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

Misner-Thorne-Wheeler, p.92, Box 4.1, typo?

  1. Oct 26, 2009 #1
    In Misner-Thorne-Wheeler Gravitation, Chapter 4, Page 92, Box 4.1, at section 4, there is a formula for the contraction of a p-form and a p-vector. Now, it states that the contraction of a p-form basis with a p-vector basis gives the antisymmetrizer symbol, [tex]\left\langle {\omega ^{i_1 } \wedge \ldots \wedge \omega ^{i_p } ,e_{j_1 } \wedge \ldots \wedge e_{j_p } } \right\rangle = \delta ^{i_1 \ldots i_p } _{j_1 \ldots j_p } [/tex] and there is a reference to exercises 3.13 and 4.12. I tried this part many many times and I always find the result to be p! times the antisymmetrizer. I also compared it for the case p=2 using the definition of the symbol from exercise 3.13, still the same result, I get an overall 2. Can anybody please explain what am I doing wrong here?
  2. jcsd
  3. Oct 26, 2009 #2
    No typo. The symbol [tex]\delta^{ij}_{kl}\equiv \delta^{[i}_{k}\delta^{j]}_{l}\equiv \frac{1}{2!}\left(\delta^{i}_{k}\delta^{j}_{l}-\delta^{j}_{k}\delta^{i}_{l}\right)[/tex] (which generalizes to n indices with a 1/n! factor), and basis 1-forms act on basis vectors as [tex]\omega^{i}(e_{j})=\delta^{i}_{j}[/tex].
    Last edited: Oct 26, 2009
  4. Oct 26, 2009 #3
    Thanks for the reply. However, if you look on page 88, you will see that the definition for [tex] \delta ^{\alpha \beta } _{\mu \nu } = \delta ^\alpha _\mu \delta ^\beta _\nu - \delta ^\alpha _\nu \delta ^\beta _\mu [/tex] according to MTW does not carry the 1/2! factor that you mention. Furthermore, if you expand the wedge products into tensor products within the contraction symbol, you get [tex]\left\langle {\omega ^\alpha \wedge \omega ^\beta ,e_\mu \wedge e_\nu } \right\rangle = \left\langle {\omega ^\alpha \otimes \omega ^\beta - \omega ^\beta \otimes \omega ^\alpha ,e_\mu \otimes e_\nu - e_\nu \otimes e_\mu } \right\rangle[/tex]

    [tex] = \left\langle {\omega ^\alpha \otimes \omega ^\beta ,e_\mu \otimes e_\nu } \right\rangle - \left\langle {\omega ^\alpha \otimes \omega ^\beta ,e_\nu \otimes e_\mu } \right\rangle - \left\langle {\omega ^\beta \otimes \omega ^\alpha ,e_\mu \otimes e_\nu } \right\rangle + \left\langle {\omega ^\beta \otimes \omega ^\alpha ,e_\nu \otimes e_\mu } \right\rangle [/tex]

    [tex] = \delta ^\alpha _\mu \delta ^\beta _\nu - \delta ^\alpha _\nu \delta ^\beta _\mu - \delta ^\beta _\mu \delta ^\alpha _\nu + \delta ^\beta _\nu \delta ^\alpha _\mu = 2\left( {\delta ^\alpha _\mu \delta ^\beta _\nu - \delta ^\alpha _\nu \delta ^\beta _\mu } \right) = 2 \delta ^{\alpha \beta } _{\mu \nu } [/tex]

    again, using all the conventions of the book up to this point.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook