Infrared behavior of Closed Superstrings in Strong Magnetic and Gravitational Fields

A large class of four-dimensional supersymmetric ground states of closed superstrings with a non-zero mass gap are constructed. For such ground states we turn on chromo-magnetic fields as well as curvature. The exact spectrum as function of the chromo-magnetic fields and curvature is derived. We examine the behavior of the spectrum, and find that there is a maximal value for the magnetic field Hmax ∼ M planck. At this value all states that couple to the magnetic field become infinitely massive and decouple. We also find tachyonic instabilities for strong background fields of the order O(μMplanck) where μ is the mass gap of the theory. Unlike the field theory case, we find that such ground states become stable again for magnetic fields of the order O(M2 planck). The implications of these results are discussed. CERN-TH/95-171 August 1995 On leave from Ecole Normale Supérieure, 24 rue Lhomond, F-75231, Paris, Cedex 05, FRANCE. e-mail addresses: KIRITSIS,[email protected]