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TRANSCRIPT
TeV Seesaws and
Signatures at LHC
Yong-Yeon KeumKorea U. and CTP-BUE
APCTP-2009 LHC-physics Workshop 25-27 Aug. 2009, Konkuk University
Contents:
• Origin of -mass: Seesaws
• Why TeV Seesaws?
• Type-I Seesaw and LHC-signatures
• Type-II Seesaw and LHC-signatures
• Type-(I+II) Seesaw and LHC-signatures
• Type-III Seesaw and LHC-signatures
Origin of -mass: Seesaws
A natural theoretical way to understand why 3 -masses are very small.
Type-III: SM + 3 triplet fermions (Foot, Lew, He, Joshi 89)
Type-I: SM + 3 right-handed Majorana ’s (Minkowski 77; Yanagida 79; Glashow 79; Gell-Mann, Ramond, Slanski 79; Mohapatra, Senjanovic 79)
Type-II: SM + 1 Higgs triplet (Magg, Wetterich 80; Schechter, Valle 80; Lazarides et al 80; Mohapatra, Senjanovic 80; Gelmini, Roncadelli 80)
Other variations or combinations (e.g., type-I + type-II in SO(10) GUT)
Some Recent Works★ Han, Zhang, PRL (06)★ Buckley, Murayama, PLB (06)★ del Aguila et al, JPCS (06)★ Bar-Shalon et al, PLB (06)
★ de Gouvea et al, PRD (07)
★ Atwood et al, PRD (07)
★ del Aguila et al, JHEP (07)
★ de Almeidaet al, PRD (07)★ Chen, Mahanthappa, PRD (07)★ Bajc et al, PRD (07)★ Graesser, PRD (07)★ Kersten, Smirnov, PRD (07) ★ Xing, PLB (08)★ de Gouvea, Jenkins, PRD (08)★ Chen et al, arXiv:0801.2011★ Bar-Shalon et al, arXiv:0803.2835★ Hirsch et al, arXiv:0804.4072★ del Aguila et al, arXiv:0806.0876★ Cogollo et al, arXiv:0806.3087★ Murayama, arXiv:0807.3775★ Perez et al., arXiv:0907.4186………
★ Hektor et al, NPB (07)★ Han et al, PRD (07)★ Dorsner, Mocioiu, NPB (08)★ Goravoa, Schwetz, JHEP (08)★ Chao et al, PRD (08)★ Akeroyd et al, PRD (08)★ McDonald et al, JCAP (08)★ Xing, PRD (08)★ Ren, Xing, PLB (08)★ Gogoladze et al, arXiv:0802.3257
★ Chao et al, arXiv:0804.1265
★ Fileviez Perez et al, arXiv:0805.3536★ Hirsch et al, arXiv:0806.3361★ ……
★ Barr, Dorsner, PLB (06)★ Bajc, Senjanovic, JHEP (07)★ Fileviez Perez, PLB (07)★ Dorsner, Fileviez Perez, JHEP (07)★ Abada et al, JHEP (07)★ Abada et al, arXiv:0803.0481
★ Franceschini et al, arXiv:0805.1613
★ Gogoladze et al, arXiv:0805.2129★ Mohapatra et al, arXiv:0807.4524★ Tong Li, X.G. He, arXiv:0907.4193……..
Type-I
Type-II
Type-III
How to experimentally distinguish one type from another?
What is the first step to test seesaws at the LHC?
ANSWER:
to discover the Higgs boson(s)
and
to verify the Yukawa interactions
Why TeV Seesaws?
Is the seesaw mechanism of -mass generation testable or not?
Planck
Fermi
GUT to unify strong, weak & electromagnetic forces?
TeV to solve the unnatural gauge hierarchy problem?
Is the “seesaw scale” close to a fundamental physics scale?
Conventional (Type-one) Seesaw Picture: close to the GUT scale
TeV Seesaw Idea: driven by testability at LHC
Naturalness? Testability?
RD M/M~S~RSeesaw:
Strength of Unitarity Violation
Hence V is not unitary
Diagonalization (flavor basis mass basis):
Type-I Seesaw: add 3 right-handed Majorana neutrinos into the SM.
or
Type-I Seesaw
Natural or Unnatural?
