⚛️ phenomenology

Dark matter scattering with pre-supernova neutrinos

This paper proposes using the attenuation of pre-supernova neutrino fluxes in large-volume detectors like KamLAND, JUNO, and Super-K to derive upper limits on dark matter-neutrino scattering cross sections, offering a unique MeV-energy probe that complements post-b supernova constraints and tests early-universe dark matter models.

Original authors: Sangeetha N. Tallur, Nirmal Raj

Published 2026-07-07

📖 4 min read🧠 Deep dive

CC BY 4.0

Original authors: Sangeetha N. Tallur, Nirmal Raj

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 a giant, dark ocean, and we are trying to find out if there are invisible fish (Dark Matter) swimming in it. Usually, scientists try to catch these fish by waiting for them to bump into a net (a detector) on the ocean floor. But what if the fish are too shy to hit the net directly?

This paper proposes a clever new way to "see" these invisible fish by watching how they mess with a very specific kind of light: neutrinos (ghostly particles) coming from a dying star just before it explodes.

Here is the story of the paper, broken down into simple parts:

1. The "Warning Light" (Pre-Supernova Neutrinos)

Before a massive star explodes (a supernova), it goes through a final, chaotic day of burning fuel. During this time, it emits a steady stream of neutrinos. Think of this as the star's "warning light" or a final heartbeat before it goes dark.

The Problem: These neutrinos are faint and low-energy, making them hard to catch.
The Opportunity: Because they are emitted before the explosion, they give us a unique window of time to study them.

2. The Invisible Obstacle Course (Dark Matter Scattering)

The paper suggests that on their journey from the dying star to Earth, these neutrinos might bump into Dark Matter particles.

The Analogy: Imagine you are throwing a bunch of tennis balls (neutrinos) from a stadium in India to a stadium in the US. If the air between the two stadiums is filled with invisible, sticky cotton candy (Dark Matter), some of the tennis balls will get stuck or knocked off course.
The Result: When the balls finally arrive at the US stadium, there will be fewer of them than you expected.

3. The Detective Work (Counting the Missing Balls)

The authors looked at three giant "nets" (detectors) on Earth: Super-Kamiokande, KamLAND, and JUNO. These are massive tanks of water or liquid that can catch neutrinos.

They calculated exactly how many neutrinos should arrive from a nearby dying star (about 150 light-years away).
They then asked: "If Dark Matter is there, how many neutrinos would be missing?"
If the detectors count significantly fewer neutrinos than the math predicts, it's a sign that Dark Matter intercepted them.

4. Why This is Special (The "Low Energy" Advantage)

You might think, "Why not just wait for the big explosion (the supernova)?" The paper argues that the pre-explosion neutrinos are actually better for certain types of Dark Matter.

The Analogy: Think of the explosion neutrinos as high-speed race cars (high energy) and the pre-explosion neutrinos as slow-moving bicycles (low energy).
If the invisible cotton candy (Dark Matter) is sticky only for slow things, the race cars might zoom right through it, but the bicycles will get stuck.
The paper shows that these "bicycle" neutrinos (around 2 MeV of energy) are perfect for testing specific theories about Dark Matter that other methods miss.

5. The "Cosmic Clue" (Lyman-alpha Data)

There is a hint from deep space data (called Lyman-alpha data) that suggests Dark Matter might be interacting with neutrinos in the early universe, suppressing the formation of small structures.

The paper shows that if this hint is true, the "missing neutrino" test using pre-explosion signals could be the perfect way to confirm it. It's like finding a fingerprint that matches a suspect seen in a blurry security camera photo.

Summary of the Conclusion

The authors didn't find Dark Matter in this paper; instead, they built a blueprint for how to find it.

They calculated the limits: "If we see fewer neutrinos than this, we know Dark Matter exists."
They showed that even if the next supernova is a rare event, watching for these "pre-explosion" signals gives us a unique, independent way to check our theories about the invisible universe.
It's a "cross-check": If we see the same result with these slow neutrinos as we do with the fast ones from an explosion, we can be very confident in our understanding of Dark Matter.

In short: The paper suggests using the "final warning" of a dying star as a cosmic flashlight to see if invisible Dark Matter is blocking the light on its way to Earth.

Technical Summary: Dark Matter Scattering with Pre-Supernova Neutrinos

Problem Statement
The particle identity of dark matter (DM) remains unknown, and while direct detection experiments have placed extensive constraints on DM interactions with nuclei and electrons, the possibility that the dominant Standard Model (SM) portal to DM is the neutrino sector has been less explored in the context of pre-supernova environments. While post-bounce supernova neutrinos (SN $\nu$ ) have been used to constrain DM-neutrino scattering via flux attenuation and time-delay effects over kiloparsec baselines, pre-supernova neutrinos (preSN $\nu$ )—emitted during the final days of a massive star's evolution—offer a distinct, albeit lower-statistics, probe. The central problem addressed is whether the attenuation of the preSN $\nu$ flux due to scattering with Galactic dark matter can be used to derive competitive or unique constraints on the DM-neutrino reduced scattering cross section ( $\sigma_{\chi\nu}/m_\chi$ ), particularly in the MeV energy regime.

