何红建何红建清华大学清华大学

LHC: Seeking the Origin of LHC: Seeking the Origin of Symmetry Breaking and MassSymmetry Breaking and Mass

LHC: LHC: 探索对称性破缺与质量起源探索对称性破缺与质量起源

Nanchang, April 17-19, 2010.

LHC: this not the end of the beginning --

L H C

It is beginning of the new start !

What discovery expected at LHC ?What discovery expected at LHC ?

What should What should WeWe dodo for it ? for it ?

LHC Runs: 7TeV…10TeV…14TeV……

All Matter(Spin-1/2)+Forces(Spin-1) are discovered in SM!The only Missing Particle: Higgs Boson H0 (Spin-0).Higgs Boson gives Masses to All Particles except γ, gluons.

All SM Particles: All SM Particles: Area of circle Area of circle ∝∝ Particle-Mass Particle-Mass Only Top, W/Z and Only Top, W/Z and HiggsHiggs stand out ! stand out !

All spin-1/2 matter particles have Masses ∝∝ Arbitrary Yukawa Couplings:

??

( Mw = g v/2 )

SM: (Un)Naturalness of Matter MassesSM: (Un)Naturalness of Matter Masses

•Only Top & Neutrino masses are Natural

(adding Right-handed Neutrinos):

•But, Why All Other Yukawa’s so tiny ?? e.g.,

It is often said that It is often said that LHCLHC is just to find is just to find a light fundamental Higgs Bosona light fundamental Higgs Boson..

BUT, this is a quite misleading statement BUT, this is a quite misleading statement －－

1. 1. Higgs Boson may be Higgs Boson may be heavyheavy. .

2. 2. Higgs may be Higgs may be more than one more than one andand charged charged..

3. 3. Higgs Boson may be Higgs Boson may be compositecomposite. .

4. 4. Higgs Boson may Higgs Boson may Not exit Not exit at all.at all.

5. 5. Smoking-Gun Signals Smoking-Gun Signals other than Higgsother than Higgs..

10

The two best measurements of

sin2W do not agree :

NO compelling evidence for

Light Higgs Boson even in SM !

★ Possibility of Heavy Higgs or No Higgs is fully open !

See: Gian Giudice (CERN), talk at Tsinghua on 3-28-2010

Heavy Higgs vs Precision Data:Heavy Higgs vs Precision Data: No Problem !No Problem !

HJH etal, TopSeesaw Composite Higgs mH ≈ 400-500GeV

Top Seesaw Model

““Natural” SUSY requires heavier Higgs too !Natural” SUSY requires heavier Higgs too !

’

’

MSSM is alreadyFine-tuned !

Extended SUSYs give:

Barbieri et al, 1004.2256

Fine-Tuning Problem ? Fine-Tuning Problem ?

● Radiative Corrections to Higgs Mass:

● Degree of Fine-Tuning (DFT):

Fine-Tuning Fine-Tuning is ais a Technical ProblemTechnical Problem ! !

Not strong enough for LHC (ILC) !Not strong enough for LHC (ILC) !

3TeV

6.5TeV

0.05

10TeV

0.01

7TeV

14.5TeV

Mysteries of Mass Origin: Mysteries of Mass Origin: What can LHC probe ? What can LHC probe ?

GeV

ν10-2 eV

Origin of Electroweak Symmetry Breaking: -- Why are (W, Z) Massive but photon Massless ?

Does t-Quark conspire Electroweak Symmetry Breaking: -- Why is t-Quark Mass so Close to W/Z Masses ? Why is Neutrino Mass so tiny ? → Seesaw Mechanism !

Origin of Electroweak Symmetry Breaking:Origin of Electroweak Symmetry Breaking: Why Why Higgs Boson (light or heavy)Higgs Boson (light or heavy) at all ?!? at all ?!?

Real Physics ProblemReal Physics Problem withwith Electroweak Symmetry BreakingElectroweak Symmetry Breaking isis

Unitarity ViolationUnitarity Violation

inin High Energy ScatteringHigh Energy Scattering !!!!!!!!!!

Unitarity of WUnitarity of WLLWWLL → W → WLLWWLL: :

Electroweak Symmetry Breaking ScaleElectroweak Symmetry Breaking Scale

Much Stronger & More Robust than Fine-tuning bound!

No Way to Escape this Physics Bound !!!

0.7

A A New Way New Way to to RestoreRestore UnitarityUnitarity::

Higgsless TheoryHiggsless Theory !!!!!!

Crucial Observation:

New Spin-1 Gauge Bosons can Replace Spin-0 Higgs to Restore Unitarity !!!

Chivukula,Dicus,He, 2001: New Gauge Bosons from 5d-KKChivukula,He, 2002: New Gauge Bosons from 4d-Deconstructionand 19 series papers in 2003-2009

LHC Signals for Higgsless W1 Boson: pp→W1 Z→WZZ→jj+4Leptons pp→jjWZ (including WZ─W1*→WZ→3l+nu)

HJH, YPK,YHQ, BZ & MSU arXiv:0708.2588

LHC Sensitivity for WLHC Sensitivity for W11

in WZZ & jjWZ Channels:in WZZ & jjWZ Channels:

HJH, YPK, YHQ, BZ & MSU

Does top-Quark Conspire Electroweak Symmetry Breaking ??

