[Paper Review] Matter density, symmetry breaking, and neutrino oscillation

H. Mohseni Sadjadi, Amir-Pouyan Khosravi|arXiv (Cornell University)|Nov 15, 2017

Cosmology and Gravitation Theories14 references3 citations

TL;DR

This paper proposes a neutrino mass mechanism where neutrino mass arises from spontaneous $Z_2$ symmetry breaking of a scalar field nonminimally coupled to gravity, leading to mass generation only in low-density regions. In dense environments, the scalar field preserves $Z_2$ symmetry and keeps neutrinos massless, while in diluted regions, the symmetry breaks and neutrinos acquire mass, modifying neutrino oscillation lengths and enhancing the MSW effect—offering a potential explanation for density-dependent neutrino anomalies.

ABSTRACT

A proposal for the neutrino mass, based on neutrino-scalar field interaction, is introduced. The scalar field, in turn, is nonminimally coupled to the Ricci scalar, and hence relates the neutrino mass to the matter density. In a dense region, the scalar field obeys the $Z_2$ symmetry, and the neutrino is massless. In a diluted region, the $Z_2$ symmetry breaks and neutrino acquires mass from the non-vanishing expectation value of the scalar field. We consider this scenario in the framework of a spherical dense object whose outside is a diluted region. In this background, we study the neutrino flavors oscillation, along with the consequences of the theory on oscillation length and MSW effect. This preliminary model may shed some lights on the existing anomalies within the neutrino data, concerning the different oscillating behavior of the neutrinos in regions with different densities.

Motivation & Objective

• To address discrepancies in neutrino oscillation data across varying matter densities.
• To propose a dynamical mechanism where neutrino mass depends on local matter density through scalar field dynamics.
• To investigate how this mechanism affects neutrino oscillation length and the MSW effect in inhomogeneous matter.
• To explore whether this model can resolve existing anomalies in neutrino data, particularly in dense astrophysical environments.

Proposed method

• Introduce a scalar field nonminimally coupled to the Ricci scalar, linking it to spacetime curvature and matter density.
• Implement $Z_2$ symmetry such that the scalar field vanishes in high-density regions, keeping neutrinos massless.
• Allow spontaneous $Z_2$ symmetry breaking in low-density regions, leading to a non-zero vacuum expectation value and neutrino mass generation.
• Model a spherically symmetric dense object with a diluted exterior to study neutrino propagation and flavor oscillations.
• Derive effective neutrino mass terms dependent on the scalar field’s vacuum expectation value in the exterior region.
• Analyze neutrino oscillation probabilities, focusing on oscillation length and MSW resonance conditions in the inhomogeneous background.

Experimental results

Research questions

• RQ1 How does the neutrino mass dynamically depend on local matter density through scalar field interactions?
• RQ2 What is the impact of $Z_2$ symmetry restoration in dense regions on neutrino mass and flavor oscillations?
• RQ3 How does the nonminimal coupling of the scalar field to gravity affect the effective neutrino mass in low-density regions?
• RQ4 To what extent does this model modify the neutrino oscillation length and MSW effect compared to standard models?
• RQ5 Can this framework explain observed anomalies in neutrino oscillation data, particularly in regions of varying matter density?

Key findings

• Neutrino mass is dynamically generated only in low-density regions due to spontaneous $Z_2$ symmetry breaking of a scalar field coupled to gravity.
• In high-density regions, the scalar field remains zero, ensuring neutrinos remain massless, consistent with $Z_2$ symmetry preservation.
• The effective neutrino mass in diluted regions is proportional to the vacuum expectation value of the scalar field, which depends on the local matter density via the nonminimal coupling.
• The model predicts a modified neutrino oscillation length in low-density regions due to the density-dependent mass term.
• The MSW effect is enhanced in this framework due to the strong dependence of the neutrino mass on matter density, potentially explaining anomalies in neutrino data.
• The scenario provides a natural mechanism linking neutrino mass generation to cosmological and astrophysical matter density gradients.