Scalar nonstandard neutrino interactions in galactic supernovae

The gist: Supernova neutrinos provide an exceptional environment to probe scalar nonstandard interactions, leveraging their unique features to resolve sharp time features of the neutronization burst.

Introduction and Motivation

Supernova neutrinos are produced in core-collapse supernovae, where more than 99% of the released gravitational energy is carried away by them <ref:2508.16558#pg2>. The study focuses on scalar nonstandard interactions (SNSI), which modify resonant flavor conversion and the neutronization burst signal <ref:2508.16558#pg3>. In the presence of SNSI, neutrinos propagating out of the dense supernova environment acquire a density-squared–dependent contribution to their mass-squared differences, which in turn modifies the energy levels of the neutrino mass eigenstates <ref:2508.16558#pg2>. This phenomenon is not present in less dense environments like the Earth or the Sun <ref:2508.16558#pg3>. For a given mass ordering, supernova neutrinos can improve the sensitivity to SNSI parameters by up to four orders of magnitude compared to that achievable with solar or terrestrial neutrino sources <ref:2508.16558#pg2>.

The Neutronization Burst and Standard Physics

The neutronization burst phase is the initial and most sharply defined in time phase of the neutrino emission, characterized by an intense, short-lived peak in the νe luminosity <ref:2508.16558#pg3>. This sharp temporal feature is a prominent and robust characteristic of virtually all spherically symmetric supernova simulations <ref:2508.16558#pg2>. During standard flavor conversion, neutrinos free-streaming in matter are described by the evolution Hamiltonian given in Eq. (2) <ref:2508.16558#pg2>. The occurrence of two distinct resonances, the H-resonance at ρH and the L-resonance at ρL, is a direct consequence of the existence of two separate mass-squared differences <ref:2508.16558#pg2>. In normal ordering, the initial νe flux transforms into a pure ν3 flux by the time it reaches Earth <ref:2508.16558#pg2>.

Scalar Nonstandard Interactions (SNSI)

In the presence of a new scalar particle ϕ that mediates non-standard interactions between neutrinos and fermions, the flavor transition probabilities are modified for neutrinos propagating through sufficiently dense media <ref:2508.16558#pg2>. The effective non-standard part of the Lagrangian is given by L eff f ⊃ −yf yαβ m2ϕ [¯νανβ][¯ff] <ref:2508.16558#pg2>. This interaction has the effect of modifying neutrino masses as Mαβ → Mαβ + δMαβ, where δMαβ = X f Nf yf yαβ m2ϕ <ref:2508.16558#pg2>. The SNSI parameter η⊙ αβ is defined as η⊙ αβ = p 3yqyαβρ⊙ ∆m221 m2ϕmN <ref:2508.16558#pg2>. This allows the mass shift to be incorporated into the neutrino Hamiltonian as δMαβ = q ∆m221 η⊙ αβ ρ/ρ⊙ <ref:2508.16558#pg2>.

Impact of Non-Zero SNSI

The evolution Hamiltonian in the presence of SNSI is given by HF = 1/2E Udiag(m1, m2, m3)U† + δM Udiag(m1, m2, m3)U† + 1/2E δM† + V diag(1, 0, 0) <ref:2508.16558#pg7>. The analysis shows distinct regimes determined by the local matter density and the SNSI parameter η⊙ ττ <ref:2508.16558#pg8>. For η⊙ ττ > 0.1, the term 2cτ τ δMτ τ starts to become comparable to, or even dominate over, the standard matter potential 2EV <ref:2508.16558#pg9>. In this regime, the details depend on the sign of η⊙ ττ and will be thoroughly analyzed in Sec. V C <ref:2508.16558#pg10>.

Observable Consequences at DUNE

For SNSI with ητ τ ≥ 10−4, the electron neutrino is produced as the second heaviest instantaneous eigenstate, i.e., νe ≈ ν m2 <ref:2508.16558#pg11>. If propagation remains adiabatic, the initial νe flux arrives at Earth as an incoherent flux of ν2 <ref:2508.16558#pg11>. This leads to a partial survival of the original electron neutrinos and allows the neutronization peak to become visible in terrestrial detectors such as DUNE <ref:2508.16558#pg11>. The visibility of the neutronization peak constitutes a potential smoking-gun signal of new physics, such as SNSI <ref:2508.16558#pg11>.

Conclusion

Supernova neutrinos provide an exceptional environment to probe SNSI parameters involving only non-electron flavors down to 10−4 <ref:2508.16558#pg14>. This highlights the importance of the next nearby supernova as a natural laboratory for BSM physics <ref:2508.16558#pg15>. The quadratic scaling of SNSI with density makes the supernova environment particularly suitable for testing them <ref:2508.16558#pg14>. The DUNE experiment could, in principle, be sensitive to η⊙ ττ values as small as 10−4 within the currently allowed ranges of oscillation parameters assuming m1 ≪ 0.01 eV.

