[Paper Review] Superluminal Neutrinos and Monopoles

Peng Wang, Houwen Wu+1 more|arXiv (Cornell University)|Oct 3, 2011

Neutrino Physics Research53 references15 citations

TL;DR

This paper proposes that superluminal neutrinos observed in the OPERA experiment could result from an interaction with a 't Hooft-Polyakov monopole, which distorts spacetime locally for neutrinos but not photons. The monopole induces a fixed 60 ns time lead for neutrinos over photons, reconciling OPERA's results with supernova neutrino data and excluding cosmic strings as a viable explanation.

ABSTRACT

In this letter, we show that superluminal neutrinos announced by OPERA could be explained by the existence of a monopole, which is left behind after the spontaneous symmetry breaking (SSB) phase transition of some scalar fields in the universe. We assume the 't Hooft-Polyakov monopole couples to the neutrinos but not photon fields. The monopole introduces a different effective metric to the neutrinos from the one experienced by photons. We find that the superluminal propagation only exists in a very short distance from the monopole, about $10^3$ cm in OPERA. No matter how far they travel, neutrinos always arrive earlier than photons by the same amount of time, provided a monopole existing on or close to their trajectories. This conclusion can be tested by future experiments. The result reconciles the contradiction between OPERA and supernova neutrinos. We further exclude cosmic strings as a possible theoretical explanation.

Motivation & Objective

• To resolve the contradiction between OPERA’s superluminal neutrino results and the observed arrival time of neutrinos from SN 1987A.
• To explore whether topological defects like monopoles could explain the 60 ns early arrival of neutrinos in OPERA.
• To test the viability of monopoles versus cosmic strings as theoretical explanations for superluminal neutrino propagation.
• To demonstrate that the time difference between neutrinos and photons remains constant regardless of travel distance, provided a monopole is on or near the trajectory.

Proposed method

• Assumes a scalar triplet Higgs field in an SU(2) gauge theory that breaks spontaneously to U(1), producing a 't Hooft-Polyakov monopole.
• Introduces a coupling between the monopole’s gauge and scalar fields and neutrinos, but not photons, via a non-minimal interaction term in the Lagrangian.
• Derives an effective metric for neutrinos that differs from the Minkowski metric experienced by photons, based on the monopole’s field profiles.
• Uses the BPS soliton solution for the monopole (with λ→0) to analytically evaluate the neutrino propagation time, focusing on the short-distance region near the monopole.
• Calculates the time difference ∆t = t_c - t_ν between photons and neutrinos using the radial coordinate ρ = m_w r, showing it is dominated by a region δ ~ 10^3 cm from the monopole.
• Compares the predicted time delay with OPERA’s 60 ns measurement and evaluates consistency with SN 1987A neutrino observations.

Experimental results

Research questions

• RQ1 Can the presence of a monopole explain the 60 ns early arrival of neutrinos observed in the OPERA experiment?
• RQ2 Does the monopole-induced time delay remain constant over varying baseline distances, reconciling OPERA with SN 1987A data?
• RQ3 Why are cosmic strings ruled out as an explanation, despite their potential to alter neutrino propagation?
• RQ4 How does the effective metric for neutrinos differ from that of photons in the presence of a monopole?
• RQ5 What is the spatial scale over which the time delay is primarily generated, and how does it relate to the OPERA baseline?

Key findings

• The time difference between neutrinos and photons is fixed at approximately 60 ns, regardless of the total travel distance, due to the monopole's influence.
• The dominant contribution to the time delay arises from a very short region of about δ ~ 10^3 cm along the neutrino path, centered on the monopole.
• The monopole's effect is localized; the effective metric for neutrinos differs from the Minkowski metric of photons due to coupling via (D_μφ)^a(D^μφ)^a terms.
• The BPS soliton solution for the monopole yields a time delay consistent with the OPERA measurement when κ ~ O(1) and m_w ~ 100 GeV.
• Cosmic strings are excluded due to the 'deficit angle catastrophe'—they would cause observable gravitational lensing and destabilize nearby matter, which has not been detected.
• The model explains why supernova neutrinos from SN 1987A did not show a similar early arrival: the probability of a monopole lying on their path is extremely low.