A New String in Ten Dimensions?

TL;DR

This paper explores the theoretical possibility of a new string in ten dimensions, supported by orientifold physics and K-theory, and discusses novel decoupling limits in heterotic/type I theories with implications for matrix models.

Contribution

It introduces the concept of a new ten-dimensional string and analyzes its evidence and implications within string theory and M-theory frameworks.

Findings

Evidence from orientifold physics and K-theory supports the new string hypothesis.

Decoupled theories on type I D-strings are three-dimensional, not two-dimensional.

Matrix model definitions for heterotic/type I strings are proposed.

Abstract

I suggest the possibility of a new string in ten dimensions. Evidence for this string is presented both from orientifold physics and from K-theory, along with a mystery concerning the M-theory description. Motivated by this possibility, some novel aspects of decoupling limits in heterotic/type I theories are described; specifically, the decoupled theory on type I $D$-strings is argued to be three-dimensional rather than two-dimensional. These decoupled theories provide the matrix model definitions of the heterotic/type I strings.