Neutrino Constraints on Scalar-Tensor Gravity

TL;DR

This work tackles scalar–tensor gravity by treating a static, inhomogeneous scalar background as a source of density-dependent SM masses via $m_{eff}=m_0 A(\varphi)$ and by studying neutrino observables. The authors develop a model-agnostic EFT framework for the conformal factor $A(\varphi)$, derive the neutrino propagation and oscillation dynamics in both Jordan and Einstein frames, and derive bounds from eight years of IceCube DeepCore atmospheric data as well as SN1987A time-delay considerations, finding no evidence for ST effects at 95% CL. They translate these bounds into constraints on screening models, notably the Symmetron and Chameleon, showing complementary sensitivity: atmospheric neutrinos probe smaller $M_s$ values while supernova neutrinos access larger $M_s$, with the Symmetron offering relatively broad sensitivity and the Chameleon remaining subdominant due to existing tests. The results illustrate that neutrino experiments provide a unique and complementary probe of scalar–tensor theories, capable of exploring parameter regions inaccessible to laboratory tests, and set the stage for stronger constraints with future SN events and precision neutrino measurements.

Abstract

In this work, we derive novel constraints on scalar-tensor theories from neutrino physics. Spatial variations of the background scalar field effectively generate density and position-dependent Standard Model masses, including neutrinos. Neutrinos are a unicum in the SM due to their ability both to propagate over galactic distances and to traverse dense media such as Earth. This makes them an ideal probe of the background scalar field, which can in turn alter flavour oscillations and supernova time delays. As we enter the era of precision neutrino physics, we are compelled to explore such a scenario. We derive expressions for the relevant observables and obtain new bounds on a broad class of scalar-tensor models. We finally map the bounds to popular screening mechanisms models, such as the Symmetron and Chameleon.

Figures (5)

• Figure 1: Summary of the region excluded in this work for the effective parameters defined in Eq. \ref{['eq:effective']}. For each analysis, we also include the EFT limit corresponding to $|\Delta m|\equiv|m_{\text{eff}}-m_0| = m_{0}$.
• Figure 2: Constraints at $95\%$ C.L. on the parameters of the Symmetron and of the Chameleon. EFT limits are represented by crossed fillings, and future prospects by dashed lines.
• Figure 3: Earth density profile. In this figure, we compare the Earth's density given by PREM associated with the Jordan frame with the new density obtained in scalar-tensor theories for $n = -0.5$ and $\alpha = 0.5$, computed in the Einstein frame.
• Figure 4: Muon survival probability ($P(\nu_{\mu} \rightarrow \nu_{\mu})$). We calculate the probability that muon neutrinos survive after crossing the Earth, for both the standard scenario (right) and the ST case with parameters $n = -0.5$ and $\alpha = 0.5$ (left).
• Figure 5: Event distribution. We present data corresponding to $9.3$ years of IceCube DeepCore observations (black dots), binned according to the $L/E$ ratio and including statistical uncertainties. The distributions are shown for track- and cascade-like events (left) and for track-like events only (right). Alongside the data, we display the MC predictions for three scenarios: the standard $3\nu$ scenario, a no-flavour-oscillation case, and the ST scenario with parameters $n = -0.5$ and $\alpha = 0.5$