Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Energy and Angular Momentum of a Relativistic String

  1. May 26, 2010 #1
    The problem is 2.1.b in Becker, Becker, and Schwarz. I can't figure out what I'm doing wrong... any help would be appreciated, I'm probably missing something dumb.

    1. The problem statement, all variables and given/known data

    For [tex]X^0=B\tau[/tex], [tex]X^1=B\cos \tau\cos\sigma[/tex], [tex]X^2=B\sin\tau\cos\sigma[/tex], [tex]X^i=0[/tex] for i>2, compute the energy and angular momentum and show that [tex]E^2|J|^{-1}=2\pi T[/tex].

    2. Relevant equations

    [tex]J^{\mu\nu}=T\int_0^\pi d\sigma\, {X}^\mu\dot{X}^\nu-{X}^\nu\dot{X}^\mu[/tex]

    3. The attempt at a solution

    [tex]J^{12}=B^2 T\int_0^\pi d\sigma\,\cos^2\tau\cos^2\sigma+\sin^2\tau\cos^2\sigma=\frac{\pi}{2}B^2T[/tex]

    which is off by a factor of [tex]\pi^2[/tex]. Any ideas?

  2. jcsd
  3. May 26, 2010 #2
    I'm actually fairly convinced that this is a typo in the book, so don't spend as much time on it as I did...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook