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High Energy Physics - Theory, hep-th,Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO
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 "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.
