Finite N effects on the collapse of fuzzy spheres

TL;DR

This paper investigates finite N effects on the dynamics and collapse of fuzzy 2-spheres in flat spacetime using the non-Abelian DBI action, revealing non-monotonic collapse times and conditions where higher derivative corrections are negligible.

Contribution

It introduces a simplified form for symmetrised traces at finite N and proposes generalized trace formulas for higher-dimensional fuzzy spheres, advancing understanding of D-brane dynamics.

Findings

Finite N affects collapse times non-monotonically.

Exotic bounce phenomena are absent at finite N.

Higher derivative corrections can be neglected in certain regimes.

Abstract

Finite N effects on the time evolution of fuzzy 2-spheres moving in flat spacetime are studied using the non-Abelian DBI action for N D0-branes. Constancy of the speed of light leads to a definition of the physical radius in terms of symmetrised traces of large powers of Lie algebra generators. These traces, which determine the dynamics at finite N, have a surprisingly simple form. The energy function is given by a quotient of a free multi-particle system, where the dynamics of the individual particles are related by a simple scaling of space and time. We show that exotic bounces of the kind seen in the 1/N expansion do not exist at finite N. The dependence of the time of collapse on N is not monotonic. The time-dependent brane acts as a source for gravity which, in a region of parameter space, violates the dominant energy condition. We find regimes, involving both slowly collapsing and rapidly collapsing branes, where higher derivative corrections to the DBI action can be neglected. We propose some generalised symmetrised trace formulae for higher dimensional fuzzy spheres and observe an application to D-brane charge calculations.