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キーワード:
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要旨:
We consider the graviton propagator in a de Sitter background. The propagator depends upon the choice of a gauge-fixing term Lgauge=1/2F2, and we consider the ‘‘ε gauges’’ with Fv=∇u(huv-εguvhσ σ). We show that the propagator is completely finite and has no infrared divergences provided that ε is not given certain ‘‘exceptional’’ values. It is only for these ‘‘exceptional’’ values of ε that the propagator has an infrared divergence. We then show that in these exceptional cases the divergences are gauge artifacts and are not physical: they make no contribution to any physical tree-level scattering amplitudes. Furthermore, we show that at one-loop order the zero modes which arise (only) if ε is given one of the exceptional values are canceled by the Faddeev-Popov ghosts. There is thus no evidence that the de Sitter background is inconsistent when gravitational fluctuations are considered.
