Extra-natural production of superheavy Kaluza-Klein particles

TL;DR

This paper explores how gauge fields in extra dimensions can produce superheavy Kaluza-Klein particles during and after inflation, potentially contributing to dark matter or influencing cosmic evolution.

Contribution

It demonstrates that KK particle production is a generic outcome in extra-natural inflation models with multiple charged fields, including scenarios where the gauge field is a spectator.

Findings

KK particles can become superheavy dark matter candidates.

Production occurs during inflation and post-inflation oscillations.

KK particle production is a common feature when gauge potentials are light.

Abstract

Gauge fields in extra compact dimensions can drive inflation in the four-dimensional (4D) non-compact spacetime, a scenario known as extra-natural inflation. A time-dependent gauge field configuration generates the electric field along the compact dimension, enabling the production of Kaluza-Klein (KK) particles charged under the field via the Schwinger effect. We construct the extra-natural inflation model within a five-dimensional (5D) quantum electrodynamics (QED) framework coupled to gravity including matter fields that generate the inflationary one-loop effective potential. In general, multiple charged fields can exist, and we show that KK particle production occurs under these conditions. Since KK momentum is conserved, the produced KK particles may become superheavy dark matter or dominate the universe, depending on the model parameters. Furthermore, we show that even when the gauge field acts not as the inflaton but as a spectator field, its post-inflationary oscillations, initiated when the Hubble friction becomes negligible, can also generate superheavy KK modes. This suggests that KK particle production is a generic outcome when gauge potentials along compact dimensions are light.