Gravothermal Evolution of Self-Interacting Dark Matter Halos across Knudsen Numbers
Abstract
If the dark matter self-interacts elastically via a light mediator, then at relative velocities above a scale w dictated by particle physics parameters, the cross section scales as σ∝ v−4. Depending on the value of w, the self-interaction cross section in low-mass halos could be (much) larger than has been previously studied extensively. We perform kinetic simulations of isolated self-interacting dark matter halos using the code KiSS-SIDM for a wide range of halo masses, concentrations, and cross sections from 50 cm2 g−1 to 250,000 cm2 g−1, including several velocity-dependent and fully differential (anisotropic) cross sections. We demonstrate that for idealized NFW halos the collapse time can be predicted from the Knudsen number at the scale radius of the halo. We perform similar calculations for halos extracted from cosmological simulations using either N-body (collisionless) or SPH (strongly collisional) dynamics, and then evolve cutouts with KiSS-SIDM. For these halos, the collapse times differ from the idealized NFW simulations by up to a factor of a few. Further, we calibrate a hydrostatic fluid model to these results, which solves the structure equations as a boundary value problem via two-point shooting. The fluid calculation predicts that for velocity-independent cross sections, a convective region of the halo develops late in the collapse. The collapse times agree well between the kinetic simulations and the fluid code, especially in the velocity-independent case. The density profiles agree well in some cases, which include all of the velocity-dependent cross section runs.
Related
- TNGC-SIDM I: Evolution of massive cluster mergers under the self-interacting dark matter paradigm
- Revisiting self-interacting dark matter with DESI DR2 baryon acoustic oscillation observations
- Quantum corrections as a Bound for Detecting Self-Interacting Ultralight Dark Matter
- Testing the Isothermal Jeans Model for Self-interacting Dark Matter Halos in the Collapse Phase
- Hints of self-interacting dark matter from strong gravitational lensing
BibTeX
@misc{gurian2026gravothermal,
title = {{Gravothermal Evolution of Self-Interacting Dark Matter Halos across Knudsen Numbers}},
author = {James Gurian and Suroor Seher Gandhi and Neal Dalal and Simon May},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.28745},
eprint = {2610.28745},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.28745},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Gravothermal Evolution of Self-Interacting Dark Matter Halos across Knudsen Numbers
AU - James Gurian
AU - Suroor Seher Gandhi
AU - Neal Dalal
AU - Simon May
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.28745
UR - https://arxiv.org/abs/2610.28745
AB - If the dark matter self-interacts elastically via a light mediator, then at relative velocities above a scale w dictated by particle physics parameters, the cross section scales as σ∝ v^−4. Depending on the value of w, the self-interaction cross section in low-mass halos could be (much) larger than has been previously studied extensively. We perform kinetic simulations of isolated self-interacting dark matter halos using the code KiSS-SIDM for a wide range of halo masses, concentrations, and cross sections from 50 cm^2 g^−1 to 250,000 cm^2 g^−1, including several velocity-dependent and fully differential (anisotropic) cross sections. We demonstrate that for idealized NFW halos the collapse time can be predicted from the Knudsen number at the scale radius of the halo. We perform similar calculations for halos extracted from cosmological simulations using either N-body (collisionless) or SPH (strongly collisional) dynamics, and then evolve cutouts with KiSS-SIDM. For these halos, the collapse times differ from the idealized NFW simulations by up to a factor of a few. Further, we calibrate a hydrostatic fluid model to these results, which solves the structure equations as a boundary value problem via two-point shooting. The fluid calculation predicts that for velocity-independent cross sections, a convective region of the halo develops late in the collapse. The collapse times agree well between the kinetic simulations and the fluid code, especially in the velocity-independent case. The density profiles agree well in some cases, which include all of the velocity-dependent cross section runs.
ER -