Neutrino Mass Origin of
Matter: Probing at LHC
R. N. Mohapatra
MPI-Heidelberg Seminar,2009
Universe is full of matter
and “no” anti-matter

How do we know ?
(i) Solar probes have not exploded(ii) Sun sends us billions of particles and no
antiparticles since there are no natural fireworks
in the sky(iii) Anti-matter fraction in cosmic rays: 1 in 10,000
(completely understandable in terms of known
particle physics.)
Big Bang Nucleosynthesis

In the beginning, when the Universe was only a
second old, there were only protons and
neutrons- so how did all the elements we are
made of formed ?
Nuclear Reactions
responsible:
Things would have
been different if there
was anti-matter…
Matter Amount

Detailed analysis

CMB
B
nB  nB
10

 (6.2  0.15) 10
n
Was it put in by hand at
the beginning ?
Not tenable since inflation empties the
universe—

It must be created by microphysics during
evolution
Baryon asymmetry from
Microphysics





Sakharov Proposed 3 conditions for generating
baryon asymmetry using microphysics (1967)
Baryon number violation;
CP violation;
Out of Thermal Equilibrium.
Standard model cannot doalthough it has both CP and Bviolation (too small CPV and not light enough
Higgs).
Premise of the Talk:

Discovery of neutrino mass requires new
physics beyond SM which has provided a
promising possibility for explaining the matterantimatter asym.

Can we test this physics at LHC ?

TeV scale Z’ related to
(Blanchet, Chacko, Granor, RNM: arXiv:0904.2974)

-mass:





Seesaw Paradigm for
neutrino mass
Why m  mq ,l ?
N R to SM with
Add right handed neutrinos
Majorana mass:
LY  h L HN R  M R NN
Breaks B-L
2
2
sym. of SM:
h vwk
After electroweak m   M
R
symmetry breaking
11
Note: if MR=0, h  10
(too small)
SM
whereas even with TeV MR, h  he (more reasonable)
MR
B-L breaking crucial
to seesaw:
Minkowski; Gell-Mann, Ramond Slansky,Yanagida, R.N.M.,Senjanovic,Glashow
Seesaw and Origin of
matter

Proposal:
(Fukugita and Yanagida ,1986)
R  (1   )
R  (1   )




Generates lepton asymmetry:
Gets converted to baryons via sphaleron interactions
of SM (‘t Hooft)
(Kuzmin,Rubakov,Shaposnikov)
No new interactions needed other than those already
used for generating neutrino masses !!
Seesaw provides a common understanding of both
neutrino masses and origin of matter in the Universe.
Scale

What is the seesaw scale ?

Is scale right for baryogenesis ?

Important because scale determines
whether the idea is testable !!
Seesaw scale


Neutrino masses do not determine the seesaw
scale- we do not know mD  h vwk in seesaw formula
2
Type
I
seesaw
+

m
mD  mt
atm
 M R  10 GeV
GUT -10
GeVSmall neutrino mass could be indication for SUSYGUT;
Many interesting SO(10) GUT models.
No collider signals ! Possible tests in nu-osc.
With SUSY, in   e   (dependent on SUSY scale)
mD  me Seesaw scale is around TeV
(corresponding Yukawa~10 6 ) ;
16
14
-



Natural -protected by chiral sym. N  N
Many collider signals, possibly 
 e   , 0
Leptogenesis Scale




Diagrams:
Two classes of models depending on RH mass pattern
High Scale leptogenesis: Expected in GUT theories:
Adequate asymmetry M  109 GeV for lightest RH
(for hierarchical masses)(Buchmuller, Plumacher,di Bari; Davidson, Ibarra)
Resonant leptogenesis: degenerate
N’s, self
1
energy diagram dominates:~ M i 2  M j 2  M ;
Resonance when M i  M j ;works for all B-L scales.
(Liu and Segre’94; Covi et al’95 ; Flanz et al.’95 Pilaftsis’97)
An Issue with High scale
SUSY Leptogenesis





Recall the lower bound on the lightest RH neutrino
mass M N  109 GeV for enough baryons in GUTs
Problem for supersymmetric models:
they have gravitinos with TeV mass that are produced during
inflation reheat along with all SM particlesWill overclose the universe if stable for TR>10^9 GeV.
If unstable, Once produced they live too long -affect
67
T

10
GeV . (Kohri et al.)
BBN. R
Possible tension between LFV and leptogen.
Tension between gravitino
and high scale leptogenesis

Overclosure for stable and BBN constraint for
unstable ones: (Kawasaki, Kohri, Moroi,Yatsuyanagi,2008)
Leptogenesis and   e  

Both depend on RH neutrino mass hierarchy !!

