Cho–Maison MAPs: Yang–Mills & Electroweak Insights

• Cho–Maison MAPs are nonperturbative field configurations featuring localized monopole and antimonopole cores connected by quantized magnetic flux in SU(2) YMH and electroweak theories.
• They are constructed using an axially symmetric ansatz with winding numbers, and numerical methods like finite-difference and Gauss–Newton solvers achieve precision with errors around 10⁻⁴.
• MAPs reveal dual stabilization via Higgs-mediated and Z-boson repulsions, offering insights applicable to lattice simulations and collider phenomenology.

Cho–Maison Monopole–Antimonopole Pairs (MAPs) are nonperturbative, unstable or metastable, finite-energy (or, for electroweak realization, regulated infinite-energy) field configurations exhibiting localized monopole and antimonopole cores connected by quantized magnetic flux, and governed by nontrivial winding in internal space. Originating in the context of SU(2) Yang–Mills–Higgs (YMH) theories and the SU(2)×U(1) Weinberg–Salam model, these solutions generalize the classic Dirac, Wu–Yang, and ’t Hooft–Polyakov monopole constructions, adapting them to situations without net topological charge but with rich internal structure. Their stability, formation, and interactions involve a delicate interplay of gauge fields, the Higgs sector, and, in the Standard Model realization, additional vector boson and symmetry-breaking effects.

1. Mathematical Structure and Ansatz Construction

In SU(2) YMH theory, classic studies (Teh et al., 2010) showed that MAP solutions can be constructed via an axially symmetric ansatz involving internal-space winding numbers: θ-winding number $m$ and φ-winding number $n$. The field configurations are parameterized by the Higgs field

$$\Phi^a = X_1(r,\theta) \hat n_1^a + X_2(r,\theta) \hat n_2^a,$$

where the internal-space unit vectors $\hat n_{1,2}^a$ have dependence on $(m\theta, n\phi)$. The integer $m$ characterizes the θ-dependence, while $n$ fixes the $\phi$-winding. MAPs classically used forms with $m>1$ but numerical instabilities increased with $m$.

A reformulation (Teh et al., 2010) reduced $m$ to 1, introducing a single integer parameter $s$ such that the asymptotic Higgs field at small $r$ ($r\to0$) corresponds to the trivial vacuum ($s=0$), while at large $r$ ($r\to\infty$) it involves an angular phase shift parameterized by $s\geq1$: $$X_1(\infty, \theta) = (h+\beta r) \cos[(2s-1)\theta], \quad X_2(\infty, \theta) = - (h+\beta r) \sin[(2s-1)\theta].$$ Here, $s=1$ yields a single MAP; higher $s$ correspond to MAP chains. Importantly, these solutions are numerically tractable with errors $\sim10^{-4}$ when discretized via non-uniform grids and solved with finite-difference and Gauss–Newton methods using platforms such as Maple and Matlab.

2. Integer Parameterization, Winding Numbers, and Topological Aspects

The parameter $s$ serves a dual analytic and topological role: it labels the “twist” needed for the Higgs and gauge fields to interpolate between distinct asymptotic vacua (trivial at the origin, nontrivial at infinity), and it indexes the number of MAPs or MACs present. The coexistence and transition between sectors is imposed through well-defined boundary conditions:

• For $r\to 0$, $s=0$ (trivial vacuum): $X_1(0)=X_2(0)=0$.
• For $r\to\infty$, $s\geq1$, leading to nontrivial internal “twists”.

Despite local monopole and antimonopole structure, the net topological magnetic charge vanishes, as shown via the ’t Hooft–Polyakov prescription: $M_{\text{net}} = M_+ + M_- = 1 + (-1) = 0.$ This places MAPs in the topologically trivial sector, distinguishing them from isolated monopole solutions and classifying them as non-topological solitons.

The interplay between θ-winding ($m$) and φ-winding ($n$) numbers is essential to preserve axial symmetry and enforce the internal “locking” that stabilizes the field configuration. The φ-winding is typically fixed at $n=1$ to maintain axial symmetry. The reduction $m>1 \to m=1$—with the twist mapped into the parameter $s$—retains the full physics by translating higher winding into the field's phase structure.

