NNbar program:
• 3:30-5:30
• R. N. Mohapatra: 3:30-4:00 (25+5)
What physics from NNbar ?
• K. S. Babu: 4:00-4:25 (20+5)
Origin of matter and NNbar
• R. Shrock: 4:25-4:50 (20+5)
Extra D and NNbar
• Y. Kamyshkov: 4:50-5:10 (15+5)
Experimental issues
• Discussion 5:10-5:30
Working group members
•
•
•
•
•
•
•
•
•
K. S. Babu
Z. Berezhiani
A. Dolgov
G. Gabadadze
A. Gal
Y. Kamyshkov
B. Kopeliovich
R. N. Mohapatra
R. Shrock
……………..
What can N-N-bar Oscillation
teach us about physics
Beyond the standard model ?
R. N. Mohapatra
University of Maryland
DUSEL Theory Workshop,
Columbus, Ohio; April 4-6,2008.
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 another neutral particle- it could
oscillate to anti-neutrons. What can it tell us
about physics beyond the standard model ?
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 an important 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.
B-L : new symmetry in Nature ?
• What happens to B-L symmetry
beyond standard model ?
• Remain exact or gets broken ?
• If broken, what is the scale of its
breaking ?
• Physics associated with this
breaking e.g. is B-L part of GUT ?
• Two expts that can probe it directly
are 0 and N-N-bar oscillation.
Neutrino Mass and B-L=2
• If neutrino is Majorana particle, it
breaks B-L by two units; observation
of 0 decay will confirm this but
by itself will not tell us much about
new physics associated with  (B-L).
•N-N-bar observation MAY
supply this information !!
• (with normal nu-hierarchy, 0 may be very
difficult to observe leaving NNbar as only way)
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.
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 indicated by neutrino
mass ?
- Are there decent theories EMBEDDING
small neutrino masses where scale N-N-bar
oscillation is observable?
• Is it cosmologically safe to have observable
N-N-bar oscillation ?
• The answer to all these questions is YES .
Phenomenology of N-N-bar Osc
  n 
  n   m  V1
 
i    
m  V2  n 
t  n   
2
Pnn
  
 Sin 2 (V1  V2 )t
 
 V1  V2 
Two cases :
(i)(V1  V2 )t  1:
(ii )(V1 V2 )t  1
Pnn
Pnn
 t
 
  nn
2


2
  

 
 V1  V2 
Theme Group 2
March 2005
Present expt situation in N-N-bar Osc.
Range accessible to current reactor fluxes:
 n n ~ 108  1011 sec.
Present limit:ILL experiment: Baldoceolin et al. (1994)
 n n  10 sec .
8
New proposal (Y. Kamyshkov et al.) for an expt. In DUSEL
10
GOAL:  n n > 10 sec.
Figure of merit ~
or factor 1,000-10,000
in appearance probability
 t
Flux  
  n n



2
Could proton decay set-up be used to
Could Proton decay
set-up
be
used
to
discover
NNbar
?
discover N-N-bar ?
• Nuclei will become unstable with N-N-bar interaction; but
rate suppressed due to nuclear potential diff. between N
and N-bar. (Gal et al; Alberico et al; Kopeliovich et al.)
 Nuc  R
2
free
• Present limits:
• Sudan, IMB, SK- ~ 3  108 s
• Nuclear Uncertainties !
• Atmos, Bg makes
discovery reach very
limited
R  0.5 10 sec
23
1
Mass scales probed by N-N-bar
To see what is probed by N-N-bar, do operator
analysis for B  2 processes:
OB 2
1 c c c c c c
 5u d d u d d
M
Note M5 suppression
mn n  OB2 QCD
 n n   / mn n ~ M
giving  n n ~ 10 sec . M
8
6
5
/ 6
 10
5.5
GeV
Scale Reach of N-N-bar
• Is the scale reach of N-N-bar
limited to only 300 TeV in generic
models as suggested ?
• NO- once new physics at TeV scale
is entertained e.g. SUSY, new
Higgs !
Weaker suppression with SUSY
A.
Dominant operator with SUSY:
Can probe
M_B-L upto
109 GeV
B. SUSY
+ diquark Higgs field
TeV scale
 u cu c
, at
Probe M_{B-L}
to 1012 GeV.
theory For N-N-bar
• Neutrino mass points to New
electroweak symmetry with B-L
• Gauge group:
Left-right sym th.
SU (2) L  SU (2) R U (1) BL
 uR 
    
d
d
R

 L
• Fermion:  u L 
P
 L  P  R 
    
 eL   eR 
• New approach to observed parity violation
i.e. it is only a low energy phenomenon !!
• The true weak interaction theory is parity
conserving like strong, EM and gravity !!
scale of new B-L physics ?
One attractive possibility suggested by
coupling constant unification is that it
is 1016 GeV.
Local B-L is part of a grand unifying symmetry
and it breaks at GUT scale. Related physics
is GUT physics. Group: SO(10)
Alternative B-L Unification
•
•
New physics below GUT scale
Only 16 fermions unified but not gauge
couplings: SU (2) L  SU (2) R  SU (4) c
(Pati, Salam, 73)
Only restriction on B-L scale is nu mass
(not coupling unification) and hence
M 224  10 GeV  10 GeV -even 100 TeV
11
16
N-N-bar is an effective probe in
this case;
Non-SUSY G(224) and N-N-bar
• The Feynman diagram for N-N-bar in NonSUSY 224 model (RNM, Marshak, 80)
 n  n   / mn  n ~ M 5
 n n   / mn n ~ M / 
5
6
4

