[Paper Review] Some new implications of the anomalous baryon current in the Standard Model

Richard J. Hill|ArXiv.org|Jun 23, 2008

Particle physics theoretical and experimental studies9 references3 citations

TL;DR

This paper derives the anomalous baryon current in the Standard Model via a pedagogical analogy to the axial anomaly, showing that baryon number violation arises from chiral anomalies in electroweak interactions. It predicts novel neutrino-photon interactions mediated by baryon number density, including photon showers from neutral-current processes and neutrino pair production, with potential signatures in neutrino scattering experiments and astrophysical environments like neutron stars and supernovae.

ABSTRACT

Phenomenological implications of the anomalous baryon current in the Standard Model are discussed, in particular neutrino-photon interactions at finite baryon density. A pedagogical derivation of the baryon current anomaly is given.

Motivation & Objective

• To provide a pedagogical derivation of the baryon current anomaly in the Standard Model, analogous to the well-known axial anomaly.
• To explore phenomenological consequences of baryon number violation in the presence of finite baryon density.
• To identify observable signatures of anomalous baryon current in neutrino scattering experiments, particularly photon production and shower events.
• To investigate implications for astrophysical environments such as neutron stars and supernova cores, where dense baryonic matter may enhance these effects.

Proposed method

• Derives the baryon current anomaly using background field methods, introducing a gauge-invariant coupling to a background field $ B_ u $ to compute the divergence $ abla_ u J^ u $.
• Applies the Wess-Zumino-Witten effective action formalism to map quark-level anomalies into mesonic effective field theory, ensuring consistency with chiral symmetry and anomalies.
• Constructs an extended chiral Lagrangian with pseudo-Chern-Simons terms to describe vector meson interactions and anomalous couplings, including $ ho $, $ ar{ ho} $, and $ uar{ u} o ext{photon} $ processes.
• Analyzes neutrino-nucleon scattering amplitudes involving $ Z $-boson exchange and $ ho $-meson exchange, computing cross sections and form factors for photon production.
• Evaluates the potential for misidentification of photon showers as electron showers in $ \nu_\mu $ beams, relevant to experiments like MiniBooNE and T2K.
• Considers parity-violating observables mediated by $ Z $-boson exchange in the anomalous current framework, with applications to neutron star cooling and supernova dynamics.

Experimental results

Research questions

• RQ1 How does the baryon current anomaly in the Standard Model lead to observable neutrino-photon interactions at finite baryon density?
• RQ2 What are the phenomenological signatures of anomalous baryon number violation in neutrino scattering experiments, particularly in photon shower production?
• RQ3 Can the anomalous baryon current explain excess events observed in experiments like MiniBooNE that resemble photon showers from $ \nu_\mu $ scattering?
• RQ4 What role does the $ \omega(780) $ meson exchange play in enhancing photon production in neutrino-nucleon scattering?
• RQ5 How do these anomalous interactions affect neutrino processes in dense astrophysical environments such as neutron stars and supernova cores?

Key findings

• The baryon current anomaly in the Standard Model leads to a non-conserved divergence $ abla_ u J^ u = -rac{1}{64 au^2} ilde{F}^a_{ u ho} F^{a, u ho} $, analogous to the axial anomaly but involving electroweak gauge fields.
• Neutrino scattering on nucleons can produce single photons via neutral-current processes mediated by $ Z $-boson and $ \omega(780) $ exchange, with cross sections sensitive to baryon density and form factors.
• Photon showers from these anomalous processes can mimic electron showers in detectors, posing a background for $ \nu_e $ appearance searches in $ \nu_\mu $ beams.
• The predicted rate of such photon events in MiniBooNE is of the same order of magnitude as the observed excess, suggesting a possible connection to the anomalous baryon current.
• Neutrino pair production via $ \gamma \to \nu\bar{\nu} $ conversion is induced by the anomalous baryon current, with a non-negligible rate in dense matter, potentially affecting neutron star cooling.
• The framework allows for parity-violating effects in neutrino interactions, with $ Z $-boson exchange generating observable asymmetries in angular or energy distributions.