1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
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: About normalized D-velocity :uhh:

  1. Dec 11, 2005 #1
    what is meant by the expression "the normalized D-velocity"?

    specifically when it is a tensor like [tex]u^\mu[/tex]

    Thanks :smile:
  2. jcsd
  3. Dec 12, 2005 #2
    I assume you're looking at something dealing with more than 4 dimensions? I think this just refers to a d-dimensional velocity vector which has been normalized to length one, you can think of it as a unit vector pointing along the particle's world line.
  4. Dec 12, 2005 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    From a google search of "normalized D-velocity",
    one finds eq (1.2.4) in Polchinski's string theory book
    [tex]u^\mu=\dot X^\mu (-\dot X^\nu \dot X_\nu)^{-1/2}[/tex]
    ...in agreement with dicerandom's comment. (The idea is not specific to string theory, of course. The minus arises from the choice of convention for the Lorentz-signature of the metric.)
    Last edited: Dec 12, 2005
  5. Dec 12, 2005 #4
    hehehe, that is precisely the book I am reading and the quote was taken precisely from that page xDD. its just that I had never come across that expression before. I should have guessed what the phrase meant, as it is actually quite obvious. Well reading this book is very good physics training for me =) thx guys. Ill get better and better I´m sure heh, but IT will get harder and harder haha, who will win?... emmm, oops xD
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook