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Quantifying the scientific potential of intermediate and extreme mass ratio inspirals with the Laser Interferometer Space Antenna

Lorenzo Speri1,2,*, Francisco Duque3, Susanna Barsanti4, Alessandro Santini3, Shubham Kejriwal5, Ollie Burke6, and Christian E. A. Chapman-Bird7

  • *Contact author: lorenzo.speri@esa.int
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Phys. Rev. D 114, 064012 – Published 4 September, 2026

DOI: https://doi.org/10.1103/k15y-nq5f

Abstract

The Laser Interferometer Space Antenna (LISA) will enable precision studies of extreme and intermediate mass ratio inspirals (EMRIs/IMRIs), providing unique probes of astrophysical environments of galactic nuclei and strong-field gravity. Using a fully relativistic pipeline across primary masses m1∈[5×104,107]M⊙ and secondary masses m2∈[1,104]M⊙, we map instrumental performance directly to detection horizons and parameter measurement precision. EMRIs with m1=107M⊙ and m2∼1M⊙ are the most sensitive to instrument degradation, with redshift horizons at z∼0.01, while IMRIs are the least sensitive to degradation and reach redshifts z∼1–3. All prograde systems considered achieve subpercent spin precision within 3 months of observation. The full 4.5-yr mission increases the horizon of systems with m1=107M⊙ and m2∼1M⊙ by a factor of ∼4 and improves sky localization by 1 to 2 orders of magnitude reaching <10  deg2. IMRI detection is robust against degradation, but their parameter estimation is more vulnerable due to fewer cycles in band. With the full baseline, EMRI observations constrain scalar dipole emission and Kerr quadrupole deviations below ground-based bounds by 1 to 2 orders of magnitude. We release the accompanying software and an interactive website to enable the community to rapidly quantify the scientific potential of EMRIs and IMRIs.

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Phys. Rev. D 114, 064012– Published 4 September, 2026
  • Received 28 May 2026
  • Accepted 31 July 2026
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