1. March 2005 Theme Group 2 What can N-N-bar Oscillation teach us about physics Beyond the standard model ? R. N. Mohapatra University of Maryland NANO workshop, February, 2011

2. Feb. 2011 Particle oscillations Oscillations of quantum mechanical states is a familiar phenomenon in Nature. In particle physics, electrically neutral particles e.g. Kaons and neutrinos have been observed to oscillate, teaching us a great deal about the fundamental forces and matter. Neutron is a neutral particle- its oscillation to anti-neutrons is allowed by electric charge conservation. What can it teach us about physics beyond the standard model ?

3. Feb. 2011 Mohapatra Neutron-anti-neutron Oscillation : Violates baryon number by two units: Any Indication of B-violation in Nature ? (i) Standard model has B-violation (but it leaves B-L symmetry exact and B-L is emerging as a new symmetry of Nature ) !! (ii) Understanding the origin of matter requires B-Violation and often involves B-L violation !! (iii) Most physics scenarios of physics BSM have B-violation e.g. Grand unified th.

4. Feb. 2011 Mohapatra B-L : new symmetry in Nature ? B-L : new symmetry in Nature ? Is B-L symmetry of standard model exact ? If not, what is the scale of its breaking ? What physics associated with this breaking ? Hints from neutrino observations: If neutrino is Majorana, it breaks B-L by two units; observation of decay will confirm this but by itself will not tell us much about new physics associated with B-L breaking. N-N-bar observation will supply this information !!

5. Neutrino mass-NNbar connection Majorana neutrino -> implies B-L=2; In quark-lepton unified theories B and L get connected and L=2 implies B =2 via B-L symmetry and hence N-N-bar oscillation. There are reasons to think that there may be quark lepton unification at high energies. Discovery of neutrino mass therefore provides a very strong motivation to search for N-N-bar oscillation, which can be new window to Q-L unification as well as B-L symmetry.

6. Questions for N-N-bar oscillation Can the possible reach of N-N-bar oscillation time in existing facilities probe interesting range for new physics ? OR Are there decent theories EMBEDDING THE SEESAW MECHANISM for small neutrino masses where a viable Seesaw scale leads to observable N-N-bar oscillation ? Is it cosmologically safe to have observable N-N-bar oscillation ? The answer to all these questions is YES.

7. March 2005 Theme Group 2 Operator analysis of N-N-bar To see what is probed by N-N-bar, do operator analysis for processes: Note M^5 suppression

8. Scale Reach of N-N-bar Is the scale reach of N-N-bar limited to only upto 300 TeV in generic models as suggested ? NO- once new physics at TeV scale is entertained e.g. SUSY, new Higgs !

9. March 2005 Theme Group 2 Weaker suppression with SUSY A. Dominant operator with SUSY: B.SUSY + diquark Higgs field, at TeV scale Can probe M_B-L upto 10^9 GeV Probe M_{B-L} to 10^12 GeV.

10. theory For N-N-bar Neutrino mass points to New electroweak symmetry with B-L Gauge group : Left-right sym th. Fermion assignment: Higgs fields:

11. March 2005 Theme Group 2 Probing B-L scale and related physics Note that SUSY at TEV SCALE + no new physics till GeV implies that coupling constants unify: This suggests that perhaps local B-L is part of a grand unifying symmetry and it breaks at GUT scale. Related physics is GUT physics.

12. March 2005 Theme Group 2 B-L- GUT (A): SO(10) : the minimal GUT theory with B-L motivated by Gauge coupling unification: All fermions unified to one {16} dim rep. Breaks to MSSM below 10^16 GeV; B-L scale is GUT scale due to unification. N-N-bar suppressed and unobservable.

13. March 2005 Theme Group 2 Nucleon Decay in Generic Signature Key test of GUTS: Gauge Boson mediated p-decay: Lower life time predictions are highly model dependent.

14. March 2005 Theme Group 2 Alternative B-L Unification Alternative B-L Unification New physics below GUT scale Only 16 fermions unified but not gauge couplings: 2. Cantains B-L for seesaw; Only restriction on B-L scale is nu mass (not coupling unification) and hence N-N-bar can be observable in this case ; No proton decay.

15. Non-SUSY G(224) and N-N-bar That these models lead to observable nn-bar oscillation was pointed out in RNM, Marshak, 80. vertex needed for baryogenesis. With M= N-N-bar observable only if

16. March 2005 Theme Group 2 SUSY makes N-N-bar probe higher scales Two points: (i) naturally at 100 GeV scale due to accidental global symmetry caused by supersymmetry- (ii) Power suppression is rather than 1/M^5 (as in non-susy case). Improves observability of N-N-bar osc.

17. March 2005 Theme Group 2 Estimate of N-N-bar in Minimal 224 model: New Feynman diagram for N-N-bar osc. Observable N-N-bar osc for M_seesaw~10^11 GeV. (Dutta, Mimura, RNM; PRL (2006)

18. March 2005 Theme Group 2 Origin of matter in N-N-bar models Usual argument : E arly universe baryon asymmetry erased by fast N-N-bar being in equilibrium: -- hard to generate baryons: NOT TRUE --e.g. NonSUSY NNbar model: No leptogenesis; Out of eq. temp for NNbar operator is: 10 TeV; New source of baryon asymmetry: post-sphaleron baryogenesis: Babu,RNM, Nasri PRL, (2006,2007);

19. Does baryon asymmetry  observable NN-bar ? ObservableNN-bar, earlier matter asymmetry gets erased. Must regenerate below sphaleron decoupling scale ~ 140 GeV. 2224 model experience  adequate amount of matter  light color sextet Higgs  observable NN-bar. Not theorem but very palusible. (Babu, Dev, RNM’09; Babu’s talk). March 2005 Theme Group 2

20. Other models that can be probed by Nnbar Extra dimension models generically have lots of new physics around the TeV scale- could lead to NN-bar oscillation: Warped models  realistic models locate various fermions in 5 th dim-NN-bar can be observable. (Winslow, Ng’10) Similar conclusions for flat LED type models: ( Nussinov, Shrock; Gabadadze, Dvali) Non-observation or observation of Nnbar will throw light on these models too.

21. March 2005 Theme Group 2 Proton decay vs N-N-bar oscillation

22. March 2005 Theme Group 2 Conclusion With the discovery of neutrino mass the case for N-N-bar oscillation is a lot stronger now than before. Urge new search at the level of 10^10 sec to test for B-L seesaw scale less than 10^11 GeV vs GUT scale seesaw. N-N-bar discovery will completely change the thinking on grand unification. As far as Proton decay goes, predictions below 10^36 yrs are model dependent; while they should be done, the true value of P- decay as a test of GUT idea is the 10^36 yrs level search and should be the ultimate goal.