1. Electroweak Vacuum Stability & Diphoton Excess @ 750 GeV
Jue Zhang ( 张 珏）
IHEP, CAS
January 7, 2016
JZ and Shun Zhou, arXiv:

2. Outline Paper Excess after Diphton Excess A Simple Model
Connection with Electroweak Vacuum Stability
Summary

5. Paper Excess after Diphton Excess

6. hep-ph arXiv papers (2010 - 2015)
Excess Discovered!

7. Trend of Papers on Diphoton Excess

8. A Simple Model

9. SM + a singlet scalar + a VL fermion pair
Note: Loop particles can NOT be SM particles only! S
dijet search
Additional decay mode of S: S
Z/γ
ZZ / Zγ search
Z/γ

10. Additional Coupling with SM Higgs
"Everything not forbidden is compulsory."
--T.H.White (borrowed by Gell-Mann)
1. S can mix with SM Higgs!
2. S can decay to SM Higgs!

11. Diphoton Excess and Other Constraints
R. Franceschini et al., arXiv:
Note: Width info is NOT used!
Other Constraints:

12. Allowed Parameter Space from LHC
A. Falkowski, et al., arXiv:
QF = 3
QF = 5

13. Electroweak Vacuum Stability

14. SM Electroweak Vacuum Stability
Xing, Zhang and Zhou,

15. Can S Help Stablize EW Vacuum?
Vacuum Stable Condition:
Subject to constraints:
RGE Running:
2-loop SM RGEs
1-loop SM RGEs
+ New RGEs
Check Stability & Perturbativity mZ mS

16. Allowed Parameter Space from Stability
Planck Scale:
GUT Scale:
NO OVERLAP!
Seesaw Scale:
Same as SM:

17. A Closer Look depending on mixing angle θ ! too large yS
λS runs towards negative quickly!

18. More Vector-like Fermions?
F1, F2, F3, ...

19. Deeper Thoughts & More Data are Needed!
Summary
The community is on fire due to diphoton excess!
SM + a singlet scalar + a pair of vector-like fermion
Diphoton excess & Electroweak Vacuum Stability
(in our set-up)
Deeper Thoughts & More Data are Needed!
Stay Tuned!