Abstract
The recent measurements of the cosmological parameter $H_0$ from the direct local observations and the inferred value from the Cosmic Microwave Background show $\sim 4 \sigma$ discrepancy. This may indicate new physics beyond the standard $\Lambda$CDM. We investigate the keV gravitino dark matter that has a small fraction of non-thermal component (e.g. from the late decay of NLSP bino) under various cosmological constraints. We find such a scenario is highly predictive and can be tested by searching for the dilepton plus missing energy events at the LHC. Besides, we also discuss its implication for Hubble tension, however, which can be reduced to $3\sigma$ level marginally.
Highlights
INTRODUCTIONThe ΛCDM model combining cold dark matter (CDM) with a cosmological constant Λ is remarkably successful in describing the results of cosmological observations
We investigate the keV gravitino dark matter that has a small fraction of nonthermal components under various cosmological constraints
The ΛCDM model combining cold dark matter (CDM) with a cosmological constant Λ is remarkably successful in describing the results of cosmological observations
Summary
The ΛCDM model combining cold dark matter (CDM) with a cosmological constant Λ is remarkably successful in describing the results of cosmological observations. One possible way of solving these problems is to introduce warm dark matter (DM) particles.The freestreaming motion of such warm DM particles reduces power on small scales but keeps the CDM predictions for the formation of large-scale structure. When the gravitino dark matter is light enough and nonthermally produced from the late decay of the heavier next-to-LSP (NLSP), it can contribute to the radiation density by mimicking an extra neutrino species. Such a light gravitino dark matter may reduce the Hubble tension. Our framework is highly predictive and can be tested by the LHC experiment
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