Looking for New Effects in Electroweak Precision Data

1. Looking for New Effects in Electroweak Precision Data J. de Blas In collaboration with F. del Águila & M. Pérez-Victoria XXXI Reunión Bienal de la Real Sociedad Española de Física Granada, 11 de Septiembre de 2007

2. 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.

3. 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.

4. Outline • Effective lagrangians: • Heavy vectors • Heavy fermions: Dirac, Majorana • Electroweak Precision Data: • Effects of new physics. • Example: Bounds on heavy fermions • Conclusions

5. 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)

6. Heavy Vectors • Construct the most general lagrangian for a heavy vector coupled to the SM particles. • Renormalizability+Lorentz&Gauge invariance leaves two possibilities:

7. Heavy Vectors: Operators

8. Heavy vector-like Dirac Fermions • JHEP 09 (2000) 011 • Vector-like Quarks: F.del Águila et al. • Easily generalized for vector-like Leptons:

9. Heavy Dirac Quarks: Operators

10. Heavy Dirac Leptons: Operators

11. 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

12. Heavy Majorana Leptons: Operators

13. Electroweak Precision Data • The program includes: • Z-pole measurements: • Low-Energy measurements: • LEP II measurements: • New physics effects linear in .

14. Effects of new physics 4-Fermion 

15. Example: Bounds on SM-like Heavy Fermions • Bounds at 1-σ:

16. Example: Bounds on SM-like Heavy Fermions • Example: Heavy B quark singlet with mass MB=500 GeV. (D type) • Mixing with the SM b quark?→ ,v=246GeV. • Read the bound on YDQ3and apply the formula. MixingbB < 0.03

17. 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. Conclusions

18. Looking for New Effects in Electroweak Precision Data Backup slides

19. 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. →

20. Example II: Bounds over Exotic Heavy Fermions • Bounds at 1-σ: