Abstract
The phenomenon of cosmological gravitational particle production (CGPP) is
expected to occur during the period of inflation and the transition into a hot
big bang cosmology. Particles may be produced even if they only couple directly
to gravity, and so CGPP provides a natural explanation for the origin of dark
matter. In this work we study the gravitational production of massive spin-2
particles assuming two different couplings to matter. We evaluate the full
system of mode equations, including the helicity-0 modes, and by solving them
numerically we calculate the spectrum and abundance of massive spin-2 particles
that results from inflation on a hilltop potential. We conclude that CGPP might
provide a viable mechanism for the generation of massive spin-2 particle dark
matter during inflation, and we identify the favorable region of parameter
space in terms of the spin-2 particle's mass and the reheating temperature. As
a secondary product of our work, we identify the conditions under which such
theories admit ghost or gradient instabilities, and we thereby derive a
generalization of the Higuchi bound to Friedmann-Robertson-Walker (FRW)
spacetimes.
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