Unstable solitons in noncommutative gauge theory

We find a class of exact solutions of noncommutative gauge theories corresp onding to unstable non-BPS solitons. In the two-dimensional euclidean (or 2 +1 dimensional lorentzian) U(1) theory we find localized solutions carrying nonzero magnetic flux. In four euclidean dimensions we find non-BPS soluti ons with the same Pontrjagin charge but greater energy than the usual self- dual Yang-Mills instanton. We conjecture that these solutions and generaliz ations thereof correspond to non-supersymmetric configurations of D(p - 2k) -branes (or intersections thereof) in a Dp-brane in the noncommutative scal ing limit of large B-field. In the particular case of a 0-brane on a 2-bran e the analysis of small fluctuations reveals an infinite tower of states wh ich agrees exactly with that of the 0-2 CFT in the scaling limit. The spect rum contains a tachyon, and we show explicitly that the endpoint of tachyon condensation corresponds to the 0-brane dissolved in the 2-brane.