Published January 1, 2006
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A noncritical Ramond-Neveu-Schwarz string with one end fixed
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We study a Ramond-Neveu-Schwarz string with one end fixed on a D0-brane and the other end free as a qualitative guide to the spectrum of hadrons containing one very heavy quark. The mixed boundary conditions break half of the worldsheet supersymmetry and allow only odd alpha and even d modes in the Ramond sector, while the Neveu-Schwarz oscillators b's become odd-integer moded. Boson-fermion masses can still be matched if space-time is nine-dimensional; thus SO(8) triality still plays a role in the spectrum, although full space-time supersymmetry does not survive. We quantize the system in a temporal-like gauge where X-0 similar to tau. Although the gauge choice eliminates negative-norm states at the outset, there are still even-moded Virasoro and even (odd) moded super-Virasoro constraints to be imposed in the NS(R) sectors. The Casimir energy is now positive in both sectors; there are no tachyons. States for alpha'M-2 < 13/4 are explicitly constructed and found to be organized into SO(8) irreps by (super) constraints, which include a novel "root L-0" operator in the Neveu-Schwarz and Gamma(0) +/- I in the Ramond sectors. GSO projections are not allowed. The preconstraint states above the ground state have matching multiplicities, indicating space-time supersymmetry is broken by the (super) constraints. A distinctive physical signature of the system is a slope twice that of the open RNS string. When both ends are fixed, all leading and subleading trajectories are eliminated, resulting in a spectrum qualitatively similar to the J/phi and Upsilon particles.
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