The High Energy, Cosmology and Astroparticle Physics (HECAP) Abu Dhabi Workshop, held at New York University Abu Dhabi on Saadiyat Island from 13 to 15 January, brought together more than 30 researchers to discuss some of the deepest mysteries in fundamental physics.
A central theme was the effort to unravel the nature of dark matter (DM) and understand its production mechanisms, both in the early universe and in laboratory experiments. The traditional freeze-out paradigm, in which DM was once in thermal equilibrium with ordinary matter and froze out as the universe expanded and cooled, was contrasted with freeze-in scenarios, where DM is never in equilibrium and is produced through extremely weak interactions. In particular, Andrzej Hryczuk (NCBJ) analysed the production of multi-component dark sectors, including non-equilibrium effects such as conversions and cannibalisation processes, and Hyun Min Lee (Chung-Ang University) explored gravity-mediated DM scenarios. Complementary perspectives on DM phenomenology were presented by Nuria Rius (IFIC/UV), who discussed scenarios with warped extra dimensions where DM interacts gravitationally with Standard Model (SM) particles.
Search and research
The possible signatures of dark sectors at colliders were discussed by Giovanna Cottin (UC Chile), who emphasised that dark-sector particles may be long-lived and produce displaced vertices or other unconventional signatures at the LHC. The importance of dedicated searches and of reinterpreting existing LHC data was highlighted, together with the prospects offered by future facilities such as the Future Circular Collider.
A recurring theme was the connection between the origin of matter and the nature of dark matter. Cosmological observations directly establish a quark–antiquark asymmetry, conventionally identified with a baryon asymmetry under the assumption that the dark sector carries no compensating baryon number. Whether this assumption holds, and what its breakdown would imply, was a recurring question. Pilar Hernández (UV) discussed the link of this puzzle to neutrino masses, while a complementary scenario was presented in which the observed quark–antiquark asymmetry predicts the existence of DM, stabilised by the same symmetry that prevents proton decay.
Several presentations focused on the early universe as a probe of new physics. Javier Rubio (Universidad Complutense de Madrid) discussed Hubble-induced phase transitions triggered by the evolution of the scalar component of spacetime curvature after inflation, which can amplify field fluctuations, generate transient topological defects, and potentially lead to observable gravitational-wave signals. The role of early-universe dynamics in uncovering new physics was also highlighted by Basabendu Barman (SRM University), who discussed how cosmological observations may provide unique information about physics beyond the SM.
Closely related to these questions is the study of vacuum decay in scalar field theories. José Ramón Espinosa (IFT) showed that the standard semiclassical “bounce” picture can be extended to include pseudo-bounce and antibounce configurations, revealing a richer structure of vacuum decay channels than previously considered.
Thermal history
The reheating epoch following inflation was also discussed as a crucial stage in the thermal history of the universe, when it evolved from a nearly empty state to a hot radiation-dominated plasma. The details of this transition can significantly affect DM production and enlarge the viable parameter space for DM candidates, as discussed by Yann Mambrini (Université Paris-Saclay) and Kuldeep Deka (NYU Abu Dhabi).
Gravitational waves provide an important observational probe of these early-universe processes. Antonio Junior Iovino (NYU Abu Dhabi) discussed gravitational-wave signatures from primordial black holes across a wide range of frequencies and the prospects for detecting them with experiments ranging from pulsar timing arrays to the LIGO–Virgo–KAGRA network. Related aspects of gravitational-wave production in the early universe were addressed by Xunjie Xu (IHEP), who discussed the thermal generation of a cosmic gravitational-wave background.
A recurring theme was the connection between the origin of matter and the nature of dark matter
The workshop also covered precision tests of the SM. Yosef Nir (WIS, Rehovot) presented recent developments in flavour physics, including the puzzling measurement of the branching fraction of Bs → K0K0, which appears to be in tension with SM expectations based on flavour-symmetry relations. The decay proceeds dominantly through loop diagrams and is therefore sensitive to virtual contributions from new heavy particles. In addition, measurements of CP asymmetries in B → J/ψ π decays were discussed, as they help refine the determination of the CKM parameter sin(2β).
Alberto Casas (IFT) discussed how high-energy experiments can test fundamental aspects of quantum mechanics, including quantum entanglement and Bell non-locality, at unprecedented energy scales. In addition, Juan José Gómez Cadenas (DIPC) reviewed the status of searches for lepton-number violation and the progress of the NEXT experiment in probing neutrinoless double-beta decay.
Overall, the workshop provided an excellent forum to discuss recent developments at the interface of particle physics, cosmology and astroparticle physics, in particular in the search for physics beyond the SM. Many of the discussions illustrated how progress in understanding DM, the early universe and fundamental interactions increasingly relies on the interplay between theoretical work, laboratory experiments and astrophysical observations.
