Sterile Neutrinos and WDM

R.Svoboda

Sterile Neutrinos as DM?• As WIMP searches getting well below the weak

interaction scale for large range of masses and collider limits now limit smaller masses. What if no WIMPs are found to well below weak scale?

Spin-dependentSpin-independent

"Satellite" problem

• CDM seems to imply many more small galaxies (e.g. dwarf galaxies around the Milky Way) than is actually seen. Like 100's predicted and 10's see,

• Are small galaxies broken up at some point?• Are their selection effects that cause them to

not to be found yet?

Leo –I(800k LY)

Willman and Strader 2012

Constraints on Sterile Neutrino DM

• How would it be produced?• Tremaine-Gunn bound• X-ray constraints• Lyman-a Forest and large scale structure• Direct Experimental Limits?

Thermal vrs Non-Thermal Production

In general, direct production from thermal equilibrium withfreeze out occurring when relativistic causes problemswith the relic density being too high. Need non-thermal.

m/T determines densityAt freeze out

density

Way too much!

usual stuff

Rapid expansion

e.g. production byOscillation!

Tremaine-Gunn Bound

• A phase space argument based on velocity and mass of WDM particle relativistic freeze out compared to observed size of galactic halos today

• MDM > ~300-500 eV

X-Ray constraints

• heavy sterile neutrinos that mix with light neutrinos have a radiative decay mode proportional to M5 sin22q

• Can look in DM rich regions for x-rays from such decays

• Non definitively found thus far

J.W. den Herder, et alarXiv:0906.1788

Lyman-a

• Observation of QSO spectra show red-shifted La lines due to neutral hydrogen clouds between us and QSO

• The "forest" of lines is a measure of the matter density (assuming neutral hydrogen clouds trace DM distribution) as a function of z

• This can be turned into a "scale size" of the universe versus z

• This sets limits on contributions from WDM

So in general WDM with sterileneutrinos prefers heavy mass >2 keVand very small mixing

This is in tension with observedlack of small satellite galaxiesand the theoretical motivationfor leptogenesis

Reactor Neutrino Anomaly

Allowed Region from Reactors andGNO calibrations

Oscillation length for light/heavy mixing

1.27 Dm2 L/E = p/2 gives L ~ (1.2)E/Dm2

For MH = 1 keV and E = 30 MeV, then L << 1 mm!

Essentially, a two detector experiment notpossible at these energies

Other experiments?

MINOS

arXiv:hep-ex:1104.3922

Look at NC identified eventsIn FD. Note: these look likene to them.

High background and correlation to q13 reducesensitivity

90% cl limit of 40% of oscillated nm going to sterile

SNS could certainly do better

Where would SNS fit in?

• It is possible to do a NC disappearance experiment – essentially comparing predicted and measured NC component

• Unlike reactors, the flux seems easier to predict, and there is a "golden" NC (not CC) tag if you use carbon target (see OscSNS proposal)

NC Disappearance at SNS

OscSNS Proposal, 3 years.

Proposal calculates NC interactionrate in miniBooNE like detector(50% efficiency) of 1300/year.

Issues:(a) cross section precision(b) absolute neutrino fluxprediction (need 1% to competewith reactor measurements)

Conclusions

• There is interest in heavy sterile neutrinos in astrophysics as well as physics community

• relevant experiments will be ONE DETECTOR due to short oscillation length. Absolute flux measurement is needed.

• Astrophysics would prefer very small mixing angle – but very model dependent

• New Territory!