Production mechanisms for kev sterile neutrino dark matter in the Early Universe

Production mechanisms for kev sterile neutrino dark matter in the Early Universe based on JCAP06 (2015) 011, JCAP04 (2016) 003 & 1509.01289 in collaboration with J. König, A. Merle and A. Schneider Maximilian Totzauer September 09, 2016 Corfu Summer Institute

1 Introduction to sterile ν Dark Matter 2 Production mechanisms for kev sterile neutrino DM 3 Assessing structure formation 4 Conclusion & Outlook

Introduction to sterile ν Dark Matter Introduction to sterile ν Dark Matter

Introduction to sterile ν Dark Matter Why think about ν S? explain non-zero active neutrino masses via the seesaw-mechanism

Introduction to sterile ν Dark Matter Why think about ν S? explain non-zero active neutrino masses via the seesaw-mechanism might resolve small-scale-problems such as missing satellite problem

Introduction to sterile ν Dark Matter Why think about ν S? explain non-zero active neutrino masses via the seesaw-mechanism might resolve small-scale-problems such as missing satellite problem can play substantial role in leptogenesis

Introduction to sterile ν Dark Matter Why think about ν S? explain non-zero active neutrino masses via the seesaw-mechanism might resolve small-scale-problems such as missing satellite problem can play substantial role in leptogenesis could close a weird gap in the SM:

Introduction to sterile ν Dark Matter Why think about ν S? explain non-zero active neutrino masses via the seesaw-mechanism might resolve small-scale-problems such as missing satellite problem can play substantial role in leptogenesis could close a weird gap in the SM: (#(ν S ) unrestricted,#(ν S ) 2 to generate m 2 sol and m 2 atm) via seesaw

Introduction to sterile ν Dark Matter Why think about ν S? explain non-zero active neutrino masses via the seesaw-mechanism might resolve small-scale-problems such as missing satellite problem can play substantial role in leptogenesis could close a weird gap in the SM: (#(ν S ) unrestricted,#(ν S ) 2 to generate m 2 sol and m2 atm via seesaw)

Introduction to sterile ν Dark Matter How to look for sterile ν Dark Matter?

Introduction to sterile ν Dark Matter The fingerprint of sterile neutrino DM If present as cosmic DM and if θ iα 0, decay N i ν α + γ occurs:

Introduction to sterile ν Dark Matter The fingerprint of sterile neutrino DM If present as cosmic DM and if θ iα 0, decay N i ν α + γ occurs: γ W W N i θ αi lα ν α

Introduction to sterile ν Dark Matter The fingerprint of sterile neutrino DM If present as cosmic DM and if θ iα 0, decay N i ν α + γ occurs: γ W W N i θ αi lα ν α sharp X-ray feature at E γ = m N /2.

Introduction to sterile ν Dark Matter The fingerprint of sterile neutrino DM If present as cosmic DM and if θ iα 0, decay N i ν α + γ occurs: γ W W N i θ αi lα ν α sharp X-ray feature at E γ = m N /2. signal strongly depending on m N : Γ N νγ m 5 N sin2 θ iα

Introduction to sterile ν Dark Matter The fingerprint of sterile neutrino DM If present as cosmic DM and if θ iα 0, decay N i ν α + γ occurs: γ W W N i θ αi lα ν α sharp X-ray feature at E γ = m N /2. signal strongly depending on m N : Γ N νγ m 5 N sin2 θ iα signal claimed by two groups in 2014 (Astrophys. J. 789(2014) 13, Phys. Rev.Lett. 113(2014) 251301), controversially discussed. (see also new results on charge exchange on sulphur, talk by M. Lindner.)

Introduction to sterile ν Dark Matter The fingerprint of sterile neutrino DM If present as cosmic DM and if θ iα 0, decay N i ν α + γ occurs: γ W W N i θ αi lα ν α sharp X-ray feature at E γ = m N /2. signal strongly depending on m N : Γ N νγ m 5 N sin2 θ iα signal claimed by two groups in 2014 (Astrophys. J. 789(2014) 13, Phys. Rev.Lett. 113(2014) 251301), controversially discussed. (see also new results on charge exchange on sulphur, talk by M. Lindner.) Non-observation gives bounds in the plane m N vs. sin 2 (θ αi )

Production mechanisms for kev sterile neutrino DM What models are on the market? A short overview

Production mechanisms for kev sterile neutrino DM What types of DM production are there?

Production mechanisms for kev sterile neutrino DM Brief review on freeze-in and freeze-out In freeze-out, particles drop out of thermal equilibrium when H Γ int. Particles left with thermal distribution except for small distortions. Ω DM σ 1.

