“In the open string the gauge charges are carried by the Chan-Paton degrees of freedom at the endpoints. In the closed string the charges are carried by fields that move along the string.”

—  Joseph Polchinski

[String theory: Volume 2, superstring theory and beyond, Cambridge University press, 1998, https://books.google.com/books?id=WKatSc5pjOgC&pg=PA59] (page 59)

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physicist working on string theory 1954–2018

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