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High Energy Phenomenology, Experiment, and Cosmology Seminar Series artwork
September 28, 20224:00 pm – 5:00 pm (CDT)

A New Step in Interacting Dark Sector Cosmologies for the Hubble Tension and Large Scale Structure


Taewook Youn (University of Texas, Austin)


Doojin Kim



Mitchell Institute for Fundamental Physics & Astronomy

College Station, Texas 77843

Event Details

In this talk, I propose Stepped Partially Acoustic Dark Matter (SPartAcous), a new class of

interacting dark sector models with a qualitatively new cosmological behavior that can simultaneously address

the two most important tensions in cosmological data, the H0 and S8 tensions. The defining element of this class

of models is an interacting dark radiation that includes a component with a light mass, which becomes nonrelativistic

close to the time of matter-radiation equality, and which interacts with a fraction of dark matter. This

generalizes the scenario known as Partially Acoustic Dark Matter (PAcDM) by adding a mass to one of its

massless dark radiation components. As the light component annihilates, the remaining dark radiation heats up,

leading to a step-like increase in Neff, which has been shown to significantly reduce the H0 tension. In addition,

the interaction with dark matter reduces the matter power spectrum at small scales and thus alleviates the S8

tension, while its eventual decoupling leaves the power spectrum at larger scales identical to ΛCDM.

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