New ghost-free extensions of general relativity

Abstract

The method of algebraic extension is shown to yield a large class of gravitational theories which are extensions of general relativity. Requiring positivity of energy in the flat-space limit of such theories provides some constraints, but a large set of theories of potential phenomenological interest survives this condition. Explicit examples of such theories include the non-symmetric gravitational theory of Moffat, algebraically extended Hilbert gravity and a one-parameter family of theories with dynamical torsion. In general such theories do not alter general relativistic post-Newtonian predictions for time delay experiments; rather they alter the non-linearities of the post-Newtonian gravitational potential. Such effects may be probed by measuring periastron shifts, as in the eclipsing binary systems Di Her and AS Cam, as well as in the binary pulsar PSR 1913+16.

The Nonsymmetric Kaluza-Klein Theory and Modern Physics A Novel Approach

“…Skewon has a spin zero and has a positive energy in the case of a pure real or hypercomplex Hermitian Theory (see Ref. ).…”

On some developments in the Nonsymmetric Kaluza–Klein Theory

“…Moreover it does not results in ghosts (see Ref. [8] and references cited therein, especially Ref. [9]).…”

Massive NGT and spherically symmetric systems

“…Using this asymptotic behavior to determine h from (12) results in a source with ∼ 1/r behavior, causing the field h not to fall off as r → ∞ along the forward light cone. This analysis is correct since one has assumed that the background curvature falls off fast enough, and hence the potential term in (13) can be treated as a source, without changing the asymptotic behavior of the fields. It must be stressed that one is assuming that the background and the radiative fields fall off at least as fast as ∼ 1/r, and what has actually been derived here is a contradiction of this, since h is driven to a constant and can no longer be considered as a perturbative mode.…”