Lastrings

Lastrings are a theoretical construct used to describe one-dimensional filamentary excitations in certain speculative models of quantum field theory and condensed matter physics. They resemble extended defects or strings within a medium, carrying energy and tension along their length and supporting propagating modes. In these frameworks, a lastring behaves as an elastic filament with finite tension T and linear energy density μ, whose dynamics are governed by a lengthwise wave equation and nonlinear corrections.

Realizations and modeling: In numerical simulations lastrings are represented as discretized chains with curvature- and tension-driven motion, subject to reconnection rules when segments meet. In laboratory analogs, lastring-like structures can appear as phase defects in Bose-Einstein condensates, lines of polarization in photonic lattices, or laser-induced refractive-index channels in nonlinear optical media. These contexts enable study of string-like dynamics without invoking fundamental strings.

Properties and phenomenology: Lastrings can form closed loops or networks, support low-energy excitations traveling along their length, and exchange energy through reconnection events or interactions with external fields. Topology, such as knots and linking, plays a central role in their dynamics and stability, though the precise behavior depends on the chosen model.

Status and purpose: Lastrings remain a theoretical and computational concept, with no experimental observation as fundamental objects. They are used as toy models to explore topological defects, string-like dynamics, and analog quantum simulations.

See also: cosmic strings, vortex lines, topological defects, quantum simulators.