Some Properties of String Field Algebra

We examine string field algebra which is generated by star product in Witten's string field theory including ghost part. We perform calculations using oscillator representation consistently. We construct wedge like states in ghost part and investigate algebras among them. As a by-product we have obtained some solutions of vacuum string field theory. We also discuss some problems about identity state. We hope these calculations will be useful for further investigation of Witten type string field theory.Comment: 26 pages, typos corrected, v3:Eq.(92) corrected, v4:to be published in JHE

Comments on Gauge Equivalence in Noncommutative Geometry

We investigate the transformation from ordinary gauge field to noncommutative one which was introduced by N.Seiberg and E.Witten (hep-th/9908142). It is shown that the general transformation which is determined only by gauge equivalence has a path dependence in `\theta-space'. This ambiguity is negligible when we compare the ordinary Dirac-Born-Infeld action with the noncommutative one in the U(1) case, because of the U(1) nature and slowly varying field approximation. However, in general, in the higher derivative approximation or in the U(N) case, the ambiguity cannot be neglected due to its noncommutative structure. This ambiguity corresponds to the degrees of freedom of field redefinition.Comment: 10 pages, LaTeX2e, note adde

Comments on Solutions for Nonsingular Currents in Open String Field Theories

We investigate analytic solutions to Witten's bosonic string field theory and Berkovits' WZW-type superstring field theory. We construct solutions with parameters out of simpler ones, using a commutative monoid that includes the family of wedge states. Our solutions are generalizations of solutions for marginal deformations by nonsingular currents, and can also reproduce Schnabl's tachyon vacuum solution in bosonic string field theory. This implies that such known solutions are generated from simple solutions which are based on the identity state. We also discuss gauge transformations and induced field redefinitions for our solutions in both bosonic and super string field theory.Comment: 23 pages; v2: PTPTeX, typos correcte

Comments on Observables for Identity-Based Marginal Solutions in Berkovits' Superstring Field Theory

We construct an analytic solution for tachyon condensation around identity-based marginal solutions in Berkovits' WZW-like open superstring field theory. Using this, which is a kind of wedge-based solution, the gauge invariant overlaps for the identity-based marginal solutions can be calculated analytically. This is a straightforward extension of a method in bosonic string field theory, which has been elaborated by the authors, to superstring. We also comment on a gauge equivalence relation between the tachyon vacuum solution and its marginally deformed one. From this viewpoint, we can find the vacuum energy of the identity-based marginal solutions to be zero, which agrees with the previous result as a consequence of $\xi$ zero mode counting.Comment: 16 page

A universal nonlinear relation among boundary states in closed string field theory

We show that the boundary states satisfy a nonlinear relation (the idempotency equation) with respect to the star product of closed string field theory. This relation is universal in the sense that various D-branes, including the infinitesimally deformed ones, satisfy the same equation, including the coefficient. This paper generalizes our analysis (hep-th/0306189) in the following senses. (1) We present a background-independent formulation based on conformal field theory. It illuminates the geometric nature of the relation and allows us to more systematically analyze the variations around the D-brane background. (2) We show that the Witten-type star product satisfies a similar relation but with a more divergent coefficient. (3) We determine the coefficient of the relation analytically. The result shows that the alpha parameter can be formally factored out, and the relation becomes universal. We present a conjecture on vacuum theory based on this computation.Comment: 35 pages, 7 figures, references added, v3:PTPTeX, typos correcte