Sterile Neutrinos in the Cosmos

Sterile neutrinos in the cosmos

Maria Archidiacono University of Milan

NF02 Mini-Workshop, September 25th, 2020 1 dof1 ∆χ dof2 profile ∆χ2 profile 10 10 102 90.0090.00 % % 2 2 5 5 95.0095.00 % % ∆χ ∆χ 99.0099.00 % % 2 2

10 108 8 2 2 6 26 dof2 ∆χ dof contours ∆χ contours Which sterile neutrinos? 4 4

] 10 2 2 2 1 1 10 108 8 1 dof 6 6 1 dof ) ) ) 2 4

4 [eV 2 2 2 ∆χ ∆χ 2 2 41 (eV 2 2 profile (eV profile (eV 0 0 m 41 10 108 8 ∆ • eV2 sterile6 6 neutrinos 1 2 new 2 new 4 4 m m m Δ

∆ 2 ∆ 2 Gallium −1 −1 10 108 8 68.27% CL (1σ) 6 6 4 4 95.45% CL (2σ) 99.73% CL (3 ) 2 2 σ −2 −2 −1 10 10 10 23456782345678 2345678 2345678 2345678 2345678 −3 −3 −2 −2 −1 −1 0 0 Motivation−2 −1 : Cosmology: Hot Dark Matter 5 5 10 10 10 10 1 10 10 10 10 2 2 10 10 10 10 sin 2sin(2!θ (2θ) ) ∆χ2∆χ2 2 sin 2 new14 new sin (2θee) (a) The reactor anomaly [81]. MiniBooNE(b) The gallium anomaly2018 [142].

2 ) 2 ) 2 10

2 10 (eV 2 41 (eV

m MiniBooNE 2 41 Δ

m 90% CL Δ 99% CL 10 10 KARMEN2 90% CL Karmen CCFR OPERA 90% CL Bugey

1 NOMAD 1

− 1 10 10−1 LSND 90% CL LSND 90% CL LSND 99% CL LSND 99% CL

− 2 10 −2 10−3 10−2 10−1 1 10 2 10−3 10−2 10−1 1 sin 2θeμ 2 sin 2θeμ (c) The LSND anomaly [121]. (d) The MiniBooNE anomaly [122].

Figure 12: Best-ﬁt regions of the anomalies. (a) The regions allowed by the reactor anomaly • keV[81]. Thesterile blue and green linesneutrinos enclose the regions allowed at 90% and 95% CL. The red line excludes the region on the right at 99% CL. (b) The lines enclose the regions allowed by the gallium anomaly [142]. (c) The shaded regions are allowed by the LSND anomaly [121]. (d) The lines with the colors indicated in the legend enclose the regions allowed at diﬀerent CL’s by the MiniBooNE anomaly [122]. Motivation: Cosmology: Warm Dark Matter

gamma is emitted after a mean capture time of14 about 200 µs.Toimprovetheprobabilityfor neutron captures and for better background discrimination,Bulbul the LS+ is sometimes2014 doped with gadolinium (Gd). In this case the gamma energy upon neutron capture is increased to about ) ) 155 -1 8 MeV. Moreover, due to the very high cross section-1 for thermal neutron capture for Gd and 157Gd, the coincidence time is signiﬁcantly reduced. For typical Gd-concentrations at 0.8 XMM - MOS 3.51 ± 0.03 (0.05) XMM - PN

3.57 ± 0.02 (0.03) keV keV 1.2 Full Sample -1 27-1 Full Sample 0.7 6 Ms 2 Ms 1 0.6 Flux (cnts s Flux (cnts s 0.8 0.015 0.04

