arXiv subjects

Yoichi Kazama

Publications and source records attributed to Yoichi Kazama.

25 records · Page 2Linked to original sources

arXiv2003

A New First Class Algebra, Homological Perturbation and Extension of Pure Spinor Formalism for Superstring

Based on a novel first class algebra, we develop an extension of the pure spinor (PS) formalism of Berkovits, in which the PS constraints are removed. By using the homological perturbation theory in an essential way, the BRST-like charge $Q$ of the conventional PS formalism is promoted to a bona fide nilpotent charge $\hat{Q}$, the cohomology of which is equivalent to the constrained cohomology of $Q$. This construction requires only a minimum number (five) of additional fermionic ghost-antighost pairs and the vertex operators for the massless modes of open string are obtained in a systematic way. Furthermore, we present a simple composite "$b$-ghost" field $B(z)$ which realizes the important relation $T(z) = \{\hat{Q}, B(z)\} $, with $T(z)$ the Virasoro operator, and apply it to facilitate the construction of the integrated vertex. The present formalism utilizes U(5) parametrization and the manifest Lorentz covariance is yet to be achieved.

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arXiv1998

Generalized Conformal Symmetry in D-Brane Matrix Models

We study in detail the extension of the generalized conformal symmetry proposed previously for D-particles to the case of supersymmetric Yang-Mills matrix models of Dp-branes for arbitrary p. It is demonstrated that such a symmetry indeed exists both in the Yang-Mills theory and in the corresponding supergravity backgrounds produced by Dp-branes. On the Yang-Mills side, we derive the field-dependent special conformal transformations for the collective coordinates of Dp-branes in the one-loop approximation, and show that they coincide with the transformations on the supergravity side. These transformations are powerful in restricting the forms of the effective actions of probe D-branes in the fixed backgrounds of source D-branes. Furthermore, our formalism enables us to extend the concept of (generalized) conformal symmetry to arbitrary configurations of D-branes, which can still be used to restrict the dynamics of D-branes. For such general configurations, however, it cannot be endowed a simple classical space-time interpretation at least in the static gauge adopted in the present formulation of D-branes.

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arXiv1998

Interaction of D-string with F-string: A Path-Integral Formalism

A path integral formalism is developed to study the interaction of an arbitrary curved Dirichlet (D-) string with elementary excitations of the fundumental (F-) string in bosonic string theory. Up to the next to leading order in the derivative expansion, we construct the properly renormalized vertex operator, which generalizes the one previously obtained for a D-particle moving along a curved trajectory. Using this vertex, an attempt is further made to quantize the D-string coordinates and to compute the quantum amplitude for scattering between elementary excitations of the D- and F-strings. By studying the dependence on the Liouville mode for the D-string, it is found that the vertex in our approximation consists of an infinite tower of local vertex operators which are conformally invariant on their respective mass-shell. This analysis indicates that, unlike the D-particle case, an off-shell extension of the interaction vertex would be necessary to compute the full amplitude and that the realization of symmetry can be quite non-trivial when the dual extended objects are simultaneously present. Possible future directions are suggested.

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arXiv1997

Scattering of Quantized Dirichlet Particles

As a step toward satisfactory understanding of the quantum dynamics of Dirichlet \break (D-) particles, the amplitude for the basic process describing the scattering of two quantized D-particles is computed in bosonic string theory. The calucluation is performed and cross-checked using three different methods, namely, (i) path integral, (ii) boundary state, and (iii) open-channel operator formalism. The analysis is exact in $\al'$ and includes the first order correction in the expansion with respect to the acceleration of the D-particles. The resultant Lorentz-invariant amplitude is capable of describing general non-forward scattering with recoil effects fully taken into account and it reproduces the known result for the special case of forward scattering in the limit of infinitely large D-particle mass. The expected form of the amplitude for the supersymmetric case is also briefly discussed.

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arXiv1997

Scattering of Closed String States from a Quantized D-Particle

By developing an appropriate path-integral formalism, we compute, in bosonic string theory, the disk amplitude for the scattering of closed string states from a D-particle, in which the collective coordinate of the D-particle is fully quantized. As a consequence, the recoil of the D-particle is naturally taken into account. Our result can be readily factorized in the closed string channel to yield the boundary state describing the recoiling D-particle. This turned out to agree with the BRST invariant vertex recently proposed by Ishibashi to the leading order in the derivative expansion, but it will receive corrections in subsequent orders. The advantage of our formalism is that it is extendable to deal with more general processes involving multiple D-particles. A viewpoint regarding our work as describing a dynamical transition of CFT's is also discussed.

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arXiv1995

On Quantum Black Holes

A pedagogical discussion is given of some aspects of \lq\lq quantum black holes", primarily using recently developed two-dimensional models. After a short preliminary concerning classical black holes, we give several motivations for studying such models, especially the so called dilaton gravity models in $1+1$ dimensions. Particularly attractive is the one proposed by Callan,Giddings, Harvey and Strominger (CGHS), which is classically solvable and contains black hole solutions. Its semi-classical as well as classical properties will be reviewed, including how a flux of matter fields produces a black hole with a subsequent emission of Hawking radiation. Breakdown of such an approximation near the horizon, however, calls for exactly solvable variants of this model and some attempts in this direction will then be described. A focus will be placed on a model with 24 matter fields, for which exact quantization can be performed and physical states constructed. A method will then be proposed to extract space-time geometry described by these states in the sense of quantum average and examples containing a black hole will be presented. Finally we give a (partial) list of future problems and discuss the nature of difficulties in resolving them.

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arXiv1993

On the Exact Operator Formalism of Two-Dimensional Liouville Quantum Gravity in Minkowski Spacetime

A detailed reexamination is made of the exact operator formalism of two-dimensional Liouville quantum gravity in Minkowski spacetime with the cosmological term fully taken into account. Making use of the canonical mapping from the interacting Liouville field into a free field, we focus on the problem of how the Liouville exponential operator should be properly defined. In particular, the condition of mutual locality among the exponential operators is carefully analyzed, and a new solution, which is neither smoothly connected nor relatively local to the existing solution, is found. Our analysis indicates that, in Minkowski spacetime, coupling gravity to matter with central charge $d<1$ is problematical. For $d=1$, our new solution appears to be the appropriate one; for this value of $d$, we demonstrate that the operator equation of motion is satisfied to all orders in the cosmological constant with a certain regularization. As an application of the formalism, an attempt is made to study how the basic generators of the ground ring get modified due to the inclusion of the cosmological term. Our investigation, although incomplete, suggests that in terms of the canonically mapped free field the ground ring is not modified.

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