Probing multi-state dark matter via optical absorption lines in DESI spectra
Abstract
We search for dark matter through absorption lines imprinted on the spectra of background sources whose sightlines pass through foreground dark matter halos. Such a line is a generic feature of multi-state dark matter models that couple to photons through higher-order electromagnetic moments. We focus on the minimal case of a two-state system with a magnetic dipole transition, in which the ground state absorbs a photon and makes a transition to the excited state. For transition energy ΔE ∼ O (eV), the line falls in the optical band, within reach of spectroscopic surveys such as DESI. Stacking 145,087 spectra of DESI Early Data Release objects paired with foreground GAMA galaxy groups, we find a stacked optical depth consistent with zero and place 2σ upper limits on the magnetic dipole transition cross-section. The limits are strongest at ΔE ∼ 3-5 eV for a few MeV dark matter mass in the parameter space that is inaccessible to both cosmological (BBN+CMB) and direct detection experiments. We forecast that the full DESI and the next-generation spectroscopic surveys will tighten these limits by more than an order of magnitude, establishing spectroscopic stacking as a competitive probe of electromagnetically interacting multi-state dark matter.
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BibTeX
@misc{ganguly2026probing,
title = {{Probing multi-state dark matter via optical absorption lines in DESI spectra}},
author = {Anoma Ganguly and Shadab Alam},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.16547},
eprint = {2609.16547},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.16547},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Probing multi-state dark matter via optical absorption lines in DESI spectra
AU - Anoma Ganguly
AU - Shadab Alam
PY - 2026
DA - 2026/09/20
PB - arXiv
DO - 10.48550/arxiv.2609.16547
UR - https://arxiv.org/abs/2609.16547
AB - We search for dark matter through absorption lines imprinted on the spectra of background sources whose sightlines pass through foreground dark matter halos. Such a line is a generic feature of multi-state dark matter models that couple to photons through higher-order electromagnetic moments. We focus on the minimal case of a two-state system with a magnetic dipole transition, in which the ground state absorbs a photon and makes a transition to the excited state. For transition energy ΔE ∼ O (eV), the line falls in the optical band, within reach of spectroscopic surveys such as DESI. Stacking 145,087 spectra of DESI Early Data Release objects paired with foreground GAMA galaxy groups, we find a stacked optical depth consistent with zero and place 2σ upper limits on the magnetic dipole transition cross-section. The limits are strongest at ΔE ∼ 3-5 eV for a few MeV dark matter mass in the parameter space that is inaccessible to both cosmological (BBN+CMB) and direct detection experiments. We forecast that the full DESI and the next-generation spectroscopic surveys will tighten these limits by more than an order of magnitude, establishing spectroscopic stacking as a competitive probe of electromagnetically interacting multi-state dark matter.
ER -