Compare · The Dark Universe

Self-Interacting Dark Matter (SIDM) vs Sterile Neutrinos

← Back to Self-Interacting Dark Matter (SIDM)

Dark Matter Candidates· within family

	Self-Interacting Dark Matter (SIDM) Frontier	Sterile Neutrinos Frontier
Proposed	2000 / 2018	1994 / 1999
Key figures	David Spergel, Paul Steinhardt, Sean Tulin, Hai-Bo Yu	Scott Dodelson, Lawrence Widrow, Xiang-Dong Shi, George Fuller
In one sentence	Dark matter that interacts with itself via some non-gravitational force, with cross sections tuned so the interactions thermalize the inner regions of dwarf galaxies (creating cores instead of cusps) but barely affect large-scale structure.	Hypothetical neutrinos with masses around a few keV that don't feel the weak force at all, only gravity and a tiny mixing with the three Standard Model neutrinos. They would warm-dark-matter the universe and decay into X-rays, producing a detectable line in galaxy spectra. A tentative 3.5 keV X-ray line has been the subject of a decade-long debate.
Predictions	Cored density profiles in dwarf and low-surface-brightness galaxies, with core sizes correlated with halo mass and velocity dispersion Reduced central densities and rounder inner halos in galaxy clusters compared to pure CDM, but a smaller effect than in dwarfs (because clusters have higher velocity dispersion and shorter halo crossing times relative to the SIDM mean free path) Possible offsets between dark matter and galaxies in merging cluster systems, depending on the velocity dependence of the cross-section	Radiative decay line at E ≈ m_s / 2 in galaxy and galaxy-cluster X-ray spectra, with line strength scaling with dark-matter column density Small-scale structure suppression: altered Lyman-α forest at z ~ 3-5, fewer dwarf satellites of the Milky Way, lower-density halo cores If an X-ray decay line is detected, its energy and brightness would pin down both the sterile neutrino's mass and how strongly it mixes with ordinary neutrinos (the mixing angle θ), since the production rate scales as sin²(2θ) × (m_s)²
Where it breaks	Baryonic physics (star formation feedback, AGN) can also produce cores within CDM, reducing the necessity of SIDM Cluster shapes and ellipticity from gravitational lensing constrain σ/m below the value needed to affect dwarf cores, requiring velocity-dependent cross-sections that some models can produce but not all Missing-satellites and too-big-to-fail problems aren't fully addressed by SIDM alone; they require additional fixes Critics view SIDM as introducing a free parameter (the cross-section) rather than proposing a specific candidate particle	Hitomi (2017) failed to confirm the 3.5 keV line in the Perseus cluster (the satellite was destined for deeper sensitivity but lost before extended observations) Dessert et al. (2020) found the line absent in XMM blank-sky observations, arguing the original signal is inconsistent with a dark-matter origin Lyman-α forest and dwarf-galaxy structure constrain the simplest Dodelson-Widrow production, disfavoring sterile neutrinos as 100% of dark matter unless production is tuned The active-sterile mixing parameter space is heavily constrained by X-ray searches (XMM, Chandra, NuSTAR) over a wide mass range
Key unresolved problem	The mimicry problem: ordinary effects like exploding stars and black-hole winds can carve out the same smooth galaxy centers that self-interacting dark matter (SIDM) would, so nothing observed yet clearly requires the particles to collide with each other.	The 3.5 keV line ambiguity: a faint X-ray glow that could be sterile neutrinos decaying has neither been confirmed nor ruled out, and researchers are waiting on sharper XRISM data to settle whether it is real or an instrument artifact.
Reader vote	No votes yet	No votes yet

Self-Interacting Dark Matter (SIDM)

2000 / 2018 · Frontier

Sterile Neutrinos

1994 / 1999 · Frontier

Proposed

2000 / 2018

1994 / 1999

Key figures

David Spergel, Paul Steinhardt, Sean Tulin, Hai-Bo Yu

Scott Dodelson, Lawrence Widrow, Xiang-Dong Shi, George Fuller

In one sentence

Dark matter that interacts with itself via some non-gravitational force, with cross sections tuned so the interactions thermalize the inner regions of dwarf galaxies (creating cores instead of cusps) but barely affect large-scale structure.

Hypothetical neutrinos with masses around a few keV that don't feel the weak force at all, only gravity and a tiny mixing with the three Standard Model neutrinos. They would warm-dark-matter the universe and decay into X-rays, producing a detectable line in galaxy spectra. A tentative 3.5 keV X-ray line has been the subject of a decade-long debate.

Predictions

Cored density profiles in dwarf and low-surface-brightness galaxies, with core sizes correlated with halo mass and velocity dispersion
Reduced central densities and rounder inner halos in galaxy clusters compared to pure CDM, but a smaller effect than in dwarfs (because clusters have higher velocity dispersion and shorter halo crossing times relative to the SIDM mean free path)
Possible offsets between dark matter and galaxies in merging cluster systems, depending on the velocity dependence of the cross-section

Radiative decay line at E ≈ m_s / 2 in galaxy and galaxy-cluster X-ray spectra, with line strength scaling with dark-matter column density
Small-scale structure suppression: altered Lyman-α forest at z ~ 3-5, fewer dwarf satellites of the Milky Way, lower-density halo cores
If an X-ray decay line is detected, its energy and brightness would pin down both the sterile neutrino's mass and how strongly it mixes with ordinary neutrinos (the mixing angle θ), since the production rate scales as sin²(2θ) × (m_s)²

Where it breaks

Baryonic physics (star formation feedback, AGN) can also produce cores within CDM, reducing the necessity of SIDM
Cluster shapes and ellipticity from gravitational lensing constrain σ/m below the value needed to affect dwarf cores, requiring velocity-dependent cross-sections that some models can produce but not all
Missing-satellites and too-big-to-fail problems aren't fully addressed by SIDM alone; they require additional fixes
Critics view SIDM as introducing a free parameter (the cross-section) rather than proposing a specific candidate particle

Hitomi (2017) failed to confirm the 3.5 keV line in the Perseus cluster (the satellite was destined for deeper sensitivity but lost before extended observations)
Dessert et al. (2020) found the line absent in XMM blank-sky observations, arguing the original signal is inconsistent with a dark-matter origin
Lyman-α forest and dwarf-galaxy structure constrain the simplest Dodelson-Widrow production, disfavoring sterile neutrinos as 100% of dark matter unless production is tuned
The active-sterile mixing parameter space is heavily constrained by X-ray searches (XMM, Chandra, NuSTAR) over a wide mass range

Key unresolved problem

The mimicry problem: ordinary effects like exploding stars and black-hole winds can carve out the same smooth galaxy centers that self-interacting dark matter (SIDM) would, so nothing observed yet clearly requires the particles to collide with each other.

The 3.5 keV line ambiguity: a faint X-ray glow that could be sterile neutrinos decaying has neither been confirmed nor ruled out, and researchers are waiting on sharper XRISM data to settle whether it is real or an instrument artifact.

Reader vote

No votes yet