fermion masses and unification
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Fermion Masses and Unification. Steve King University of Southampton. Lecture 2. Unification. Most popular Groups are:. Quarks, Leptons. Quarks, Leptons, right-handed neutrino. Quarks, Leptons, exotics, SM singlet,. GUTs. Simple Group. - PowerPoint PPT PresentationTRANSCRIPT
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Fermion Masses and Unification
Steve King
University of Southampton
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Lecture 2
Unification
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G ! SU(3)c SU(2)L U(1)YSimple Group
Quarks and Leptons unified into representations of G
Most popular Groups are:
SU(5) Quarks, Leptons ! 10©5
SO(10) Quarks, Leptons, right-handed neutrino ºR ! 16
E6 Quarks, Leptons, exotics, SM singlet, ºR ! 27
G
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G ! SU(3)c SU(2)L U(1)YSimple Group
Single coupling constant g
Applies to all three examples SU(5); SO(10); E6
spontaneously broken:G
TrfTa;Tbg=NG ±ab
) If no additional (non-SM singlet) fermions are added:
g1 ´
r53gY
Couplings assumed to ‘run’ to measured SM couplings
g3 =g2 =g1
g ! g3; g2; gY
At GUT energy.
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GUTs
E 6
(5) (1)SU U (3) (3) (3)C L RSU SU SU
(4) (2) (2)PS L RSU SU SU
(3) (2) (2) (1)C L R B LSU SU SU U
(3) (2) (1)C L YSU SU U
(5)SU
(10)SO
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EachfamilyfitsnicelyintotheSU(5)multiplets
N.BinminimalSU(5)neutrinomassesarezero.
Right-handedneutrinosmaybeaddedtogiveneutrinomassesbuttheyarenotpredicted.
SU(5)GUT GeorgiandGlashow
Withthehyperchargeembedding
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Gauge Sector of SU(5)
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Summary of Matter and Gauge Sector of SU(5)
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Candidate Higgs reps of SU(5) are contained in matter bilinears constructed from 5* and 10
Minimal suitable Higgs reps for fermion masses consist of 5H + 5*
H
Higgs Sector of SU(5)
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The smallest Higgs rep which contains a singlet under the SM subgroup is the 24 Higgs rep and is a candidate to break SU(5)
The Higgs superpotential involving the minimal Higgs sector of SU(5) consisting of the 24H plus 5H plus 5H
*
With some tuning (see later) one can achieve light Higgs doublets which can develop weak scale vevs
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The Yukawa superpotential for one family with Higgs H=5, H*=5*
good bad
c.f. good SUSY relations at MGUT: mb¼ m , ms ¼ m/3 , md ¼ 3me
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Pati-SalamPartialUnification(3) (2) (1)C L YSU SU U
(4) (2) (2)PS L RSU SU SU
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The Yukawa superpotential for one family
a xx aW F F h
2 1 1 2c c c cQh u Qh d Lh e Lh
u d e at the GUT scale
Could work for the third family, but certainly not for all three families
u d eij ij ij ijY Y Y Y at the GUT scale is bad
d eij ijY Y at the GUT scale is almost good
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Georgi-Jarlskog Textures
Gives good SUSY relations at MGUT: mb¼ m , ms ¼ m/3 , md ¼ 3me
12 1 2 21 2 1
33 3 3 22 2 2
a x a xx a x a
a x a xx a x a
W F F h F F h
F F h F F
12 12
21 22 21 22
0 0 0 0
0 , 3 0
0 0 1 0 0 1
d eY Y
(15,2,2)xa
15
1
1
1
3
V
Gives GJ factor of -3 for the lepton
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(4,2,1)L
u
d
u
e
u
d d
(4,1,2)
R
u
d
u
e
u
d d
SummaryofPati-Salam
--PredictsRHneutrinoswithleptonnumberasthe“fourthcolour”
--AllowsthepossibilityofrestoringparityifLRsymmetryisimposed
--(Quark-lepton)unificationof16familyintotwoLRsymmetricreps
--B-Lasagaugesymmetry
--QuantizationofelectricchargeQe=-Qp
--Pati-SalamcanbeunifiedintoSO(10)(4,2,1) (4,1,2) 16
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SO(10)GUT Georgi;FritzschandMinkowski
The16ofSO(10)containsasinglequarkandleptonfamilyandalsopredictsasingleright-handedneutrinoperfamily.
TheSU(5)repsareunifiedintoSO(10):
ThetwoHiggsdoubletsarecontainedina10ofSO(10)
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NeutrinomassesinSO(10)
0
16.16.10H R LR L RL
He m
H
16.16.126 126H H R R
216.16.16 16 16H H HR RM M
Diracmass
HeavyMajoranamass
SO(10)containsalltheingredientsforthesee-sawmechanismandtendstopredictahierarchicalpatternofneutrinomasses
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0 335.0 10 ( )p e y SK
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Like ‘matter’ particles,
G
Leads to new (triplet) particles D.
SU(5) SO(10) E6
All give new particles: D ´ (3;1)¡ 13
, (£3 in E6)
Problems: Spoil Unification of MSSM gauge couplings
Cause rapid proton decay
!Higgs must be embedded into representations of
e.g.
