In this proposal, we will explore the hypothesis that dark matter is made of feebly interacting particles or particle-like objects, necessarily produced via non-thermal cosmological
processes. We have selected two promising research avenues in this category, primordial black holes and cosmological scalar fields, for which we aim to:
1. Explore new cosmological production mechanisms;
2. Devise novel embeddings within SM extensions;
3. Identify innovative indirect detection methods.
The first goal is aimed at addressing particular problems with known cosmological production mechanisms, e.g. the generation of large isocurvature perturbations and fine-tuning of initial conditions in the case of axion dark matter [9]. We also plan to connect such candidates with other open problems in cosmology, namely the common origin of dark matter and the asymmetric baryonic matter suggested by their comparable abundances.
The second goal is aimed at relating dark matter candidates with other open problems in particle physics, such as neutrino masses or the strong CP-problem. Several extensions of the SM have been proposed to address these individual problems, but not necessarily in conjunction. Our main goal is to follow a "bottom-up" approach to devise minimal theoretical models that can address several problems simultaneously, with as few ingredients as possible. We expect this to be sufficiently constraining to yield distinctive predictions for the properties of dark matter. This approach will nevertheless be guided by known generic features of more complete theories such as grand unified theories or string theory, on which senior team members have a broad expertise.
Our third goal is naturally aimed at overcoming the challenges of directly detecting feebly interacting dark matter in the laboratory. In addition to large dark matter densities, strong magnetic fields can also enhance interaction processes, e.g. in the case of photon-axion conversion. Furthermore, gravitational instabilities such as black hole superradiance or other resonant effects may lead to localized dark matter overdensities, which themselves induce stronger interactions such as stimulated emission or decay [7].
Such processes remain rather unexplored but may constitute some of the most promising ways to understand the nature of dark matter, and we plan to take full advantage of this new era of multi-messenger astronomy that we are living in. In particular, we plan to use available data from gravitational wave detectors (LIGO, Virgo and KAGRA), microlensing experiments (OGLE, Subaru-HSC), CMB experiments (Planck, BICEP/Keck), X-ray telescopes (XMM-Newton) and radio telescopes (e.g. CHIME) to constrain our models. We will also make concrete predictions for planned experiments such as the LISA satellite, the CMB-S4 telescope array and the Square Kilometer Array (SKA), which will be much more sensitive to signals from our elusive dark matter candidates. Through the PI and co-PI's membership of the Portuguese "Engage SKA" team, alongside March-Russell's and Ferreira's involvement in planned axion detectors, the results of this proposal will help shaping these experiments' science goals.
We also aim to find signatures of the underlying particle physics models, which typically include other particles besides the feebly interacting dark matter candidate, that can be searched for in the laboratory, particularly at the LHC in its planned high-luminosity upgrade. |