Emergent Large Lepton Mixing from Neutrino Refraction in Dark Matter
We propose a novel origin for the disparity between quark and lepton flavor mixing based on the refractive nature of neutrino masses. We postulate that the fundamental mixing in both the quark and lepton sectors is CKM-like, together with tiny vacuum neutrino masses, while the observed PMNS mixing matrix emerges dynamically from coherent forward scattering of neutrinos on an ultralight dark matter background. The resulting in-medium Hamiltonian rotates CKM mixing angles into large effective lepton mixings, naturally realizing quark--lepton complementarity without invoking new flavor symmetries. This framework links neutrino mass generation, flavor mixing, and dark matter, and predicts environment-dependent neutrino oscillation effects testable in current and future experiments.
Dark Matter Capture in a Core-Collapse Supernova Revives Dark Photons
Core-collapse supernovae serve as powerful probes of light, weakly coupled particles, such as dark photons. The conventional SN1987A cooling bound constrains the dark photon mass-mixing parameter space by requiring that the luminosity from the proto-neutron star core not exceed the observed neutrino emission. In this work, we revisit these limits by including the effect of dark matter (DM) captured inside the progenitor star before collapse. The trapped DM acts as an additional scattering target for dark photons, modifying their free-streaming length and, consequently, the supernova cooling rate. We perform a self-consistent analysis for both annihilating and asymmetric DM scenarios, incorporating light-mediator effects in the capture rate calculation. For annihilating DM, the equilibrium density remains too small to affect the bounds significantly. In contrast, asymmetric DM can accumulate to large densities, leading to the formation of a "dark photosphere" that suppresses the dark-photon luminosity and reopens previously excluded regions of parameter space. Our results emphasise the importance of accounting for astrophysical DM populations when deriving stellar-cooling constraints on dark sectors.
Dynamic Neutrino Mass Ordering and Its Imprint on the Diffuse Supernova Neutrino Background
Neutrino masses may have evolved dynamically throughout the history of the Universe, potentially leading to a mass spectrum distinct from the normal or inverted ordering observed today. While cosmological measurements constrain the total energy density of neutrinos, they are not directly sensitive to a dynamically changing mass ordering unless future surveys achieve exceptional precision in detecting the distinct imprints of each mass eigenstate on large-scale structures. We investigate the impact of a dynamic neutrino mass spectrum on the diffuse supernova neutrino background (DSNB), which is composed of neutrinos from all supernova explosions throughout cosmic history and is on the verge of experimental detection. Since neutrino oscillations are highly sensitive to the mass spectrum, we show that the electron neutrino survival probability carries distinct signatures of the evolving neutrino mass spectrum.
Supernova Neutrinos: Flavour Conversion Mechanisms and New Physics Scenarios
Invited review for the Special Issue "Neutrinos across Different Energy Scales'':
A core-collapse supernova (SN) releases almost all of its energy in the form of neutrinos, which provide a unique opportunity to probe the working machinery of an SN. These sites are prone to neutrino–neutrino refractive effects, which can lead to fascinating collective flavour oscillations among neutrinos. This causes rapid neutrino flavour conversions deep inside the SN even for suppressed mixing angles, with intriguing consequences for the explosion mechanism as well as nucleosynthesis. We review the physics of collective oscillations of neutrinos—both slow and fast—along with the well-known resonant flavour conversion effects and discuss the current state-of-the-art of the field. Furthermore, we discuss how neutrinos from an SN can be used to probe novel particle physics properties, extreme values of which are otherwise inaccessible in laboratories.
Diffuse neutrinos from past supernovae in the Universe present us with a unique opportunity to test dark matter (DM) interactions. These neutrinos can scatter and boost the DM particles in the Milky Way halo to relativistic energies allowing us to detect them in terrestrial laboratories. Focusing on generic models of DM-neutrino and electron interactions, mediated by a vector or a scalar boson, we implement energy-dependent scattering cross-sections and perform detailed numerical analysis of DM attenuation due to electron scattering in-medium while propagating towards terrestrial experiments. We set new limits on DM-neutrino and electron interactions for DM, using recent data from XENONnT, LUX-ZEPLIN, and PandaX-4T direct detection experiments.
Effects of neutrino-ultralight dark matter interaction on the cosmic neutrino background
Ultralight dark matter interacting with sterile neutrinos would modify the evolution and properties of the cosmic neutrino background through active-sterile neutrino mixing. We investigate how such an interaction would induce a redshift dependence in neutrino masses. We highlight that cosmological constraints on the sum of neutrino masses would require reinterpretation due to the effective mass generated by neutrino-dark matter interactions. Furthermore, we present an example where such interactions can alter the mass ordering of neutrinos in the early Universe, compared to what we expect today. We also address the expected changes in the event rates in a PTOLEMY-like experiment, which aims to detect the cosmic neutrino background via neutrino capture and discuss projected constraints.
Neutrino propagation through a turbulent medium can be highly non-adiabatic leading to distinct signatures in the survival probabilities. A core-collapse supernova can be host to a number of hydrodynamic instabilities which occur behind the shockfront. Such instabilities between the forward shock and a possible reverse shock can lead to cascades introducing turbulence in the associated matter profile, which can imprint itself in the neutrino signal. In this work, we consider realistic matter profiles and seed in the turbulence using a randomization scheme to study its effects on neutrino propagation in an effective two-flavor framework. We focus on the potential of upcoming neutrino detectors — DUNE and Hyper-Kamiokande to constrain the parameters characterizing turbulence in a supernova.
In this work, we consider in detail a possibility that neutrinos are originally massless and the observed neutrino oscillations are due to refraction on ultralight scalar boson dark matter. We introduce the refractive mass squared and study its properties: dependence on neutrino energy, state of the background, etc. This allows to reconcile the values of masses extracted from oscillation experiments with the stringent bounds on sum of neutrino masses from cosmological surveys.