Post on 17-Jan-2016
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.