How it works

**: The SNSI contribution to the ντ potential exceeds the standard matter potential experienced by νe within the neutrinosphere <ref:2508.16558#pg11>. As a result, the ντ state becomes effectively heavier at the production point, and the electron neutrino is produced as the second heaviest instantaneous eigenstate, i.e., νe ≈ ν m2 <ref:2508.16558#pg11>. If propagation remains adiabatic (see Sec. V B), the initial νe flux arrives at Earth as an incoherent flux of ν2 <ref:2508.16558#pg11>. This leads to a partial survival of the original electron neutrinos and allows the neutronization peak to become visible in terrestrial detectors such as DUNE <ref:2508.16558#pg11>. The resulting νe flux is given by Φ sNSIνe = Ue22Φiνe + Ue12 + Ue32 <ref:2508.16558#pg11>. This leads to a suppression of the neutronization peak in terrestrial νe detectors such as DUNE <ref:2508.16558#pg11>. The resulting time variation of the event rates in DUNE for a 12 M⊙ progenitor, with emission modeled by the α-fit [Eq. (1) and Fig. 1], is shown by the black line in the left panel of Fig. 6, where no signature of the neutronization peak is observed <ref:2508.16558#pg11>. The right panel shows the corresponding expected DUNE energy spectrum <ref:2508.16558#pg11>. The presence of SNSI with ητ τ ≥ 10−4 modifies the standard picture. If propagation is not fully adiabatic, the initially produced ν m2 (which approximately coincides with νe at production) can partially convert into ν m3, effectively restoring the standard scenario in part <ref:2508.16558#pg11>. The final flavor composition at Earth may lie between the SNSI–modified case and the standard MSW prediction <ref:2508.16558#pg11>. This intermediate behavior is illustrated by the pink curve in Fig. 6. The neutronization peak is noticeably more suppressed, though not entirely absent, and distinguishing the SNSI scenario from the standard case should, in principle, remain feasible, albeit experimentally more demanding <ref:2508.16558#pg11>. The asymptotic probabilities in vacuum (R ≳ 10 6 km) converge to the same values for both η⊙ ττ scenarios. This is significantly larger than in the standard NO case shown in Fig. 2 <ref:2508.16558#pg11>. The time and energy signals at DUNE in Fig. 6 are shown using bins of 5 ms and 5 MeV, respectively, with an energy threshold of 4 MeV <ref:2508.16558#pg11>. The number of neutrino–electron scattering events as a function of the visible energy can be obtained from the following expression dNe(Evis)dEvis = NAr Z E max ν 0 dEν Z t max n t min n dtFνe(Eν, t)σArCC(Eν)W(Evis, Eν), where W is the resolution function <ref:2508.16558#pg11>. The time and energy signals at DUNE in Fig. 6 are shown using bins of 5 ms and 5 MeV, respectively, with an energy threshold of 4 MeV <ref:2508.16558#pg11>. The number of neutrinos as a function of time can be expressed as dNe(t)dt = NAr Z E max ν 0 dEν Z Eν0 dEvisFνe(Eν, t)σArCC(Eν)W(Evis, Eν), where W is the resolution function <ref:2508.16558#pg11>. The contributions from the excited states are subdominant compared to those of the ground state <ref:2508.16558#pg11>. The effect of negative SNSI on ητ τ ≲ -0.1 is that a new resonance is still present, and this new resonance may occur simultaneously with the standard MSW resonances.

1. No-Standard Interaction (NSI) Parameter Estimation via Supernova Neutrinos: The improved AI system can perform a four orders of magnitude sensitivity analysis for SNSI parameters by leveraging the quadratic density dependence described as SNSI modify the neutrino mass matrix in the Hamiltonian, leading to ∗ dutta@tamu.edu changes in neutrino oscillation probabilities [29–31].

2. Resonance Mapping and Parameter Space Exploration: The system can map out a comprehensive parameter space by analyzing the evolution Hamiltonian in the flavor basis in the presence of SNSI as: HF = HvacF + HsNSIF + HSIF (13), allowing it to determine if the additional terms in Eq. (15) can rearrange the energy levels and modify the standard MSW picture, or even generate new matter resonances.

3. Distinguishing SNSI from Vector NSI: The AI system can differentiate between scalar and vector NSI effects by recognizing that vector NSI scale linearly with the local density, are not enhanced by higher powers of density, and therefore require couplings of similar strength to the weak interaction to produce observable effects, contrasting this with the quadratic scaling of SNSI.

4. Flavor Conversion Probability Prediction: The system can predict neutrino flavor evolution by calculating the flip probability between the instantaneous eigenstates νm2 and νm3, given by the Landau-Zener formula [64, 65], Pf = e − π / 2γ, allowing it to distinguish between fully adiabatic and partially nonadiabatic propagation regimes based on the calculated energy levels.

5. Kinematic Distortion Analysis: The system can assess the impact of SNSI involving flavors other than ντ, specifically noting that for η⊙µτ > 10−4, "both ντ and νµ receive large contributions from the quadratic term and start as the heaviest eigenstates in matter for η⊙µτ > 10−4."

We analyze the prospects for studying scalar nonstandard interactions (SNSI) using the neutrino burst from a galactic supernova (SN). SNSI modifies the resonant flavor conversion and, correspondingly, the neutronization burst signal, and may be identifiable in future multi-tonne-scale experiments, such as Deep Underground Neutrino Experiment (DUNE). Notably, in the normal mass ordering, SNSI can lead to an anomalous (re)appearance of the neutronization-burst ν e peak at Earth, a feature otherwise strongly suppressed in the Standard Model. We show that, in the presence of SNSI, neutrinos propagating out of the dense SN environment acquire a density-squared-dependent contribution to their mass-squared differences, which in turn modifies the energy levels of the neutrino matter eigenstates. This density-squared effect is absent in less dense environments such as the Earth or the Sun and is precisely what enables SN neutrinos to probe SNSI parameters up to 4 orders of magnitude below the values accessible to solar or terrestrial neutrino sources.