Warm dark matter (WDM) is a hypothesized form ofdark matter that has properties intermediate between those ofhot dark matter andcold dark matter, causing structure formation to occur bottom-up from above their free-streaming scale, and top-down below their free streaming scale. The most common WDM candidates aresterile neutrinos andgravitinos. The WIMPs (weakly interacting massive particles), when produced non-thermally, could be candidates for warm dark matter. In general, however, the thermally produced WIMPs arecold dark matter candidates.
Sterile neutrinos with masses of a fewkeV are possible candidates for WDM. At temperatures below theelectroweak scale their only interactions with standard model particles areweak interactions due to theirmixing with ordinaryneutrinos. Due to the smallness of the mixing angle they are not overproduced because they freeze out before reaching thermal equilibrium. Their properties are consistent with astrophysical bounds coming from structure formation and thePauli principle if their mass is larger than 1-8 keV.[citation needed]
Another possible WDM candidate particle comes from introducing two new, zero charge, zerolepton numberfermions to theStandard Model of Particle Physics: "keV-mass inert fermions" (keVins) and "GeV-mass inert fermions" (GeVins). keVins are overproduced if they reach thermal equilibrium in the early universe, but in some scenarios theentropy production from the decays of unstable heavier particles may suppress their abundance to the correct value. These particles are considered "inert" because they only have suppressed interactions with theZ boson.[citation needed]
In February 2014, different analyses[1][2] have extracted from the spectrum of X-ray emissions observed byXMM-Newton, a monochromaticsignal around 3.5 keV. This signal is coming from differentgalaxy clusters (likePerseus andCentaurus) and several scenarios of warm dark matter can justify such a line. This signal could be explained by 3.5 keV WDM annihilating into 2 photons,[3] or 7 keV WDM decaying into a photon and a neutrino.[4]
In November 2019, analysis of the interaction of various galactic halo matter on densities and distribution of stellar streams, coming off the satellites of the Milky Way, they were able to constrain minimums of mass for density perturbations by warm dark matter in the GD-1 and Pal 5 streams. This lower limit on the mass of warm dark matter thermal relics mWDM > 4.6 keV; or adding dwarf satellite counts mWDM > 6.3 keV.[5]
This articleneeds additional or more specificcategories. Pleasehelp out byadding categories to it so that it can be listed with similar articles.(September 2024)
