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Gravitational wave landscape of cosmic string networks with varying tension

Luca Brunelli1,2,*, Filippo Revello3,4,†, and Gonzalo Villa5,‡

  • 1Dipartimento di Fisica e Astronomia, Università di Bologna, via Irnerio 46, 40126 Bologna, Italy
  • 2INFN, Sezione di Bologna, viale Berti Pichat 6/2, 40127 Bologna, Italy
  • 3Instituut voor Theoretische Fysica, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
  • 4Leuven Gravity Institute, KU Leuven, Celestijnenlaan 200D, B-2415 Leuven, Belgium
  • 5DAMTP, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Road, Cambridge, CB3 0WA, United Kingdom

  • *Contact author: l.brunelli@unibo.it
  • †Contact author: filippo.revello@kuleuven.be
  • ‡Contact author: gv297@cam.ac.uk
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Phys. Rev. D 114, 043555 – Published 28 August, 2026

DOI: https://doi.org/10.1103/6npx-fnnw

Abstract

We fully classify the phenomenology of gravitational wave emission from scaling cosmic string networks with varying tension and compute the spectral indices of the resulting stochastic backgrounds. In string compactifications, periods of varying tension occur when moduli acquire a time dependence. We present concrete examples in type IIB string theory as D3- and NS5-branes wrapping internal cycles, which become dynamical due to the effect of moduli potentials. Moreover, we use swampland constraints to derive general bounds on the allowed time variation of the effective string tension in Friedmann-Lemaitre-Robertson-Walker backgrounds and on the resulting spectral indices.

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Phys. Rev. D 114, 043555– Published 28 August, 2026
  • Received 28 January 2026
  • Accepted 13 August 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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