- #1
Dixanadu
- 254
- 2
Hey guys,
So I'm reading a textbook which has the following equation:
[itex]\dot{X}^{-}\pm X^{-\prime}=\dfrac{1}{4\alpha' p^{+}}\left( \dot{X}^{I}\pm X^{I\prime} \right)^{2}[/itex].
Please note that the [itex]+,-,I[/itex] are indices. Then the author says:
[itex] \dot{X}^{-}= \dfrac{1}{4\alpha' p^{+}}\left( \dot{X}^{I}\dot{X}_{I}+X^{I\prime}X_{I}^{'} \right) [/itex]
where the repeated up and down index is using Einstein's summation convention.
I have no idea how you can get this equation from the first one...can someone explain please?
Thanks...
So I'm reading a textbook which has the following equation:
[itex]\dot{X}^{-}\pm X^{-\prime}=\dfrac{1}{4\alpha' p^{+}}\left( \dot{X}^{I}\pm X^{I\prime} \right)^{2}[/itex].
Please note that the [itex]+,-,I[/itex] are indices. Then the author says:
[itex] \dot{X}^{-}= \dfrac{1}{4\alpha' p^{+}}\left( \dot{X}^{I}\dot{X}_{I}+X^{I\prime}X_{I}^{'} \right) [/itex]
where the repeated up and down index is using Einstein's summation convention.
I have no idea how you can get this equation from the first one...can someone explain please?
Thanks...