Production mechanisms for kev sterile neutrino DM Brief review on freeze-in and freeze-out In freeze-out, particles drop out of thermal equilibrium when H Γ int. Particles left with thermal distribution except for small distortions. Ω DM σ 1. In freeze-in, particle never enters thermal equilibrium due to very feeble interactions. Intrinsically non-thermal spectrum of the particle should work on the level of momentum distributions, not only particle densities! Ω DM σ +1.

Production mechanisms for kev sterile neutrino DM Brief review on freeze-in and freeze-out Log[nrelic] freeze-in n σ freeze-out n 1/σ Log[σ χχ XSM X SM ]

Production mechanisms for kev sterile neutrino DM Boltzmann equations rates vs. spectra Boltzmann rate equation, commonly encountered in thermal freeze-out: ṅ (t) + 3H (t) n (t) = σv [ n 2 (t) n 2 eq (t) ] where n (t) is the particle number density.

Production mechanisms for kev sterile neutrino DM Boltzmann equations rates vs. spectra Boltzmann rate equation, commonly encountered in thermal freeze-out: ṅ (t) + 3H (t) n (t) = σv [ n 2 (t) n 2 eq (t) ] where n (t) is the particle number density. Boltzmann equation on distribution level f (t, p) f t H (t) p f p where C [f ] is a functional of f. = C [f ] (1)

Production mechanisms for kev sterile neutrino DM What production mechanisms are there for sterile neutrinos?

Production mechanisms for kev sterile neutrino DM Dodelson-Widrow production (DW) Non-resonant active-sterile conversion via θ iα 0: ν α + X N Production and decay very closely linked.

Production mechanisms for kev sterile neutrino DM Dodelson-Widrow production (DW) Non-resonant active-sterile conversion via θ iα 0: ν α + X N Production and decay very closely linked. Ω DW = Ω DM is ruled out from combination of X-ray bounds and structure formation (we ll get there).

Production mechanisms for kev sterile neutrino DM Dodelson-Widrow production (DW) Non-resonant active-sterile conversion via θ iα 0: ν α + X N Production and decay very closely linked. Ω DW = Ω DM is ruled out from combination of X-ray bounds and structure formation (we ll get there). However, active-sterile conversion affects other production mechanisms and can cause corrections of a few percent (JCAP1604 (2016) 003).

Production mechanisms for kev sterile neutrino DM Dodelson-Widrow production (DW) Non-resonant active-sterile conversion via θ iα 0: ν α + X N Production and decay very closely linked. Ω DW = Ω DM is ruled out from combination of X-ray bounds and structure formation (we ll get there). However, active-sterile conversion affects other production mechanisms and can cause corrections of a few percent (JCAP1604 (2016) 003). Freeze-in type mechanism non thermal spectrum of DM.

Production mechanisms for kev sterile neutrino DM Shi-Fuller production (SF) Resonant active-sterile conversion similar to MSW resonance: Large conversion rate even for small sin 2 θ iα.

Production mechanisms for kev sterile neutrino DM Shi-Fuller production (SF) Resonant active-sterile conversion similar to MSW resonance: Large conversion rate even for small sin 2 θ iα. Can yield somewhat colder spectra than DW. Very non-thermal spectra (due to resonance condition).

Production mechanisms for kev sterile neutrino DM Shi-Fuller production (SF) Resonant active-sterile conversion similar to MSW resonance: Large conversion rate even for small sin 2 θ iα. Can yield somewhat colder spectra than DW. Very non-thermal spectra (due to resonance condition). Resonance needs primordial lepton asymmetry.

Production mechanisms for kev sterile neutrino DM Shi-Fuller production (SF) Resonant active-sterile conversion similar to MSW resonance: Large conversion rate even for small sin 2 θ iα. Can yield somewhat colder spectra than DW. Very non-thermal spectra (due to resonance condition). Resonance needs primordial lepton asymmetry. Lepton asymmetry can be generated in the νmsm framework, at the cost of (somewhat tuned) additional assumptions.

Production mechanisms for kev sterile neutrino DM Shi-Fuller production (SF) Resonant active-sterile conversion similar to MSW resonance: Large conversion rate even for small sin 2 θ iα. Can yield somewhat colder spectra than DW. Very non-thermal spectra (due to resonance condition). Resonance needs primordial lepton asymmetry. Lepton asymmetry can be generated in the νmsm framework, at the cost of (somewhat tuned) additional assumptions. New analyses concerning cosmic structure formation put some tension on SF production (we ll get there).

