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  • Open Access

Tachyonic instability in Randall-Sundrum braneworld scenarios

Abhirup Karmakar* and Soumitra SenGupta†

  • *Contact author: abhirup04karmakar@gmail.com
  • †Contact author: tpssg@iacs.res.in
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APS Open Sci. 1, 000133 – Published 15 September, 2026

DOI: https://doi.org/10.1103/xv43-tr6m

Abstract

Low-energy effective theories provide a natural description of four-dimensional physics in higher-dimensional geometries, where the imprint of the bulk geometry appears as parameters of the lower-dimensional theory. Inspired by the Damour-Esposito-Farése model of spontaneous scalarization in first-generation scalar-tensor theories of gravity, we investigate the possibility of tachyonic instability and spontaneous scalarization in braneworld scenarios. We consider the two-brane Randall-Sundrum (RS) model where the low-energy effective theory on either brane is of scalar-tensor nature with the extra-dimensional radion playing the role of the scalar. We have determined the possibilities for tachyonic (in)stability of the radion field on either brane in three scenarios: the RS model with fine-tuning conditions in which the potential of the radion field vanishes identically, the RS model without fine-tunings where the radion potential arises purely from the gravity sector, and the RS model with a bulk stabilizing field that generates a radion potential with a minimum. With the bulk stabilizing field, we have found that on-brane matter with T>0 changes the vacuum expectation value (VEV) of the radion, destroying the resolution of the gauge hierarchy problem, whereas on-brane matter with T<0 does not alter the stability and VEV of the radion. We further determined the exact condition of tachyonic (in)stability of radion field with the on-brane dS4 and AdS4 geometries.

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APS Open Sci. 1, 000133– Published 15 September, 2026
Vol. 1
  • Received 26 May 2026
  • Accepted 2 September 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.

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