Methodology
The authors estimate the sensitivity of large-volume, low-threshold detectors (Super-Kamiokande, KamLAND, and JUNO) to DM-preSN $\nu$ interactions. The methodology proceeds as follows:

Flux Modeling: The study utilizes preSN $\nu$ spectra from a $15M_\odot$ progenitor model (Ref. [30], tabulated in Ref. [47]), focusing on electron anti-neutrinos ( $\bar{\nu}_e$ ) produced primarily via $e^+e^-$ pair annihilation. The differential luminosity $d^2N_\nu/dE_\nu dt$ is tracked from hours to minutes before core collapse.
Event Rate Calculation: Expected event counts ( $N_{tot}$ ) in the inverse beta decay (IBD) channel ( $\bar{\nu}_e + p \to n + e^+$ ) are calculated for a progenitor distance of $d_\star = 150$ pc. The calculation integrates the energy-dependent cross section over the detector energy thresholds ( $E_{th}$ ) and the time evolution of the flux, distinguishing between the progenitor phase ( $t > 0.1$ s) and the collapse phase ( $t < 0.1$ s).
Attenuation Criterion: The signal is defined as a deficit in the expected event count due to DM scattering. The optical depth $\tau_\chi$ is defined as $\tau_\chi = \rho_\chi (\sigma_{\chi\nu}/m_\chi) d_\star$ , assuming a local DM density $\rho_\chi = 0.4$ GeV/cm $^3$ .
Limit Derivation: Upper limits on the reduced cross section are derived by requiring a flux deficit corresponding to a $2\sigma$ significance. This is achieved by setting $\tau_\chi = 2 \times \text{total fractional uncertainty}$ , where uncertainties are the quadrature sum of statistical ( $\sqrt{N_{tot}}$ ) and systematic errors. The resulting limit is given by $(\sigma_{\chi\nu}/m_\chi) \leq 2 / (\rho_\chi d_\star \sqrt{N_{tot}})$ .

Key Contributions and Results

First Application of PreSN $\nu$ to BSM Physics: This work represents the first attempt to use pre-supernova neutrinos to study physics beyond the Standard Model, specifically DM-neutrino scattering.
Quantitative Sensitivities: The authors derive upper limits on $\sigma_{\chi\nu}/m_\chi$ for Super-K, KamLAND, and JUNO. For a $15M_\odot$ progenitor at 150 pc, the $2\sigma$ limits range from approximately $0.54 \times 10^{-21}$ cm $^2$ /GeV (JUNO, collapse phase) to $26 \times 10^{-21}$ cm $^2$ /GeV (KamLAND, progenitor phase). JUNO provides the strongest constraints due to its large target mass and low energy threshold (1.8 MeV).
Energy Dependence and Model Discrimination: The paper highlights that while preSN $\nu$ $ν$ limits are generally weaker than those from post-bounce SN $\nu$ $ν$ (due to smaller DM column densities and lower statistics), they probe a distinct energy range (centered around 2 MeV, extending to 5–7 MeV) compared to the $\mathcal{O}(10)$ $O (10)$ MeV range of post-bounce neutrinos. This allows for the testing of models with:
- Resonant scattering peaked near 1 MeV.
- Light mediators that enhance infrared (soft) scattering.
- Specific energy dependencies (e.g., $\sigma \propto E_\nu^n$ ), where the ratio of limits between pre- and post-bounce neutrinos could reveal the cross-section's energy scaling.
Cosmological Cross-Check: The authors demonstrate that preSN $\nu$ measurements can test the $3\sigma$ hint from Lyman- $\alpha$ data suggesting DM-neutrino scattering suppresses small-scale power. They show that for interaction models where the cross section scales steeply with energy (e.g., $\sigma_{\chi\nu} \propto E_\nu^{3.8}$ ), preSN $\nu$ data could provide the necessary constraints to test this cosmological hint, a regime where other limits are less sensitive.

Significance and Claims
The paper claims that preSN $\nu$ provide a unique and necessary cross-check to post-bounce SN $\nu$ limits, rather than merely a weaker alternative. The significance rests on several distinct advantages:

Reduced Systematics: The preSN $\nu$ flux is determined by stellar evolution codes and thermodynamic profiles (temperature, density, electron fraction), which are theoretically cleaner than the complex explosion dynamics, shock instabilities, and equation-of-state dependencies governing post-bounce SN $\nu$ fluxes.
Local DM Density: The sub-kiloparsec baselines of preSN $\nu$ depend only on the local DM density (uncertainty $\sim 100\%$ ), avoiding the large uncertainties associated with integrating DM column densities over the $\mathcal{O}(10)$ kpc distances of typical supernovae.
Robustness to "Failed" Supernovae: In scenarios where a progenitor collapses directly to a black hole without a successful explosion (a "failed" supernova), post-bounce neutrino signals may be absent or severely suppressed, whereas the preSN $\nu$ flux remains a viable probe.
Dark Disk Scenarios: In models featuring a dissipative dark disk aligned with the baryonic disk, the DM column density for distant supernovae might be dominated by the disk, potentially weakening standard SN $\nu$ limits, thereby elevating the importance of the local preSN $\nu$ probe.

The authors conclude that while the occurrence of a nearby ( $\sim 100$ pc) supernova is a rare event, the distinct characteristics of preSN $\nu$ make them a worthwhile and independent probe for cornering new fundamental physics, particularly regarding the energy dependence of DM-neutrino interactions.