0.01 0.02 0.005 0 0 Residuals Residuals -0.005 -0.02 Kuhlen+ 2012 3 3.2 3.4 3.6 3.8 4 3 3.2 3.4 3.6 3.8 4 Energy (keV) Energy (keV) 2 ) ) -1 -1 XMM - MOS XMM - MOS Centaurus+

keV Rest of the Sample keV 3.57 keV 3.57 keV -1 -1 Coma + (69 Clusters) Ophiuchus 4.9 Ms 525.3 ks 0.25 Flux (cnts s Flux (cnts s 0.01

0.005

0 Residuals Residuals -0.005

3 3.2 3.4 3.6 3.8 4 Energy (keV) ) -1 0.75 XMM - PN 3.57 keV Rest of the Sample keV

-1 (69 Clusters) 1.8 Ms

0.5 Flux (cnts s

0.02

0 Residuals

-0.02 3 3.2 3.4 3.6 3.8 4 Energy (keV) Figure 6. 3 4keVbandoftherebinnedXMM-Newton spectra of the detections.The spectra were rebinned to make the excess at 3.57 keV more apparent. (APJ VERSION INCLUDES ONLY THE REBINNED MOS SPECTRUM OF THE FULL SAMPLE).⇠

nax dwarf galaxies (Boyarsky et al. 2010; Watson et al. at a 1 level. Since the most confident measurements 2012), as showin in Figure 13(a). It is in marginal ( 90% are provided by the highest signal-to-noise ratio stacked significance) tension with the most recent Chandra⇠limit MOS observations of the full sample, we will use the flux from M31 (Horiuchi et al. 2014), as shown in Figure at energy 3.57 keV when comparing the mixing angle 13(b). measurements for the sterile neutrino interpretation of For the PN flux for the line fixed at the best-fit MOS this line. energy, the corresponding mixing angle is sin2(2✓)= +1.2 +1.8 11 4.3 1.0 ( 1.7) 10 . This measurement is consistent with that obtained⇥ from the stacked MOS observations 3.2. Excluding Bright Nearby Clusters from the Sample eV sterile neutrinos Status 7 4 4/3 Gariazzo+ (2019) ⇢ = ⇢ 1+ N rad 8 11 e↵ " ✓ ◆ # Ne↵ = N⌫ + Ne↵ Ne↵ =3.045 + Ne↵ Allowed by Planck CMB Planck 2018 TTTEEE + lowE +0.36 Neff = 2.92 -0.37 (95%cl)

Light sterile neutrino problem

Oscillation Theoretical Cosmological experiments efforts observations (LOI: NuSte: Global Light Sterile BSM physics Neutrino fits; Gariazzo+) 3 Theoretical efforts BSM physics

LOI: Sterile Neutrinos with Non-Standard Interactions; Archidiacono, Hannestad+ Early Universe Late Universe 1 -1 0.9 Archidiacono+ 2014 ns ns èf 4 0.8 -1 -1 ns ns èf ns ns èf 10

0.7 ] 3 0.6 1000 eff 0.5 N d 0.4 Pseudoscalar P(k) [(Mpc/h) 0.3 100 best-ﬁt Planck 2015 mν,s =0.1eV 0.2 mν,s =1eV 0.1 mν,s =3eV 10 0 −6 −5 10 10 0.001 0.01 0.1 1 g s k [h/Mpc]

4 Theoretical efforts BSM physics

LOI: Sterile Neutrinos with Non-Standard Interactions; Archidiacono, Hannestad+ Early Universe Late Universe 1 -1 0.9 Archidiacono+ 2014 ns ns èf 4 0.8 -1 -1 ns ns èf ns ns èf 10

0.7 ] 3 0.6 1000 eff 0.5 N d 0.4 Pseudoscalar P(k) [(Mpc/h) 0.3 100 best-ﬁt Planck 2015 mν,s =0.1eV 0.2 mν,s =1eV 0.1 mν,s =3eV 10 0 −6 −5 10 10 0.001 0.01 0.1 1 g s k [h/Mpc] Future directions Cosmology Astrophysics Particle Physics

d u d u dR(L) uR(L)

GF eL ✏ eR F WR(L) (✓ ) ⌫ eR g N J J ⌫ ⌫ N H h i ⌫ ⇥ eL GF eL GF eL d u d 5 u d u

FIG. 1. Feynman diagrams for ordinary 0⌫J Majoron decay (left), 0⌫ decay triggered by

3 an e↵ective operator of the form ⇤ (¯u d)(¯e ⌫) (center) and possible ultraviolet completion NP O O of the latter in a Left-Right symmetric model (right).

