arXiv subjects

Isao Kishimoto

Publications and source records attributed to Isao Kishimoto.

At least 37 records · Page 2Linked to original sources

arXiv2013

Tachyon Vacuum of Bosonic Open String Field Theory in Marginally Deformed Backgrounds

We consider bosonic open string field theory in marginally deformed backgrounds, which is obtained by expanding the string field around the identity-based solutions associated with marginal deformations. We find a new set of string fields which satisfies the KBc algebra, but the nilpotent kinetic operator is that of the theory expanded around the identity-based marginal solution. By use of these string fields, we construct the tachyon vaccum solution in marginally deformed backgrounds. The vacuum energy density is equivalent to that of the tachyon vacuum without marginal deformations. The gauge invariant overlap is changed according to the effect of marginal deformations, as expected from known results in CFT. These results suggest that the vacuum energy is zero for the identity-based marginal solutions in the original theory.

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arXiv2012

On Nontrivial Solutions around a Marginal Solution in Cubic Superstring Field Theory

We construct tachyon vacuum and half-brane solutions, using an extension of KBc algebra, in the theory around a type of identity-based marginal solutions in modified cubic superstring field theory. With explicit computations, we find that their vacuum energies are the same as those of corresponding solutions around the original theory. It implies that the vacuum energy for the identity-based marginal solution vanishes although straightforward computation of it is subtle. We also evaluate the gauge invariant overlaps for those nontrivial solutions. The values for them are deformed according to the marginal solution in the same way as the case of bosonic string field theory.

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arXiv2012

Homotopy Operators and One-Loop Vacuum Energy at the Tachyon Vacuum

We construct the homotopy operators for the BRST operator in the theory around the identity-based solutions, which are believed to represent the tachyon vacuum in cubic bosonic open string field theory. Using the homotopy operators, we find that the one-loop vacuum energy at the tachyon vacuum is independent of moduli such as interbrane distances, which are included in the BRST operator. We also revisit the cohomology problem, which was solved earlier without the homotopy operators.

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arXiv2011

Homotopy Operators and Identity-Based Solutions in Cubic Superstring Field Theory

We construct a class of nilpotent operators using the BRST current and ghost fields in superstring theory. The operator can be realized in cubic superstring field theory as a kinetic operator in the background of an identity-based solution. For a particular type of the deformed BRST operators, we find a homotopy operator and discuss its relationship to the cohomology in a similar way to the bosonic case, which has been elaborated by the authors.

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arXiv2010

An Algebraic Model for the su(2|2) Light-Cone String Field Theory

We investigate algebraic structure of light-cone string field theory which respects the spacetime supersymmetry su(2|2). Extracting building blocks from the explicit oscillator expressions of light-cone superstring field theory on the pp-wave and the flat background, we propose a model for more generic backgrounds by giving an algebraic procedure to construct supercharges and Hamiltonian without referring to explicit oscillator expressions. Based on this strategy, we systematically construct interaction terms of light-cone string field theory on the pp-wave background and some examples of its generalization. We also study the supergravity limit of the interaction terms on the pp-wave background.

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arXiv2009

Numerical Evaluation of Gauge Invariants for a-gauge Solutions in Open String Field Theory

We evaluate gauge invariants, action and gauge invariant overlap, for numerical solutions which satisfy the "a-gauge" condition with various values of $a$ in cubic open bosonic string field theory. We use the level truncation approximation and an iterative procedure to construct numerical solutions in the twist even universal space. The resulting gauge invariants are numerically stable and almost equal to those of Schnabl's solution for tachyon condensation. Our result provides further evidence that these numerical and analytical solutions are gauge equivalent.

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arXiv2009

Exploring Vacuum Structure around Identity-Based Solutions

We explore the vacuum structure in bosonic open string field theory expanded around an identity-based solution parameterized by $a(>=-1/2)$. Analyzing the expanded theory using level truncation approximation up to level 20, we find that the theory has the tachyon vacuum solution for $a>-1/2$. We also find that, at $a=-1/2$, there exists an unstable vacuum solution in the expanded theory and the solution is expected to be the perturbative open string vacuum. These results reasonably support the expectation that the identity-based solution is a trivial pure gauge configuration for $a>-1/2$, but it can be regarded as the tachyon vacuum solution at $a=-1/2$.

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arXiv2009

Vacuum structure around identity based solutions

We explore vacuum structure in bosonic open string field theory expanded around an identity based solution parameterized by $a$ (>= -1/2). Analyzing the expanded theory by using level truncation approximation up to level 14, we find that the theory has a stable vacuum solution for $a$>-1/2. The vacuum energy and the gauge invariant overlap numerically approach those of the tachyon vacuum solution with increasing truncation level. Also we find that, at $a$=-1/2, there exists an unstable vacuum solution in the expanded theory and it rapidly becomes the trivial zero configuration just above $a$=-1/2. The numerical behavior of the two gauge invariants suggests that the unstable solution corresponds to the perturbative open string vacuum. These results reasonably support the expectation that the identity based solution is a trivial pure gauge configuration for $a$>-1/2, but it can be regarded as the tachyon vacuum solution at $a$=-1/2.

