Early dark energy triggered by spacetime dynamics that encodes cosmic radiation-matter transition

Early dark energy (EDE), introduced at the epoch of matter -radiation equality to alleviate the Hubble tension, has posed a new coincidence problem: why does EDE appear at matter -radiation equality when their physics are completely unrelated? To solve this coincidence problem, we propose a new EDE model based on scalar -tensor gravity with the idea that EDE is triggered by spacetime dynamics that encodes the cosmic radiation -matter transition. Our model can induce EDE naturally at matter -radiation equality without unnatural parameter tuning. Compared with other EDE models, a distinguishing feature of ours is that it can also induce a new energy component during cosmic matter -dark energy transition. This is testable with low-redshift observations.