Prospects for finding sterile neutrino dark matter at KATRIN

Open Access

Prospects for finding sterile neutrino dark matter at KATRIN

Cristina Benso, Vedran Brdar, Manfred Lindner, and Werner Rodejohann

Phys. Rev. D 100, 115035 – Published 20 December 2019

Abstract

We discuss under what circumstances a signal in upcoming laboratory searches for keV-scale sterile neutrinos would be compatible with those particles being a sizable part or all of dark matter. In the parameter space that will be experimentally accessible by KATRIN/TRISTAN, strong x-ray limits need to be relaxed and dark matter overproduction needs to be avoided. We discuss postponing the dark matter production to lower temperatures, a reduced sterile neutrino contribution to dark matter, and a reduction of the branching ratio in photons and active neutrinos through cancellation with a new physics diagram. Both the Dodelson-Widrow and the Shi-Fuller mechanisms for sterile neutrino dark matter production are considered. As a final exotic example, potential consequences of $C P T$ violation are discussed.

Received 8 November 2019

DOI:https://doi.org/10.1103/PhysRevD.100.115035

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Particle dark matter

Particles & Fields

Authors & Affiliations

Cristina Benso^*, Vedran Brdar^†, Manfred Lindner^‡, and Werner Rodejohann^§

Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany

^*cristina.benso@mpi-hd.mpg.de
^†vedran.brdar@mpi-hd.mpg.de
^‡manfred.lindner@mpi-hd.mpg.de
^§werner.rodejohann@mpi-hd.mpg.de

Article Text

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Issue

Vol. 100, Iss. 11 — 1 December 2019

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Images

Figure 1
Feynman diagrams for the decay of a sterile neutrino $ν_{s}$ into an active neutrino and a photon. In each diagram, the photon line can be attached to any of the internal charged particles. In the left panel we show the “standard” case with the electroweak $W_{L}$ boson, whereas in the right panel a new scalar particle is exchanged (see text for details).
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Figure 2
“Cocktail scenario”: The colored regions in all panels show the x-ray constraints [39, 90, 91] for the indicated contributions of sterile neutrinos to the total DM density. In each panel these regions are shown in several shades of the same color. The lines, on the other hand, show the parameter space where the indicated amount of DM is produced via the Dodelson-Widrow mechanism below a critical temperature that is different (shown in black boxes) in each panel. We also show KATRIN [24], ECHo [30] and future Troitsk [26] sensitivity for testing keV-scale sterile neutrinos as well as the constraint on sterile neutrino lifetime (gray-shaded region), arising from its main decay channel into three active neutrinos. By comparing x-ray constraints and respective lines for the DM production, and by focusing on the regions where KATRIN is sensitive, one can infer that for $Ω_{s} h^{2} = 0.12$ only very marginal parameter space is testable for $T_{c} ≲ 20 MeV$ . On the other hand, if sterile neutrinos represent 10% of DM, KATRIN is sensitive to $m_{s} ≃ 2 - 3 keV$ , while if this contribution reduces to 1% even larger masses can be reached, however in such case $T_{c}$ should not exceed $T_{c} ≃ 10 MeV$ .
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Figure 3
X-ray suppression: The shaded regions represent various x-ray limits, depending on the level of relaxation. We observe that the decay rate needs to be reduced by four orders of magnitude in order to have the full KATRIN sensitivity region free from x-ray limits. The lines indicate the parameter space in which sterile neutrinos constitute the total DM abundance for the indicated values of $T_{c}$ . We also show KATRIN sensitivity at different stages of the experiment (see previous figure) as well as the limit from structure formation (gray region). Stars indicate four benchmark points, which lie in the future sensitivity region of KATRIN, for which we further explore connection between DM abundance and $T_{c}$ (see Fig. 4).
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Figure 4
The figure represents, for four chosen benchmark points, the dependence of the abundance of sterile neutrino DM (normalized to the observed amount of DM) on $T_{c}$ . BP1 and BP3 lie on the KATRIN statistical sensitivity curve, while BP2 and BP4 indicate the potential of TRISTAN to search for sterile neutrinos (see also Fig. 3). In the considered low $T_{c}$ regime, the produced sterile neutrino DM abundance linearly depends on $T_{c}$ on our logarithmic scale. For our chosen benchmark points, $T_{c}$ values for which the correct amount of DM is produced lie between $T_{c} = 20 MeV$ and $T_{c} = 60 MeV$ .
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Figure 5
Scenario with nonzero lepton asymmetries: The curves indicate the parameter space with $Ω_{s} h^{2} = 0.12$ for $T_{c} = 30 MeV$ and several values of $L$ ranging between 0.05 and 0.3. These curves match the corresponding Dodelson-Widrow line at larger values of $m_{s}$ while resonant effects stemming from lepton asymmetries are prominent for $m_{s} ≲ 10 keV$ . Part of the region in which the curves deviate from the Dodelson-Widrow line is testable at KATRIN, however in some tension with structure formation limits. We also show relaxed x-ray limits as discussed in Sec. 3 and presented in Fig. 3.
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Figure 6
$C P T$ violating scenario: The lines indicate values of lepton asymmetry $L$ for which sterile antineutrinos can generate an abundance of $Ω_{s} h^{2} = 0.12$ . The discovery with TRISTAN is feasible only with $L ≳ 0.1$ while an order of magnitude smaller asymmetries are testable in the final KATRIN stage. As in Fig. 3, we show the relaxation of x-ray limits (for details see Secs. 2 and 3).
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Physical Review D

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