Sterile Neutrinos As Subdominant Warm Dark MatterD.T. CumberbatchOxford University, Astrophysics Dept. A. Palazzo, D. Cumberbatch, A. Slosar and J. Silk (arXiv:0707.1495)

OutlineIntroduction Sterile neutrino propertiesMotivations for keV sterile neutrino dark matter (SN DM)

Current experimental constraints on dominant SN DMX-raysLyman-

Experimental constraints on sub-dominant SN DMHEAO-1 (diffuse X-ray background)SDSS (Ly-)

Theoretical predictions vs. Experimental constraintsQualitative/Quantitative treatments of hadronic uncertaintiesDetermination of upper limits on fs

Summary & Conclusions

What are Sterile Neutrinos?Electroweak singlet (Bruno Pontecorvo, (1967) )No weak interactions (i.e. sterile or right-handed)Naturally explanation for small (but finite) active neutrino masses Introduced through the seesaw Lagrangian (Minkowski) Variety of production mechanismsNon-resonant oscillationsResonant oscillations Ma100GeV or as small as ~eVFor Ma ~ EEW and ya, MSM provides correct a massesMasses of lightest neutrinos suppressed by / Ma

Non-resonant OscillationsProduced through a-s oscillations involving off-diagonal elements of mixing matrix (hence no coupling to SM Gauge bosons)Dont require finite lepton asymmetrySimplest model: Dodelson-Widrow (DW) mechanismStandard thermal historyNo additional couplings requiredProduces minimal relic densityAlternatives to DWEntropy dilution (Abazajian & Fuller, Abazajian & Koushiappas)Additional Couplings (e.g. to Inflaton (Shaposhnikov & Tkachev))Low TR models (Gelmini et al., Yaguna et al.)Resonant OscillationsRequires L0 (Shi & Fuller)

Decay modesDominant decay to 3 active neutrinos (s 3a)

Loop-suppressed radiative decay (s a)

Photon Energy E=(ms2-ma2)/2msms/2 for msmaFor ms~1keV X-raysUse X-ray observations to constrain ms and sin2(2s) (and later, fs for keV SN DM (Barger et al., Pal & Wolfenstein)

Motivations for keV SN DMResolution to inconsistencies from CDM halo simulations Central cores in low-mass galaxies (Dalcanton & Hogan)Overpopulation of small-scale satellites (Kauffman et al., Klypin et al.)

Contribution to unresolved diffuse X-ray background (Abazajian et al.)

Facilitates HI production/star formation Early Reionisation (Mapelli et al., Biermann & Kusenko)

Pulsar kick velocities (Kusenko & Segre, Fuller et al.)

Re-generation of Supernova shockwaves (Hidaka and Fuller)

Formation of early SMBH (109M at z6.5) (Munyaneza & Biermann)

Baryon asymmetry (Asaka et al.)

Neutrino oscillations (LSND/MiniBoonE require at least 2 light (~eV) SNs) (Goswami & Rodejohann)

Experimental constraints on ms and sin2(2s)X-rays (Clusters, dSphs, MW, Galaxies, XRB) All these sources have similar NH, but different thermal emissions F.O.V and Energy resolution of instruments dictate sensitivity(Ruchayskiy, arXiv:0704.3215)

Experimental constraints on ms and sin2(2s)Lyman-Sensitive to small-scale matter perturbations where SN are significantOperates at high-z before non-linear growth erases free-streaming effects ms >14 keV includes 10% suppression from non-thermal nature of SNRecent calculations imply / can be as low as 0.8 ms>11.5 keV (/~0.8)(Abazajian, astro-ph/0511630) (Seljak et al., astro-ph/0602430)

Is Dodelson-Widrow SN DM still permitted?(Yuskel et al., arXiv:0706.4084)

Spectral Analysis of HEAO-1 XRB dataFit HEAO-1 data to a prescribed model (Gruber et al.)

Add MW and extragalactic (EG) contributions from SN DM (for given ms), correcting for finite energy resolution of HEAO-1 (E/E~0.25)

Vary CXRB, TXRB, XRB and sin2(2s) until 2 worsens by 2 corresponding to a 3 C.L.

Determine sin2(2s) for all ms within range of data

Spectral Analysis of HEAO-1 XRB data(Boyarsky et al., astro-ph/0512509 )

EG and MW flux from SN DMExtragalactic differential energy flux

Flat, -matter dominated Universe (dm 0.21)

Local differential energy flux from MW

X-ray constraints on ms and sin2(2s) For fs

Ly- constraints on ms and sin2(2s) (fs11.5 keV (fs=1) from limiting suppression of P(k) for k>~Mpc-1

For fs

P(kf,fs)~0.23PCDM(kf,fs=1)Ly- constraints on ms and sin2(2s) (fs

Experimental constraints & Theoretical predictions (2)DW SN DM excluded for fs=1DW SN DM permitted for fs=0.2

(2.5

Theoretical uncertaintiesSN which are non-resonantly produced have a relic abundance (Asaka et al.)

Accounting for hadronic uncertainties during QCD epoch, best-fit relation between fs, ms and sin2(2s) is

Pushing all errors in the same direction, one either obtains the minimal

or the maximal abundances

We conservatively consider these extreme cases to represent a 2 C.L.

Constraints on the DW scenario (2)Plot corresponding points (A,B), (C,D) and (E,F) for all fs

Theoretical uncertainties (Quantitative treatment)Vary fs around fsav. given by best-fit formula.

Adopt a normal distribution of log10(fs) with a s.d. equal to half the excursion (wrt log10(fsav.) determined by extreme formulae.

This corresponds to adding a penalty factor to the total 2

with 1 (asymmetric) errors

Marginalising 2 wrt fs, ms or sin2(2s), we obtain new constraints

Constraints on the DW scenario (fs)max.0.7 (2), (fs)max.=1 (~3) fs1fs0.7

Summary & ConclusionsRecent results disfavour keV dominant sterile neutrino dark matter produced via the Dodelson-Widrow mechanism.Relaxing the presumption that s=dm, we have shown how X-ray and Ly- constraints can be re-interpreted for s