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Jun Nishimura

Publications and source records attributed to Jun Nishimura.

160 records · Page 9Linked to original sources
arXiv1998

Dynamical Aspects of Large N Reduced Models

We study the large N reduced model of D-dimensional Yang-Mills theory with special attention to dynamical aspects related to the eigenvalues of the N by N matrices, which correspond to the space-time coordinates in the IIB matrix model. We first put an upper bound on the extent of space time by perturbative arguments. We perform a Monte Carlo simulation and show that the upper bound is actually saturated. The relation of our result to the SSB of the U(1)^D symmetry in the Eguchi-Kawai model is clarified. We define a quantity which represents the uncertainty of the space-time coordinates and show that it is of the same order as the extent of space time, which means that a classical space-time picture is maximally broken. We develop a 1/D expansion, which enables us to calculate correlation functions of the model analytically. The absence of an SSB of the Lorentz invariance is shown by the Monte Carlo simulation as well as by the 1/D expansion.

hep-th↗
arXiv1998

Numerical Studies of the Double Scaling Limit in Large N Reduced Model

We study the two-dimensional Eguchi-Kawai model as a toy model of the IIB matrix model, which has been recently proposed as a nonperturbative definition of the type IIB superstring theory. While the planar limit of the model is known to reproduce the two-dimensional Yang-Mills theory, we find through Monte Carlo simulation that the model allows a different large $N$ limit, which can be considered as the double scaling limit in matrix models.

hep-lat↗
arXiv1998

Numerical Study of the Double Scaling Limit in Two-Dimensional Large N Reduced Model

We study the two-dimensional Eguchi-Kawai model as a toy model of the IIB matrix model, which has been recently proposed as a nonperturbative definition of the type IIB superstring theory. While the planar limit of the model is known to reproduce the two-dimensional Yang-Mills theory, we find through Monte Carlo simulation that the model allows a different large N limit, which can be considered as the double scaling limit in matrix models.

hep-th↗
arXiv1998

Unitary IIB Matrix Model and the Dynamical Generation of the Space Time

We propose a unitary matrix model as a regularization of the IIB matrix model of Ishibashi-Kawai-Kitazawa-Tsuchiya (IKKT). The fermionic part is incorporated using the overlap formalism in order to avoid unwanted ``doublers'' while preserving the global gauge invariance. This regularization, unlike the one adopted by IKKT, has manifest U(1)^10 symmetry, which corresponds to the ten-dimensional translational invariance of the space time. We calculate one-loop effective action around some typical BPS-saturated configurations in the weak coupling limit. We also discuss a possible scenario for the dynamical generation of the four-dimensional space time through spontaneous breakdown of the U(1)^10 symmetry in the double scaling limit.

hep-th↗
arXiv1998

Multicanonical simulation of 3D dynamical triangulation model and a new phase structure

We apply the multicanonical technique to the three dimensional dynamical triangulation model, which is known to exhibit a first order phase transition with the Einstein-Hilbert action. We first clarify the first order nature of the phase transition with the Einstein-Hilbert action in several ways including a high precision finite size scaling analysis. We then add a new local term to the action and confirm the conjecture made through the MCRG technique that the line of the first order phase transition extends to the expanded phase diagram, ending at a point. Fractal dimension at the end point is measured to be around three up to the present size.

hep-lat↗
arXiv1997

Applications of the overlap formalism to super Yang-Mills theories

We show that the idea to use the overlap formalism to formulate 4D N=1 super Yang-Mills theory on the lattice without fine-tuning can be applied to 3D N=1 case as well. Another application we propose is a regularization of the IIB matrix model, which is large N reduced model of 10D N=1 super Yang-Mills theory.

hep-lat↗
arXiv1997

Parity Invariant Lattice Regularization of Three-Dimensional Gauge-Fermion System

In three dimensions, the effective action for the gauge field induced by integrating out a massless Dirac fermion is known to give either a parity-invariant or a parity-violating result, depending on the regularization scheme. We construct a lattice formulation of the massless Dirac fermion using the overlap formalism. We show that the result is parity invariant in contrast to the formulation using Wilson fermions in the massless limit. This facilitates a non-perturbative study of three-dimensional massless Dirac fermions interacting with a gauge field in a parity invariant setting with no need for fine-tuning.

hep-th↗
arXiv1997

Lattice Formulation of Supersymmetric Yang-Mills Theories without Fine-Tuning

We present a lattice formulation which gives super Yang-Mills theories in any dimensions with simple supersymmetry as well as extended supersymmetry in the continuum limit without fine-tuning. We first formulate super Yang-Mills theories with simple supersymmetry in 3,4,6,10 dimensions, incorporating the gluino on the lattice using the overlap formalism. In 4D, exact chiral symmetry forbids gluino mass, which ensures that the continuum limit is supersymmetric without fine-tuning. In 3D, exact parity invariance plays the same role. 6D and 10D thories being anomalous, we formulate them as anomalous chiral gauge theories as they are. Dimensional reduction within lattice formulation is then applied to the theories in 3,4,6 and 10D to obtain super Yang-Mills theories in arbitrary dimensions with either simple or extended supersymmetry.