Production mechanisms for kev sterile neutrino DM Diluted thermal freeze-out Couple right-handed singlets to the thermal bath via some new interaction, e.g. extended gauge group SU (3) C SU (2) L U (1) Y G X.

Production mechanisms for kev sterile neutrino DM Diluted thermal freeze-out Couple right-handed singlets to the thermal bath via some new interaction, e.g. extended gauge group SU (3) C SU (2) L U (1) Y G X. Will generally result in Ω SN Ω DM, hence requires massive entropy dilution.

Production mechanisms for kev sterile neutrino DM Diluted thermal freeze-out Couple right-handed singlets to the thermal bath via some new interaction, e.g. extended gauge group SU (3) C SU (2) L U (1) Y G X. Will generally result in Ω SN Ω DM, hence requires massive entropy dilution. Additional entropy release hard to reconcile with BBN.

Production mechanisms for kev sterile neutrino DM Decay production Couple SM to some BSM particle X, which decays into ν S

Production mechanisms for kev sterile neutrino DM Decay production Couple SM to some BSM particle X, which decays into ν S Wide range of possibilities for parent particle X: inflaton (Phys. Lett. B 639(414), JHEP1005(010)) scalar singlet BSM (e.g. JCAP1506(011)) pion decay (Phys. Rev. D. 91(6),063502) Dirac fermions (JCAP2014(001)) light vector bosons (Phys. Rev. D78,103505, Phys. Rev.D89,113004)

Production mechanisms for kev sterile neutrino DM Decay production Couple SM to some BSM particle X, which decays into ν S Wide range of possibilities for parent particle X: inflaton (Phys. Lett. B 639(414), JHEP1005(010)) scalar singlet BSM (e.g. JCAP1506(011)) pion decay (Phys. Rev. D. 91(6),063502) Dirac fermions (JCAP2014(001)) light vector bosons (Phys. Rev. D78,103505, Phys. Rev.D89,113004) spectral features of ν S dependent on whether a) X freezes-in b) X decays in-equilibrium before freeze-out c) X freezes-out and decays out-of-equilibrium d) combination of b) & c) non-trivial spectra with more than one scale possible.

Production mechanisms for kev sterile neutrino DM A simple model for singlet scalar decay Field content beyond SM: real scalar singlet S and one sterile neutrino N.

Production mechanisms for kev sterile neutrino DM A simple model for singlet scalar decay Field content beyond SM: real scalar singlet S and one sterile neutrino N. Lagrangian: [ L = L SM + in / N + 1 2 ( µs) ( µ S) y ] 2 SNc N + h.c. V scalar where V scalar = µ 2 Φ Φ Φ 1 ) 2+ 2 µ2 S S 2 +λ Φ (Φ λ ( ) S Φ 4 S 4 +2λ Φ Φ S 2

Production mechanisms for kev sterile neutrino DM A simple model for singlet scalar decay Field content beyond SM: real scalar singlet S and one sterile neutrino N. Lagrangian: [ L = L SM + in / N + 1 2 ( µs) ( µ S) y ] 2 SNc N + h.c. V scalar where V scalar = µ 2 Φ Φ Φ 1 ) 2+ 2 µ2 S S 2 +λ Φ (Φ λ ( ) S Φ 4 S 4 +2λ Φ Φ S 2 Processes for DM production: SS ΦΦ (from plasma) S NN

Production mechanisms for kev sterile neutrino DM A simple model for singlet scalar decay Field content beyond SM: real scalar singlet S and one sterile neutrino N. Lagrangian: [ L = L SM + in / N + 1 2 ( µs) ( µ S) y ] 2 SNc N + h.c. V scalar where V scalar = µ 2 Φ Φ Φ 1 ) 2+ 2 µ2 S S 2 +λ Φ (Φ λ ( ) S Φ 4 S 4 +2λ Φ Φ S 2 Processes for DM production: SS ΦΦ (from plasma) S NN Mixing θ α switched off in this model (cf. JCAP1604 (2016) 003).

Production mechanisms for kev sterile neutrino DM A simple model for scalar decay parameters The relevant parameters of the setup: Yukawa coupling y ( L y 2 SNc N). Higgs portal λ ( L 2λ ( Φ Φ ) S 2 ) different production channels before and after EWPT. scalar mass m S. mass of sterile neutrino m N.

