Constructing Gravitational Dimensions

TL;DR

This work investigates whether a low-energy effective theory can arise from a compactified higher-dimensional space by studying discrete gravitational dimensions. It shows that a minimal nearest-neighbor discretization tends to produce a nonlocal continuum limit, and that for a single graviton the strong-coupling scale is limited to $Lambda_3 = (m_g^2 M_Pl)^{1/3}$, making locality difficult to achieve. It then proves that any non-linear extension of the Fierz-Pauli Lagrangian cannot push the breakdown scale above $Lambda_3$, ruling out a local cure in that approach. Conversely, a truncated KK theory maintains locality in the continuum limit because heavy KK modes, along with the radion and graviphoton, can cancel or soften dangerous amplitudes. Overall, the work delineates the limits of purely local discretizations and highlights KK-truncated constructions as a viable pathway to local higher-dimensional physics in lattice-like gravity models.

Abstract

It would be extremely useful to know whether a particular low energy effective theory might have come from a compactification of a higher dimensional space. Here, this problem is approached from the ground up by considering theories with multiple interacting massive gravitons. It is actually very difficult to construct discrete gravitational dimensions which have a local continuum limit. In fact, any model with only nearest neighbor interactions is doomed. If we could find a non-linear extension for the Fierz-Pauli Lagrangian for a graviton of mass mg which does not break down until the scale Lambda_2=(mg Mpl)^(1/2), this could be used to construct a large class of models whose continuum limit is local in the extra dimension. But this is shown to be impossible: a theory with a single graviton must break down by Lambda_3 = (mg^2 Mpl)^(1/3). Next, we look at how the discretization prescribed by the truncation of the KK tower of an honest extra diemsinon rasies the scale of strong coupling. It dictates an intricate set of interactions among various fields which conspire to soften the strongest scattering amplitudes and allow for a local continuum limit. A number of canditate symmetries associated with locality in the discretized dimension are also discussed.