hep-th↗
arXiv1997

Four-Dimensional N=1 Supersymmetric Yang-Mills Theory on the Lattice without Fine-Tuning

We propose a method to formulate four-dimensional N=1 super Yang-Mills theory on the lattice without fine-tuning. We first show that four-dimensional Weyl fermion in a real representation, which is equivalent to Majorana fermion, can be formulated using the domain wall approach with an addition of a Majorana mass term only for the unwanted mirror fermion. This formalism has manifest gauge invariance. Fermion number conservation is violated only by the additional Majorana mass term for the mirror fermion and the violation is propagated to the physical fermion sector through anomalous currents. Due to this feature, the formalism, when applied to the gluino in the present case, ensures the restoration of supersymmetry in the continuum limit without fine-tuning, unlike the proposal by Curci and Veneziano.

hep-lat↗
arXiv1996

On Existence of Nontrivial Fixed Points in Large $N$ Gauge Theory in More than Four Dimensions

Inspired by a possible relation between large $N$ gauge theory and string theory, we search for nontrivial fixed points in large $N$ gauge theory in more than four dimensions. We study large $N$ gauge theory through Monte Carlo simulation of the twisted Eguchi-Kawai model in six dimensions as well as in four dimensions. The phase diagram of the system with the two coupling constants which correspond to the standard plaquette action and the adjoint term has been explored.

hep-lat↗
arXiv1995

Two-loop Renormalization in Quantum Gravity near Two Dimensions

We study two--loop renormalization in $(2+ε)$--dimensional quantum gravity. As a first step towards the full calculation, we concentrate on the divergences which are proportional to the number of matter fields. We calculate the $β$ functions and show how the nonlocal divergences as well as the infrared divergences cancel among the diagrams. Although the formalism includes a subtlety concerning the general covariance due to the dynamics of the conformal mode, we find that the renormalization group allows the existence of a fixed point which possesses the general covariance. Our results strongly suggest that we can construct a consistent theory of quantum gravity by the $ε$ expansion around two dimensions.

hep-th↗
arXiv1994

Scaling Dimensions of Manifestly Generally Covariant Operators in Two-Dimensional Quantum Gravity

Using (2+$ε$)-dimensional quantum gravity recently formulated by Kawai, Kitazawa and Ninomiya, we calculate the scaling dimensions of manifestly generally covariant operators in two-dimensional quantum gravity coupled to $(p,q)$ minimal conformal matter. Although the spectrum includes all the scaling dimensions of the scaling operators in the matrix model except the boundary operators, there are also many others which do not appear in the matrix model. We argue that the partial agreement of the scaling dimensions should be considered as accidental and that the operators considered give a new series of operators in two-dimensional quantum gravity.

hep-th↗
arXiv1994

Fractal Structure in Two-Dimensional Quantum Regge Calculus

We study the fractal structure of the surface in two-dimensional quantum Regge calculus by performing Monte Carlo simulation with up to 200,000 triangles. The result can be compared with the universal scaling function obtained analytically in the continuum limit of dynamical triangulation, which provides us with a definite criterion whether Regge calculus serves as a proper regularization of quantum gravity. When the scale-invariant measure is taken as the measure of the link-length integration, we observe the correct scaling behavior in the data for the type of loop attached to a baby universe. The data seem to converge to the universal scaling function as the number of triangles is increased. The data for the type of loop attached to the mother universe, on the other hand, shows no scaling behavior up to the present size.

hep-lat↗
arXiv1994

$R^2$ Gravity in $(2+ε)$--Dimensional Quantum Gravity

We study $R^2$ gravity in $(2+ε)$--dimensional quantum gravity. Taking care of the oversubtraction problem in the conformal mode dynamics, we perform a full order calculation of string susceptibility in the $ε\rightarrow 0$ limit. The result is consistent with that obtained through Liouville approach.

hep-th↗
arXiv1992

Monte Carlo Calculation of Phase Shift in Four Dimensional O(4) $ϕ^4$ Theory

The phase shift of the O(4) symmetric $ϕ^4$ theory in the symmetric phase is calculated numerically using the relation between phase shift and energy levels of two-particle states recently derived by Lüscher. The results agree with the prediction of perturbation theory. A practical difficulty of the method for a reliable extraction of the phase shift for large momenta due to the necessity of a precise determination of excited two-particle energy levels is pointed out.

hep-lat↗