•
vertex needed for baryogenesis .
• With M= M   M B  L
N-N-bar
5.56
observable only if M B  L  10
GeV
Origin of matter in N-N-bar models
• Popular scenarios: e.g. leptogenesis have baryon
asymmetry generated at very high temperatues;
• Observable N-N-bar -> remains in equilibrium
down to TeV Temp: erases this asymmetry;
• Discovery of NNbar osc will point to radically
new way to understand the origin of matter
One example of such a scenario: Baryon asymmetry
after sphaleron decoupling: In the context of 224
model, it is the late decay of 0 field that can create
baryons using the CKM phase.
Post-sphaleron baryogenesis: Babu,RNM, Nasri PRL, (2006,2007);
(BABU’s talk)
Baryogenesis upper limit on NNbar Osc time.
Roughly
 NN  10  10 sec .
11
12
Preliminary conclusion:
• Non-SUSY G_224 model with ~100 TeV
B-L scale is a completely self
consistent alternative to usual GUT
scenarios !!
• No proton decay problem- NN-bar
observable and has an upper limit !
• Could imagine solving gauge hierarchy
problem via extra dim scenarios !!
Estimate of N-N-bar in SUSY 224 model:
• New Feynman diagram for N-N-bar osc.
N-N-bar osc can probe
MB-L~1011 GeV (Dutta, Mimura, RNM; PRL (2006)
Proton decay vs N-N-bar oscillation

Other Theories probed by N-N-bar
• N-N-bar is also observable in generic
low gravity scale extra dim. Models:
• (Nussinov, Shrock;
Dvali, Gabadadze; Dolgov, Bambi; )
• N-N-bar expt could also probe
mirror sector of the Universe by
searching for N-N’ oscillation:
- Current limits ~400 sec.
• (Bento, Berezhiani, 2005)
A bit more on N-N’ Oscillation:
• Berezhiani’s Talk: MIRROR WORLD
• Lee and Yang, parity paper (1957)
What is a mirror neutron ?
• u’d’d’=n’ mirrror neutron
n-n’ oscillation
• Phenomenology: very similar to n-n-bar case:
Present status of search
So Why do N-N-bar search ?
• If neutrino are Majorana, it implies B-L=2 and it is
important to know the scale of B-L breaking.
Neutrino mass by itself does not give us this
information.
• If there is quark lepton unif., N-N-bar oscillation
exists and can probe the scale and physics
associated with B-L.
• Search at 1010 sec level will test for (B-L) (seesaw)
scale < 1011 GeV vs GUT seesaw.
• NNbar discovery will fundamentally alter our
thinking about:
(i) grand unification;
(ii) Origin of matter; (Babu)
(iii) constrain CPT violation, extra dim.
(iv) N-N’ to throw light on dark matter.
Thank you for your attention.
Discussion points:
• Physics issues- mass scale probed

2
nn
 vs   nucl
• Cosmology
• Nuclear physics
• Experiment
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
>1010 sec to test for (B-L) (seesaw) scale
less than 1011 GeV vs GUT scale seesaw.
• N-N-bar discovery will completely change the
thinking on grand unification.
• Baryon asymmetry consistent with NN-bar;
Upper limit on NN-bar time in some cases.
• Reactor oscillation search much better than
decay searches due to nucl. uncertainties !!
Thank you for your attention.
B-L- Grand unification
SO(10) : the minimal GUT theory with
B-L motivated by Gauge coupling
unification:
• All fermions unified to
one {16} dim rep.
•
• (Georgi; Fritzch, Minkowski)
• B-L violation scale is GUT scale
due to unification. N-N-bar
suppressed and unobservable.
Nucleon Decay in Generic Signature
• Key test of GUTS: Gauge Boson
mediated p-decay:
Origin of Matter
• Possible scenarios:
• Leptogenesis:
• Hard to test at low energies: Strictly No
connection to neutrino mass phases;
• Electroweak baryogenesis:
• Higgs mass < 120 GeV. Testable.
Baryogenesis upper limit on  N  N
• Scenario for NON-SUSY 224
model ( S  Re   )
c c
• S has B=2 coupling;
• S Decays go out of Eq. around ~ few 100 GEV
1
• The S-particle does not decay until T  [ S M P ]1/ 2
• After which it decays and produces baryonanti-baryon asymmetry:
• The S-decay reheats the Universe to TR
TR
giving a dilution of M S
which should not too small.
These put an upper limit on NNbar time (Babu’s talk)