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A strong broadband 21 cm cosmological signal from dark matter spin-flip interactions

Dhuria, Mansi and Karambelkar, Viraj and Rentala, Vikram and Sarmah, Priyanka (2021) A strong broadband 21 cm cosmological signal from dark matter spin-flip interactions. Journal of Cosmology and Astroparticle Physics, 2021 (8). Art. No. 041. ISSN 1475-7516. doi:10.1088/1475-7516/2021/08/041.

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In the standard cosmology, it is believed that there are two relatively weak and distinct band-limited absorption features, with the first absorption minima near 20 MHz (z ∼ 70) and the other minima at higher frequencies between 50-110 MHz (z ∼ 12-27) in the global cosmological 21 cm signal, which are signatures of collisional gas dynamics in the cosmic dark ages and Lyman-α photons from the first stars at cosmic dawn, respectively. A similar prediction of two distinct band-limited, but stronger, absorption features is expected in models with excess gas cooling, which have been invoked to explain the anomalous EDGES signal. In this work, we explore a novel mechanism, where dark matter spin-flip interactions with electrons through a light axial-vector mediator could directly induce a 21 cm absorption signal which is characteristically different from either of these. We find generically, that our model predicts a strong, broadband absorption signal extending from frequencies as low as 1.4 MHz (z ∼ 1000), from early in the cosmic dark ages where no conventional signal is expected, all the way up to higher frequencies where star formation and X-ray heating effects are expected to terminate the absorption signal. We find a rich set of spectral features that could be probed in current and future experiments looking for the global 21 cm signal. In the standard cosmology and in excess gas cooling models it is expected that the gas spin temperature as inferred from the absorption signal is a tracer of the gas kinetic temperature. However, in our model we find in certain regions of parameter space that the spin temperature and kinetic temperature of the gas evolve differently, and the absorption signal only measures the spin temperature evolution. Large swathes of our model parameter space of interest are safe from existing particle physics constraints, however future searches for short range spin-dependent forces between electrons on the millimeter to nanometer scale have the potential to discover the light mediator responsible for our predicted signal.

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Additional Information:© 2021 IOP Publishing Ltd and Sissa Medialab. Received 8 April 2021; Accepted 27 July 2021; Published 19 August 2021. We thank Girish Kulkarni and Shikhar Mittal for helpful comments on the draft. We also acknowledge useful discussions with Varun Bhalerao, Subhendra Mohanty, Surhud More, Nadav Joseph Outmezguine, Arun Thalapillil, and Himanshu Verma. MD would like to acknowledge support through Inspire Faculty Fellowship of the Department of Science and Technology (DST), Government of India under the Grant Agreement number: IFA18-PH215. VR is supported by a DST-SERB Early Career Research Award (ECR/2017/000040) and an IITB-IRCC seed grant. VR would like to express a special thanks to the GGI Institute for Theoretical Physics for its hospitality and support.
Funding AgencyGrant Number
Department of Science and Technology (India)IFA18-PH215
Science and Engineering Research Board (SERB)ECR/2017/000040
Indian Institute of Technology BombayUNSPECIFIED
Issue or Number:8
Record Number:CaltechAUTHORS:20210910-172055814
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Official Citation:Mansi Dhuria et al JCAP08(2021)041; DOI: 10.1088/1475-7516/2021/08/041
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:110801
Deposited By: Tony Diaz
Deposited On:10 Sep 2021 20:13
Last Modified:10 Sep 2021 20:13

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