Affine generalizations of gravity in the light of modern cosmology

TL;DR

This paper explores new affine gravity models in multidimensional spacetimes, integrating ideas from Weyl, Eddington, and Einstein, to explain dark energy, dark matter, and inflation through geometric fields derived from a generalized Ricci tensor.

Contribution

It introduces a class of affine gravity theories with symmetric connections, where fields like dark energy, dark matter, and inflation emerge from geometric origins, extending Einstein's framework.

Findings

Dark energy naturally arises in the geometric models.

Fields such as vectons and scalars can describe massive particles or tachyons.

The geometric Lagrangian choice influences the nature of these fields.

Abstract

We discuss new models of an `affine' theory of gravity in multidimensional space-times with symmetric connections. We use and develop ideas of Weyl, Eddington, and Einstein, in particular, Einstein's proposal to specify the space - time geometry by use of the Hamilton principle. More specifically, the connection coefficients are determined using a `geometric' Lagrangian that is an arbitrary function of the generalized (non-symmetric) Ricci curvature tensor (and, possibly, of other fundamental tensors) expressed in terms of the connection coefficients regarded as independent variables. Such a theory supplements the standard Einstein gravity with dark energy (the cosmological constant, in the first approximation), a neutral massive (or tachyonic) vector field (vecton), and massive (or tachyonic) scalar fields. These fields couple only to gravity and can generate dark matter and/or inflation. The new field masses (real or imaginary) have a geometric origin and must appear in any concrete model. The concrete choice of the geometric Lagrangian determines further details of the theory, for example, the nature of the vector and scalar fields that can describe massive particles, tachyons, or even `phantoms'. In `natural' geometric theories, which are discussed here, dark energy must also arise. We mainly focus on intricate relations between geometry and dynamics while only very briefly considering approximate cosmological models inspired by the geometric approach.