Tachyon Vacuum Solution in Open String Field Theory with Constant B Field

We show that Schnabl's tachyon vacuum solution is an exact solution of the equation of motion of Witten's open bosonic string field theory in the background of constant antisymmetric two-form field. The action computed at the vacuum solution is given by the Dirac-Born-Infeld factor multiplied to that without the antisymmetric tensor field.Comment: 8 page

Marginal deformations in string field theory

We describe a method for obtaining analytic solutions corresponding to exact marginal deformations in open bosonic string field theory. For the photon marginal deformation we have an explicit analytic solution to all orders. Our construction is based on a pure gauge solution where the gauge field is not in the Hilbert space. We show that the solution itself is nevertheless perfectly regular. We study its gauge transformations and calculate some coefficients explicitly. Finally, we discuss how our method can be implemented for other marginal deformations.Comment: 23 pages. v2: Some paragraphs improved, typos corrected, ref adde

Disk Partition Function and Oscillatory Rolling Tachyons

An exact cubic open string field theory rolling tachyon solution was recently found by Kiermaier et. al. and Schnabl. This oscillatory solution has been argued to be related by a field redefinition to the simple exponential rolling tachyon deformation of boundary conformal theory. In the latter approach, the disk partition function takes a simple form. Out of curiosity, we compute the disk partition function for an oscillatory tachyon profile, and find that the result is nevertheless almost the same.Comment: 17 pages, 2 figures. v4: discussion clarified, appendix added, conclusions unchanged; version to appear in J.Phys.

Solutions from boundary condition changing operators in open superstring field theory

We construct analytic solutions of open superstring field theory in the Berkovits formulation using boundary condition changing operators under some regularity conditions, extending the previous construction in the bosonic string. We also consider the gauge-invariant observables corresponding to closed string one-point functions on the disk. We analytically calculate the gauge-invariant observables for the solutions both in the bosonic string and in the superstring and find the expected change of boundary conditions of the disk.Comment: 33 pages, no figures, LaTeX2e; v2: minor corrections; v3: minor revision, published versio

Boundary State from Ellwood Invariants

Boundary states are given by appropriate linear combinations of Ishibashi states. Starting from any OSFT solution and assuming Ellwood conjecture we show that every coefficient of such a linear combination is given by an Ellwood invariant, computed in a slightly modified theory where it does not trivially vanish by the on-shell condition. Unlike the previous construction of Kiermaier, Okawa and Zwiebach, ours is linear in the string field, it is manifestly gauge invariant and it is also suitable for solutions known only numerically. The correct boundary state is readily reproduced in the case of known analytic solutions and, as an example, we compute the energy momentum tensor of the rolling tachyon from the generalized invariants of the corresponding solution. We also compute the energy density profile of Siegel-gauge multiple lump solutions and show that, as the level increases, it correctly approaches a sum of delta functions. This provides a gauge invariant way of computing the separations between the lower dimensional D-branes.Comment: v2: 63 pages, 14 figures. Major improvements in section 2. Version published in JHE

Connecting Solutions in Open String Field Theory with Singular Gauge Transformations

We show that any pair of classical solutions of open string field theory can be related by a formal gauge transformation defined by a gauge parameter $U$ without an inverse. We investigate how this observation can be used to construct new solutions. We find that a choice of gauge parameter consistently generates a new solution only if the BRST charge maps the image of $U$ into itself. When this occurs, we argue that $U$ naturally defines a star algebra projector which describes a surface of string connecting the boundary conformal field theories of the classical solutions related by $U$. We also note that singular gauge transformations give the solution space of open string field theory the structure of a category, and we comment on the physical interpretation of this observation.Comment: V2: minor improvements, added citation

String Theory as a diffusing System

Recent results on the effective non-local dynamics of the tachyon mode of open string field theory (OSFT) show that approximate solutions can be constructed which obey the diffusion equation. We argue that this structure is inherited from the full theory, where it admits a universal formulation. In fact, all known exact OSFT solutions are superpositions of diffusing surface states. In particular, the diffusion equation is a spacetime manifestation of OSFT gauge symmetries.Comment: 1+39 pages, 1 figure; v2: section 4 expanded, main result clarified but unchanged, references adde