arXiv subjects

James Martin Speight

Publications and source records attributed to James Martin Speight.

3 recordsLinked to original sources

arXiv2025

Backreacted Coulomb energy in the Skyrme model

The Skyrme model is extended with the Maxwell action and a source term for the gauge field. We consider the specialized case of vanishing isospin states, such that only an electric potential is turned on and study the backreaction onto the Skyrme fields. In particular, we study Skyrmions with baryon numbers B=4,8,12,16 and 40. We find, in agreement with physical expectations, that the Coulomb backreaction is most pronounced for large Skyrmions and find furthermore that the dynamics of the theory is more sensitive to the backreaction than the ground states (global minimizers of the energy). Calibrating the model to Carbon-12, we find excellent agreement of the masses of the studied Skyrmions - within 1.86% of experimental data. The Coulomb energies are slightly larger than phenomenological fits suggest, but only by about 3-22%, whereas the radii are within 15% errors, with the largest errors on the smallest baryon number (B=4) and the smallest errors on the large baryon numbers.

hep-th↗

arXiv2023

Nudged Elastic Bands and Lightly Bound Skyrmions

It has become clear in recent years that the configuration space of the nuclear Skyrme model has, in each topological class, many almost degenerate local energy minima and that the number of such minima grows with the degree (or baryon number) $B$. Rigid body quantization, in which one quantizes motion on the spin-isospin orbit of just one minimum, is thus an ill-justified approximation. Instead, one should identify a (finite-dimensional) moduli space of configurations containing all local minima (for a given $B$) as well as fields interpolating smoothly between them. This paper proposes a systematic computational scheme for generating such a moduli space: one constructs an energy minimizing path between each pair of local minima, then defines the moduli space to be the union of spin-isospin orbits of points on the union of these curves, a principal bundle over a graph. The energy minimizing curves may be constructed in practice using the nudged elastic band method, a standard tool in mathematical chemistry for analyzing reaction paths and computing activation energies. To illustrate, we apply this scheme to the lightly bound Skyrme model in the point particle approximation, constructing the graphs for $5\leq B\leq 10$. We go on to complete the quantization for $B=7$, in which the graph has two vertices and a single edge. The low-lying quantum states with isospin $1/2$ do not strongly localize around either of the local energy minima (the vertices). Their energies rise monotonically with spin, conflicting with experimental data for Lithium-7.

hep-th↗

arXiv2020

Realistic classical binding energies in the $ω$-Skyrme model

An omega-meson extension of the Skyrme model - without the Skyrme term but including the pion mass - first considered by Adkins and Nappi is studied in detail for baryon numbers 1 to 8. The static problem is reformulated as a constrained energy minimisation problem within a natural geometric framework and studied analytically on compact domains, and numerically on Euclidean space. Using a constrained second-order Newton flow algorithm, classical energy minimisers are constructed for various values of the omega-pion coupling. At high coupling, these Skyrmion solutions are qualitatively similar to the Skyrmions of the standard Skyrme model with massless pions. At sufficiently low coupling, they show similarities with those in the lightly bound Skyrme model: the Skyrmions of low baryon number dissociate into lightly bound clusters of distinct 1-Skyrmions, and the classical binding energies for baryon numbers 2 through 8 have realistic values.

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