The longitudinal fivebrane and tachyon condensation in matrix theory

We study a configuration in matrix theory carrying longitudinal fivebrane c harge, i.e. a D0-D4 bound state. We calculate the one-loop effective potent ial between a D0-D4 bound state and a D0-anti-D4 bound state and compare ou r results to a supergravity calculation. Next, we identify the tachyonic fl uctuations in the D0-D4 and D0-anti-D4 system. We analyse classically the a ction for these tachyons and find solutions to the equations of motion corr esponding to tachyon condensation. (C) 2000 Elsevier Science B.V. All right s reserved.