(Chun,Evans,Morrissey,Wells’08; Petcov,Rodejohann,Shindou,Takanishi’05)
No such conflict for TeV scale leptogenesis !!
Goes well with collider friendly TeV seesaw !
Minimal TeV scale seesaw

No new interactions: N production at LHC can
happen only through   N mixing ;
cross section observable
only if   N mixing is > 10 2


(del Aguila,Aguilar-Savedra, Pittau)
However observed neutrino masses via seesaw for
M N ~100 GeV implies   10 6 Not observable at LHC.
N

Exceptions possible with specific extra global
symmetries-
TeV Seesaw with B-L
forces (Z’)



Seesaw effect observable at LHC even with tiny
  N mixings as in generic neutrino models.
pp Z’+X; Z’NN followed by N-decay;
Like sign dileptons is the tell-tale seesaw signal.
How plausible is Local B-L ?



Neutrino masses  seesaw scale much lower than
Planck scale New symmetry (B-L).
Is B-L global or local ?
SM  only Tr (B-L)[SU(2)]^2=0 but Tr ( B  L)3  0
But SM +  R  Tr ( B  L)  0
B-L is a potential gauge symmetry3




Gauged B-L eliminates R-parity problem of MSSM and
ensures proton stability and dark matter: Another
advantage of B-L (RNM’86; Martin’92)
Extend SM gauge symmetry to include B-L- many ways-
Two Faces of B-L


Separate B-L vs SO(10) inspired B-L:
For
low B-L scale(TeV range), need B-L=2 Higgs
0
 R (1,1,2) to break symmetry to implement seesaw, if
no new physics upto Planck scale.
TeV Z’ cross section at LHC

LHC Z’ reach - 4 TeV

Cross section for ppZ’NN (Z’NN branching ratio
~20%)
2.5 TeV Z’
to
5 TeV
Testing seesaw with Z’
decay
xsection for a 3 TeV Z’ ~fb
 Seesaw signal: N=Majorana


 N l W
, Z
Wjj , l
 Di and Multi-lepton events: (X=jjjj)

PPZ’+X;
()
pp  l l  X , l l l   E, l l l  l   E
\

\
Important for signal to bg: very high pT leptons
coming from N-decay; inv mass reconstruction:
(Del Aguila, Aguilar-Saavedra; Aguilar-Saavedra )
TeV scale Resonant
leptogenesis with Z’

Conditions:
(i) RH neutrinos must be degenerate in mass;
M 1  M 2  M 1, 2 since h >10^-5 degeneracy ok anywhere
from 10 2  10 10;technically natural and enough for baryogenesis!
(ii) Since there are fast processes at that
temperature, the net lepton asymmetry and
primordial lepton asym are related by
where  <1 (efficiency factor); depends on rates for Z’
 
med. scatt. e e  NN ;inverse decay lH  N
 Details

Finding  :

(Buchmuller,di Bari Plumacher)



Note:  very small, when S >> D- i.e. lighter Z’;
As MZ’ increases, S ~ D,  gets bigger and there
is a large range where adequate leptogen is
possible.
Adequate leptogenesis implies a lower limit on MZ’
Questions:
Is the lower limit in the LHC
accessible range ?
Yes; MZ’ > 2.5 TeV for MZ’ > 2MN


Can LHC directly probe the
primordial lepton asymmetry ?
Can LHC Directly probe the
primordial lepton asym. ?

Since  B  10  l , small efficiency  means  l large
; Search for where  is tiny so  l is order 1.
Detectable at LHC by searching for like sign leptons

(Blanchet, Chacko, Granor, RNM: arXiv:0904.2974)

Basic idea:

2
l

At LHC, PPZ’+X

12.5% of time


N  l W ,Z


NNl  Xl  X
Look for a CP violating observable !
()
Direct probe of resonant
leptogenesis, contd.

Direct link between primordial lepton
asymmetry and CP violating LHC observable:
 [(l l )  (ll )] 2 l



[   ]
3



For a ranges of Z’-N mass, 
very small so that  l~0.1-1;
visible at LHC:
Similarly for tri-lepton events.
Lower bound on MZ’ >2.5 TeV.
Numbers








300 fb^-1, expect 255 dilepton events (85% det eff.)
90% of events with jets or one missing E.
With no CP violation: 16 ++ and - - events;
Should rule out   0.25 at 2 sigma level.
An observation will directly probe leptogenesis, if RH
mass deg. is inferred from inv mass study.
How to tell how many N’s ?
For one N, there are 5 observables, Nl l but only two
inputs; we have three relations of type: N e  N ee N 
For 2 N’s, 4 inputs and 5 observables; only one relation.
none for three !
How natural is degenerate
RH spectrum ?


