Supersymmetric Cubic Galileons Have Ghosts

TL;DR

This paper demonstrates that supersymmetric extensions of cubic Galileons introduce higher-order equations of motion, leading to ghosts, which challenges their viability in theoretical models.

Contribution

It provides a detailed analysis showing that supersymmetry causes higher derivatives and ghosts in cubic Galileon theories, revealing a fundamental inconsistency.

Findings

Supersymmetry pairs the Galileon scalar with a second scalar.

The second scalar induces higher-order equations of motion.

Ghosts appear due to higher derivatives in the supersymmetric extension.

Abstract

Galileons are higher-derivative theories of a real scalar which nevertheless admit second order equations of motion. They have interesting applications as dark energy models and in early universe cosmology, and have been conjectured to arise as descriptions of brane dynamics in string theory. In the present paper, we study the bosonic sector of globally N=1 supersymmetric extensions of the cubic Galileon Lagrangian in detail. Supersymmetry requires that the Galileon scalar now becomes paired with a second real scalar field. We prove that the presence of this second scalar causes the equations of motion to become higher than second order, thus leading to the appearance of ghosts. We also analyze the energy scales up to which, in an effective field theory description, the ghosts can be tamed.