Decay of long-lived massive closed superstring states: Exact results

TL;DR

This paper identifies a family of long-lived superstring states with lifetimes that increase rapidly with mass, providing exact decay rates and revealing their dominant decay channels as soft massless particle emission.

Contribution

It introduces a one-parameter family of long-lived superstring states and computes their decay rates exactly, showing a power-law dependence on mass and stability characteristics.

Findings

Lifetime increases rapidly with mass, following a power-law.

Decay predominantly occurs via emission of soft massless particles.

The most stable state has a lifetime scaling with mass to the fifth power.

Abstract

We find a one-parameter family of long-lived physical string states in type II superstring theory. We compute the decay rate by an exact numerical evaluation of the imaginary part of the one-loop propagator. Remarkably, the lifetime rapidly increases with the mass. We find a power-law dependence of the form $T = const. g^{-2} Mass^\alpha$, where the value of $\alpha $ depends on the parameter characterizing the state. For the most stable state in this family, one has $\alpha ~= 5$. The dominant decay channel of these massive string states is by emission of soft massless particles. The quantum states can be viewed semiclassically as closed strings which cannot break during the classical evolution.