Michael Koehn, Jean-Luc Lehners, Burt Ovrut
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 "standard" Galileon Lagrangians 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. Our result suggests that supersymmetric Galileons should be regarded essentially on the same footing as other higher-derivative terms arising in effective field theories. We also analyze the energy scales up to which, in an effective description, the ghosts can be tamed.
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http://arxiv.org/abs/1302.0840
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