March 2005Theme Group 2

What can N-N-bar Oscillation What can N-N-bar Oscillation teach us about physics teach us about physics

Beyond the standard model ?Beyond the standard model ?

R. N. Mohapatra

University of Maryland

NANO workshop, February, 2011

Feb. 2011

Particle oscillationsParticle 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 ?

Feb. 2011Mohapatra

Neutron-anti-neutron OscillationNeutron-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.

Feb. 2011Mohapatra

B-L : new symmetry in B-L : new symmetry in Nature ?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 !!

0

Neutrino mass-NNbar connectionNeutrino 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.

Questions for N-N-bar oscillationQuestions 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 .

March 2005Theme Group 2

Operator analysis of N-N-barOperator analysis of N-N-bar

To see what is probed by N-N-bar, do operator analysis for processes:

2BOcccccc dduddu

M 5

1

62 QCDBnn Om

5~/ Mm nnnn 6/

giving .sec10~ 8nn GeV5.510

2B

M

Note M^5 suppression

Scale Reach of N-N-barScale 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 !

March 2005Theme Group 2

Weaker suppression with SUSYWeaker suppression with SUSY

A. Dominant operator with SUSY:

B.SUSY + diquark Higgs field , at TeV scale

ccuu

Can probe M_B-L upto10^9 GeV

Probe M_{B-L} to 10^12 GeV.

theory For N-N-bar 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:

LBRL USUSU )1()2()2(

L

L

d

u

R

R

d

u

L

L

e

R

R

e

P

P

)0,2,2( )2,1,3()2,3,1(; LR

March 2005Theme Group 2

Probing B-L scale and related physicsProbing 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.

1610

March 2005Theme Group 2

B-L- GUTB-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.

March 2005Theme Group 2

Nucleon Decay in Generic SignatureNucleon Decay in Generic Signature

• Key test of GUTS: Gauge Boson mediated p-decay:

Lower life time predictions are highly model dependent.

March 2005Theme Group 2

Alternative B-L UnificationAlternative 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.

cRL SUSUSU )4()2()2(

GeVGeVM 1611224 1010

Non-SUSY G(224) and N-N-barNon-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

5~/ Mm nnnn

6/5~/ Mm nnnn

LBMM GeVM LB65.510

4

March 2005Theme Group 2

SUSY makes N-N-bar probe higher scales 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.

ccuu

2

1

LBM

March 2005Theme Group 2

Estimate of N-N-bar in Minimal 224 model: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)

March 2005Theme Group 2

Origin of matter in N-N-bar Origin of matter in N-N-bar modelsmodels

• Usual argument : Early 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);

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Does baryon asymmetry Does baryon asymmetry observable NN-bar ? observable NN-bar ?

• ObservableNN-bar, earlier matter asymmetry gets erased.

• Must regenerate below sphaleron decoupling scale ~ 140 GeV.

• 2224 model experienceadequate amount of matter light color sextet Higgs observable NN-bar.

• Not theorem but very palusible. (Babu, Dev, RNM’09; Babu’s talk).

March 2005Theme Group 2

Other models that can be probed by Nnbar 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 5th 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.

March 2005Theme Group 2

Proton decay vs N-N-bar oscillationProton decay vs N-N-bar oscillation

March 2005Theme Group 2

ConclusionConclusion• 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.