Geometry for the accelerating universe

The Lorentzian spacetime metric is refined to an area metric which naturally emerges as a generalized geometry in quantum string and gauge theory. Employing the area metric curvature scalar, the Einstein-Hilbert gravitational action is reinterpreted as dynamics for an area metric. The area metric cosmology of the radiation-dominated early universe does not depart from general relativity, enabling successful nucleosynthesis. But intriguingly, without the need for dark energy or fine-tuning, area metric cosmology explains the observed small acceleration of the late universe.

Figure 1

The solid curves sketch the string dust-filled area metric cosmologies: from bottom to top: $\xi =0$, $\xi <0$ with $c>0$, and $\xi <0$ with $c<0$. The dashed curve depicts the case $\xi >0$. The top curve is an important new result from area geometry (and cannot be obtained as a dust-filled Einstein cosmology): late-time acceleration tending to zero.