to be infinitesimal and a constant, both of which are violated by setting epsilon equal to the expression?

2. Relevant equations

3. The attempt at a solution

2. Oct 12, 2007

### Jimmy Snyder

I thought epsilon was supposed to be infinitesimal and a constant, both of which are violated by setting epsilon equal to the expression?
Actually, just above equation (10.68) on page 177, he refers you back to Section 3.3 where on page 43, just below equation (3.19) he writes that epsilon is an arbitrary function of the coordinates.

3. Oct 12, 2007

### ehrenfest

I see. Thanks.