TLEP Precision physics at the Electroweak scale TeraZ , OkuW , MegaHiggs and Megatops
Looking for New Effects in Electroweak Precision Data
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Looking for New Effects in Electroweak Precision Data
J. de BlasIn collaboration with F. del Águila & M. Pérez-Victoria
XXXI Reunión Bienal de la Real Sociedad Española de Física
Granada, 11 de Septiembre de 2007
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Introduction
SM is a great success
Good agreement with experimental data.
But:
Theoretical Problems: Hierarchy problem.
SM must be considered as an effective theory with a cutoff Λ<ΛPlanck.
Naturalness → Λ~1 TeV
Discrepancies (≥ 2σ) with some measuments: AbFB, σHad…:
Maybe statistical fluctuations.
Otherwise, one could use these small discrepancies to obtain some information about the theory at energies E> Λ.
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Introduction
We would like to parametrize the new physics in a model independent way
→→ Effective Lagrangians
Precise measurements are necessary to constrain or exclude indirect new physics effects:
→→ Precision Electroweak Data
We have developed a code that allows us to:
Select different classes of new physics.
Incorporate different sets of Data.
Study specific models.
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Outline
Effective lagrangians:
Heavy vectors
Heavy fermions: Dirac, Majorana
Electroweak Precision Data:
Effects of new physics.
Example: Bounds on heavy fermions
Conclusions
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Effective Lagrangians
Beyond usual oblique analysis.
Decoupling scenario, weak coupling.
Heavy (~ Λ) states are integrated out
Ln involves only SM fields. LEff valid for E<< Λ.
We consider only operators up to dimension 6, classified in the basis of 1 (dim. 5) +81 (dim. 6) operators of W. Buchmüller & D. Wyler .
Integration at tree-level ( only gives a subset of the above)→ Big Effects
After EWSB L6 corrects the SM:
Nuc. Phys B268 (1986) 621-653)
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Heavy Vectors
Construct the most general lagrangian for a heavy vector coupled to the SM particles.
Renormalizability+Lorentz&Gauge invariance leaves two possibilities:
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Heavy Vectors: Operators
Vector Vector
EffectEffect
4-Fermion4-Fermion
Vector-Fermion Vector-Fermion vertexvertex
, ,Fermion Fermion massesmasses
,Vector Boson Vector Boson
massesmasses
,Higgs PotentialHiggs Potential
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Heavy vector-like Dirac Fermions
Vector-like Quarks: F.del Águila et al.
Easily generalized for vector-like Leptons:
JHEP 09 (2000) 011
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Heavy Dirac Quarks: Operators
EffectEffect
FermionFermion
Vector-Fermion vertexVector-Fermion vertex Fermion MassesFermion Masses
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EffectEffect
FermionFermion
Vector-Fermion vertexVector-Fermion vertex Fermion MassesFermion Masses
-
Heavy Dirac Leptons: Operators
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Heavy Majorana Fermions
Renormalizability+Invariance & Majorana condition leaves only two types:
Integration similar to Dirac’s case but gives also the only dimension five operator of the basis:
•Majorana mass for neutrinos
•Lepton number violation ∆L=2→→
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EffectEffect
FermionFermion
Vector-Fermion vertexVector-Fermion vertex Fermion MassesFermion Masses
Heavy Majorana Leptons: Operators
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Electroweak Precision Data
The program includes:
Z-pole measurements:
Low-Energy measurements:
LEP II measurements:
New physics effects linear in . 2
2v
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MW Z-pole Low-Energy LEP IISM Inputs:
GF, MZ
W ± & Z0
mass W ±
FF
&
Z0 FF
Vertex
Effects of new physics
4-F
erm
ion
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Example: Bounds on SM-like Heavy Fermions
Bounds at 1-σ:
Bound [x (M/1TeV)]Bound [x (M/1TeV)]
<(0.31 0.32 ----- )
<(0.40 0.30 0.16)
<(0.42 0.46 ----- )
<(0.17 0.70 0.30)
<(0.05 0.15 0.10)
<(0.06 0.25 0.11)
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Mixing with the SM b quark?→ → , v=246 GeV.
Example: Bounds on SM-like Heavy Fermions
B
DQM
vY
23
Example: Heavy B quark singlet with mass MB=500 GeV. (D type)
Read the bound on YDQ3 and apply the formula.
MixingbB < 0.03
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Conclusions
The Effective Lagrangian parametrizes heavy physics at low energies in a model independent way.
Constraints on masses and couplings of generic new particles.
Specific Models can be easily analyzed.
Electroweak Precision Tests are complementary to LHC searches.
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Looking for New Effects in Electroweak Precision Data
Backup slides
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Effects of new physics II
Best measurements: Z-pole and Low-Energy experiments.
Z-pole is the main constraint over operators that modify vector-fermion vertex.
Low-Energy and LEP II: 4-fermion operators becomes relevant.
• Heavy fermion corrections are mainly constrained by Z-pole.
• Heavy vector corrections constrained by all data.
→→
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Example II: Bounds over Exotic Heavy Fermions
Bounds at 1-σ:Bound [x (M/1TeV)]Bound [x (M/1TeV)]
<(0.15 0.24 ---- )
<(0.39 0.33 0.51)
<(0.14 0.24 0.25)
<(0.37 0.37 0.32)
<(0.23 0.22 0.66)
<(0.19 0.09 0.29)
<(0.27 0.17 0.40)
<(0.09 0.21 0.14)