Extended Analysis of Neutrino-Dark Matter Interactions with Small-Scale CMB Experiments

We explore an extension of the standard <math display="inline" id="d1e8031" altimg="si194.svg"><mi>Λ</mi></math>CDM model by including an interaction between neutrinos and dark matter, and making use of the ground based telescope data of the Cosmic Microwave Background (CMB) from the Atacama Cosmology Telescope (ACT). An indication for a non-zero coupling between dark matter and neutrinos (both assuming a temperature independent and <math display="inline" id="d1e8036" altimg="si314.svg"><msup><mrow><mi>T</mi></mrow><mrow><mn>2</mn></mrow></msup></math> dependent cross-section) is obtained at the 1<math display="inline" id="d1e8046" altimg="si3.svg"><mi>σ</mi></math> level coming from the ACT CMB data alone and when combined with the Planck CMB and Baryon Acoustic Oscillations (BAO) measurements. This result is confirmed by both fixing the effective number of relativistic degrees of freedom in the early Universe to the Standard Model value of <math display="inline" id="d1e8052" altimg="si4.svg"><mrow><msub><mrow><mi>N</mi></mrow><mrow><mi mathvariant="normal">eff</mi></mrow></msub><mo linebreak="goodbreak" linebreakstyle="after">=</mo><mn>3</mn><mo>.</mo><mn>044</mn></mrow></math>, and allowing <math display="inline" id="d1e8071" altimg="si254.svg"><msub><mrow><mi>N</mi></mrow><mrow><mi mathvariant="normal">eff</mi></mrow></msub></math> to be a free cosmological parameter. Furthermore, when performing a Bayesian model comparison, the interacting <math display="inline" id="d1e8081" altimg="si193.svg"><mi>ν</mi></math>DM (+<math display="inline" id="d1e8086" altimg="si254.svg"><msub><mrow><mi>N</mi></mrow><mrow><mi mathvariant="normal">eff</mi></mrow></msub></math>) scenario is mostly preferred over a baseline <math display="inline" id="d1e8097" altimg="si194.svg"><mi>Λ</mi></math>CDM (+<math display="inline" id="d1e8102" altimg="si254.svg"><msub><mrow><mi>N</mi></mrow><mrow><mi mathvariant="normal">eff</mi></mrow></msub></math>) cosmology. The preferred value is then used as a benchmark and the potential implications of dark matter’s interaction with a sterile neutrino are discussed.