Sudip Jana

Although the sources of astrophysical neutrinos are still unknown, they are believed to be produced by a population of sources in the distant Universe. Measurements of the diffuse, all-sky astrophysical flux can thus be sensitive to flavor- and energy-dependent propagation effects, such as very long–baseline oscillations. These oscillations are present in certain neutrino mass models, such as when neutrinos are quasi-Dirac. Assuming generic models for the source flux, we find that these oscillations can still be resolved even when integrated over wide distributions in source redshift. We use two sets of IceCube all-sky flux measurements, made with muon and all-flavor neutrino samples, to set constraints at the 3 σ level on quasi-Dirac mass splittings between ( 5 × 10 − 19 , 8 × 10 − 19 ) eV 2 . Additionally, we find that when the mass-square splittings are different between generations, the quasi-Dirac scenario can explain tensions between the all-flavor and muon-flavor measurements. We consider systematic uncertainties on the source population and find that our results are robust under alternate spectral hypotheses or physical redshift distributions. Our analysis shows that spectral features in the all-sky neutrino measurements provide strong constraints on massive neutrino scenarios and are sensitive to uncharted parameter space.

Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model. The report reviews the experimental opportunities offered by the staged implementation of FCC, beginning with an electron-positron collider (FCC-ee), operating at several centre-of-mass energies, followed by a hadron collider (FCC-hh). Benchmark examples are given of the expected physics performance, in terms of precision and sensitivity to new phenomena, of each collider stage. Detector requirements and conceptual designs for FCC-ee experiments are discussed, as are the specific demands that the physics programme imposes on the accelerator in the domains of the calibration of the collision energy, and the interface region between the accelerator and the detector. The report also highlights advances in detector, software and computing technologies, as well as the theoretical tools/reconstruction techniques that will enable the precision measurements and discovery potential of the FCC experimental programme. The content and structure of this report are guided by the scope and priorities defined in the mandate of the FCC Feasibility Study. It is therefore not intended to serve as an exhaustive review of the full physics potential of FCC. Several topics, already covered in earlier reports such as the FCC CDR, are not reiterated here or are addressed only briefly, in alignment with the study’s focus. This volume reflects the outcome of a global collaborative effort involving hundreds of scientists and institutions, aided by a dedicated community-building coordination, and provides a targeted assessment of the scientific opportunities and experimental foundations of the FCC programme.

Neutrino non-standard interactions (NSI) play a crucial role in neutrino oscillations and can provide valuable insights for constructing models of neutrino masses and mixing. While NSI have been widely explored through oscillation and scattering experiments, as well as in cosmological and astrophysical contexts, we focus on probing them at future lepton colliders like the ILC, CLIC, and FCC-$ee$. If NSI arise from heavy mediators above the electroweak scale, these colliders can offer superior sensitivity compared to neutrino experiments across a broad mass range. A notable outcome is that lepton collider data can help resolve parameter degeneracies seen in oscillation studies. We find that large NSI scenarios, proposed to address the tension between T2K and NO$ν$A results, can be completely tested at such collider facilities. We also explore the potential of future colliders like the FCC to probe leptonic NSI using lepton PDFs in proton-proton collisions.

We show that non-standard neutrino interactions (NSI) can notably modify the pattern of resonant flavor conversion of neutrinos within supernovae and significantly impact the neutronization burst signal in forthcoming experiments such as the Deep Underground Neutrino Experiment (DUNE). The presence of NSI can invert the energy levels of neutrino matter eigenstates and even induce a new resonance in the inner parts close to the proto-neutron star. We demonstrate how DUNE can use these new configurations of energy levels to have sensitivity to NSIs down to 𝒪(0.1). We also elucidate how the effect may result in a puzzling confusion of normal and inverted mass orderings by highlighting the emergence or vanishing of the neutronization peak, which distinguishes between the two mass orderings. Potential implications are analyzed thoroughly.

We propose a simple extension to the Standard Model, wherein neutrinos naturally attain small Majorana masses through a one-loop radiative mechanism featuring particles within the loops characterized by milli-charges. Unlike the conventional scotogenic model, our approach avoids imposing a discrete symmetry or expanding the gauge sector. The minuscule electric charges ensure the stability of the lightest particle within the loop as a viable dark matter candidate. We systematically investigate for both, dark matter freeze-in and freeze-out, the far-reaching phenomenological implications arising from these minuscule charges.