II. EFFECTIVE LONG-RANGE INTERACTIONS

We are interested in processes where right- and left-handed electrons are emitted along with a scalar considering as a ﬁrst approach, only (V + A)and(V A)currents.The e↵ective Lagrangian can then be written as

GF cos ✓C µ ✏RL µ ✏RR µ 0⌫ = jLJLµ + jRJLµ + jRJRµ +h.c., (1) L p2 mp mp !

with the Fermi constant GF , the Cabbibo angle ✓C , and the leptonic and hadronic currents jµ =¯eµ(1 )⌫ and J µ =¯uµ(1 )d, respectively. Here, ⌫ is a 4-spinor ﬁeld L,R ⌥ 5 L,R ⌥ 5 c of the light electron neutrino, either deﬁned by ⌫ = ⌫L + ⌫L (i.e. a Majorana spinor

constructed from the SM active left-handed neutrino ⌫L)or⌫ = ⌫L + ⌫R (a Dirac spinor

constructed from the SM ⌫L and a new SM-sterile right-handed neutrino ⌫R). Whether the light neutrinos are of Majorana or Dirac type and whether total lepton number is broken or conserved is of crucial importance for an underlying model (determined by the

chosen lepton numbers for ⌫R and )butasfarasthee↵ective interactions in Eq. (1) are

concerned, this does not play a role in our calculations. The proton mass mp is introduced in the exotic interactions as normalization to make the e↵ective coupling constants ✏RL and ✏RR dimensionless, in analogy to the e↵ective operator treatment of 0⌫ decay [10, 11]. In Eq. (1), we omit exotic operators with left-handed lepton currents; as in the standard long-range case, such contributions will be additionally suppressed by the small neutrino masses [11]. We instead focus on the process depicted in Fig. 1 (center), where

3 Cosmological observations 21 me mµ mt mb mW mt 4/3 10 5 7 4 Spin-1 ⇢rad = ⇢ 1+ Ne↵ 24 Bullet cluster -dec 1 4/3 QCD 10 n Spin- 8 11 CMB (direct) 2 2 " 7✓ 4◆ # Spin-0 ⇢rad = ⇢ 1+ Ne↵ 10 27 1 " Ne↵8= N11⌫ + Ne↵# ] N =3.045 + N✓ ◆ 2 30 e↵ e↵ 10 Meson decays 0.5 4/3 Ne↵ =gN,SM⌫ + Ne↵ cm eff [ 33 Current limit (2s) Ne↵ =0.027g , ⇤

10 N 4/3 0.2 ⇤ g (TF,)

D g ,SM DM 36 0.09 ✓ ⇤ ⇤ ◆ b < Ne↵ =0.027g , 10 Neff 0.1 ⇤ s D Next generation (2s) g ,SMg (T=F 106,) .75 0.054 ✓⇤ ⇤ ◆ 10 39 0.05 0.047 Future target g ,SM = 106.75 . 42 0 027 ⇤ 10 0.02 45 0.01 10 3 2 1 0 1 5 4 3 3 4 5 6 10 10 10 10 10 10 10 10 0.01 0.1 1 10 100 10 10 10 10 mDM [MeV] TF [GeV] Figure from LOI: Insights for Fundamental Physics and Cosmology with Light Relics; Meyers+

LOI: CMB-HD: An Ultra-Deep,High-Resolution Millimiter-Wave Survey Over Half the Sky; Sehgal+, s(Neff)=0.014

