Quantum Field Dynamics in Cosmic String Spacetimes

Quantum field dynamics in the presence of cosmic strings explores how one-dimensional topological defects, arising in various grand unified and string-theoretic models, imprint distinctive signatures on vacuum fluctuations and field propagation. The spacetime around an idealised infinite string exhibits a conical geometry, characterised by a deficit angle that alters the spectrum of quantum modes. This leads to vacuum polarisation effects, shifts in the energy–momentum tensor and induced forces that may influence early-universe phase transitions, seed structure formation or generate novel lensing phenomena. Studies encompass scalar, spinor and gauge fields, employing techniques such as mode summation, Green’s functions and renormalisation to extract finite vacuum expectation values. The resulting insights reveal how the interplay between topology, curvature and boundary conditions shapes observable imprints of cosmic strings on cosmological and particle-physics observables.

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Recent investigations into the Casimir interaction of finite-width cosmic strings have shown that the core structure plays a crucial role at scales comparable to the string thickness. By applying dimensional regularisation to the trace-logarithm formalism for a massless scalar field, it was demonstrated that the finite width removes both ultraviolet divergences and pathologies in the vacuum energy–momentum tensor, and modifies the interaction energy at separations of a few core diameters, thus refining predictions based on infinitely thin approximations.

Studies of vacuum polarisation in an anti-de Sitter background pierced by a magnetic-flux cosmic string and bounded by a brane have elucidated the competing influences of curvature, topology and boundary. The vacuum expectation values of the field squared and the energy–momentum tensor were derived separately for regions adjacent to the brane and regions dominated by the bulk string geometry. It emerged that close to the brane, boundary-induced effects dominate, while at larger distances the string-induced contribution prevails, with distinct asymptotic regimes depending on the AdS curvature radius and brane boundary conditions.

Analyses of a de Sitter universe containing a cosmic string and an orthogonal conducting plate reveal an enhancement of vacuum polarisation due to the conical defect. Closed expressions for the vacuum expectation values of the field squared and energy–momentum tensor under Robin, Dirichlet and Neumann conditions show that the string topology amplifies boundary-induced stresses and yields a non-zero normal force on the plate. Asymptotic explorations underscore how curvature and topology jointly govern vacuum stresses in expanding cosmological backgrounds.

Quantum Field Dynamics in Cosmic String Spacetimes publication trend

The graph below shows the total number of articles in quantum field dynamics in cosmic string spacetimes across all publications each year (not limited to Nature Index journals).

Technical terms

Cosmic string spacetime: A geometry characterised by a line-like topological defect producing a conical deficit angle in an otherwise flat or curved manifold.

Vacuum polarisation: The modification of the quantum vacuum state by external fields or geometry, reflected in changes to field correlators or energy densities.

Casimir effect: A force or energy arising from modifications of vacuum fluctuations due to boundary conditions or topological features.

Energy–momentum tensor: The operator describing the distribution and flow of energy and momentum of a field in spacetime.

Vacuum expectation value (VEV): The average value of a quantum operator in the vacuum state, indicating leading-order quantum corrections.

Renormalisation: A procedure to remove or absorb infinities in quantum field calculations by redefinition of parameters.

References

1. Casimir interaction of finite-width strings. Physical Review D (2023).
2. Vacuum polarization induced by a cosmic string and a brane in AdS spacetime. European Physical Journal C (2023).
3. Vacuum Effects Induced by a Plate in de Sitter Spacetime in the Presence of a Cosmic String. Universe (2023).