Why is t-Quark Mass

so Close to W/Z Masses ?

50 Years Ago

Ni60

Lee and Yang, 1956

Parity

We reveal the Intrinsic Connection between Spontaneous Parity Violation (SPV) and Electroweak Symmetry Breaking (EWSB)

SPV Scale is tied to TeV Scale

SPV Induces EWSB (W,Z Masses) as Uniquely fixed by Top-quark Mass = 174 GeV

Predictions:Predictions: A Sample Higgs Spectrum A Sample Higgs Spectrum

E.g.

：

LHC Discovery: LHC Discovery: Luminosity vs Higgs MassLuminosity vs Higgs Mass

Signals at the LHCSignals at the LHC:: andand

pp (gb) → t H+ → t t b.pp → WR → bbW

Scales of Fermion Mass GenerationScales of Fermion Mass Generation

New Physics that LHC canNot do ?New Physics that LHC canNot do ?

Exciting Future: After LHC !!!

New Physics that LHC New Physics that LHC cannotcannot do: do: Neutrino Neutrino Mixing,Mixing, CP-Violation, Matter-Antimatter CP-Violation, Matter-Antimatter Asymmetry…Asymmetry…

Daya Bay’s Daya Bay’s Physics PotentialPhysics Potential on on θ13 isis Non-trivial Non-trivial to justify:to justify:

Our Theory Prediction Our Theory Prediction givesgivesstrongest support strongest support forfor Daya BayDaya Bay !!! !!!

Ge, He, Yin, JCAP(2010), 1001.0940Ge, He, Yin, JCAP(2010), 1001.0940

KeV TeV 1019 GeV

Nature may be more complicated and more interesting than we naively thouhght !!

Many New Scales ?Many New Forces ?Is Gravity Emergent?Is M_Planck fundamental?

2010 ─ 2030

Keep Keep Your MindYour Mind Fully Open Fully Open !!!!!!

Thank You !

Backup SlidesBackup Slides

4 Fundamental Forces 4 Fundamental Forces evolve back withevolve back withTime/Temperature(Energy):UnificationTime/Temperature(Energy):Unification??

Hierarchy/Fine-Tuning Problem ?Hierarchy/Fine-Tuning Problem ?

→→ Not strong enough !Not strong enough !

Unification ?Unification ?

→→ Many possible realizations !Many possible realizations !

Light Higgs ?Light Higgs ?

→→ Not enforced by data ! Not enforced by data ! Then, Then,

WHAT best justifies TeV Scale?WHAT best justifies TeV Scale? … …

New Physics at New Physics at TeVTeV Scale ?Scale ?

Fine-Tuning Problem ?Fine-Tuning Problem ?

SM Higgs Mass 1-Loop Quadratical Divergence:

Quadratical Divergence vanishes if

→No Fine-Tuning for MH around 300GeV !

SM Higgs Potential runs intomore seriousVacuum Energy Problemeven at TREE-Level: (eg, S.Weinberg,

1989)

<ρ> = Vmin – λv4/4

= Vmin － O(100GeV)4 == (2∙10-3eV)4

→ 55 Orders of Magnitude Fine-tuning !

Soft Breaking SUSY faces the same problem!

So, WHY do we care 1% Tuning at 1-Loop?!

Neutrino Mass !

RSC, DAD, HJH

VLHC: http://vlhc.org (50-200TeV)

Lessons: (1) A Good Theory ! (2) Vigorous Experiments !! (3) Courage !!!

Origin of Masses, TeV Scale & LHCOrigin of Masses, TeV Scale & LHC

Why TeV Scale:Why TeV Scale: ( ( Strongest BoundStrongest Bound is from is from Unitarity ! Unitarity ! ))

Unitarity of WUnitarity of WLLWWLL → W → WLLWWLL ( < 1.2TeV ) ( < 1.2TeV )

JustifyJustify 1TeV Scale 1TeV Scale forfor LHC + ILC !! LHC + ILC !!

What New PhysicsWhat New Physics: : Higss vs HiggsLess Higss vs HiggsLess + SPV

Light Higgs or Heavy Higgs or HiggsLess;Light Higgs or Heavy Higgs or HiggsLess; 4d 4d DeconstructionDeconstruction vs Extra-dim vs Extra-dim →→Unitarity Unitarity !! New Spin-1 Gauge Bosons Restore Unitarity !!New Spin-1 Gauge Bosons Restore Unitarity !!

How to Observe How to Observe New Gauge BosonsNew Gauge Bosons:: SignalsSignals vs Bkgndsvs Bkgnds

LHC is very Promising to find LHC is very Promising to find WW11 by 2011-12 !!!by 2011-12 !!! 　　　　　　　　　　　　　　　　　　

Conclusions: