R. Mohapatra

1
A New way to understand the origin of
Matter
R. Mohapatra
K.S. Babu, R.N. Mohapatra, S. Nasri, Phys. Rev.
Lett. 97,131301 (2007) K.S. Babu, Bhupal Dev, R.
N. Mohapatra, in preparation.
2
Baryon asymmetry of the Universe

• Universe is full of matter and no anti-matter
• WMAP value for this
• Was it put in by hand at the beginning ?
• OR
• Was it created by microphysics during
• evolution- if so how ?

3
Sakharovs conditions

• He proposed 3 conditions for generating baryon
  asymmetry out of microphysics (1966)
• Baryon number violation
• CP violation
• Out of Thermal Equilibrium

4
How does it work ?

• A particle decays to both particles and
  anti-particles
• Generates net excess of baryons. Cond.12
• If Thermal Eq., reverse process will erase the
  excess. Hence condition 3.

5
History

• Sakharov work for the first time raised the
  possibility that baryon number may not after all
  be conserved.
• i.e. proton must be unstable or there must be
  some other form of.
• Mid- 70s- GUT theories predicted proton decay
  and provided concrete scenarios for baryogenesis
• Started intense search for proton decay as well
  as baryogenesis !
• After 25 yrs, no sign of p-decay !!

6
Things changed in 80s

• Three developments
• Rise of Sphalerons in SM
• Inflationary Universe
• Rise of leptogenesis

7
Sphalerons and B-violation

• SM violates baryon number due to sphalerons No
  need for GUTs for B-violation.
• Sphaleron induced B-violating operator
• Negligible in Lab but Important in early
  Universe Can lead to baryogenesis. (Kuzmin,
  Rukakov, Shaposnikov)

8
Sphalerons, Inflation and Baryogenesis

• Sphaleron Interaction rate in Early Univ.
• In equilibrium between GeV
• Does affect the baryon asymmetry generated above
  100 GeV- in particular, it erases GUT baryon
  asymmetry produced by B-L0 conserving
  interactions as in SU(5) !!
• Difficulty of accomodating GUT baryogenesis with
  inflation- since typical reheat temperatures
  after inflation is less than GUT scale !

9
Rise of Leptogenesis

• 1977-79 Seesaw mechanism for small neutrino
  masses were proposed
• MinkowskiYanagida, Gell-Mann, Ramond,
  Slansky Glashow R. N. M., Senjanovic
• Required Heavy RH Majorana neutrinos
• 1986 Leptogenesis proposed (Fukugita, Yanagida)
• 
  
• Produces lepton asymmetry and sphalerons convert
  it to baryons.
• No Observable baryon violation needed!

10
Issues with SUSY Leptogenesis models

• Has to be a high scale phenomenon to be
  predictive.
• In typical scenarios, lightest RH neutrino mass
  higher than
• (Davidson, Ibarra)
• The upper bound on T-reheat for generic TeV
  gravitinos is lt GeV
• (Kohri, Moroi,Yotsuyanagi )
• Conflict for SUSY
• Leptogenesis !!

11
Post-sphaleron baryogenesis

• Could baryogenesis be a lower scale phenomenon
  and thus avoid these constraints ?
• Basic idea (Babu,R.N.M.,Nasri06)
• Baryogenesis occurs after Sphalerons decouple
  
• at GeV
• Need new particle with mass 100 GeV to TeV
  decays violating B below 100 GeV.
• New particle- boson (S) or fermion (N)
• S or N must couple to B-violating current.
• B-violating processes must go out of Eq.
• at low temperature.

12
Possible B-violating couplings

• Case (i)
  )
• -Present proton decay constraints imply that
  the mass scale for this is . This
  implies that these processes go out of eq. around
  
• T . Clearly not suitable
  for post-sphaleron B-genesis.
• Case (ii)
  induced by operator
  
• -Gives rise to the process neutron-anti-neutron
  osc. Present limits -gt M10 TeV range. Out of Eq.
  
• T 100 GeV range.
• Suitable for post-sphaleron baryogenesis !!

13
S couplings
14
How can this happen ?

• Bottom-up view What are possible TeV scale mass
  scalars that could couple to SM fermions without
  making trouble ?
• Color
• quantum no.

SM
couples to
Allowed are they there ?

• Leads to
• p-decay

SM Higgs
15
Explicit Model

• We will see that these particles are not only
  allowed by bottom up view but they arise
  naturally in a class of neutrino models.

16
B violating decay of S
17
Out of Equilibrium condition

• S Decays go out of Eq. around few 100 GEV
• The S-particle does not decay until
• After which it decays and produces
  baryon-anti-baryon asymmetry
• The S-decay reheats the Universe to TR
• giving a dilution of . This dilution
  effect
• for our case is not significant.

18
CP Asymmetry Two classes of one loop diagrams
19
Model predictions Class I diagrams

• In general
• Goes down as MX increases and could be small.

20
Model Predictions Class (ii) Diagrams

• Note that even if gs are real, only CKM phase
  can give baryon asymmetry.
• Gives

21
Quantitative Details

• Define
• Constraints for adequate baryogenesis
• Dilution constr.
• Post sphal. Constr.
• Easy to satisfy with choice of f-parameters.
• f_331 M_s100
  GeV M_X300 GeV.

22
A Theory of Post -Sphaleron Baryogenesis

• Note X,Y,Z particles are crucial to this
  mechanism- what are they ?
• Neutrino mass throws light on X,Y,Z
• Seesaw for neutrino mass and left-right symmetry
• Seesaw requires RH neutrino and B-L breaking RH
  neutrino and B-L automatic in left-right model.

