Some exact computations on the twisted butterfly state in string field theory

The twisted butterfly state solves the equation of motion of vacuum string field theory in the singular limit. The finiteness of the energy density of the solution is an important issue, but possible conformal anomaly resulting from the twisting has prevented us from addressing this problem. We present a description of the twisted regulated butterfly state in terms of a conformal field theory with a vanishing central charge which consists of the ordinary bc ghosts and a matter system with c=26. Various quantities relevant to vacuum string field theory are computed exactly using this description. We find that the energy density of the solution can be finite in the limit, but the finiteness depends on the subleading structure of vacuum string field theory. We further argue, contrary to our previous expectation, that contributions from subleading terms in the kinetic term to the energy density can be of the same order as the contribution from the leading term which consists of the midpoint ghost insertion.Comment: 36 pages, no figures, LaTeX2e; v2: minor corrections; v3: typos corrected, published in JHEP; v4: a minor typo in (C.12) correcte

Solving Witten's string field theory using the butterfly state

We solve the equation of motion of Witten's cubic open string field theory in a series expansion using the regulated butterfly state. The expansion parameter is given by the regularization parameter of the butterfly state, which can be taken to be arbitrarily small. Unlike the case of level truncation, the equation of motion can be solved for an arbitrary component of the Fock space up to a positive power of the expansion parameter. The energy density of the solution is well-defined and remains finite even in the singular butterfly limit, and it gives approximately 68% of the D25-brane tension for the solution at the leading order. Moreover, it simultaneously solves the equation of motion of vacuum string field theory, providing support for the conjecture at this order. We further improve our ansatz by taking into account next-to-leading terms, and find two numerical solutions which give approximately 88% and 109%, respectively, of the D25-brane tension for the energy density. These values are interestingly close to those by level truncation at level 2 without gauge fixing studied by Rastelli and Zwiebach and by Ellwood and Taylor.Comment: 38 pages, no figures, LaTeX2e; v2: the footnote on hep-th/0302151 changed and moved to the introduction; v3: minor typos corrected, published versio

Comments on Schnabl's analytic solution for tachyon condensation in Witten's open string field theory

Schnabl recently constructed an analytic solution for tachyon condensation in Witten's open string field theory. The solution consists of two pieces. Only the first piece is involved in proving that the solution satisfies the equation of motion when contracted with any state in the Fock space. On the other hand, both pieces contribute in evaluating the kinetic term to reproduce the value predicted by Sen's conjecture. We therefore need to understand why the second piece is necessary. We evaluate the cubic term of the string field theory action for Schnabl's solution and use it to show that the second piece is necessary for the equation of motion contracted with the solution itself to be satisfied. We also present the solution in various forms including a pure-gauge configuration and provide simpler proofs that it satisfies the equation of motion.Comment: 33 pages, 4 figures, LaTeX2e; v2: minor changes, version published in JHE

Bethe Ansatz Equations for the Broken ZNZ_{N}-Symmetric Model

We obtain the Bethe Ansatz equations for the broken ${\bf Z}_{N}$-symmetric model by constructing a functional relation of the transfer matrix of $L$-operators. This model is an elliptic off-critical extension of the Fateev-Zamolodchikov model. We calculate the free energy of this model on the basis of the string hypothesis.Comment: 43 pages, latex, 11 figure

Superconducting Gap Structure of Spin-Triplet Superconductor Sr_2RuO_4 Studied by Thermal Conductivity

To clarify the superconducting gap structure of the spin-triplet superconductor Sr_2RuO_4, the in-plane thermal conductivity has been measured as a function of relative orientations of the thermal flow, the crystal axes, and a magnetic field rotating within the 2D RuO_2 planes. The in-plane variation of the thermal conductivity is incompatible with any model with line nodes vertical to the 2D planes and indicates the existence of horizontal nodes. These results place strong constraints on models that attempt to explain the mechanism of the triplet superconductivity.Comment: 5 pages, 4 figures, to be published in Phys. Rev. Let

Spectral Lag Relations in GRB Pulses Detected with HETE-2

Using a pulse-fit method, we investigate the spectral lags between the traditional gamma-ray band (50-400 keV) and the X-ray band (6-25 keV) for 8 GRBs with known redshifts (GRB 010921, GRB 020124, GRB 020127, GRB 021211, GRB 030528, GRB 040924, GRB 041006, GRB 050408) detected with the WXM and FREGATE instruments aboard the HETE-2 satellite. We find several relations for the individual GRB pulses between the spectral lag and other observables, such as the luminosity, pulse duration, and peak energy (Epeak). The obtained results are consistent with those for BATSE, indicating that the BATSE correlations are still valid at lower energies (6-25 keV). Furthermore, we find that the photon energy dependence for the spectral lags can reconcile the simple curvature effect model. We discuss the implication of these results from various points of view.Comment: 13 pages, 9 figures, accepted for the publication in PASJ (minor corrections

Solutions from boundary condition changing operators in open string field theory

We construct analytic solutions of open string field theory using boundary condition changing (bcc) operators. We focus on bcc operators with vanishing conformal weight such as those for regular marginal deformations of the background. For any Fock space state phi, the component string field of the solution Psi exhibits a remarkable factorization property: it is given by the matter three-point function of phi with a pair of bcc operators, multiplied by a universal function that only depends on the conformal weight of phi. This universal function is given by a simple integral expression that can be computed once and for all. The three-point functions with bcc operators are thus the only needed physical input of the particular open string background described by the solution. We illustrate our solution with the example of the rolling tachyon profile, for which we prove convergence analytically. The form of our solution, which involves bcc operators instead of explicit insertions of the marginal operator, can be a natural starting point for the construction of analytic solutions for arbitrary backgrounds.Comment: 21 pages, 1 figure, LaTeX2e; v2: minor changes, version published in JHE

Involvement of integrin-linked kinase in capillary/tube-like network formation of human vascular endothelial cells

Angiogenesis is a complex process involving an ECM and vascular endothelial cells (EC), and is regulated by various angiogenic factors including VEGF. The ability to form a capillary/tube-like network is a specialized function of EC. Therefore, in vitro angiogenesis was assessed by a capillary/tube-like network formation assay. There are three angiogenic parameters: capillary length, number of capillaries, and relative capillary area per field. We evaluated capillary length per field in the assay. VEGF promoted capillary/tube-like network formation of EC in a type I collagen gel matrix in vitro. Moreover, we demonstrated the involvement of ILK in a VEGF signaling pathway mediating capillary/tube-like network formation of EC using dominant-negative, kinase deficient ILK. This is a straightforward assay to monitor responses of human vascular endothelial cells