⚛️ phenomenology

Probing long-range $L_e-L_\mu$ forces with supernova neutronization burst neutrinos

This paper demonstrates that future observations of neutronization-burst neutrinos from a nearby galactic supernova, such as Betelgeuse, using the DUNE detector can provide a sensitive probe for long-range $L_e-L_\mu$ forces by detecting observable distortions in the neutrino energy and time spectra caused by flavor-dependent ultralight gauge bosons.

Original authors: Amol Dighe, Sadashiv Sahoo, Manibrata Sen

Published 2026-07-29

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CC BY 4.0

Original authors: Amol Dighe, Sadashiv Sahoo, Manibrata Sen

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the universe is filled with invisible messengers called neutrinos. These tiny particles are the ghosts of the particle world; they have almost no mass, no electric charge, and they can pass through entire planets without bumping into a single atom. For decades, scientists have known these ghosts have a secret superpower: they can change their "flavor" as they travel. Think of it like a chameleon that starts as a blue lizard, turns green halfway through a journey, and ends up yellow. This shape-shifting, known as "neutrino oscillation," proved that neutrinos have mass, which was a huge surprise because the original rulebook of physics (the Standard Model) said they should be weightless.

But here is the mystery: we don't know why they change flavors or if there are invisible forces pushing them around. Some scientists suspect there might be new, ultra-weak forces acting over vast distances, like a gentle breeze that only affects specific types of neutrinos. If such a force exists, it would be a brand-new chapter in physics, revealing a hidden layer of reality that our current tools can't see. The big question is: how do we catch a ghost force that is so weak it's almost non-existent? The answer might lie in the most violent explosions in the universe: supernovas.

This paper is a detective story about how we might catch these invisible forces using a specific kind of cosmic explosion. The authors, a team of physicists, are looking at a very short, intense flash of neutrinos that happens right when a massive star collapses. This flash is called the "neutronization burst." It's like the star's "first breath" after it implodes. During this brief moment—lasting only a few tens of milliseconds—the star spits out a pure, concentrated beam of electron-neutrinos. Because this burst is so clean and predictable, it acts like a perfect laboratory. If there is a new, long-range force acting on these neutrinos, it should leave a fingerprint on the beam as it travels to Earth.

The team focused on a specific theory involving a new kind of force carrier, a particle called a "gauge boson," which creates a long-range potential. Imagine this potential as a vast, invisible ocean of energy stretching across the galaxy. If a neutrino swims through this ocean, its path might get nudged, changing how it transforms from one flavor to another. The authors simulated what would happen if these neutrinos traveled from a nearby star, Betelgeuse (which is about 168 parsecs away), to a giant detector called DUNE (Deep Underground Neutrino Experiment) located deep underground in the United States. DUNE is a massive tank filled with 40,000 tons of liquid argon, designed to catch these ghost particles.

The researchers ran detailed computer simulations to see how the "long-range interaction" (LRI) would change the signal DUNE would see. They found that if this new force exists, it would significantly alter the number of neutrinos that survive the journey and the energy they carry. In their simulations, the presence of this force could change the "survival probability" of the electron-neutrinos from a tiny fraction (about 2%) to nearly 100%, depending on the strength of the force and the type of neutrino mass ordering. This would look like a dramatic distortion in the time and energy patterns of the neutrino burst hitting the detector.

The paper suggests that if a supernova like Betelgeuse goes off, DUNE would be sensitive enough to spot these distortions. The team calculated that for certain strengths of this new force, the detector could see a clear difference between the "standard" physics we know and this new, exotic physics. They also found that the ability to spot this force depends heavily on whether neutrinos have a "normal" or "inverted" mass ordering (a technical way of describing how heavy they are relative to each other). In the "inverted" scenario, the detector would be even more sensitive, potentially seeing effects that current experiments using atmospheric neutrinos have missed.

However, the authors are careful to note that this is a prediction based on simulations, not a discovery. They haven't seen this force yet; they are just showing that if it exists, our next big detector could find it. They also point out that if the force is too weak or the interaction range is too short, the effect would be invisible, just like trying to feel a breeze while standing in a hurricane. But if the force is strong enough and stretches far enough, the "breeze" from the Sun and the galaxy would be strong enough to nudge the neutrinos in a way DUNE can measure.

In short, this paper argues that the next time a nearby star explodes, the flash of neutrinos it sends us could be the key to unlocking a new, long-range force in nature. By watching how these particles behave during that split-second burst, we might finally catch a glimpse of physics that goes beyond what we currently understand, turning the supernova into a giant, cosmic microscope for the invisible forces of the universe.

Technical Summary: Probing Long-Range $L_e - L_\mu$ Forces with Supernova Neutronization Burst Neutrinos

Problem and Motivation
Neutrino oscillations provide the first experimental evidence of physics beyond the Standard Model (BSM), yet the origin of neutrino masses and flavor structure remains unknown. A significant class of BSM models predicts the existence of flavor-dependent long-range interactions (LRIs) mediated by ultralight gauge bosons associated with additional $U(1)'$ symmetries, such as $L_e - L_\mu$ , $L_e - L_\tau$ , and $L_\mu - L_\tau$ . While these interactions are constrained by solar, atmospheric, and long-baseline data, a substantial parameter space remains open.