23
LR Model-A natural framework for seesaw and
gauged B-L

• Gauge group
• Fermion assignment
• Higgs fields
• Low energy V-A for

24
Detailed Higgs content and Sym Breaking
is responsible for neutrino masses
and when generalized lead to qq(X,Y,Z )
couplings.
25
Symmetry breaking and seesaw for neutrinos
If MD small, neutrino mass formula becomes

26
Embedding into higher symmetry

• G
• Fermions
• Higgs
  ..
• (Marshak, R.N.M., 80)
• (contains X,Y,Z
  diquarks)
• of
  our model.

27
Details

• (1,3,10) couplings that generalize seesaw
  couplings
• ltSgt gives mass to
  the RH neutrino and does seesaw for neutrino
  masses.
• V V_0
• The last term contains the SX2Y, SXZ2 terms.
• ltSgt100 TeV M TeV or less.
• Main point is that now we can relate the diquark
  couplings to neutriono masses via the type II
  seesaw i.e.

28
Phenomenological constraints
on Yukawacoupling
Constraints by rare processes
mixing
Similarly B-B-bar etc
29
Details of FCNC constraints

• Hadronic

30
FCNC and Inverted Neutrino mass pattern

• Considerably narrows the choice for the coupling
  matrix f and predictive for neutrino masses and
  mixings (Babu,Dev,RNM)

31
Allowed mass ranges for S and X

• Allowed masses
• Predicts light
• diquarks

32
Baryogenesis Confronts Experiments

• Neutrinoless double beta decay expts running will
  test this model.
• Testing this generic mechanism
• (i) Observable Neutron-anti- neutron
  oscillation
• (ii) Light diquark Higgs- could be observable
  at LHC for generic scenario

33
Neutrinoless double beta decay

• Majorana, EXO, Gerda,NEMO,
• Null result to the level of 10 meV will rule this
  model out.

34
Neutron-Anti-neutron Oscillation

• Feynman Diagram contributing (RNM, Marshak,80)
• Gives
• N-N-bar transition time

35
Prediction in our model
Dominant operator is udsuds type Need to be
combined with Interactions
36
Observing Neutron-Anti-neutron Oscill.

• Phenomenology
• Probability of Neutron Conversion to anti-N

37
Searching for Free N-Nbar Oscillation
Figure of merit

X Running time
38
Present expt situation

• First Free neutron Oscillation expt was carried
  out in ILL, Grenoble France (Baldoceolin et al,
  1994)
• Expt. Limit
• With existing facilities, it is possible extend
  the limit to

39
N-Nbar search at DUSEL
? TRIGA research reactor with cold neutron
moderator ? vn 1000 m/s ? Vertical shaft 1000
m deep with diameter 6 m ? Large vacuum tube,
focusing reflector, Earth magnetic field
compensation ? Detector (similar to ILL N-Nbar
detector) Kamyshkov et al. Proposal Reach
40
Nucleon instability and N-N-bar

• Nuclei will become unstable by this N-N-bar
  interaction but rate suppressed due to nuclear
  potential diff. between N and N-bar.
• Present limits
• Sudan, IMB, SK-

41
Collider Signatures

• Of the X, Y, Z, only Y-coupling
• can have potentially significant collider
  signature for some range of parameters
• -Diquark Higgs at hadron colliders through uu or
  anti-u anti-u annihilations
• (Okada, Yu, RNM, 2007)

42
LHC production
These processes have no Standard Model
counterpart! As conservative study, we
consider pair production in the
Standard Model as backgrounds
To measure diquark mass (final state invariant
mass)
top quark identification
difficult to tell top or anti-top?
43
Cross section for tt production

• tt and tjet from valence quarks in model with
  type II seesaw for neutrino masses( Direct
  correlation between neutrinos and diquark
  couplings)
• Fits nu-osc data for inverted hierarchy

44
Tevatron bound on Diquark Higgs mass
Top pair production cross section at Tevatron
45
Differential cross section as a function of the
invariant mass_at_LHC
Diquark has a baryon number LHC is pp
machine ?
46
Conclusion

• Weak scale Post-sphaleron baryogenesis consistent
  with all known observations A new mechanism
• Requires high dimensional baryon violation.
• Key tests a model realization are
• (i) Inverted nu mass hierarchy large theta_13
• (ii) N-N-bar oscillation search to the level of
  1010 -1011 sec.
• (iii) Collider searches for diquarks can also
  probe some parameter ranges.

47
Conclusions contd.

• In terms of a big picture for unification
• Post-sphaleron baryogenesis and NNbar go well
  with a picture orthogonal to conventional GUT-
• Tests Int scale B-L models for nu masses
• Does not need supersym although it is consistent
  with it.

48
Collider Search for Majorana

• In the 224 model, quark couplings are same as RH
  neutrino couplings
• mass in the TeV range
• Mixes with LH neutrinos and therefore can be
  produced in W-decays
• Like sign dilepton jets and no missing energy
  signal.

49
RH Nu Search

• Recent work Han, Zhang (2006)
• Not easy-
• mixing too small

50
Basics formulas
No angle dependence
with the total decay width as the sum if each
partial decay width
51
At Tevatron
At LHC
We employ CTEQ5M for the parton distribution
functions (pdf)
52
Example of couplings
satisfies the constraints from rare decay
process
Tevatron bound on Diquark Higgs mass
Top pair production cross section measured at
Tevatron
53
Differential cross section as a function of the
invariant mass _at_ LHC
Diquark has a baryon number LHC is pp
machine ?
54
Angular distribution of the cross section _at_ LHC
SM background
Diquark is a scalar ? No angular dependence SM
backgrounds? gluon fusion ? peak forward
backward region
55
(No Transcript)