A Comment on Brane Bending and Ghosts in Theories with Infinite Extra Dimensions

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  • 8 March 2000
Abstract
Theories with infinite extra dimensions open exciting opportunities for particle physics. We argued recently that along with attractive features there are phenomenological difficulties in this class of models. In fact, there is no graviton zero-mode in this case and 4D gravity is obtained by means of continuum bulk modes. These modes have extra polarization degrees of freedom which do not decouple at low energies and lead to inconsistent predictions for light bending and Mercury perihelion. In recent papers, [hep-th/0003020] and [hep-th/0003045] the authors made use of brane bending in order to cancel the unwanted physical polarization of gravitons. In this note we point out that this mechanism does not solve the problem since it uses a {\it ghost} which cancels the extra degrees of freedom. In order to have a consistent model the ghost should be eliminated. As soon as this is done the 4D gravity becomes unconventional and contradicts to General Relativity. We also comment on a naive expectation that the theory at large distances becomes 5-dimensional and that ghosts could decay. New mechanisms are needed to remedy these models.

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