Neutrino backgrounds in matter-wave interferometry: implications for dark matter searches and beyond-Standard Model physics

We present a comprehensive theoretical analysis of neutrino-induced decoherence in macroscopic matter-wave interferometry experiments designed to search for dark matter and beyond-Standard Model physics. Our calculation includes contributions from the cosmic neutrino background (C$ν$B), solar neutrinos, and reactor antineutrinos, accounting for coherent scattering processes across nuclear, atomic, and macroscopic length scales. Within the Standard Model, we find negligible decoherence rates for planned experiments such as MAQRO ($s/σ_s \sim 10^{-27}$) and terrestrial interferometers like Pino ($s/σ_s \sim 10^{-22}$). However, these experiments achieve competitive sensitivity to beyond-Standard Model physics through light vector mediator interactions, with C$ν$B constraining coupling products to $g_νg_n \lesssim 10^{-17}$ for $Z’$ masses below 1 eV. Our results provide a theoretical framework for interpreting matter-wave interferometry measurements in terms of neutrino interaction physics and for deriving constraints on BSM models from experimental data.

💡 Research Summary

This paper presents a comprehensive theoretical study of neutrino‑induced decoherence in macroscopic matter‑wave interferometers that are being developed for dark‑matter (DM) searches and for probing physics beyond the Standard Model (BSM). The authors first establish a formalism in which the loss of interference contrast is described by a complex amplitude γ = exp(−s + iϕ); the decoherence rate s is directly proportional to an interaction rate R that depends on the incident neutrino flux, the number of scattering targets of each type, the differential cross‑section, and a geometric decoherence probability p_decoh. The latter encodes the requirement that only momentum transfers with a component along the interferometer baseline Δx can resolve the spatial superposition; for |q·Δx|≪1 the probability scales as (q·Δx)²/2, while for |q·Δx|≫1 it saturates at unity.

A key contribution of the work is the identification of three distinct coherence regimes that arise from the hierarchical structure of the interferometer target: (1) Incoherent scattering (|q| r_particle ≫ 1) where neutrinos interact with individual nucleons or electrons and the cross‑section scales linearly with the number of constituents N; (2) Nuclear and atomic coherent scattering (|q| r_nuc ≲ 1 or |q| r_atom ≲ 1) where the neutrino wavelength is comparable to nuclear or atomic dimensions, leading to enhancements proportional to A² (nuclear) or Z² (atomic); (3) Macroscopic coherent scattering (|q| r_T ≲ 1) where the wavelength exceeds the whole target (typically a nanoparticle containing ~10¹⁰ atoms), giving the maximal N² A enhancement. The authors provide explicit differential cross‑sections for each regime, including nuclear, atomic, and macroscopic form‑factors that ensure smooth transitions and avoid double counting.

Three neutrino sources are considered: the cosmic neutrino background (CνB) with a relic density of ≈112 cm⁻³ per flavor and energies in the meV range, solar neutrinos (keV–MeV), and reactor antineutrinos (MeV). The CνB is essentially isotropic, with a small dipole anisotropy (β⊕≈10⁻³) due to Earth’s motion, while the solar and reactor fluxes are highly directional. The authors integrate the fluxes over energy and solid angle, applying the appropriate decoherence probability for each source and coherence regime.

Within the Standard Model, only neutral‑current vector couplings are relevant. Using realistic parameters for upcoming space‑based interferometers such as MAQRO (mass ≈10⁻¹⁷ kg, baseline Δx≈100 nm) and terrestrial setups like Pino (mass ≈10⁻¹⁸ kg, Δx≈50 nm), the calculated decoherence parameters are s ≈ 10⁻²⁷ and s ≈ 10⁻²² respectively—far below the experimental sensitivity. Hence, SM neutrinos constitute a negligible background for these experiments.

The paper then explores BSM scenarios featuring a light vector mediator Z′ with mass below 1 eV. In this case the effective coupling product g_ν g_n can be dramatically larger than the SM weak coupling, and the decoherence rate becomes appreciable. By demanding that the induced decoherence not exceed the projected sensitivity of MAQRO and Pino, the authors derive an upper bound g_ν g_n ≲ 10⁻¹⁷ for Z′ masses below 1 eV. This limit is competitive with, and in some parameter regions stronger than, existing astrophysical and cosmological constraints, highlighting the unique reach of matter‑wave interferometry in the ultra‑low‑energy regime.

The authors conclude that while neutrino‑induced decoherence is irrelevant for Standard Model physics in forthcoming interferometers, the same mechanisms provide a powerful probe of new light forces. The multi‑scale coherent scattering framework developed here offers a robust theoretical foundation for interpreting future interferometric data, assessing background contributions, and extracting limits on BSM interactions. Moreover, the analysis suggests that, should experimental sensitivities improve further, matter‑wave interferometers could even achieve the first laboratory‑based detection of the relic cosmic neutrino background.