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Probing Neutrinophilic Long-Range Forces at DUNE

This paper investigates a dark neutrino portal scenario where a light $U(1)_D$ gauge boson mediates ultra-long-range neutrinophilic forces, demonstrating that the Deep Underground Neutrino Experiment (DUNE) can probe previously unexplored parameter space that simultaneously addresses neutrino oscillation anomalies and the Hubble tension.

Original authors: Sudip Jana, Pragyanprasu Swain

Published 2026-07-07

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Sudip Jana, Pragyanprasu Swain

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

The Big Picture: Ghosts, Invisible Strings, and a Giant Detector

Imagine neutrinos as ghosts. They are tiny, invisible particles that pass through almost everything in the universe without bumping into it. Because they are so shy, they are perfect spies for discovering new, hidden forces of nature that we can't see with our current tools.

This paper proposes a new theory: What if these ghostly neutrinos are connected to a hidden "dark" world by an invisible string? This string is a force carried by a very light particle (a mediator) that only talks to neutrinos and a few other dark particles, ignoring everything else in our normal world.

The authors want to know: Can the upcoming DUNE experiment (a massive underground detector in the US) feel the tug of this invisible string?

The Setup: The "Dark Neutrino" Portal

Usually, we think of neutrinos interacting with matter (like the Earth or the Sun) through standard forces. But this paper suggests a new scenario:

The Hidden Door: There is a "dark sector" (a hidden room in the universe) where special "dark neutrinos" live.
The Mix: Our normal neutrinos occasionally "mix" with these dark neutrinos, like two people swapping hats for a moment.
The Invisible String: Because of this mix, our normal neutrinos can feel a new, ultra-long-range force generated by the dark sector.

The Analogy: Imagine you are walking through a crowded room (the Earth). Usually, you only bump into people you touch. But in this new theory, everyone in the room is also holding a very long, invisible rubber band connected to a giant, invisible trampoline in space. Even if you don't touch anyone, the tension in those rubber bands from the whole room pulls on you. This "pull" changes how you walk (how the neutrino moves).

The Two Types of "Pulls"

The paper looks at two ways this invisible string works, depending on how heavy the "string" particle is:

Short-Range (The Contact High-Five): If the string particle is heavy, the force is like a quick high-five. It only happens when particles are very close together. This is similar to what scientists have studied before (called Non-Standard Interactions).
Long-Range (The Cosmic Tug-of-War): If the string particle is incredibly light (almost weightless), the force stretches across huge distances. It's like a rubber band that can reach from the Earth to the Moon, the Sun, and even across the galaxy.
- The Effect: The paper calculates that the combined mass of the Earth, the Moon, the Sun, and the entire Milky Way galaxy creates a "matter potential" (a background pressure) that pushes or pulls on the neutrinos as they travel. This changes the way they oscillate (switch flavors) on their way to the detector.

The Experiment: DUNE as a Giant Net

The DUNE experiment is described as a 40,000-ton tank of liquid argon buried deep underground in a mine. It is 1,300 kilometers away from a particle accelerator in Illinois.

The Beam: Scientists shoot a beam of neutrinos from Illinois to South Dakota.
The Journey: As these neutrinos travel through the Earth, they pass through the "invisible rubber bands" created by the Earth's mass, the Sun's mass, and the galaxy's mass.
The Detection: If the invisible strings exist, they will change the pattern of neutrinos that arrive at the detector. The paper uses computer simulations to predict exactly how the "arrival pattern" would look different if these forces were real.

The "Double Bonus": Solving a Cosmic Mystery

Here is the most exciting part of the paper. The same invisible string that changes how neutrinos move through the Earth also makes neutrinos talk to each other in the early universe.

The Hubble Tension: There is a current disagreement in cosmology about how fast the universe is expanding. Some measurements say it's fast; others say it's slow. This is called the "Hubble Tension."
The Connection: The paper shows that if these invisible strings exist with the right strength, they would make neutrinos in the early universe stick together (self-interact) instead of flying apart freely. This "stickiness" could slow down the expansion just enough to fix the disagreement between the different measurements.

The Analogy: Imagine a party where the guests (neutrinos) usually dance alone. The invisible string makes them hold hands and dance in a group. This group dance changes the rhythm of the party (the universe's expansion) in a way that solves a mystery about how fast the party is growing.

What the Paper Actually Found

The authors ran simulations to see what DUNE could detect:

Sensitivity: DUNE is powerful enough to detect these forces even if they are incredibly weak. It can probe a vast range of "string" weights (from extremely light to heavier ones).
Flavor Matters: The effect depends on which type of neutrino is involved. The paper found that the detector is very good at spotting these forces if they affect electron and muon neutrinos, but less sensitive if they only affect muon and tau neutrinos.
The Sweet Spot: They identified specific ranges of "string strength" and "string weight" that DUNE could find. Crucially, some of these detectable ranges are exactly the ones needed to fix the Hubble Tension.

Summary

In short, this paper argues that the DUNE experiment isn't just a neutrino detector; it's a cosmic scale. By watching how neutrinos wiggle as they travel through the Earth, DUNE could detect the faint gravitational-like pull of a hidden dark sector. If found, this would not only prove the existence of a new force but could also explain why the universe is expanding at the rate we observe, solving one of the biggest puzzles in modern physics.

