1. Implications of D-Mixing for New Physics
Meson mixing has historical significance
Charm quark (and mass) inferred from Kaon mixing
Top mass predicted from Bd mixing
Strong constraints on New Physics (SUSY, LRM, …) that has affected collider searches
Each meson is different (x = m/):
And thus each measurement is important
J. Hewett
SLAC DOE 07

2. The observation of D-mixing is exciting!
1st Observation of Flavor Changing Neutral Currents in the up-quark sector!
1st Glimpse of flavor physics in the up-quark sector
1st Constraints on flavor violation in up-quark sector
Sparked much interest in the community
Catalogue of New Physics Contributions
Golowich, JLH, Pakvasa, Petrov arXiv:

3. Compilation of Predictions for D-Mixing
D-Mixing provides important constraints for model building
Flavor physics provides strong constraints on models
Many models poorly tested in +2/3 quark sector
Many models shove flavor violation into up-quark sector in order to satisfy K mixing  large effects in D mixing
H. Nelson, Lepton-Photon 1999

4. D-Mixing in the Standard Model: Short Distance
Box diagram is tiny
GIM is efficient!
b-quark contribution is
CKM suppressed
s-quark contribution is
suppressed by SU(3) breaking
xbox ~ 10-5 , ybox ~ 10-7
Higher orders in the OPE may give larger results
Georgi; Bigi

5. D Mixing in the Standard Model: Long Distance
Charm is neither light or heavy, so well-developed theoretical techniques don’t apply.
Sum over all possible, multi-particle, intermediate hadronic states
yD is less model-dependent; calculate yD and use dispersion relations to obtain xD
Results in: yD ~ xD ~ 1%
Possible that experimental result is explained by
SM effects

6. Constraining New Physics
Assume no interference between SM & NP
NP alone does not exceed measured value of xD
Use 1 value:
xD < 11.7 x 10-3
Allow for 2 and for future exp’t improvements:
xD < 3, 5, 8, 15 x 10-3

7. New Physics in D-mixing: Formalism
Compute LO QCD corrections
Use the OPE to define an
effective Hamiltonian
Complete set of
independent operators:
Evolve matching conditions to the charm scale
Evaluate hadronic matrix
elements

8. Heavy Q=-1/3 Quark Present in, e.g., E6 GUTS 4th generation
Constraints in mass-mixing plane
Removes strong GIM suppression Of SM 3
Unitarity of CKM matrix gives |Vub’Vcb’|< 0.02 5 8
D-mixing improves this constraint by one order of magnitude!
11.7
15 x 10-3

9. Heavy Q=2/3 Singlet Quarks
Induces FCNC couplings of the Z
Violation of Glashow-Weinberg-Paschos
conditions
Tree-level contribution to D mixing
Constraints on mixing improved over CKM unitarity bounds by TWO orders of magnitude!

10. Little Higgs Models These models contain heavy vector-like T-quark
Arkani-Hamed, Cohen, Katz, Nelson
These models contain heavy vector-like T-quark
Sample particle spectrum
Strongest bounds on this sector!
Will affect T-quark decays and collider signatures

11. Supersymmetry (MSSM) Large contribution from squark-gluino exchange
in box diagram
helicity index
Super-CKM basis:
squark and quark fields rotated by
same matrices to get mass eigenstates
Squark mass matrices non-diagonal
Squark propagators expanded to
include non-diagonal mass insertions
mass insertion
Strong constraints from K mixing has historically lead to assumption of degenerate squarks in collider production

12. Constraints on up/charm-squark mass difference
LL,RR
LL=RR
LR,RL
LR=RL

13. Compare to constraints on down/strange-squark mass difference from Kaon mixing (green curve)
Bagger, Matchev, Zhang  
LL,RR
LL=RR  
LR,RL
LR=RL

14. Supersymmetry (MSSM)
1st two generations of squark masses now constrained to be degenerate to same level of precision in both Q=+2/3 and -1/3 sectors!
Historically used as a theoretical assumption, now determined experimentally
Degenerate squarks lead to large squark production cross Tevatron/LHC

15. Supersymmetry with Alignment
Nir, Seiberg
Quark & squark mass matrices are approximately aligned and diagonalized such that gluino interactions are flavor diagonal
Squark mass differences are not constrained
Bounds from Kaon mixing prevent generation of Cabibbo angle in the down-sector
Sets mq ≥ 2 TeV
LHC! ~

16. Extra Dimensions Split fermion scenario:
Fermions localized at
specific locations in
extra flat dimension
Suppresses proton
decay
Generates fermion
hierarchy
Arkani-Hamed, Schmaltz
Generates tree-level FCNC for gauge boson Kaluza Klein states via overlap of wavefunctions
Gen

17. Constraints on Split Fermion Scenario
Compactification scale
Distance between u- & c-quarks in 5th dimension
u- & c-quarks are localized very close or extra dimensions VLHC

18. Warped Extra Dimensions
Based on Randall-Sundrum models
Bulk = Slice of AdS5
SM in the bulk
Induces tree-level FCNC
Result dependent on
fermion localization
1st gauge KK state
M > 2-3 TeV
Restricts LHC search range

19. Summary of Model Constraints

20. Conclusions
Observation of D-mixing yields stringent bounds on New Physics
These bounds surpass or compete with other constraints
These bounds affect collider(LHC) physics
Look forward to future experimental refinements!
Observation of CP Violation would be clear signal of New Physics…