See also LOI: Cosmological Neutrinos; Grohs+

6 Astrophysical observations IceCube-Gen2 Collaboration

LOI: IceCube Neutrino Observatory; Grant, Halzen+, IceCube Collaboration LOI:IceCube-Gen2: The Window to the Extreme Universe; Karle, Kowalski+, IceCube-Gen2 Collaboration

LOI: Cosmic Neutrino Probes of Fundamental Physics; Bustamante+

• Sterile neutrinos (energy spectrum) Flavour • NSI (energy spectrum) composition • DM – n interactions (arrival direction)

7 Astrophysical observations IceCube-Gen2 Collaboration

LOI: IceCube Neutrino Observatory; Grant, Halzen+, IceCube Collaboration LOI:IceCube-Gen2: The Window to the Extreme Universe; Karle, Kowalski+, IceCube-Gen2 Collaboration

LOI: New physics with astrophysical neutrino flavour; Arguelles+, IceCube-Gen2 Collaboration

8 Astrophysical observations IceCube-Gen2 Collaboration

LOI: IceCube Neutrino Observatory; Grant, Halzen+, IceCube Collaboration LOI:IceCube-Gen2: The Window to the Extreme Universe; Karle, Kowalski+, IceCube-Gen2 Collaboration

LOI: Supernova Burst and Other Low40 -Energy NeutrinoES Physics 40 35 νe Ar 40 in DUNE; Patterson, Worcester+, DUNE Collaborationνe Ar 30

25 Theoretical uncertainties and computational20 effort: 15 LOI: Deciphering explosion physics Events per 0.5 MeV from the supernova 10 neutrino signal; Friedland+ 5

0 5 10 15 20 25 30 35 40 45 50 Observed energy (MeV) 9

Figure 2: Left: Expected measured spectrum in DUNE as a function of observed energy, after detector response smearing and integrated over time, for the model in [13]. Event rates are computed using SNOwGLoBES [14] with a transfer matrix based on full DUNE simula- tion and reconstruction. Right: Sensitivity regions in ( E , ") space (proﬁled over pinching h ⌫i parameter ↵)forthe⌫e spectrum for three di↵erent supernova distances. SNOwGLoBES assumes a transfer matrix made using MARLEY [15] with a 20% Gaussian resolution on detected energy, and a step eciency function with a 5 MeV detected energy threshold.

Study of the energy balance of a supernova burst can provide constraints on new physics scenarios, the existence of which would alter the energy transport process within the explosion. The complexity of the neutrino flavor transformation probabilities is greater in asupernovaburstbecauseofthekinematicsoftheexplosionitselfandthepossibilityfor neutrino-neutrino scattering and collective modes of oscillation. These e↵ects will imprint on the neutrino signal and can be used to study these phenomena experimentally. The true neutrino mass ordering has a strong impact on the expected signal [16], particularly in early times including the neutronization burst. Knowledge of the mass ordering from other experiments may be used to better extract other particle and astrophysical knowledge from the observed supernova burst signal. Neutrinos and antineutrinos from other astrophysical sources, such as solar [17] and dif- fuse background supernova neutrinos [18], are also potentially detectable. While detection of these sources will be challenging, particularly because of the presence of radioactive background in the detector, initial studies suggest potential for DUNE to select a sample of solar 2 neutrinos that would allow a significant improvement in the measurement of m21 as well as observations of the the hep and 8B solar neutrino flux. Development of reconstruction, calibration, and triggering/DAQ infrastructure will play an important role in enabling a broader physics program at low energies. DUNE will have good sensitivity to a supernova burst within the Milky Way, and possibly beyond, allowing study of a wide range of astrophysics and particle physics topics. DUNE will participate in the worldwide multi-messenger astronomy e↵ort, with unique sensitivity to the electron-neutrino component of the supernova burst.

