Impacting on Hubble tension by Bound Dark Matter model

The Hubble constant values derived from early-Universe observations exhibit a 4.4[Formula: see text] tension compared to late-Universe measurements within the standard [Formula: see text]CDM model. This discrepancy may be resolved by introducing additional relativistic degrees of freedom beyond the [Formula: see text]CDM paradigm. In this work, we recommend a dark matter model called Bound Dark Matter, which can provide extra relativistic degrees of freedom in the early Universe. Our results indicate that the BDM model may slightly alleviate the Hubble tension. Using CMB+BAO+Union3 dataset, our analysis yields [Formula: see text], which can reduce the tension to 3.73[Formula: see text]. This demonstrates the potential of BDM as a physical mechanism to alleviate cosmological parameter inconsistencies.