Standard terrestrial experiments struggle to detect these interactions if the mediators are sufficiently light, as the forces are extremely weak. However, astrophysical neutrinos traveling over macroscopic distances offer a unique laboratory. Specifically, the neutronization burst phase of a core-collapse supernova (CCSN)—occurring within the first $\sim 25$ ms after core bounce—is dominated by electron neutrinos ( $\nu_e$ ) produced via electron capture. In the standard scenario, adiabatic propagation through the stellar envelope causes these $\nu_e$ to emerge as specific mass eigenstates ( $\nu_3$ for Normal Mass Ordering (NMO) and $\nu_2$ for Inverted Mass Ordering (IMO)). The authors propose that ultralight mediators could generate a long-range potential sourced by electrons in the supernova, the Sun, the Earth, and the galaxy. This potential persists over astronomical distances, potentially altering the effective mixing angles and survival probabilities of neutrinos arriving at Earth, thereby distorting the observable signal in terrestrial detectors.

Methodology
The authors investigate the sensitivity of the Deep Underground Neutrino Experiment (DUNE), specifically its 40 kt Liquid Argon Time Projection Chamber (LArTPC), to LRIs within the anomaly-free $U(1)'_{L_e - L_\mu}$ framework.

Theoretical Framework:
- The study incorporates a long-range potential $V'_e$ generated by the $L_e - L_\mu$ symmetry. This potential is sourced by the electron number density of various astrophysical bodies (Supernova, Sun, Earth, Moon, Milky Way, and extragalactic regions).
- The effective Hamiltonian for neutrino propagation includes the standard vacuum term, the standard MSW matter potential ( $V_{cc}$ ), and the new LRI potential ( $V'_e$ ).
- The authors derive the electron-neutrino survival probability ( $P_{ee}$ ) at Earth as a function of the effective mixing angles ( $\tilde{\theta}^E_{12}, \tilde{\theta}^E_{13}$ ) modified by the combined potentials. They analyze the level-crossing diagrams for both NMO and IMO scenarios.
Simulation and Detector Response:
- Source: The benchmark source is Betelgeuse, located at $\sim 168$ pc, modeled using a 1D hydrodynamical simulation of a $25 M_\odot$ progenitor (Garching group).
- Signal: The simulation focuses on the neutronization burst, assuming a pinched quasi-thermal energy spectrum.
- Detection: The dominant channel is the charged-current interaction $\nu_e + ^{40}\text{Ar} \to ^{40}\text{K}^* + e^-$ . The analysis uses the MARLEY event generator and models detector resolution via Gaussian smearing ( $\sigma_E = 0.11\sqrt{E/\text{MeV}} + 0.2(E/\text{MeV})$ ).
- Statistical Analysis: A frequentist approach is employed using a binned $\chi^2$ analysis over reconstructed energy and post-bounce time. The analysis accounts for systematic uncertainties (flux normalization, cross-section, and overall normalization) using pull variables. The sensitivity is quantified by $\Delta \chi^2$ between the Standard Model Interaction (SMI) hypothesis and the LRI hypothesis.

Key Contributions and Results

Modification of Survival Probability: The authors demonstrate that when the LRI potential is comparable to or dominates the vacuum oscillation term, the electron-neutrino survival probability ( $P_{ee}$ $P_{ee}$ ) can be significantly modified.
- In the NMO scenario, $P_{ee}$ can vary from the standard value of $\approx 0.022$ up to nearly unity.
- In the IMO scenario, $P_{ee}$ can vary from $\approx 0.30$ up to $\approx 0.98$ .
- These variations depend on the neutrino energy and the magnitude of the potential, which is a function of the coupling $g'_e$ and the mediator mass $m_{Z'}$ (or interaction range $\lambda$ ).
Observable Distortions: The modification of $P_{ee}$ leads to distinct distortions in both the temporal and energy distributions of the event rates in DUNE. The study shows that for a benchmark point ( $g'_e = 10^{-25}, \lambda = 1$ kpc), the solar contribution to the potential dominates, producing observable deviations from the standard SMI profile.
Sensitivity Projections:
- The projected sensitivity of DUNE to the coupling $g'_e$ is presented in the $(g'_e, m_{Z'})$ plane.
- The sensitivity is highly dependent on the interaction range $\lambda$ . For very short ranges, the potential is suppressed; for very long ranges, it saturates. The transition region, where $\lambda$ is comparable to astrophysical distances (Earth-Sun, Earth-SN), shows the most rapid improvement in sensitivity.
- Mass Ordering Dependence: The sensitivity is significantly stronger for the Inverted Mass Ordering (IMO) than for NMO. This is attributed to the higher baseline survival probability in IMO ( $\approx 0.30$ ), which allows for larger absolute deviations in event rates compared to the very small baseline in NMO ( $\approx 0.022$ ).
- For a Betelgeuse-like supernova, the projected sensitivity in the IMO case can exceed current constraints derived from multi-GeV atmospheric neutrinos in IceCube (DeepCore) over a significant portion of the parameter space.

Significance
The paper claims that future observations of galactic supernova neutrinos, particularly from a nearby event like Betelgeuse, provide a sensitive and complementary probe of flavor-dependent long-range leptonic interactions. The neutronization burst is highlighted as an exceptionally clean laboratory because its initial flavor composition is well-understood (dominated by $\nu_e$ ) and largely independent of collective oscillation effects or uncertainties in the supernova explosion mechanism.

The authors emphasize that this method allows for the exploration of extremely small coupling regimes and ultralight mediator masses that are inaccessible to conventional laboratory experiments. While the sensitivity is maximized for nearby sources, the methodology remains robust for more distant galactic supernovae, offering a unique window into new forces in the lepton sector. The results suggest that DUNE could provide constraints that are competitive with or superior to existing global fits and astrophysical bounds, depending on the true neutrino mass ordering.

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