The emergence of expanding space-time and intersecting D-branes from classical solutions in the Lorentzian type IIB matrix model

TL;DR

This paper explores classical solutions in the Lorentzian type IIB matrix model, demonstrating the emergence of expanding space-time and intersecting D-branes, which are key features in understanding the origin of our universe in string theory.

Contribution

It introduces a numerical approach to find classical solutions that exhibit expanding space-time and intersecting D-branes within the Lorentzian type IIB matrix model, advancing nonperturbative string theory research.

Findings

Emergence of (3+1)-dimensional expanding space-time.

Block-diagonal structure indicating intersecting D-branes.

Zero mode of the Dirac operator for certain D-brane solutions.

Abstract

The type IIB matrix model is a promising candidate for a nonperturbative formulation of superstring theory. As such, it is expected to explain the origin of space--time and matter at the same time. This has been partially demonstrated by the previous Monte Carlo studies on the Lorentzian version of the model, which suggested the emergence of (3+1)-dimensional expanding space--time. Here we investigate the same model by solving numerically the classical equation of motion, which is expected to be valid at late times since the action becomes large due to the expansion of space. Many solutions are obtained by the gradient descent method starting from random matrix configurations, assuming a quasi-direct-product structure for the (3+1)-dimensions and the extra 6 dimensions. We find that these solutions generally admit the emergence of expanding space--time and a block-diagonal structure in the extra dimensions, the latter being important for the emergence of intersecting D-branes. For solutions corresponding to D-branes with appropriate dimensionality, the Dirac operator is shown to acquire a zero mode in the limit of infinite matrix size.