TeV-scale (right-handed) Majorana neutrinos: small masses of light Majorana neutrinos come from sub-leading perturbations.
Unnatural case: large cancellation in the leading seesaw term.
TMMMM D
1
RD
-
0.01 eV 100 GeVTeV 1
2
1
RD
-
10
10 ~Violation Unitarity
~M/M~S~R
Natural case: no large cancellation in the leading seesaw term.
TMMMM D
1
RD
-
0.01 eV 100 GeV
GeV 1015
26
13
RD
-
10
10 ~Violation Unitarity
~M/M~S~R
Structural Cancellation
Given diagonal M_R with 3 eigenvalues M_1, M_2 and M_3, the leading (i.e., type-I seesaw) term of the light neutrino mass matrix vanishes, if and only if M_D has rank 1, and if
(Buchmueller, Greub 91; Ingelman, Rathsman 93; Heusch, Minkowski 94; ……; Kersten, Smirnov 07).
0D
1
RD T
ν M-
MMM
DM
Tiny -masses can be generated from tiny corrections to this complete “structural cancellation”, by deforming M_D or M_R .
Simple example:
Lessons
Lesson 1: two necessary conditions to test a seesaw model with heavy right-handed Majorana neutrinos at the LHC:
(A) Masses of heavy Majorana neutrinos must be of O (1) TeV or below; (B) Light-heavy neutrino mixing (i.e., M_D/M_R) must be large enough.
Lesson 2: LHC-collider signatures of heavy Majorana ’s are essentially decoupled from masses and mixing parameters of light Majorana ’s.
Lesson 3: non-unitarity of the light neutrino flavor mixing matrix might lead to observable effects in neutrino oscillations and rare processes.
Lesson 4: nontrivial limits on heavy Majorana neutrinos can be derived at the LHC, if the SM backgrounds are small for a specific final state.
L = 2 like-sign dilepton events
Collider Signature
Lepton number violation: like-sign dilepton events at hadron colliders, such as Tevatron (~2 TeV) and LHC (~14 TeV).
collider analogue to 0 decay
N can be produced on resonance
dominant channel
Numerical Illustration
Han, Zhang (hep-ph/0604064, PRL): cross sections are generally smaller for larger masses of heavy Majorana neutrinos.
Tevatron LHC
Del Aguila et al (hep-ph/0606198): signal & background cross sections (in fb) as a function of the heavy Majorana neutrino mass (in GeV).
A single heavy N(minimal Type-II)
Type-II Seesaw
Type-II (Triplet) Seesaw: add 1 SU(2)_L Higgs triplet into the SM.
or
Potential:
L and B–L violationNaturalness? (t’ Hooft 79, …, Giudice 08)(1) M_ is O(1) TeV or close to the scale of gauge symmetry breaking. (2) _ must be tiny, and _ =0 enhances the symmetry of the model.
M
YM2
L
v
0.01 eV TeV 1
......
10
10 1,
106
12
12 ~Y~
~~Y
~Y
Collider Signature
From the viewpoint of direct tests, the triplet seesaw has an advantage: The SU(2)_L Higgs triplet contains a doubly-charged scalar that can be produced at colliders, depending only on its mass and independently of the Yukawa coupling.
Signatures: Rough number of events for pair (N_4l) and single (N_2l) production of doubly-charged Higgs at the LHC (See, e.g., Han et al07; Akeroyd et al 08; Perez et al 08; ……)
Type-(I+II) Seesaw
Incomplete cancellation between two leading terms of the light neutrino mass matrix in type-II seesaw scenarios. The residue of this incomplete cancellation generates the neutrino masses:
not small
not small
collider signature
tiny mass generation
Collider signatures: both heavy Majorana neutrinos and doubly-charged scalars are possible to be produced at the LHC (e.g., Azuleos et al 06; del Aguila et al 07; Han et al 07; ….). But decoupling between collider physics & the mechanism of neutrino mass generation is very possible.
Discrete flavor symmetries may be used to arrange the textures of two mass terms, but fine-tuning seems unavoidable in the (Big – Big) case.
