[Paper Review] Large Neutrino Secret Interactions, Small Impact on Supernovae

Damiano F. G. Fiorillo, Georg G. Raffelt+1 more|arXiv (Cornell University)|Jul 27, 2023

Neutrino Physics ResearchPhysics and Astronomy3 citations

TL;DR

This paper investigates large neutrino secret interactions (ν SI) in core-collapse supernovae using relativistic hydrodynamics, showing that even strong ν SI do not significantly alter the neutrino burst duration or spectrum. Instead, the neutrino fluid rapidly evolves into a fireball with constant thickness, independent of initial conditions, leading to minimal observable effects on supernova physics and neutrino signals.

ABSTRACT

When hypothetical neutrino secret interactions ($ν$SI) are large, they form a fluid in a supernova (SN) core, flow out with sonic speed, and stream away as a fireball. For the first time, we tackle the complete dynamical problem and solve all steps, systematically using relativistic hydrodynamics. The impact on SN physics and the neutrino signal is remarkably small. For complete thermalization within the fireball, the observable spectrum changes in a way that is independent of the coupling strength. One potentially large effect beyond our study is quick deleptonization if $ν$SI violate lepton number. By present evidence, however, SN physics leaves open a large region in parameter space, where laboratory searches and future high-energy neutrino telescopes will probe $ν$SI.

Motivation & Objective

• To resolve long-standing debates about whether large neutrino secret interactions (ν SI) could extend the duration of the neutrino burst from supernovae.
• To determine whether the fluid-like behavior of strongly coupled neutrinos leads to observable changes in the neutrino signal, such as altered energy spectra or time profiles.
• To establish a physically consistent dynamical model of neutrino emission from a protoneutron star using relativistic hydrodynamics with realistic boundary conditions.
• To challenge previous claims—particularly from Ref. [17]—that sudden release of a neutrino fluid ball could produce a prolonged burst due to homologous expansion.
• To demonstrate that the system universally evolves into a fireball solution with frozen pulse profile, regardless of initial density profile or emission mechanism.

Proposed method

• Solves the full relativistic hydrodynamics problem in spherical symmetry, modeling neutrino emission from a protoneutron star with physical boundary conditions.
• Uses a simplified source model with a defined start and end time for thermal emission, simulating quasi-steady neutrino release from the PNS surface.
• Applies numerical simulations to track the evolution of the neutrino fluid from initial rest to relativistic expansion, focusing on the formation of a luminal front.
• Analyzes the system’s transition from a localized fluid ball to a fireball with constant thickness, using the comoving frame to study isotropization via ν SI.
• Compares results with known solutions from gamma-ray burst (GRB) fireball models, confirming that the pulse profile remains unaltered during expansion.
• Validated against prior works (e.g., Ref. [28]) and shows that the fireball solution is robust even under varied initial density profiles.

Experimental results

Research questions

• RQ1 Does large neutrino secret interaction lead to a prolonged neutrino burst in core-collapse supernovae, as previously suggested?
• RQ2 How does the neutrino fluid evolve dynamically after emission from the protoneutron star, particularly under strong ν SI?
• RQ3 To what extent does the initial density profile or emission mechanism affect the final neutrino signal properties?
• RQ4 Can the system evolve into a fireball with constant thickness, as predicted by relativistic fluid theory, and is this independent of coupling strength?
• RQ5 Why do previous claims of homologous expansion and signal lengthening fail to hold under rigorous hydrodynamic modeling?

Key findings

• The neutrino fluid rapidly evolves into a fireball with constant thickness, regardless of the initial density profile or emission conditions.
• The pulse profile remains frozen during expansion, meaning the neutrino burst duration is unchanged compared to the standard case.
• The flux spectrum and average energy are only weakly dependent on the ν SI coupling strength, with changes independent of the coupling magnitude.
• The fireball solution is robust and universal: even a ball initially at rest evolves into a luminal, constant-thickness shell expanding at the speed of light.
• The results contradict claims from Ref. [17] that sudden release leads to homologous expansion and signal lengthening, showing instead that such behavior is unphysical under relativistic hydrodynamics.
• The only potentially large effect beyond this study is quick deleptonization if ν SI violate lepton number, though this remains speculative and not addressed here.