Periodic Report Summary 2 - NUMASS (Neutrinos: a different portal to new physics Beyond the Standard Model)
The NuMass project focuses on the possibility that new physics, namely particles and/or interactions, exist at low energy scales, below the one reachable at the LHC. This approach is opposite to widely studied Standard Model extensions, which invoke new physics at scales so high that they will never be tested directly, and orthogonal to TeV models accessible at the LHC. The NuMass idea is that new particles in Nature could be hidden away not because they are too heavy but because, although light, they interact too weakly with ordinary matter. Neutrinos play a unique role as they are by far the least understood of the standard fermions: if new particles or interactions indeed exist at low scales, they could couple more strongly to neutrinos than to other standard particles, e.g. quarks. Therefore, neutrinos are a unique portal into low energy physics.
The NuMass project combines particle theory, phenomenology and cosmology in order to test this possibility. The project is progressing well and has made significant advances towards its objectives. A key results is the novel explanation for the MiniBooNE low energy excess of events, which invokes the existence of MeV sterile neutrinos and new light bosons. In this way, it has combined the usually separated fields of neutrino physics and dark photon searches with interesting consequences which will be further explored in the second part of the project. The currently running MicroBooNE experiment will be able to test this explanation. NuMass has also shown that this experiment, together with ICARUS and SBND in the SBN programme at Fermilab, can reach the best sensitivity to searches of heavy sterile neutrinos, exploiting the presence of a cluster of detectors and the unprecedented LAr event reconstruction capabilities. In addition to these short baseline neutrino experiments, NuMass has also considered the physics reach of long baseline neutrino oscillation experiments, combining T2HK and DUNE, and their ability to measure with precision the leptonic mixing parameters, providing key inputs to test their origin. NuMass has studied the latter problem, in terms of new flavour symmetries in the leptonic sector, and has addressed the related problem of the origin of neutrino masses, considering possible signatures of these models such as charge lepton flavour violation and collider signals. Complementary to this, NuMass has also considered the cosmological consequences of these models, proposing a novel mechanism for baryogenesis, arising from a CP-violating phase transition in the Early Universe, studying the possibility of interactions between dark matter and neutrinos and assessing the viability of non-standard cosmological models, specifically modified gravity ones.
The NuMass project combines particle theory, phenomenology and cosmology in order to test this possibility. The project is progressing well and has made significant advances towards its objectives. A key results is the novel explanation for the MiniBooNE low energy excess of events, which invokes the existence of MeV sterile neutrinos and new light bosons. In this way, it has combined the usually separated fields of neutrino physics and dark photon searches with interesting consequences which will be further explored in the second part of the project. The currently running MicroBooNE experiment will be able to test this explanation. NuMass has also shown that this experiment, together with ICARUS and SBND in the SBN programme at Fermilab, can reach the best sensitivity to searches of heavy sterile neutrinos, exploiting the presence of a cluster of detectors and the unprecedented LAr event reconstruction capabilities. In addition to these short baseline neutrino experiments, NuMass has also considered the physics reach of long baseline neutrino oscillation experiments, combining T2HK and DUNE, and their ability to measure with precision the leptonic mixing parameters, providing key inputs to test their origin. NuMass has studied the latter problem, in terms of new flavour symmetries in the leptonic sector, and has addressed the related problem of the origin of neutrino masses, considering possible signatures of these models such as charge lepton flavour violation and collider signals. Complementary to this, NuMass has also considered the cosmological consequences of these models, proposing a novel mechanism for baryogenesis, arising from a CP-violating phase transition in the Early Universe, studying the possibility of interactions between dark matter and neutrinos and assessing the viability of non-standard cosmological models, specifically modified gravity ones.