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arXiv2009

Numerical Evaluation of Gauge Invariants for $a$-gauge Solutions in Open String Field Theory

We evaluate gauge invariants (vacuum energy and gauge invariant overlap) for numerical classical solutions in cubic open string field theory under Asano-Kato's $a$-gauge fixing condition. We propose an efficient iterative procedure for solving the equations of motion so that the BRST invariance of the solutions is numerically ensured. The resulting gauge invariants are numerically stable and almost equal to those of Schnabl's tachyon vacuum solution in the well-defined region of a gauge parameter. These results provide further evidence that the numerical and analytical solutions are gauge equivalent.

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arXiv2008

Comments on gauge invariant overlaps for marginal solutions in open string field theory

We calculate the gauge invariant overlaps for Schnabl/Kiermaier-Okawa-Rastelli-Zwiebach's marginal solution with nonsingular current. The obtained formula is the same as that for Fuchs-Kroyter-Potting/Kiermaier-Okawa's marginal solution, which was already computed by Ellwood. Our result is consistent with the expectation that they may be gauge equivalent. We also comment on a gauge invariant overlap for rolling tachyon solutions in cubic open string field theory.

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arXiv2008

Gauge Invariant Overlaps for Classical Solutions in Open String Field Theory

We calculate gauge invariant observables for Schnabl's solution with analytic method and with the level truncation approximation. We also compute them for the numerical solution initially obtained by Sen and Zwiebach in the level truncation approximation to compare with the one for Schnabl's solution. The results are consistent with the expectation that they may be gauge equivalent. We briefly discuss the gauge invariant observables and the action for a marginal solution with a nonsingular current.

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arXiv2008

Schnabl's Solution and Boundary States in Open String Field Theory

We discuss that Schnabl's solution is an off-shell extension of the boundary state describing a D-brane in the closed string sector. It gives the physical meaning of the gauge invariant overlaps for the solution in our previous paper and supports Ellwood's recent proposal in the operator formalism.

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arXiv2007

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.

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arXiv2007

On LCSFT/MST Correspondence

It was suggested that light-cone superstring field theory (LCSFT) and matrix string theory (MST) are closely related. Especially the bosonic twist fields and the fermionic spin fields in MST correspond to the string interaction vertices in LCSFT. Since CFT operators are characterized by their OPEs, in our previous work we realized the most important OPE of the twist fields by computing contractions of the interaction vertices using the bosonic cousin of LCSFT. Here using the full LCSFT we generalize our previous work into the realization of OPEs for a vast class of operators.

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arXiv2007

Twist Field as Three String Interaction Vertex in Light Cone String Field Theory

It has been suggested that matrix string theory and light-cone string field theory are closely related. In this paper, we investigate the relation between the twist field, which represents string interactions in matrix string theory, and the three-string interaction vertex in light-cone string field theory carefully. We find that the three-string interaction vertex can reproduce some of the most important OPEs satisfied by the twist field.

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arXiv2005

Analytical Tachyonic Lump Solutions in Open Superstring Field Theory

We construct a classical solution in the GSO(-) sector in the framework of a Wess-Zumino-Witten-like open superstring field theory on a non-BPS D-brane. We use an su(2) supercurrent, which is obtained by compactifying a direction to a circle with the critical radius, in order to get analytical tachyonic lump solutions to the equation of motion. By investigating the action expanded around a solution we find that it represents a deformation from a non-BPS D-brane to a D-brane-anti-D-brane system at the critical value of a parameter which is contained in classical solutions. Although such a process was discussed in terms of boundary conformal field theory before, our study is based on open superstring field theory including interaction terms.

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arXiv2005

Marginal Deformations and Classical Solutions in Open Superstring Field Theory

We construct a class of classical solutions in the Berkovits' open superstring field theory. The resulting solutions correspond to marginal boundary deformations in conformal field theory. The vacuum energy vanishes exactly for the solutions. Investigating the theory expanded around one of the solutions, we find that it reflects the effect of background Wilson lines. The solution has a well-defined Fock space expression and it is invariant under space-time supersymmetry transformation.

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arXiv2004

Cardy states, factorization and idempotency in closed string field theory

We show that boundary states in the generic on-shell background satisfy a universal nonlinear equation of closed string field theory. It generalizes our previous claim for the flat background. The origin of the equation is factorization relation of boundary conformal field theory which is always true as an axiom. The equation necessarily incorporates the information of open string sector through a regularization, which implies the equivalence with Cardy condition. We also give a more direct proof by oscillator representations for some nontrivial backgrounds (torus and orbifolds). Finally we discuss some properties of the closed string star product for non-vanishing $B$ field and find that a commutative and non-associative product (Strachan product) appears naturally in Seiberg-Witten limit.

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