Evidence for String Substructure

We argue that the behavior of string theory at high temperature and high longitudinal boosts, combined with the emergence of p-branes as necessary ingredients in various string dualities, point to a possible reformulation of strings, as well as p-branes, as composites of bits. We review the string-bit models, and suggest generalizations to incorporate p-branes.Comment: Latex file, 21 pages, 11 postscript figure

Galilean Supersymmetry in 2+1 Dimensions

We review work done in collaboration with C.B. Thorn on Super-Galilei invariant field theory and its application to the reformulation of superstring theory in terms of constituent superstring-bits.Comment: 10 pages, Latex. Talk given at the workshop on low dimensional field theory, Telluride, C

A note on D0-branes and instantons in 5d supersymmetric gauge theories

We refine a previous proposal for obtaining the multi-instanton partition function from the supersymmetric index of the 1d supersymmetric gauge theory on the worldline of D0-branes. We provide examples where the refinements are crucial for obtaining the correct result.Comment: 30 pages, 6 figures. Typos correcte

A note on instanton operators, instanton particles, and supersymmetry

We clarify certain aspects of instanton operators in five-dimensional supersymmetric gauge theories. In particular, we show how, in the pointlike limit, they become supersymmetric and provide the natural bridge with the instantonic states contributing to the index as well as with the zero mode counting leading to broken current multiplets

Super-Galilei Invariant Field Theories in 2+1 Dimensions

We extend the Galilei group of space-time transformations by gradation, construct interacting field-theoretic representations of this algebra, and show that non-relativistic Super-Chern-Simons theory is a special case. We also study the generalization to matrix valued fields, which are relevant to the formulation of superstring theory as a $1/N_c$ expansion of a field theory. We find that in the matrix case, the field theory is much more restricted by the supersymmetry.Comment: 25 pages + 2 postscript figures, phyzzx and psfig require

Magnetic properties of dense holographic QCD

We investigate the Sakai-Sugimoto model at nonzero baryon chemical potential in a background magnetic field both in the confined phase and in the deconfined phase with restored chiral symmetry. In this case the 8-brane Chern-Simons term becomes important. In the confined phase it generates a gradient of the pseudo-scalar "pion", which carries a non-vanishing baryon charge. Above a critical value of the chemical potential there is a second order phase transition to a mixed phase which includes also ordinary baryonic matter. However, at fixed baryon charge density the matter is purely "pion"-gradient above a critical magnetic field. In the deconfined chiral-symmetric phase at nonzero chemical potential the magnetic field induces an axial current. We also compute the magnetization of the baryonic matter and find that it is paramagnetic in all three phases but with nonlinear behavior at large magnetic field.Comment: 20 pages, 19 figures; v2 figure and reference added; v3 corrected treatment of boundary terms in CS action leading to small quantitative adjustments; v4 explanation of boundary terms improved, to appear in PR