# Zwiebach chapter 9-12

1. Nov 2, 2007

### ehrenfest

1. The problem statement, all variables and given/known data
I am having trouble keeping track of how the dynamical variables alpha and a keep changing through these chapters. Can people help me construct a "lifeline" of these variables here?
Let's start with chapter 9.

Zwiebach first uses the four-vector $$a^{\mu}_n$$ and its complex conjugate in equation 9.49. In this context they are just being used to replace some constants of integration in the equation of motion for the string.

Then on page 159, Zwiebach defines the four-vector $$\alpha^{\mu}_{n}$$ and $$\alpha^{\mu}_{-n}$$, seemingly only because it allows him to sum over all n in equation 9.57.

That is all that happens in chapter 9. Good so far?

2. Relevant equations

3. The attempt at a solution

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