3 keV sterile neutrinos Status

+ strong lensing Gilman+ 2019 Drewes+ (2019)

Figure 14: Constraints on sterile neutrino DM. The solid lines represent the most important constraints that are largely model independent, i.e., they can be derived for a generic SM-singlet fermion N of mass M and a mixing angle ✓ with SM neutrinos, without speciﬁcation of the model that this DM candidate is embedded in. The model independent phase space bound (solid purple line) is based on Pauli’s exclusion 10 principle (c.f. Section 3.1). The bounds based on the non-observation of X-rays from the decay N ⌫ (violet area, see Section 3.2 for details) assume that the decay occurs solely through mixing with the active! neutrinos with the decay rate given by eq. (29). In the presence of additional interactions, these constraints could be stronger, see e.g. [520]. All X-ray bounds have been smoothed and divided by a factor 2 to account for the uncertainty in the DM density in the observed objects. They are compared to two estimates of the ATHENA sensitivity made in ref. [234]. The blue square marks the interpretation of the 3.5 keV excess as decaying sterile neutrino DM [184, 188]. All other constraints depend on the sterile neutrino production mechanism. As an example, we here show di↵erent bounds that apply to thermally produced sterile neutrino DM, cf. section 4.2. The correct DM density is produced for any point along black solid line via the non-resonant mechanism due to ✓-suppressed weak interactions (24) alone (Section 4.2.1). Above this line the abundance of sterile neutrinos would exceed the observed DM density. We have indicated this overclosure bound by a solid line because it applies to any sterile neutrino, i.e., singlet fermion that mixes with the SM neutrinos. It can only be avoided if one either assumes signiﬁcant deviations from the standard thermal history of the universe or considers a mechanism that suppresses the neutrino production at temperatures of a few hundred MeV, well within the energy range that is testable in experiments, cf. e.g. [521]. For parameter values between the solid black line and the dotted green line, the observed DM density can be generated by resonantly enhanced thermal production (Section 4.2.2). Below the dotted green line the lepton asymmetries required for this mechanism to work are ruled out because they would alternate the abundances of light elements produced during BBN [584]. The dotted purple line represents the lower bound from phase space arguments that takes into account primordial distribution of sterile neutrinos, depending on the production mechanism [22]. As a structure formation bound we choose to display the conservative lower bound on the mass of resonantly produced sterile neutrinos, based on the BOSS Lyman-↵ forest data [268] (see Section 3.3 for discussion). The structure formation constraints depend very strongly on the production mechanism (Section 4). The dashed red line shows the sensitivity estimate for the TRISTAN upgrade of the KATRIN experiment (90% C.L., ignoring systematics, c.f. Section 5.2).

58 keV sterile neutrinos Future prospects

+ strong lensing Gilman+ 2019 Drewes+ (2019)

