Dynamical Symmetry Breaking and Collider Physics (Review Talk) 201 - PowerPoint PPT Presentation

Dynamical Symmetry Breaking and Collider Physics (Review Talk) 201 ７ .1 ２ . ２３ at Osaka U. Mic ichio H Has ashimo imoto to (Chubu U)

I will talk 1. Concept of Dynamical Symmetry Breaking Scenarios 2. Introduction to DSB Approaches 3. Introduction to my recent work and recent MCHM analysis 4. Summary

Concept of DSB Scenarios

Spontaneous Symmetry Breaking (SSB) and DSB When a continuous group G spontaneously breaks down to H, there appear Nambu-Goldstone Bosons (NGB’s) associated with the broken currents J: order parameter  If it is a composite operator, we may call this SSB Dynamical Symmetry Breaking (This topics is appropriate to this room ^_^;;)

Nambu-Goldstone theorem tells us f: decay constant (scale of SSB) Good example is the low-energy QCD: NGB: order param: DSB!! The scale is f = 93 MeV or

For the EW gauge symmetry breaking, we know the scale is v=246 GeV, which corresponds to v v The SM answers that the order param. is the elementary scalar field H, so called the Higgs doublet: Is this really elementary?

However, the SM looks like the linear sigma model for QCD: This is OK as an effective theory of Hadron Physics, but, in reality, we know the fundamental theory is QCD. For the EWSB, it is still one of a central problem whether the Higgs field is elementary or composite. If composite, there must exist more fundamental theory beyond the SM!!

DSB approaches There are many DSB approaches: 1. Technicolor/Walking TC 2. Little Higgs models 3. Strongly Interacting Light Higgs (SILH) Related 4. Pseudo Nambu-Goldstone Boson (pNGB) etc.

1. Technicolor (TC) S. Weinberg , PRD13,974(1976);PRD19,1277(1979); L. Susskind, PRD20,2619(1979). We may just scale up the QCD scale to the EW scale, The experiments already have showed that Nature is Not so Simple.  Existence of h(125) Higgless/heavy Higgs  Precision Test, S < 0.1 Big S-parameter  No exotica Many Technihadrons, etc. ,

Constraint from Precision measurements QCD-like TC (1 Family type = 4 weak doublets) Peskin & Takeuchi; Holdom & Terning, Gorden & Landall For N TC = 4 S = 1.6 !!

CERN-EP-2017-250 arXiv: 1712.06518 No Z’ and W’ 19th December 2017

arXiv: 1710.07235

arXiv: 1707.03347 No Top partner

2. Little Higgs models f: typical scale of LH In the Little Higgs models, we introduce (also W’ is introduced for cancellation of W loop) Canceling mechanism of the top-loop quadratic divergence No W’ and/or T severely constrain the LH models…

3. SILH approach We assume only one light Higgs boson and some underlying dynamics yields higher dim. operator:

Relations between the model parameters and obs. The triple gauge couplings are also modified. I don’t show the global fit, because so complicated…

4. Higgs as pNGB A composite Higgs doublet field can be realized as a pNGB. Base on the DSB of SO(5)  SO(4), whose scale is f, Minimal Composite Higgs Models (MCHM’s), which contain only one Higgs doublet, have been proposed. These are concrete models of the SILH approach. However, there are many variations depending on the representation of the fermions. Deviations from the SM: Later, I will show you a recent work of MCHM.

Possibility of Enhanced top Yukaw a coupling The top Yukawa coupling is still unclear and thus there is a room of BSM. However, simple models cannot yield an enhanced top Yukawa coupling consistently with the experimental constraints. The Simplest Vector-like Quark model Yt Always suppressed! Other Simple Cases gg  h inevitably enhanced when Yt is bigger. Big Yt requires more extra fields!

Recently, I studied the vector-like quark model with exotic hypercharge assuming one composite Higgs doublet: MH, arXiv: 1704.02615

MH, arXiv: 1704.02615

In the lowest order of the 1/M expansion, In our case, we can show

If an enhanced Yt is confirmed, the mass of VLQ must be

Quite recently, numerical analyses of several MCHM’s are performed: arXiv: 1712.07494 Several patterns of fermion representations are studied:

The constraint is relaxed for up to 10% smaller

Summary  There is a longstanding problem concerning with the origin of the Higgs field. The Higgs compositeness is still important issue.  Based on DSB approach, many studies are uninterruptedly performed. In my impression (prejudice), the pNGB approach seems to get popular now.  I’d like to emphasize that the size of the top Yukawa coupling is still unclear and some of BSM, for example, the VLQ models and MCHM’s, can be testable via Yt.

Thank you!