Search for the most stable massive state in superstring theory

TL;DR

This paper investigates the stability and decay properties of massive states in superstring theory, identifying the most stable configurations and their lifetimes, with implications for understanding string decay channels and spectra.

Contribution

It introduces the concept of a highly stable rotating ring state in superstring theory and quantifies its lifetime and decay channels, a novel insight into string stability.

Findings

The average string state lifetime scales as 1/(g^2 M).

The most stable state, the rotating ring, has a lifetime proportional to M^5/g^2.

Decay spectra of rotating rings resemble thermal spectra with a maximum and exponential tail.

Abstract

In ten dimensional type II superstring, all perturbative massive states are unstable, typically with a short lifetime compared to the string scale. We find that the lifetime of the average string state of mass M has the asymptotic form T < const.1/(g^2 M). The most stable string state seems to be a certain state with high angular momentum which can be classically viewed as a circular string rotating in several planes ("the rotating ring"), predominantly decaying by radiating soft massless NS-NS particles, with a lifetime T = c_0 M^5/g^2. Remarkably, the dominant channel is the decay into a similar rotating ring state of smaller mass. The total lifetime to shrink to zero size is ~ M^7. In the presence of D branes, decay channels involving open strings in the final state are exponentially suppressed, so the lifetime is still proportional to M^5, except for a D brane at a special angle or flux. For large mass, the spectrum for massless emission exhibits qualitative features typical of a thermal spectrum, such as a maximum and an exponential tail. We also discuss the decay properties of rotating rings in the case of compact dimensions.