content_image/305616.jpg content_image/305612.jpg content_image/305613.jpg content_image/305614.jpg content_image/305615.jpg
we find the metric takes the form 

which we will find useful later on. 

## D branes and Chan-Paton Factors 

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<img src='content_image/305613.jpg'>

<img src='content_image/305614.jpg'>

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Besides strings, string theory necessarily involves nonperturbative objects upon which open strings may end; these are D branes, D for Dirichlet, or 

