Sterile neutrinos in Cosmology

Transcription

1 Sterile neutrinos in Cosmology ev sterile neutrinos Dark Radiation/HDM kev sterile neutrinos WDM N eff in low-scale seesaw models versus the lightest neutrino mass P. Hernandez, J. Lopez-Pavon, M. Kekic (13) talk by Marija Kekic Dark Matter in the minimal Inverse Seesaw mechanism A. Abada, G. Arcadi, M. Lucente (14) talk by Michele Lucente kev neutrino model building A. Merle (13)

2 ev sterile neutrinos Hot Dark Matter ' ρ r = 1+ 7! 4 $ ) # & () 8 " 11% 4/3 N eff *, +, ρ γ N eff = N s eff + ΔN eff s N eff = 3.46

3 TABLE 5 19 Hints: CMB The angular power spectrum 19 Planck+WP+BICEP To be confirmed Angular scale 1..1 Planck+WP+highl+BAO+H Planck+WP+highl WMAP 9+SPT(13)+ACT(13) D`[µK ] WMAP 7+ACT(13)+BAO+H WMAP 7+ACT(13) Multipole moment, ` WMAP 7+SPT(1)+BAO+H WMAP 7+SPT(1) WMAP 7+SPT(11)+BAO+H WMAP 7+SPT(11) WMAP 7+ACT(1)+BAO+H WMAP 7+ACT(1) l(l +1)Cl/(π) [µk ] WMAP9 SPT 15 GHz ACT 148 GHz s N eff N eff = Multipole l Fig. 1. State of the art of CMB temperature power spectrum measurements from the WMAP 9-year data release (Bennett et al. 1; Hinshaw et al. 1), the South Pole Telescope (Story et al. 1) and ACT (this work). The solid line shows the best fit model tothe ACT 148 GHz data combined with WMAP 7-year data (Larson et al. 11). The dashed line shows the CMB-only component of the same best fit model. Although we compute the power spectrum down to l =,wedonotusedatabelowl =54intheanalysis.

4 Constraints +.67 Planck+WMAP9polarization N eff = (95%c.l.) +highl(spt+act) mν <.6eV Planck+WMAP9polarization +highl(spt+act) + BAO Planck+WP+highL Planck+WP+highL+BAO thermal s ν sterile m = (T / T )m alleviate the tension thermal sterile = (ΔN eff ) m Neff m [ev].8.18 Neff. 3/4 Ω h = Ω h Ωhdm h 3. % 3 ( sterile Ωhdm h = ' mν i + meff * / ev & i=1 ). (95%c.l.) 1. ch eff sterile 4. c dm mν <.8eV N eff = (95%c.l.).5 ΔNeff > might potentially Planck Collaboration: parameters Planck collaboration (13) betweencosmological Planck and HST (95%c.l.) meff, sterile [ev].96.88

