N E Mavromatos | Searcharxiv

arXiv2026

On the stability of Born-Infeld-regularised electroweak monopoles

The Cho-Maison monopole provides a monopole solution of the electroweak field equations, but possesses an infinite classical energy due to the Maxwell form of the hypercharge sector. Motivated by string-inspired effective field theories, we study the perturbative stability of the Cho-Maison monopole when the hypercharge kinetic term is regularised by a Born-Infeld extension, which renders the monopole energy finite. Focusing on the bosonic electroweak theory with an unmodified $SU(2)_L$ sector and a Born-Infeld U(1)_Y sector, we analyze linear fluctuations about the regularised monopole background. Using a complex tetrad and a spin-weighted harmonic decomposition, we reduce the fluctuation equations to coupled radial Schroedinger-type eigenvalue problems and examine the spectrum of the resulting operators. We extend the separation-of-variables framework developed by Gervalle and Volkov to this non-linear gauge-field setting. We show that, after appropriate gauge fixing and constraint elimination, the Born-Infeld deformation preserves the angular channel structure of the Maxwell theory and leads to a self-adjoint Sturm-Liouville type problem for the stability of the radial modes, with modified radial coefficients determined by the background Born-Infeld profile. The resulting operator represents a smooth deformation of the Maxwell case and retains positive kinetic weight. Our results provide plausible evidence for the stability of the Born-Infeld deformed monopole and, most importantly, a systematic framework for future numerical or variational studies aimed at a definitive spectral analysis.

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arXiv1993

A String Derivation of the $\nd{S}$ matrix

We show that, in string theory, as a result of the $W_{\infty}$-symmetries that preserve quantum coherence in the {\it full} string theory by coupling different mass levels, transitions between initial- and final-state density matrices for the effective light-particle theory involve non-Hamiltonian terms $\nd{δH}$ in their time evolution, and are described by a $\nd{S}$ matrix that is not factorizable as a product of field-theoretical $S$ and $S^\dagger$ matrices. We exhibit non-trivial string contributions to $\nd{δH}$ and the $\nd{S}$ matrix associated with topological fluctuations related to the coset model that describes an s-wave black hole. These include monopole-antimonopole configurations on the world-sheet that correspond to black hole creation and annihilation, and instantons that represent back-reaction via quantum jumps between black holes of different mass, both of which make the string supercritical. The resulting Liouville mode is interpreted as the time variable, and the arrow of time is associated with black hole decay. Since conformal invariance is broken in the non-critical string theory, monopole and antimonopole, or instanton and anti-instanton, are not separable, and the

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