3. Non-BPS Extensions and MAP Dyons

Extension to electrically charged MAPs (dyons) generalizes the classic MAP configuration to carry simultaneous magnetic and electric charges (Lim et al., 2010). These solutions use a continuous parameter $-1\leq\eta\leq1$ controlling the net electric charge. The axially symmetric ansatz, after insertion into the full second-order SU(2) YMH field equations, yields eight coupled nonlinear PDEs. The Higgs potential strength $\lambda$ has critical effects:

• For $\lambda=0$ (Prasad–Sommerfield limit), as $\eta\to\pm1$, separation $d$, energy $E$, and electric charge $Q$ all diverge exponentially, since the time-component of the gauge field aligns with the Higgs and electric repulsion dominates.
• For $\lambda=1$, these quantities saturate: the Higgs potential introduces sufficient attractive interaction to balance electromagnetic repulsion; critical values (e.g., for $n=1$, $d\approx5.18$, $Q\approx17.61$) are observed.

MAP dyons also reveal nontrivial spatial structures (dumbbell-like for $n=1$, toroidal for $n=2$) and confirm that finite-energy, non-BPS, axially symmetric solutions exist robustly in the parameter space.

4. MAPs in the SU(2)×U(1) Weinberg–Salam Theory

The Cho–Maison realization in the Weinberg–Salam (WS) electroweak model produces monopole-antimonopole pair solutions (“Cho–Maison MAPs”) with rich phenomenology (Zhu et al., 2022):

• The non-Abelian ansatz (for $SU(2)$ and $U(1)$ fields plus the Higgs doublet) leads to a system of seven coupled PDEs, discretized and solved on finite grids.
• Each pole carries a quantized charge $Q_M=\pm4\pi/e$, confirmed via electromagnetic Gauss's law, corresponding to the unique 4π/e periodicity of electroweak monopoles.
• The monopole and antimonopole are spatially separated along the $z$-axis, with the pole separation $d_z$ and magnetic dipole moment $\mu_m$ varying with both the Weinberg angle $\theta_W$ and the Higgs self-coupling $\beta$.
• The total energy of the configuration is formally infinite due to the Dirac string singularity unless a regularization (e.g., a hypercharge permeability function) is introduced.

These solutions retain the essential topological properties (nontrivial flux attachment, no net topological charge) and extend the analysis to a realistic Standard Model setting.

5. Stabilization Mechanisms: Interplay of Higgs and $Z$-Boson Repulsions

MAP stability arises from the balancing of attractive and repulsive contributions in the full WS theory (Zhu et al., 22 Aug 2025). Two stabilization mechanisms are identified via detailed stress-energy tensor analysis:

• Higgs-mediated repulsion: Non-monotonic in Higgs self-coupling ($\beta$) and ø-winding number ($n$). For increasing $\beta$, pole separation initially decreases (due to enhanced magnetic attraction/Yukawa suppression), then “recovers” (i.e., increases) for large $\beta$ as Higgs-induced repulsion becomes topologically dominant.
• Z-boson field core repulsion: The $SU(2)$ sector, decomposed into electromagnetic and $Z$-fields, generates localized repulsive cores of radius $R_c\sim0.8\,m_W^{-1}$, set by the weak scale. The effect is confirmed via the neutral charge distribution; repulsion aligns with positions of monopoles, providing a short-range stabilization core.

The result is dual stabilization: the Higgs field produces long-range, topologically encoded repulsion, while Z-boson exchange yields localized core repulsion at the weak scale. Both effects ensure that MAPs do not collapse into singular configurations and remain dynamically stable over a range of physical parameters.

6. Implications for Physical Realizations and Extensions

The theoretical insights from Cho–Maison MAP studies inform purposes from field theory to collider phenomenology:

• Lattice gauge theory simulations observe phase transitions related to MAP production and dissolution (Cairano et al., 2023): third-order “precursor” transitions signal the nucleation and pairing of monopoles, while higher-energy transitions correspond to pair unbinding; these patterns articulate the microscopic mechanisms governing topological defect populations in lattice models.
• Experimental searches at colliders: The MAPs' unique field structure and scaling impact production mechanisms and signal selection. For electroweak MAPs, the magnetic dipole field predicts specific angular scattering features for charged particles traversing the MAP's field (Vento et al., 2019).
• General framework for topological solitons: The dual stabilization effects seen in Cho–Maison MAPs naturally generalize to other topological defects, such as vortex rings and sphaleron chains, within the Standard Model. The combination of topological and vector boson–driven repulsions constitutes a unifying mechanism for the dynamic longevity of these configurations (Zhu et al., 22 Aug 2025).

The implementation algorithms and analytic techniques underlying MAP investigation (numerical PDE solvers, stress–energy tensor decomposition, winding number mapping, and parameter reduction strategies) set the methodology for current and future exploration of solitonic structure in non-Abelian gauge theories.