# Dark Energy From Dynamical Projective Connections

## TL;DR

This paper develops a gravitational model called TW Gravity, linking dynamical projective connections to dark energy and dark matter, and finds that the cosmological constant relates to the Universe's angular momentum scale.

## Contribution

It introduces a novel gravitational framework based on dynamical projective connections, connecting dark energy and dark matter phenomena to geometric actions from string theory.

## Key findings

- The cosmological constant is inversely proportional to a coupling constant related to the Universe's angular momentum.
- The model predicts a universal axial scalar coupling to all fermions, acting as a dark matter portal.
- For the current dark energy density, the model's parameters align with the Universe's angular momentum scale.

## Abstract

We further develop the gravitational model, Thomas-Whitehead Gravity (TW Gravity), that arises when projective connections become dynamical fields. TW Gravity has its origins in geometric actions from string theory where the TW projective connection appears as a rank two tensor, $\mathcal{D}_{ab}$, on the spacetime manifold. Using a Gauss-Bonnet (GB) action built from the $(\mathrm{d}+1)$-dimensional TW connection, and applying the tensor decomposition $\mathcal{D}_{ab} = D_{ab} + 4\Lambda /(\mathrm{d}(\mathrm{d}-1)) g_{ab}$, we arrive at a gravitational model made up of a $\mathrm{d}$-dimensional Einstein-Hilbert + GB action sourced by $D_{ab}$ and with cosmological constant $\Lambda$. The $\mathrm{d}=4$ action is studied and we find that $\Lambda \propto 1/J_0$, with $J_0$ the coupling constant for $D_{ab}$. For $\Lambda$ equal to the current measured value, $J_0$ is on the order of the measured angular momentum of the observable Universe. We view this as $\Lambda$ controlling the scale of patches of the Universe that acquire angular momentum, with the net angular momentum of multiple patches vanishing, as required by the cosmological principle. We further find a universal axial scalar coupling to all fermions where the trace, $\mathcal{D} = \mathcal{D}_{ab}g^{ab}$ acts as the scalar. This suggests that $\mathcal{D}$ is also a dark matter portal for non-standard model fermions.