Degenerate RH neutrino specctrum might look odd
since quark and charged lepton masses are very
hierarchical:
RH vs Q,L masses:
(i) RH nu’s are Majorana masses whereas q, l masses
are Dirac;
(ii) RH masses arise at different scale and from a
different mechanism (B-L breaking) as against the
Q, L masses which arise from SM symmetry br.
(iii) Already large neutrino mixings are an indication
that in the seesaw formula RH neutrinos must
have some peculiarity.
A model

Gauge group
SU (2) L  U (1) I  U (1) B  L xO(3)
 O(3)Hglobal
with RH nu’s triplet under O(3)H – all other fermion
fields singlet.
 (1,1,2)1 ; (1,0,0) a1,2 + SM like Higgs.
Higgs: 
Seesaw arises from following Yukawa
Lagrangian:
 i ,a N a i ,a N b j ,b 
3R


L  fNa N a   hLHN a


M

M
2
 h.c.
 
5
~
10
Choose
will give desired parameters.
M
Since Dirac Yukawas are ~10^-5, RH neutrino mass
splitting is radiatively stable.
Left-right embedding

Left-right Model: SU (2) L  SU (2) R U (1) BL

Solves SUSY and Strong CP in addition to automatic RP

Unless MWR > 18 TeV,

L-violating scatterings e.g.
eR  uR  N  d R
will erase lepton asymmetry.
(Frere, Hambye and Vertongen)
- Sym br. to U(1)I3RxU(1)B-L  SM at TeVto do resonant leptogenesis.
Avoiding the WR bound:

If there are heavy vector like D-quarks mixing with d
in such a way that the doublet coupling to WR
becomes:  uR  for D-mass in the 10 TeV range,
 D  d 
R
 R

the dominant process does not occur. We need
4
  10 to avoid the WR bound.
WR can be in the LHC range but the decay modes
purely leptonic.
Resonant leptogenesis in
generic LR model


Key question is whether degenerate RH neutrino
spectrum is radiatively stable to have leptogeneesis
possible generic LR models !!
Yes- since largest rad correction to RH masses
M N
h2
is
6
~
10
MN
16 2

2
~



Whereas CP asymmetry is:
Im[( h h) ]
~
 M N
h h
5 M N
Which gives for h~10^-5.5,  ~ 10
Not visible from Z’ decay but nonetheless a viable low
scale model for leptogenesis and dark matter !!
A specific LR model:

LR+extra symmetries: SU (2) L  SU (2) R U (1) BL xU(1)xxU(1)Z

Leads to RH mass matrix of form:



 M1

 0
 0

0
0
M
0

M
0 
Leads to two deg RH nu’s;
Dirac mass matrix:
 0 * *


 * 0 *
 * * 0


Leads to realistic nu masses and mixings as well as
resonant leptogenesis with tiny sym br. Effects.
New collider signals for LR
case





Even if WR may be out of reach due to baryogenesis
constraints, other exotic Higgs bosons in LHC reach
 1





 (1,1,2) gets embedded into  2



 0




1 
 
2 
Predicts doubly charged Higgs bosons in the sub-TeV
mass range coupling to like sign dileptons:
Resonant leptogenesis     e  e  ,   
dominant modes;
No   3e but   ee allowed.
Unification Prospects: An
SO(10) possibility


Triplets with B-L=2 hard to unify to SUSY SO(10).
Both for TeV Z’ and WR, unification possible with B-L
=1 doublets breaking
Malinsky, Romao, Valle’05);
U(1)B-L; (Deshpande, Keith and Rizzo; 93;
Neutrino masses

Requires double seesaw for neutrino masses: Add an extra singlet field S in
addition to left and RH neutrinos which are part of {16};

Double seesaw: (

(RNM’86; RNM,Valle’86)


 0

 hvwk
 0

N
S)
hvwk
0

M
 
0
M
m  m M M mD
T
D
1
mD  hvwk
1
Important: Unlike type I seesaw, Majorana character of RH
N depends on how large M is.
Suppresses like sign dileptons at LHC unless M ~1.
Leptogenesis possible but visible only for

M
~1.
Low scale SUSY LR-an
Alternative to MSSM

MSSM:
SO(10) Unified SUSYLR
1.
Rapid p-decay due to 1.No dim4 p-decay due to B-L
RP breaking
2. Neutrino mass not easy 2.Double seesaw for nu mass
3.
EW baryo in a corner
of parameter space.
4. Light Higgs and stop
3. Explains Origin of matter
5.
4. Z’ and like sign dileptons
at LHC
5. DM gravitino/Neutralino
DM gravitino/Neutra
lino
Conclusion:




