keVscale

KeV-scale refers to energies on the order of kilo-electronvolts (1 keV = 1000 eV). In physics, the term describes photons, electrons, or particle masses in the keV range. The keV scale sits between the lower-energy electronic volt (eV) range and higher-energy MeV and above, and is particularly relevant for X-ray phenomena and certain beyond-Standard Model scenarios.

In particle physics and cosmology, keV-scale masses are commonly discussed for sterile neutrino dark matter. A sterile neutrino with mass in the keV range would constitute warm dark matter, potentially produced in the early universe by neutrino oscillations or resonant production. These models aim to match large-scale structure with observational constraints.

In astrophysics, keV-scale photons are produced in hot astrophysical plasmas. Clusters of galaxies and the interstellar medium emit X-rays with characteristic energies of a few keV. Spectral lines and continua at keV energies are routinely observed by X-ray telescopes. Claims of an unidentified 3.5 keV line have been proposed as possible signals of dark matter decay, but remain contested.

Laboratories and detectors also work with keV-scale X-rays, arising from electronic transitions and radioactive decays. Experimental searches for keV-scale dark matter focus on looking for monochromatic X-ray lines from sterile neutrino decays, while X-ray backgrounds and instrumental systematics constrain such scenarios.

Constraints on keV-scale new physics come from cosmology, such as the Lyman-alpha forest and the cosmic X-ray background, as well as from direct detection and collider data. The keV regime therefore provides a testing ground between high-energy particle physics and astrophysical observations, informing sterile neutrino models, dark matter properties, and hot gas physics.