Figure 14: Constraints on sterile neutrino DM. The solid lines represent the most important constraints that are largely model independentLOI:, i.e., Prospects they can befor derived keV forSterile a generic Neutrino SM-singlet Searches fermion Nwithof mass KATRIN M and a mixing angle ✓ with SM neutrinos, without speciﬁcation of the model that this DM candidate is embedded in. The model independentMertens phase space+ bound (solid purple line) is based on Pauli’s exclusion 11 principle (c.f. Section 3.1). The bounds based on the non-observation of X-rays from the decay N ⌫ (violet area, see Section 3.2 for details) assume that the decay occurs solely through mixing with the active! neutrinos with the decay rate given by eq. (29). In the presence of additional interactions, these constraints could be stronger, see e.g. [520]. All X-ray bounds have been smoothed and divided by a factor 2 to account for the uncertainty in the DM density in the observed objects. They are compared to two estimates of the ATHENA sensitivity made in ref. [234]. The blue square marks the interpretation of the 3.5 keV excess as decaying sterile neutrino DM [184, 188]. All other constraints depend on the sterile neutrino production mechanism. As an example, we here show di↵erent bounds that apply to thermally produced sterile neutrino DM, cf. section 4.2. The correct DM density is produced for any point along black solid line via the non-resonant mechanism due to ✓-suppressed weak interactions (24) alone (Section 4.2.1). Above this line the abundance of sterile neutrinos would exceed the observed DM density. We have indicated this overclosure bound by a solid line because it applies to any sterile neutrino, i.e., singlet fermion that mixes with the SM neutrinos. It can only be avoided if one either assumes signiﬁcant deviations from the standard thermal history of the universe or considers a mechanism that suppresses the neutrino production at temperatures of a few hundred MeV, well within the energy range that is testable in experiments, cf. e.g. [521]. For parameter values between the solid black line and the dotted green line, the observed DM density can be generated by resonantly enhanced thermal production (Section 4.2.2). Below the dotted green line the lepton asymmetries required for this mechanism to work are ruled out because they would alternate the abundances of light elements produced during BBN [584]. The dotted purple line represents the lower bound from phase space arguments that takes into account primordial distribution of sterile neutrinos, depending on the production mechanism [22]. As a structure formation bound we choose to display the conservative lower bound on the mass of resonantly produced sterile neutrinos, based on the BOSS Lyman-↵ forest data [268] (see Section 3.3 for discussion). The structure formation constraints depend very strongly on the production mechanism (Section 4). The dashed red line shows the sensitivity estimate for the TRISTAN upgrade of the KATRIN experiment (90% C.L., ignoring systematics, c.f. Section 5.2).

58 keV sterile neutrinos Future prospects

+ strong lensing Gilman+ 2019 Drewes+ (2019)

LOI: CMB-HD: An Ultra-Deep,High-Resolution MillimiterFigure 14:-WaveConstraintsSurvey Over on sterile Half neutrinothe Sky; DM. SehgalThe+, solid lines represent the most important constraints that are largely model independentLOI:, i.e., Prospects they can befor derived keV forSterile a generic Neutrino SM-singlet Searches fermion Nwithof mass KATRIN M and a mixing angle ✓ with SM neutrinos, without speciﬁcation of the model that this DM candidate is embedded in. The model independentMertens phase space+ bound (solid purple line) is based on Pauli’s exclusion 12 principle (c.f. Section 3.1). The bounds based on the non-observation of X-rays from the decay N ⌫ (violet area, see Section 3.2 for details) assume that the decay occurs solely through mixing with the active! neutrinos with the decay rate given by eq. (29). In the presence of additional interactions, these constraints could be stronger, see e.g. [520]. All X-ray bounds have been smoothed and divided by a factor 2 to account for the uncertainty in the DM density in the observed objects. They are compared to two estimates of the ATHENA sensitivity made in ref. [234]. The blue square marks the interpretation of the 3.5 keV excess as decaying sterile neutrino DM [184, 188]. All other constraints depend on the sterile neutrino production mechanism. As an example, we here show di↵erent bounds that apply to thermally produced sterile neutrino DM, cf. section 4.2. The correct DM density is produced for any point along black solid line via the non-resonant mechanism due to ✓-suppressed weak interactions (24) alone (Section 4.2.1). Above this line the abundance of sterile neutrinos would exceed the observed DM density. We have indicated this overclosure bound by a solid line because it applies to any sterile neutrino, i.e., singlet fermion that mixes with the SM neutrinos. It can only be avoided if one either assumes signiﬁcant deviations from the standard thermal history of the universe or considers a mechanism that suppresses the neutrino production at temperatures of a few hundred MeV, well within the energy range that is testable in experiments, cf. e.g. [521]. For parameter values between the solid black line and the dotted green line, the observed DM density can be generated by resonantly enhanced thermal production (Section 4.2.2). Below the dotted green line the lepton asymmetries required for this mechanism to work are ruled out because they would alternate the abundances of light elements produced during BBN [584]. The dotted purple line represents the lower bound from phase space arguments that takes into account primordial distribution of sterile neutrinos, depending on the production mechanism [22]. As a structure formation bound we choose to display the conservative lower bound on the mass of resonantly produced sterile neutrinos, based on the BOSS Lyman-↵ forest data [268] (see Section 3.3 for discussion). The structure formation constraints depend very strongly on the production mechanism (Section 4). The dashed red line shows the sensitivity estimate for the TRISTAN upgrade of the KATRIN experiment (90% C.L., ignoring systematics, c.f. Section 5.2).