LHC can directly probe the seesaw mechanism for neutrino
masses if the seesaw scale is in the TeV range and there is a
TeV scale Z’ regardless of neutrino mass pattern.
For certain ranges of the Z’-N mass, LHC can probe
resonant leptogenesis mechanism for the origin of
matter directly -find Z’-N in the allowed range
simultaneously with large like sign dilepton CP
asymmetry.
Use of inv mass peak and large PT leptons to reduce
background.
There are left-right and SO(10) SUSY GUT models
where such scenarios can be embedded, providing
theoretical motivation for low scale Z’ as well as TeV
scale leptogenesis .
Extra slides

Post-sphaleron baryogenesis and color
sextet scalars at LHC.
What if RH neutrinos are TeV
scale but non-degenerate ?


Can one have seesaw scale around a TeV so
LHC can see it and still understand the origin
of matter related to seesaw physics ?
Yes- baryogenesis can arise from seesaw
related physics below 100 GeV (but not from
RH N decay) (post-sphaleron baryogenesis)
(Babu, RNM, Nasri’06)

Predicts light color sextet Higgs (< TeV) that
can be observed at LHC via decay to two tops.
Q-L unify TeV seesaw




SU(2)LxU(1)RxU(1)B-L  SU(2)LxU(1)RxSU(4)PS.
 u    u R  R
  ,   ,

 d  L  e  L d R eR
Recall Origin
of RH nu mass for seesaw is from NN 

Q-L unif. implies quark partners for   i.e. u
- color sextet scalars coupling to up quarks ;
similar for dd- only right handed quarks couple. Come
from (1, 1, 10)
R R
R R
SU(4)PS breaks to U(1)B-L
above 100 TeV
c c
u
Baryon violation graph

+

 u cu c  d c d c  d c d c  R R

+ h. c.
 B=2 but no  B=1; hence proton is stable but
neutron can convert to anti-neutron!
N-N-bar diagram

 coupling crucial to get baryogenesis (see later)

Origin of matter



(Babu, Nasri, RNM, 2006)
Call Re  R R= Sr ; TeV mass : S-vev generates seesaw
and
leading to B-violating decays
Baryogenesis: Due to high dimension of operator, Bviolating process goes out of eq. below 100 GeV.
Upper limits on Sr and
color sextet masses:

Two key constraints:
 MS < 500-700 GeV
to get right amount of
baryons.

Decay before QCD phase transition temp:

Implies MS< MX < 2 MS.
Two experimental implications:

nn
oscillation: successful baryogenesis implies
that color sextets are light (< TeV) (Babu, RNM, Nasri,06; Babu, Dev,
RNM’08);
n  n arises via the diagram:
 nn  10  10 sec .
9



11
Present limit: ILL >10^8 sec. similar bounds from
Soudan,S-K etc.
10^11 sec. reachable with available facilities !!
A collaboration for NNbar search with about 40
members exists-Exploration of various reactor sites
under way for a second round search.
Color sextet scalars at LHC
Low seesaw scale + baryogenesis requires that sextet scalars
must be around or below a TeV:
 Two production modes at LHC:
(I) Single production:
xsection calculated in (RNM, Okada, Yu’07;) resonance peaks above
SM background- decay to tt or tj depending on RH nu
Majorana coupling; directly measures seesaw parameters.

(II) Drell-Yan pair production: qq  G   u cu c  *u cu c
( Chen, Klem, Rentala, Wang, 08)
 Leads to ttt t final states:
LHC reach < TeV
Single Sextet production at
LHC:
Diquark has a baryon number & LHC is ``pp’’ machine

Depends on Yukawa coupling
Pair Production of Deltas



Due to color sextet nature, Drell-Yan production
reasonable- independent of Yukawa coupling
Leads to ttt t final states:
Can be probed upto a TeV
using like sign dilepton mode.
Phenomenological Aspects
 f ij  d c d c di d cj  ...
c
Constraints by rare processes
mixing
K K
 u cu c exchange
d
c
d
c
s
c
s
c
Similarly B-B-bar etc. Can generate
neutrino masses - satisfying FCNC
 d cdc
Details of FCNC
constraints:

Hadronic:
  e 
Examples of color sextet
couplings that work.

Down sector:
10
 .3 * * 


f uu   * 0 * 
 * * .3 



Fits neutrino mass via type I seesaw.
2
Collider signal with WR


Depends on mass of WR; for WR in the few TeV
range, N-decay profile changes:
1 
1 
1  
No WR case:
N  l jj  l jj  l l E
3



With WR (TeV)
3
3
\
3 
3 
1
N  l jj  l jj  llljj
8
8
4
No missing E in second case;
Trilepton signal very sub-dominant.