The Electroweak Sphaleron Revisited: I. Static Solutions, Energy Barrier, and Unstable Modes

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Main Authors: Matchev, Konstantin T., Verner, Sarunas
Format: Preprint
Published: 2025
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author Matchev, Konstantin T.
Verner, Sarunas
author_facet Matchev, Konstantin T.
Verner, Sarunas
contents The electroweak sphaleron is a static, unstable solution of the Standard Model classical field equations, representing the energy barrier between topologically distinct vacua. In this work, we present a comprehensive updated analysis of the sphaleron using current Standard Model parameters with the physical Higgs boson mass of $m_H = 125.1$ GeV and $m_W = 80.4$ GeV, rather than the $m_H = m_W$ approximation common in earlier studies. The study includes: (i) a complete derivation of the $SU(2)\times U(1)$ electroweak Lagrangian and field equations without gauge fixing constraints, (ii) high-precision numerical solutions for the static sphaleron configuration yielding a sphaleron energy $E_{\rm{sph}} \simeq 9.1$ TeV, (iii) an analysis of the minimum energy path in field space connecting the sphaleron to the vacuum (a 1D potential barrier as a function of Chern-Simons number), and (iv) calculation of the sphaleron single unstable mode with negative eigenvalue $ω^2_{-} = -2.7m^2_W$, providing analytical fits for its eigenfunction. We find that using the measured Higgs mass modifies the unstable mode frequency, with important implications for baryon number violation rates in both early universe cosmology and potential high-energy collider signatures. These results provide essential input for accurate lattice simulations of sphaleron transitions and precision calculations of baryon number violation processes.
format Preprint
id arxiv_https___arxiv_org_abs_2505_05607
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle The Electroweak Sphaleron Revisited: I. Static Solutions, Energy Barrier, and Unstable Modes
Matchev, Konstantin T.
Verner, Sarunas
High Energy Physics - Phenomenology
High Energy Physics - Theory
The electroweak sphaleron is a static, unstable solution of the Standard Model classical field equations, representing the energy barrier between topologically distinct vacua. In this work, we present a comprehensive updated analysis of the sphaleron using current Standard Model parameters with the physical Higgs boson mass of $m_H = 125.1$ GeV and $m_W = 80.4$ GeV, rather than the $m_H = m_W$ approximation common in earlier studies. The study includes: (i) a complete derivation of the $SU(2)\times U(1)$ electroweak Lagrangian and field equations without gauge fixing constraints, (ii) high-precision numerical solutions for the static sphaleron configuration yielding a sphaleron energy $E_{\rm{sph}} \simeq 9.1$ TeV, (iii) an analysis of the minimum energy path in field space connecting the sphaleron to the vacuum (a 1D potential barrier as a function of Chern-Simons number), and (iv) calculation of the sphaleron single unstable mode with negative eigenvalue $ω^2_{-} = -2.7m^2_W$, providing analytical fits for its eigenfunction. We find that using the measured Higgs mass modifies the unstable mode frequency, with important implications for baryon number violation rates in both early universe cosmology and potential high-energy collider signatures. These results provide essential input for accurate lattice simulations of sphaleron transitions and precision calculations of baryon number violation processes.
title The Electroweak Sphaleron Revisited: I. Static Solutions, Energy Barrier, and Unstable Modes
topic High Energy Physics - Phenomenology
High Energy Physics - Theory
url https://arxiv.org/abs/2505.05607