On Tensionless Strings in $3+1$ Dimensions

TL;DR

This paper explores phase transitions in 3+1 dimensions involving tensionless strings, their spectrum, and origins in M-theory, highlighting their role in entropy calculations and supersymmetry.

Contribution

It proposes the existence of tensionless strings in 3+1 dimensions and links their emergence to intersecting 5-branes in M-theory, providing new insights into their spectrum and physical implications.

Findings

Tensionless strings appear at phase transitions in 3+1 dimensions.

The massless spectrum includes an N=2 vector and linear multiplet, without a graviton.

Non-critical strings from intersecting 5-branes explain near-extremal entropy.

Abstract

We argue for the existence of phase transitions in $3+1$ dimensions associated with the appearance of tensionless strings. The massless spectrum of this theory does not contain a graviton: it consists of one $N=2$ vector multiplet and one linear multiplet, in agreement with the light-cone analysis of the Green-Schwarz string in $3+1$ dimensions. In M-theory the string decoupled from gravity arises when two 5-branes intersect over a three-dimensional hyperplane. The two 5-branes may be connected by a 2-brane, whose boundary becomes a tensionless string with $N=2$ supersymmetry in $3+1$ dimensions. Non-critical strings on the intersection may also come from dynamical 5-branes intersecting the two 5-branes over a string and wrapped over a four-torus. The near-extremal entropy of the intersecting 5-branes is explained by the non-critical strings originating from the wrapped 5-branes.