Spontaneous growth of spinor fields in gravity

TL;DR

This paper demonstrates that spinor fields nonminimally coupled to gravity can spontaneously grow in matter-rich environments, potentially causing significant deviations from general relativity in strong gravitational fields, relevant to neutron star physics and gravitational waves.

Contribution

It introduces the concept of spontaneous spinorization, showing how a tachyonic Dirac equation leads to instability and growth of spinor fields in gravitational settings.

Findings

Spontaneous spinorization can cause order-of-unity deviations from GR in strong fields.

The phenomenon is analogous to spontaneous scalarization but involves spinor fields.

Potential implications for gravitational wave observations and neutron star astrophysics.

Abstract

We show that spinor fields nonminimally coupled to gravity can grow spontaneously in the presence of matter. We name this phenomenon spontaneous spinorization after the spontaneous scalarization scenario in scalar-tensor theories. Underlying reason for the growth of the spinor is an instability similar to the tachyon of spontaneous scalarization. We first present the structure of a tachyonic Dirac equation, and incorporate it into the matter coupling in gravity. This causes the zero-spinor solution to be unstable and leads to spontaneous growth. We investigate the behavior of the resulting theory for a spherically symmetric neutron star that has grown a spinor cloud. Spontaneous spinorization has the potential to lead to order-of-unity deviations from general relativity in strong fields in a similar manner to its close relative spontaneous scalarization. This makes the theory especially relevant to gravitational wave science and neutron star astrophysics.