Production mechanisms for kev sterile neutrino DM Different regimes for the production of the scalar S regime Φ S production channels I Φ S h S II h h S S W + W h S S Z Z h S S f f h S S h h h S S III h S W + W h S S Z Z h S S f f h S S h h h S S h S S regime I: before EWPT regime II: after EWPT, m S > m h /2 regime III: after EWPT, m S m h /2

Production mechanisms for kev sterile neutrino DM The interplay of the different regimes 10 4 30 60 65 500 10 3 freeze-in (FIMP) freeze-out (WIMP) I T [GeV] T EWPT 10 2 III II T PT 10 1 10 1 m h /2 10 2 10 3 m S [GeV]

Production mechanisms for kev sterile neutrino DM Exampe spectrum of sterile neutrinos in scalar decay A (not really contrived) example distribution f of sterile neutrinos from scalar decay ξ 2 fn(ξ,r) 10-2 10-4 10-6 10-8 Distribution Function ms=60gev λ=10-6.86 y=10-8.69 mn=20kev 0.44 ξ 8.66 51.4 426 10-10 10-12 r=0.21 10-4 0.001 0.010 0.100 1 10 100 ξ

Assessing structure formation Constraints from structure formation

Assessing structure formation How to assess structure formation

Assessing structure formation Hot, warm or cold Dark Matter? Structure formation Matter distribution on small scales (top) and large scales (bottom) for cold (left), warm (centre) and hot (right) thermal Dark Matter

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt Structures with λ λ FS are heavily suppressed.

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt Structures with λ λ FS are heavily suppressed. Usual classification

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt Structures with λ λ FS are heavily suppressed. Usual classification λ FS 0.01 Mpc behaves like cold DM.

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt Structures with λ λ FS are heavily suppressed. Usual classification λ FS 0.01 Mpc behaves like cold DM. 0.01 Mpc < λ FS 0.1 Mpc distinguishable from CDM on small scales. Often dubbed warm DM.

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt Structures with λ λ FS are heavily suppressed. Usual classification λ FS 0.01 Mpc behaves like cold DM. 0.01 Mpc < λ FS 0.1 Mpc distinguishable from CDM on small scales. Often dubbed warm DM. λ FS > 0.1 Mpc dubbed hot DM. Erases too much structure, hence excluded.

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt Structures with λ λ FS are heavily suppressed. Usual classification λ FS 0.01 Mpc behaves like cold DM. 0.01 Mpc < λ FS 0.1 Mpc distinguishable from CDM on small scales. Often dubbed warm DM. λ FS > 0.1 Mpc dubbed hot DM. Erases too much structure, hence excluded. Note m DM kev warm DM!

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt Structures with λ λ FS are heavily suppressed. Usual classification λ FS 0.01 Mpc behaves like cold DM. 0.01 Mpc < λ FS 0.1 Mpc distinguishable from CDM on small scales. Often dubbed warm DM. λ FS > 0.1 Mpc dubbed hot DM. Erases too much structure, hence excluded. Note m DM kev warm DM! Shortcoming of this analysis: classifaction boundaries are only indicative. average velocity might not be meaningful.

Assessing structure formation Structure Formation Particle Physicists comfort zone Easy estimator for structure formation, free-streaming horizon: λ FS = t 0 t prod v (t) a (t) dt Structures with λ λ FS are heavily suppressed. Usual classification λ FS 0.01 Mpc behaves like cold DM. 0.01 Mpc < λ FS 0.1 Mpc distinguishable from CDM on small scales. Often dubbed warm DM. λ FS > 0.1 Mpc dubbed hot DM. Erases too much structure, hence excluded. Distribution Function 10-2 ms=60gev ξ 8.66 λ=10 Note m DM kev warm DM! -6.86 10-4 y=10-8.69 426 mn=20kev 51.4 10 Shortcoming of this analysis: -6 0.44 10 classifaction boundaries are only indicative. -8 10 average velocity might not be meaningful. -10 r=0.21 10-12 ξ 2 fn(ξ,r) -4 10 0.001 0.010 0.100 1 10 100 ξ

Assessing structure formation Structure formation Leaving the comfort zone Compute linear power spectrum P (k) and compare to observations from Lyman-α observations to capture more spectral information.

Assessing structure formation Structure formation Leaving the comfort zone Compute linear power spectrum P (k) and compare to observations from Lyman-α observations to capture more spectral information. Lyman-α spectra from QUASARS

Assessing structure formation Structure formation Leaving the comfort zone Lyman-α spectra from close (top) and far (bottom) QUASARS:

Assessing structure formation Constraints on the models for sterile neutrino dark matter

Assessing structure formation Shi-Fuller-mechanism and structure formation Temperature map of SF (taken from 1601.07553 by A. Schneider)

Assessing structure formation Shi-Fuller-mechanism and structure formation II Constraints from # of MW satellites and Lyman-α-forest (1601.07553). 1e-08 1e-09 Non-res. production Ω sn >Ω dm sin 2 (2θ) 1e-10 1e-11 1e-12 Ω sn <Ω dm 3 4 5 7 10 15 20 25 m sn [kev]

