The scientific program is focused on the investigation of the origin of mass and its consequences. The notion of mass and its generation permeates many aspects of fundamental physics. At the microscopic level it is intimately related to the mysterious nature of the vacuum and how particles acquire mass, to the questions of how matter forms and why there is much more matter than anti-matter.

At the macroscopic level, it is intimately related to gravity, and to the observation that there is roughly five times more dark, non-luminous matter than ordinary matter. It is deeply rooted in the dynamics and history of the Universe through the even more mysterious presence of dark energy and the accelerating expansion. The project is original and innovative as it brings together physicists from different fields, from particle physics to cosmology, using different methodological approaches (from mathematical physics to instrumentation), sharing a common interest in the enigma of mass.

The program is organized in three work packages, as described below with strong interconnections between them.

Work Package 1: Origin of mass and search for new physics

During Enigmass1, the Higgs boson was discovered. This constitutes a major achievement in the domain of the enigma of mass. The consortium played a key role in both this discovery and the exploitation of the early results on the Higgs couplings. The experimental data acquired so far point to the simplest, renormalizable version of spontaneous symmetry breaking. Non-discovery of new physics at the LHC, combined with the particular value of the Higgs mass, has ushered a new paradigm.
Enigmass2 will probe some of the key issues of this new landscape. Higgs physics and the concomitant understanding of the structure of the vacuum feature prominently in its research program. Searches for sources of CP violation beyond the standard model (SM) are the second key theme as they are relevant to the matter/anti-matter asymmetry in the Universe.

The search for new physics (NP) requires novel strategies. NP can still be energetically accessible at the LHC but difficult to detect. In this respect, long-lived particles are interesting possibilities that call for new search methods. For instance, new models put forward by members of the consortium need a strong collaboration with experimentalists to resolve detector issues in the corresponding searches (tracker, as well as jet reconstruction). The connection of these non-conventional particles to dark matter (DM) should also be looked at in a new light. Through the DM connection, this topic straddles all three WPs.

Work package 2: Gravitational waves and multi-messenger science

The discovery of gravitational waves (GW) was one of the major milestones achieved during Enigmass1, opening up a rich science program initiated with the results obtained from the binary black hole and binary neutron star mergers detected so far by LIGO and Virgo. The binary neutron star merger GW170817 was also a spectacular and ground-breaking multi-messenger event, with its short gamma ray burst and kilonova counterparts. Multi-wavelength and multi-messenger observations are key tools to characterize GW sources, the high-energy sky, and cosmic rays, in order to address major open questions in fundamental physics, astrophysics and cosmology. Through remarkable synergies, the consortium is in a unique position to have a high-impact contribution in this line of research within Enigmass2, through experimental and theoretical activities, including strong involvement in several ESFRI projects.

Work package 3: Dark matter and dark energy in the Universe or the standard model of cosmology

One of the prominent problems of modern physics is the existence of the so-called dark matter. This essential component of the Universe is still of unknown nature. It cannot be made of ordinary atoms, yet it pervades galaxies and clusters. Its presence on cosmological scales has been confirmed by the Planck mission, a project in which Enigmass1 was deeply involved. Planck results are also consistent with a Universe dominated by dark energy, a fluid whose negative pressure is driving a re-acceleration of the expansion. The seeds at the origin of galaxies and clusters of galaxies have presumably been processed during a primordial phase of inflation. Understanding the nature of DM is one of the goals of the consortium, tackled using four different approaches.