Technical Summary: Probing Neutrinophilic Long-range Forces at DUNE

Problem Statement
While neutrino oscillations have established a robust framework for describing neutrino propagation, the origin of neutrino masses and mixing remains unknown, motivating the search for physics beyond the Standard Model (SM). Nonstandard neutrino interactions (NSIs) are a primary avenue for such exploration. Existing literature has largely focused on short-range contact interactions mediated by heavy particles. However, ultralight mediators can induce long-range interactions (LRIs) where the cumulative matter distributions of astrophysical and cosmological structures generate significant matter potentials. A specific challenge in this domain is constructing models that generate flavor-dependent matter effects relevant for oscillations without violating stringent constraints from charged leptons and quarks. Standard flavor-universal extensions (e.g., $U(1)_{B-L}$ ) often fail to produce the necessary flavor structure or are heavily constrained by laboratory data.

Methodology
The authors investigate a "dark neutrino portal" scenario based on a $U(1)_D$ gauge symmetry. In this framework:

Model Structure: All Standard Model fermions are neutral under $U(1)_D$ , while right-handed (dark) neutrinos carry non-zero charges. The dark sector communicates with the SM exclusively through active–dark neutrino mixing and gauge boson mixing (kinetic and mass mixing between the SM $Z$ and the dark $Z_D$ ).
Interaction Mechanism: The model induces a neutrinophilic mediator. The mixing between active and dark neutrinos generates effective couplings to active neutrinos, while $Z$ – $Z_D$ mass mixing induces interactions with matter. This results in a new matter potential, $V_{\alpha\beta}$ , which acquires a non-trivial flavor structure proportional to $U_{\alpha4}U^*_{\beta4}$ (where $U_{\alpha4}$ represents the mixing between active flavor $\alpha$ and the dark state).
Regimes: The study analyzes both the short-range regime (mediator mass $m_{Z_D} \gtrsim 10^{-12}$ eV, reducing to contact interactions) and the long-range regime ( $m_{Z_D} \lesssim 10^{-12}$ eV), where the potential is described by a Yukawa form. In the long-range regime, the total potential includes contributions from the Earth, Moon, Sun, Milky Way, and cosmological matter distribution.
Benchmark Scenarios: To isolate flavor effects, the authors consider three benchmark textures where only one $2\times2$ submatrix of the interaction potential is non-zero: $e\mu$ , $e\tau$ , and $\mu\tau$ sectors.
Simulation: The authors utilize the Deep Underground Neutrino Experiment (DUNE) configuration (40 kt liquid-argon TPC, 1285 km baseline, 1.2 MW beam, 10 years exposure). They employ the GLoBES simulation framework with the snu.c probability engine to incorporate the new potentials. A Poissonian $\chi^2$ analysis is performed, varying the uncertain oscillation parameters $\theta_{23}$ and $\delta_{CP}$ while assuming normal mass ordering.

Key Contributions and Results

Flavor-Dependent Sensitivity: The study demonstrates that the oscillation phenomenology is strongly flavor-dependent.
- The $e\mu$ and $e\tau$ sectors exhibit resonance-like features in oscillation probabilities and event rates when the new potential strength approaches the vacuum and standard matter potentials ( $V_{new} \approx H_{vac} + V_{mat}$ ).
- The $\mu\tau$ sector does not exhibit such resonances because the new potential effectively reduces the standard matter potential, leading to lower sensitivity for DUNE in this specific configuration.
Projected Sensitivities:
- DUNE is projected to probe effective couplings as small as $g_{eff} \lesssim 10^{-28}$ for mediator masses of order $10^{-35}$ eV.
- The 3 $\sigma$ upper limits on the long-range potential $|V_{LRI}|$ are found to be $1.401 \times 10^{-14}$ eV ( $e\mu$ ), $9.604 \times 10^{-15}$ eV ( $e\tau$ ), and $1.672 \times 10^{-14}$ eV ( $\mu\tau$ ).
- These limits are competitive with existing constraints from global oscillation analyses, atmospheric neutrinos, and astrophysical observations.
Connection to Neutrino Self-Interactions (NSSI): A central finding is the intrinsic link between neutrino-matter interactions and neutrino self-interactions in this model. The same active–dark mixing parameters govern both phenomena.
- The authors map the DUNE sensitivity regions onto the effective neutrino self-interaction strength ( $G_{eff}^{4\nu}/G_F$ ).
- They identify regions of parameter space accessible to DUNE that correspond to self-interaction strengths relevant for alleviating the Hubble tension ( $G_{eff}^{4\nu} \sim (4.7^{+1.2}_{-1.8} \text{ MeV})^{-2}$ ).
- The results show that sizable neutrino self-interactions, capable of delaying neutrino free-streaming in the early Universe, can coexist with current oscillation constraints and be probed by DUNE.

Significance
The paper claims that the Deep Underground Neutrino Experiment (DUNE) is uniquely suited to probe neutrinophilic long-range forces due to its long baseline and pronounced matter effects. The study establishes that DUNE can access previously unexplored regions of parameter space for dark neutrino portals. Crucially, it demonstrates that a single underlying coupling mechanism can simultaneously generate observable long-range matter effects in terrestrial experiments and sizable neutrino self-interactions with cosmological implications. This provides a novel, unified probe for neutrino mass generation in secluded dark sectors and offers a potential pathway to resolving the Hubble tension through neutrino physics, all while remaining consistent with current oscillation data.