# Open Strings and Electric Fields in Compact Spaces

## TL;DR

This paper investigates open strings with background electric and magnetic fields in compact spaces, revealing quantization conditions, periodic D-brane motion, Landau level degeneracies, and implications for energy loss in inflationary models.

## Contribution

It provides a detailed analysis of electric and magnetic field effects on open strings in compact spaces, including quantization, Landau levels, and energy loss, extending previous work to oblique fields and multiple brane stacks.

## Key findings

- Electric fields in a torus must be quantized, leading to periodic D-brane motion.
- Magnetic flux quantization relates to Landau level degeneracy via gcd of flux numbers.
- Compact dimensions increase energy loss compared to non-compact cases.

## Abstract

We analyse open strings with background electric fields in the internal space, T-dual to branes moving with constant velocities in the internal space. We find that the direction of the electric fields inside a two torus, dual to the D brane velocities, has to be quantised such that the corresponding direction is compact. This implies that D-brane motion in the internal torus is periodic, with a periodicity that can be parametrically large in terms of the internal radii. By S-duality, this is mapped into an internal magnetic field in a three torus, a quantum mechanical analysis of which yields a similar result, i.e. the parallel direction to the magnetic field has to be compact. Furthermore, for the magnetic case, we find the Landau level degeneracy as being given by the greatest common divisor of the flux numbers. We carry on the string quantisation and derive the relevant partition functions for these models. Our analysis includes also the case of oblique electric fields which can arise when several stacks of branes are present. Compact dimensions and/or oblique sectors influence the energy loss of the system through pair-creation and thus can be relevant for inflationary scenarios with branes. Finally, we show that the compact energy loss is always larger than the non-compact one.