World Sheet Geometry of Classical Solutions in String Field Theory

We investigate classical solutions of string field theory proposed by Takahashi and Tanimoto in the case of even order polynomial functions. The BRS charge and the Feynman propagator of open string field theory expanded around the solution are specified by Jenkins-Strebel quadratic differential, which describes geometry of the string worldsheet. We show that the solution becomes nontrivial when two second order poles of the quadratic differential coincide each other on the unit disk. In this case, an open string boundary shrinks to a point.Comment: 23 pages, LaTeX with PTPTeX.cls, 10 figures; published version; Sec. 4.3 added and errors correcte

VSFT revisited

We argue validity of purely ghost kinetic operator in open string field theory from the perspective of the modern analytic method based on the $K B c$ subalgebra. A purely ghost kinetic operator is obtained as a result of gauge fixing string field theory around the identity based tachyon vacuum solution. It is shown that the obtained kinetic operator is not equivalent to the midpoint insertion of the conformal ghost which is extensively studied in literature. We also find that the equation of motion does not allow any nontrivial solutions.Comment: 6 pages, Section 2 is added for publicatio

Classical solution for ghost D-branes in string field theory

A ghost D-brane has been proposed as an object that cancels the effects of a D-branes. We construct a classical solution with an arbitrary number of D-branes and ghost D-branes in the context of open string field theory. Cancellation of BRST cohomolgy between D-branes and ghost D-branes is shown.Comment: 15 pages, title modified, references adde

Tachyon potential in KBc subalgebra

We evaluate the classical action and the effective tachyon potential of open string field theory within KBc subalgebra, which is extensively used in analytic solution for tachyon condensation recently found by Erler and Schnabl. It is found that the level expansion of the string field terminates at level 3. We find that the closed string vacuum is a saddle point of the classical action. We also evaluate the effective potential for tachyon field. The closed string vaccum becomes stable by integrationg out an auxiliary field. It is found that the effective potential is bounded below hence has no runaway direction. We also argue validity of simple identity based solution.Comment: 14 pages, 3 figures, references adde

A Matrix model from string field theory

We demonstrate that a Hermitian matrix model can be derived from level truncated open string field theory with Chan-Paton factors. The Hermitian matrix is coupled with a scalar and a $U(N)$ vector which are responsible for the D-brane at the tachyon vacuum. Effective potential for the scalar is evaluated both in finite and large $N$. Increase of potential height is observed in both examples. The large $N$ matrix integral is identified with a system of $N$ ZZ branes and a ghost FZZT brane.Comment: 16 pages, 4 figures, section 3 improved for publicatio

Gauge Fixing and Scattering Amplitudes in String Field Theory Expanded around Universal Solutions

We study a gauge fixed action of open string field theory expanded around the universal solution which has been found as an analytic classical solution with one parameter a. For a>-1/2, we are able to reproduce open string scattering amplitudes in the theory fixed in the Siegel gauge. At a=-1/2, all scattering amplitudes vanish and there is no open string excitation in the gauge fixed theory. These results support the conjecture that the universal solution can be regarded as pure gauge or the tachyon vacuum solution.Comment: 23 pages, LaTeX with PTPTeX.cls, 1 eps figure. minor corrections, published versio