Assessing structure formation Shi-Fuller-mechanism and structure formation II Constraints from # of MW satellites and Lyman-α-forest (1601.07553). 1e-08 1e-09 Non-res. production Ω sn >Ω dm sin 2 (2θ) 1e-10 1e-11 1e-12 Ω sn <Ω dm 3 4 5 7 10 15 20 25 m sn [kev]

Assessing structure formation Shi-Fuller-mechanism and structure formation II Constraints from # of MW satellites and Lyman-α-forest (1601.07553). 1e-08 sin 2 (2θ) 1e-09 1e-10 1e-11 # obs. MWS > # pred. MWS Non-res. production Lyman-α Ω sn >Ω dm 1e-12 Ω sn <Ω dm 3 4 5 7 10 15 20 25 m sn [kev]

Assessing structure formation Scalar Decay and structure formation

Production mechanisms for kev sterile neutrino dark matter in the Early Universe Assessing structure formation Scalar Decay and structure formation II

Production mechanisms for kev sterile neutrino dark matter in the Early Universe Assessing structure formation Log[n relic] Scalar Decay and structure formation II freeze-in n σ freeze-out n 1/σ Log[σχχ XSM XSM]

Conclusion & Outlook Conclusion and Outlook

Conclusion & Outlook Synopsis of current and future bounds ( θ) - - - - - ( ) τ> τ< - ( ) - - [ ] courtesy of A. Merle

Conclusion & Outlook Conclusion & Outlook Sterile neutrinos might remedy several open physical problems (active ν masses, leptogenesis, cosmic DM, small scale problems)

Conclusion & Outlook Conclusion & Outlook Sterile neutrinos might remedy several open physical problems (active ν masses, leptogenesis, cosmic DM, small scale problems) Production models are getting cut decisively, decay production among most promising mechanisms

Conclusion & Outlook Conclusion & Outlook Sterile neutrinos might remedy several open physical problems (active ν masses, leptogenesis, cosmic DM, small scale problems) Production models are getting cut decisively, decay production among most promising mechanisms If confirmed, a signal at 3 5 kev would be able to put decisive cuts into the parameter space of the model.

Conclusion & Outlook Conclusion & Outlook Sterile neutrinos might remedy several open physical problems (active ν masses, leptogenesis, cosmic DM, small scale problems) Production models are getting cut decisively, decay production among most promising mechanisms If confirmed, a signal at 3 5 kev would be able to put decisive cuts into the parameter space of the model. Detailed predictions on structure formation combined with Lyman-α data is key to differentiate between the SF and SD mechanisms.

Conclusion & Outlook Conclusion & Outlook Sterile neutrinos might remedy several open physical problems (active ν masses, leptogenesis, cosmic DM, small scale problems) Production models are getting cut decisively, decay production among most promising mechanisms If confirmed, a signal at 3 5 kev would be able to put decisive cuts into the parameter space of the model. Detailed predictions on structure formation combined with Lyman-α data is key to differentiate between the SF and SD mechanisms. Work in progress on abundance of ultra-distant galaxies (Menci et. al) back up Lyman-α analyses.

Conclusion & Outlook Conclusion & Outlook Sterile neutrinos might remedy several open physical problems (active ν masses, leptogenesis, cosmic DM, small scale problems) Production models are getting cut decisively, decay production among most promising mechanisms If confirmed, a signal at 3 5 kev would be able to put decisive cuts into the parameter space of the model. Detailed predictions on structure formation combined with Lyman-α data is key to differentiate between the SF and SD mechanisms. Work in progress on abundance of ultra-distant galaxies (Menci et. al) back up Lyman-α analyses. Complementary input from lab experiments such as KATRIN, ECHo or Project8 might provide orthogonal insights on kev steriles.

Conclusion & Outlook Some shameless advertising at the end König, Merle & MT, arxiv:1609.01289 Fully numerical analysis of scalar decay in the whole relevant mass range. Drewes et al., arxiv:1602.04816, A White Paper on kev Sterile Neutrino Dark Matter Whitepaper on the field released in 02/16 with contributions from O (100) authors.

Conclusion & Outlook Thank you for your attention!

Backup Backup

Backup Halfmode-Analysis ( ) ( )/ ( ) - -α - ( / )= / ( ) ( )/ ( ) - ( / )= / - -α -α ( ) [ / ] -α ( ) [ / ]

Backup Benchmark cases for m S = 60 GeV, FIMP & WIMP