; D ´ (3;1) 13
1
2
5 uH
h
D
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Say representation of
To produce SM Yukawa terms one generally uses termsFFH
Gives following SM interactions:
e:g: 10 f or SO(10)
e:g: 16 f or SO(10)
But also gives ‘dangerous’ terms involving with SM particles:
uchuQ; dchdQ; echdL
D;D
G
And quarks and leptons representation of
hu;hd;D;D ! H
! F G
DQQ; Ddcuc; ecDuc;QLD Proton decay
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D D
1
DM
DQQ; Ddcuc; ecDuc;QLD
D-exchange generates superfield operators
In terms of scalar and fermion components some examples of dangerous operators are shown below
D
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u u u u
p
K
p
K
D
1
DM
Minimal SU(5) is ruled out by proton decay -- but it gives unacceptable fermion masses anyway
2( )p K c loop RG matrix element
331.6 10 ( )p K y SK
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Two possible types of solutions:
a Give large GUT scale masses to D;D
b Allow TeV scale masses to but suppress interactions D;D
! Doublet-Triplet splitting
Yukawa suppression is required
a ‘Solves’ Proton Decay and Unification problems
b ‘Solves’ Proton Decay problem but leaves Unification problem
!
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Nontrivial to give huge masses to but not D;D hu;hd
e.g. most simple mass term would be in SU(5)MGUT 55
! MGUT huhd + MGUTDD
Minimal superpotential contains:
Fine tuning to within 1 part in 1014
) DD(¹ +23¸m) + huhd(¹ ¡ ¸m)Superpotential:
SU(5) ! SM
GUT EW scale
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Pair up H with a G representation that contains (colour) triplets
Take superpotential to contain:
e:g: minimal SU(5)
5 50< 75>+ 5 50< 75>
Under :SU(5) ! SM
) Nothing for Higgs hu , hd to couple to
Problems: Large rank representations
‘Missing – partner’ mechanism’
but not (weak) doublets (at least after G is broken).
Proton decay via triplet Higgsino from
And in direction gives mass couplings to <75> (1;1)0 D;D
effective term.
problem for Higgs mass
50 contains (3,1) but not (1,2)
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•Theproblem(lightHiggsmass)isintimatelyrelatedtothedoublet-tripletsplittingproblem(heavytripletmass)
•OneapproachistoallowbothlightHiggsdoubletsandtriplets
•Requirements:generateTeVscalemasstermsforthelightHiggsdoubletsandtriplets,suppressprotondecayduetotripletexchangewhileallowingtripletstodecayinlessthat0.1stoavoidproblemswithnucleosynthesis
•TheExceptionalSupersymmetricStandardModel(ESSM)isanexampleofamodelwithextralowenergyexoticmatterformingcomplete27’sofE6plusthetwoHiggsdoubletsoftheMSSM:
[5*+10+(5+5*)+1+1]xthreefamilies+(H,H’)Quarks, leptons
Triplets,Higgs, singlets
27
Non-Higgs
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15 14 4(1) (1) (1) NU U U
(10) (5) (1)SO SU U 6 (10) (1)E SO U
E6 ! SU(5)£U(1)N MGUT
TeV U(1)N broken, Z’ and triplets get mass, term generated
27',27'
Incomplete multiplets
(required for unification)
Right handed neutrino masses
MString E8 £ E8 ! E
6
Quarks, leptons
Triplets and Higgs
Singlets and RH s
H’,H’-bar
MW SU(2)L£ U(1)Y broken
Right handed neutrinos are neutral under:
ESSM= MSSM+3(5+5ESSM= MSSM+3(5+5**))+Singlets+Singlets
! SM £ U(1)N
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Family Universal Anomaly Free Charges:
Most general E6 allowed couplings from 273:
Allows p and D,D* decay
FCNC’s due to extra Higgs
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Rapid proton decay + FCNCs extra symmetry required:
•Introduce a Z2 under which third family Higgs and singlet are even all else odd forbids W1 and W2 and only allows Yukawa couplings involving third family Higgs and singlet
•Forbids proton decay and FCNCs, but also forbids D,D* decay so Z2 must be broken!
•Yukawa couplings g<10-8 will suppress p decay sufficiently
•Yukawa couplings g>10-12 will allow D,D* decay with lifetime <0.1 s (nucleosynthesis)
This works because D decay amplitude involves single g while p decay involves two g’s
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Unification in the MSSMUnification in the MSSMBlow-up of GUT region
MSUSY=250 GeV
3
21
2 loop, 3(MZ)=0.118
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Unification with Unification with MSSM+3(5+5MSSM+3(5+5**))
3
2
1
250 GeV
1.5 TeV
Blow-up of GUT region2 loop, 3(MZ)=0.118
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MESSM= 3x27’s (no H,H’)MESSM= 3x27’s (no H,H’)
(10) (4) (2) (2)PS L RSO SU SU SU6 (10) (1)E SO U
MGUT
TeV U(1)X broken, Z’ and triplets get mass, term generated
Right handed neutrino masses
MPlanck
Quarks, leptons
Triplets and Higgs
Singlet
MW SU(2)L£ U(1)Y broken
E6! SU(4)PS£ SU(2)L £ SU(2)R
SU(4)PS£ SU(2)L £ SU(2)R £ U(1) ! SM £ U(1)X
(4,2,1) (4,1,2) (6,1,1) (1,2,2) (1,1,1) 27 x three families
£U(1)
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Planck Scale Unification with Planck Scale Unification with 3x27’s3x27’s
Low energy (below MGUT) three complete families of 27’s of E6
High energy (above MGUT» 1016 GeV) this is embedded into a left-right symmetric Pati-Salam model and additional heavy Higgs are added.
MPlanck MPlanck