Type-III Seesaw
• Type-III Seesaw: add left-handed triplet leptons into the SM.
• Unlike type I seesaw model, the doublet charged leptons mix with the triplet charged leptons to tree level flavor changing neutral current involving changed leptons
• LHC-signatures:
(1) Heavy triplet lepton production:
C
0 0
L 0 0
L Y(1,3,0) under SU(3) x SU(2) x U(1)
, Charge Conj. form
Define: ; and
/ 2 / 2
/ 2 / 2
, )
0(
c c
L
c c
L L L L R
L
l
m R R
L
L L Lc
Lc c
L L L L
mL l
Y M
0
0
+ h.c.
0 / 2 2 ( , ) + h.c.
/ 2 2 / 2
L
L
Lc c
L L
L
l
Y v
Y M
* * +
*
Z E E
W E N
pp
pp
Collider Signature
E ,N 0
0
Singnal channels for E and N:
1) 1-lepton channel
E Z, W ,
s:
2) 2-lepton channels:
H
N W , ,
H
l jjjj
l l jjjj
l l
l Z
,
3) 3-lepton channels:
4) 4-lepton channels:
5) 5-lepton channels:
6) 6-lepton channels:
l l
l l l
l l l l
l l l l l
l l l l
l l
Some Recent Works★ Han, Zhang, PRL (06)★ Buckley, Murayama, PLB (06)★ del Aguila et al, JPCS (06)★ Bar-Shalon et al, PLB (06)
★ de Gouvea et al, PRD (07)
★ Atwood et al, PRD (07)
★ del Aguila et al, JHEP (07)
★ de Almeidaet al, PRD (07)★ Chen, Mahanthappa, PRD (07)★ Bajc et al, PRD (07)★ Graesser, PRD (07)★ Kersten, Smirnov, PRD (07) ★ Xing, PLB (08)★ de Gouvea, Jenkins, PRD (08)★ Chen et al, arXiv:0801.2011★ Bar-Shalon et al, arXiv:0803.2835★ Hirsch et al, arXiv:0804.4072★ del Aguila et al, arXiv:0806.0876★ Cogollo et al, arXiv:0806.3087★ Murayama, arXiv:0807.3775★ Perez et al., arXiv:0907.4186………
★ Hektor et al, NPB (07)★ Han et al, PRD (07)★ Dorsner, Mocioiu, NPB (08)★ Goravoa, Schwetz, JHEP (08)★ Chao et al, PRD (08)★ Akeroyd et al, PRD (08)★ McDonald et al, JCAP (08)★ Xing, PRD (08)★ Ren, Xing, PLB (08)★ Gogoladze et al, arXiv:0802.3257
★ Chao et al, arXiv:0804.1265
★ Fileviez Perez et al, arXiv:0805.3536★ Hirsch et al, arXiv:0806.3361★ ……
★ Barr, Dorsner, PLB (06)★ Bajc, Senjanovic, JHEP (07)★ Fileviez Perez, PLB (07)★ Dorsner, Fileviez Perez, JHEP (07)★ Abada et al, JHEP (07)★ Abada et al, arXiv:0803.0481
★ Franceschini et al, arXiv:0805.1613
★ Gogoladze et al, arXiv:0805.2129★ Mohapatra et al, arXiv:0807.4524★ Tong Li, X.G. He, arXiv:0907.4193……..
Type-I
Type-II
Type-III
How to experimentally distinguish one type from another?
Remarks
Naturalness of the SM implies that there should exist a kind of new physics at the TeV scale. We wonder whether it is also responsible for the neutrino mass generation ---- TeV seesaws.
An uneasy feeling ---- the generation of tiny neutrino masses seems always to be decoupled from appreciable collider signals of TeV Majorana neutrinos. Unnatural? Unnatural? Unnatural?
Non-unitary CP Violation is a straightforward consequence of TeV seesaws---- it might manifest itself in both the oscillations of light neutrinos and the decays of heavy neutrinos.
It seems that people are struggling for a convincing reason to consider TeV seesaws ---- a balance between TH naturalness and EX testability as the guiding principle?