Open Strings and the Relative Modular Group (TOPCITE: 54 citazioni su INSPIRE HEP)

At genus greater than one, the surfaces contributing to open-string partition functions admit the action of a non-trivial subgroup of Sp (2g, l). The "relative modular group" is not solely associated with modular-invariant closed-string subdiagrams. In particular, at genus two, combining the degeneration of dividing channels with the action of this group leads to spin-statistics restrictions for open strings, in complete analogy with the closed-string case. In addition, it shows that only totally left-right symmetric closedstring models may descend to open-string ones, and essentially induces the GSO-like projections in the open and unoriented channels.