58 heat from coupling onto the detectors during the first flight launch. With the largely successful demonstra- tion of the instrument during the first flight, modifications are being implemented from the lessons learned in preparation for the SNR reflight19. The program will then be in a position to prepare modifications for a dark matter search. To reach the dark matter instrument goals Configuration First flight Dark Matter shown in Table 1, modifications are required Operating temperature 75 mK 75 mK for a larger FOV and a higher-energy band- Energy resolution 4.5 - 10 eV 3 eV 18 pass, as described in . The proposed detec- Bandpass 0.2 – 4 keV 0.5 – 10 keV tors are a Mo/Au bilayer TES with a Au/Bi Effective area 0.47 cm2 1.1 cm2 absorber (3 µm Bi, 0.7 µm Au). The expected Field of view 11.8 arcmins 33 degrees signal rate is <10 Hz across the array (<1 Observation time 300 s 300 s Hz/pixel), which is well within the readout ca- Expected counts 13,000 2,400 pabilities of the system. Table 1: Micro-X instrument specifications 3 Dark Matter Sensitivity The proposed first target is a region near the Galactic Center that is relatively quiet in the X-ray band. The background spectrum is a nearly flat continuum with 0.6 counts/flight/2.5 eV17. Using the flux derived from26, 20.3 4.5 signal events are expected in a single flight, corresponding to >5 significance18. Micro- ± X will be sensitive to both the reported 3.5 keV excess and to any X-ray signature of dark matter in this energy band. In the case of sterile neutrinos, this sensitivity can be converted into the parameters shown in Figure 2. The Micro-X observations are statistics-limited, so additional flights will further increase the sensitivity. If a linekeV is detected, Micro-Xsterile can discern between neutrinos dark matter and an atomic origin by mapping the Doppler shift of the line across the Galaxy with multiple flights27;28. An atomic background will be co-moving with the Earth, while a dark matter signal will come from the stationary halo. This “velocity spectroscopy” drives the 3 eV resolution specification of the TES array. The Micro-X observationFuture is highly complementary prospects with future XRISM satellite29;30 observations. Micro- X is optimized for the all-sky galactic signal, and its short flight precludes it from observing fainter targets. LOI: Dark MatterXRISMSearcheswill get excellentwith spectra the from Micro extragalactic-X X sources-ray likeSounding galaxy clustersRocket and dwarf spheroidals. If it were to observe the Galactic Center, it would take 35 Ms of observation time to accumulate the same signal Figueroa-Feliciano,flux as one Hubbard Micro-X flight.+ In a more realistic scenario of co-added observations, it would take >100 Ms of data to accumulate the same signal flux. Thus a combination of data from both experiments is an excellent way to enhance sensitivity to dark matter signals in the X-ray band.

Figure 2: Projected sensitivity to sterile neutrino dark matter from ﬁrst (green dotted) and second (red dash-dotted) proposed targets18. Previous claims from26,31, and7 are shown in red, maroon, and blue dots, • significantlyrespectively.less expensive Previous exclusionthan limitssatellite from X-ray missions observations (shaded), and andthe XQC instrument (black line17) arecan shown. be recovered after flight and reflown 3

• Micro-X has the sensitivity to discern between dark matter and atomic origin of the 3.5 keV line

13 Conclusions

Cosmology Astrophysics • CMB-S4 • Euclid • IceCube • CMB-HD • Vera Rubin Obs. • DUNE • SKA • Micro-X

Neutrino oscillation experiments (see next talks)