In both old and recent literature, it has been argued that the celebrated van Dam-Veltman-Zakharov (vDVZ) discontinuity of massive gravity is an artifact due to linearization of the true equations of motion. In this letter, we investigate that claim. First, we exhibit an explicit –albeit somewhat arbitrary– fully covariant set of equations of motion that, upon linearization, reduce to the stand...

If the graviton possesses an arbitrarily small (but nonvanishing) mass, perturbation theory implies that cosmic strings have a nonzero Newtonian potential. Nevertheless in Einstein gravity, where the graviton is strictly massless, the Newtonian potential of a cosmic string vanishes. This discrepancy is an example of the van Dam–Veltman–Zakharov (VDVZ) discontinuity. We present a solution for th...

We investigate the cosmological perturbations of the brane-induced (Dvali-GabadadzePorrati) model which exhibits a van Dam-Veltman-Zakharov (vDVZ) discontinuity when linearized over a Minkowski background. We show that the linear brane scalar cosmological perturbations over an arbitrary Friedmann-Lemâıtre-Robertson-Walker (FLRW) spacetime have a well defined limit when the radius of transition ...

Gravity in five-dimensional braneworld backgrounds often exhibits problematic features, including kinetic ghosts, strong coupling, and the vDVZ discontinuity. These problems are an obstacle to producing and analyzing braneworld models with interesting and potentially observable modifications of 4d gravity. We examine these problems in a general AdS5/AdS4 setup with two branes and localized curv...

Objectives: The aim of this field study was to explore the relationship between body mass and quad bike induced whole-body vibration (WBV) exposure in a group of New Zealand rural workers. Methods: WBV exposure was recorded using a seat pad mounted tri-axial accelerometer while rural workers (n=34) were driving a quad bike for approximately half an hour on a pre-marked track on farm terrain. Pe...

The target space of a nonlinear sigma model is usually required to be positive definite to avoid ghosts. We introduce a unique class of nonlinear sigma models where the target space metric has a Lorentzian signature, thus the associated group being non-compact. We show that the would-be ghost associated with the negative direction is fully projected out by 2 second-class constraints, and there ...