Astrophysical and cosmological observations, such as those from the cosmic microwave background (CMB) and galaxy rotation curves, suggest that about 26% of the universe’s total energy density is made up of dark matter. Despite its crucial role in shaping the large-scale structure of the universe, the true nature of dark matter remains one of the deepest mysteries in modern physics. Since the Standard Model (SM) of particle physics cannot explain dark matter, it has sparked extensive exploration of physics beyond the SM.
One of the most studied frameworks is the weakly interacting massive particle (WIMP) scenario, where dark matter particles weakly interact with SM particles and were once in thermal equilibrium in the early universe. However, the persistent absence of signals from direct detection experiments has increasingly challenged traditional WIMP models, motivating a search for new theoretical directions.
Pseudo-Nambu-Goldstone boson (pNGB) dark matter offers a compelling variation within the WIMP paradigm. It arises from the spontaneous and soft breaking of global symmetries, leading to naturally suppressed interactions with nucleons while still allowing efficient annihilation into SM particles. Moreover, the derivative nature of its couplings reduces scattering amplitudes at low momentum transfers, making pNGB dark matter an especially attractive and viable candidate in light of current experimental constraints.