5 kev sterile neutrinos Warm Dark Matter

6 [cts/sec/ke Hints: 3.5 kev line [cts/sec/kev] Data - model Flux (cnts s kev ) Boyarsky et al. (14) Talk by Ruchayskiy. 3. No line at 3.5 kev Line at 3.5 kev are unknown but tied to each other in any particular neutrino production model (Pal & Wolfenstein 198). The decay of sterile neutrino should produce a photon of E = ms / and an active neutrino. The mass of the sterile neutrino may lie in the kev range, which would place its decay line in the range accessible to X-ray observations of dark matter aggregations, such as clusters of galaxies, nearby galaxies, and the Milky Way (Abazajian et al. 1a,b). So far, searches in various types of massive systems have resulted only in upper limits (e.g., Boyarsky et al. 1; Abazajian et al. 1). Current X-ray archives of XMM-Newton, Chandra and 3.6 of galaxy cluster 3.8obserSuzaku 3.4 contain vast collections vations. Mining these databases can result in significant Energy [kev] improvement in sensitivity to faint spectral features compared to individual cluster observations (as proposed, e.g., by Abazajian et al. (1b)), with respect to both the statistical and (in a less obvious way) systematic or instrumental uncertainties. In this paper, we undertake XMM-MOS a fishing expedition that combines the spectra of many 3.57 ±. (.3) bright clusters from the XMM-Newton archive in order to Full1.5X-ray Sample search for any kind of faint, unidentified emission XMM-MOS ±.thermal (.3) 6 Ms lines 3.57 be they lines from previously undetected Full Sample Ms elusive sterile neutrino rare elements in the ICM or6 the 1 decay line. To improve the sensitivity to weak spectral lines and reduce systematic e ects, we stack the.4x-ray spectra. from clusters at di erent redshifts in their rest frame, rescaling the photon energies to z =. After blueshift ing each cluster spectrum to z =, any background -. lines or instrumental response artifacts are smeared out 1 (since they occur in the detector frame), but any weak line intrinsic to clusters would be amplified and may be1 come detectable in the combined spectrum. In this paper, we use this method to detect a previously unknown, extremely faint emission line at E DM kev TheEnergy line was(kev) detected in the stacked XMM-Newton X-ray spectra of 73 bright galaxy clusters in the redshift range.1 < z <.35, and independently in several subsam- counts. We first selected clusters below a redshift of.4; higher-redshift clusters are too faint to contribute signifandromeda icantly to the stacked spectrum. We then calculated the total X-ray counts expected + from these XMM-Newton observations using the ROSAT count rates reported in Perseus ebcs (Ebeling et al. ), NORAS (Bo hringer et al. ), REFLEX (Bo hringer et al. 4), XBACs (Ebeling et al. 1996), and MACS catalogs (Ebeling et al. 1) XMM-Newton and XMM-Newton exposures. X-ray To prevent nearby clusters from dominating the stacked spectrum, we used difspace Telescope ferent cluster count limits for di erent redshift ranges. We chose clusters with a minimum of 15 counts per 4. cluster for clusters with z <.1, and 14 counts per cluster for clusters with redshifts.1 < z <.4, to have a wide enough range for the redshift-smearing e ect. O set pointings were excluded from the sample. In the end, a sample of 73 clusters was selected. Included in Table 1 are 1.5 the XMM-Newton observation identification (ObBulbul ettotal al. MOS (14) sid) numbers, and PN clean exposure times, 13 (see Section.). count rates, and our best-fit redshifts 3.51 ±.3 The redshift histogram of the sample is given in Figure clusters The galaxy count rates reported in Table 1 have been used XMM-PN 3.51 ±.3 (.5) Full Sample only for sample selection. Flux (cnts s kev ) Normalized cou Ms XMM Newton + Chandra Number of NClusters Residuals.6. Residuals.1 Flux (cnts s kev ) Eff. Area (cm ) Eff. Area (cm ) The observed brightness of a decaying DM line should be pro! portional to the dark matter column density S = ρdm d% Energy (kev) integral along the line of sight of the DM density distribution: cm ) Flux (cnts s kev ).6 Residuals.7 cm ) Residuals OS spectrum of the central region of M31. Statistical Y-errorbars on the.8 t added, hence the group of positive residuals. Right: zoom onto the line Redshift z Figure 1. Redshift histogram of the total of 73 galaxy clusters in

7 Constraints Resonant production m DM = 7.6 ±.5 kev Right-handed (sterile) neutrino sin (θ) = (.- )x1 1 Lepton asymmetry in the early Universe Abazajian (14) Additional constraints: Structure formation (high-z galaxy counts and Local Group dwarf galaxy counts) constraints: m thermal > 1.3/1.7 kev (95%c.l.) Horiouchi et al. (13) Lyman-α m thermal > 3.3 kev (95%c.l.) Viel et al. (13) L 4 around 7 FIG. 1. This illustrates the parameter space for Shi-Fuller resonant production sterile neutrino models in the region of interest for producing the unidentified 3.57 kev X-ray line. The filled colored contours are the 1, and 3 regions satisfying the best-determined unidentified line flux in the 6 Ms XMM-Newton 73 stacked-cluster sample of Bulbul et al. [1]. Systematic uncertainties on the flux and mixing angle are of order the uncertainties. The blue, approximately horizontal contours are labeled by the lepton number L 4,inunitsof1 4,neededtoproduce DM h =.119. The constraint from X-ray observations of M31 from Horiuchi et al. [7] are in dashed (green), with a notable upturn at the signal region. The five stars produce the phase space distributions shown in Fig., and the three solid stars produce the linear WDM power spectrum transfer functions in Fig. 3. The contours change their orientation because the primary temperature of resonant production of the sterile neutrinos changes from prior to the quark-hadron transition to after it with increasing lepton numbers, for the case of the standard cross-over quark-hadron transition at T QCD =17MeV[14]. m thermal >. kev is a sweet spot that may address the controversies in structure formation at small scales: missing satellites, too big to fail and cusp vs core. FIG. kev 4., 4 and t trum reson trans remai quasi durin mally hp/t i As cools throu high

8 Constraints Talk by Ruchayskiy Interaction strength [Sin (θ)] Phase-space density constraints Too much Dark Matter Non-resonant production BBN limit L 6 =5 L 6 =7 L 6 =1 L 6 max =1 Not enough Dark Matter Excluded by non-observation of dark matter decay line DM mass [kev] Lyman-α bound for NRP sterile neutrino