1. Sterile Neutrinos and WDM
R.Svoboda

2. 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-dependent
Spin-independent

3. "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?

4. Leo –I
(800k LY)

5. Willman and Strader 2012

6. 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?

7. Thermal vrs Non-Thermal Production
In general, direct production from thermal equilibrium with
freeze out occurring when relativistic causes problems
with the relic density being too high. Need non-thermal.
Way too much!
Rapid expansion
density
usual stuff
m/T determines density
At freeze out
e.g. production by
Oscillation!

8. 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 > ~ eV

9. 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

10. J.W. den Herder, et al
arXiv:

11. 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

12. So in general WDM with sterile
neutrinos prefers heavy mass >2 keV
and very small mixing
This is in tension with observed
lack of small satellite galaxies
and the theoretical motivation
for leptogenesis

13. Reactor Neutrino Anomaly

14. Allowed Region from Reactors and GNO calibrations

15. 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 not
possible at these energies
Other experiments?

16. MINOS arXiv:hep-ex:1104.3922 Look at NC identified events
In FD. Note: these look like
ne to them.
High background and
correlation to q13 reduce
sensitivity

17. 90% cl limit of 40% of oscillated nm going to sterile
SNS could certainly do better

18. 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)

19. NC Disappearance at SNS
OscSNS Proposal, 3 years.
Proposal calculates NC interaction
rate in miniBooNE like detector
(50% efficiency) of 1300/year.
Issues:
(a) cross section precision
(b) absolute neutrino flux
prediction (need 1% to compete
with reactor measurements)

20. 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!