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

Dynamical Symmetry Breaking and Collider Physics

201７.1２.２３ at Osaka U.

Mic ichio H Has ashimo imoto to

(Chubu U) (Review 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

I will talk

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:

• rder parameter

 If it is a composite operator, we may call this SSB

Dynamical Symmetry Breaking

(This topics is appropriate to this room ^_^;;)

f: decay constant (scale of SSB)

Good example is the low-energy QCD: NGB:

DSB!!

• rder param:

f = 93 MeV The scale is

• r

Nambu-Goldstone theorem tells us

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

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)
• 4. Pseudo Nambu-Goldstone Boson (pNGB)

etc. Related

• 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. ,

(1 Family type = 4 weak doublets)

QCD-like TC

Constraint from Precision measurements

Peskin & Takeuchi; Holdom & Terning, Gorden & Landall

For N TC= 4 S = 1.6 !!

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

arXiv: 1710.07235

No Top partner arXiv: 1707.03347

In the Little Higgs models, we introduce f: typical scale of LH Canceling mechanism of the top-loop quadratic divergence

• 2. Little Higgs models

(also W’ is introduced for cancellation of W loop) 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…

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

• nly 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.

• 4. Higgs as pNGB

Later, I will show you a recent work of MCHM. Deviations from the SM:

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.  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.  Based on DSB approach, many studies are uninterruptedly

• performed. In my impression (prejudice), the pNGB approach

seems to get popular now.

Thank you!