Speaker
Description
Cold, collisionless dark matter successfully explains a wide range of observations, including the formation of large-scale structure. Nevertheless, tensions remain on small (galaxy) scales. Reported discrepancies include the cusp-core (inner-mass-deficit) problem; the “diversity” of inner rotation-curve shapes and central densities at fixed halo mass; possible mismatches in the abundance and structure of subhaloes inferred from strong lensing in galaxies and clusters; and hints of unexpectedly strong spatial clustering for some populations of diffuse, low-mass galaxies. No single, generally accepted explanation resolves all of these phenomena simultaneously.
Here, making use of a toy yet representative model, we demonstrate that the unique properties of interacting dark-matter nontopological solitons (Q-balls) naturally explain these small-scale halo observations. Produced during the first-order phase transition in the dark sector, these Q-balls grow in the denser regions of halos, while their cross section decreases as the soliton mass increases. Both of these processes produce diffuse gravitational waves, providing a testable signature for future observations.
