Searches for New Physics Beyond the Standard Model (BSM) · 2008. 7. 17. · Searches for New Physics Beyond the Standard Model (BSM) •Problems of the Standard Model •Supersymmetry

Searches for New Physics

Beyond the Standard Model (BSM)

• Problems of the Standard Model• Supersymmetry (SUSY)• Extra Dimensions• Further Alternatives

Standard Model Fermions

• Why 3 generations of quarks and leptons?• Why so strange hypercharges?

[Y = 2(Q − T3)]• Why flavour mixing for quarks (CKM)

and neutrinos (MNS)?• What to do with right-handed neutrinos?

(

ν′e

e

)− 12

L

(

ν′µ

µ

)− 12

L

(

ν′τ

τ

)− 12

L

e−1R µ−1R τ

−1R

(

ud′

) 16

L,r

(

cs′

) 16

L,r

(

tb′

) 16

L,r

u23R,r

d− 13R,r

c23R,r

s− 13R,r

t23R,r

b− 13R,r

(

ud′

) 16

L,g

(

cs′

) 16

L,g

(

tb′

) 16

L,g

u23R,g

d− 13R,g

c23R,g

d− 13R,g

t23R,g

d− 13R,g

(

ud′

) 16

L,b

(

cs′

) 16

L,b

(

tb′

) 16

L,b

u23R,b

d− 13R,b

c23R,b

d− 13R,b

t23R,b

d− 13R,b

Standard Model Fermions

• Why 3 generations of quarks and leptons?

• Why so strange hypercharges?[Y = 2(Q − T3)]

• Why flavour mixing for quarks (CKM)and neutrinos (MNS)?

• What to do with right-handed neutrinos?• What is the origin of fermion masses?

Why so huge fermion mass range?

Standard Model Bosons

• Does SM Higgs exist?• How can all gauge interactions be unified?

Standard Model Bosons

• Does SM Higgs exist?• How can all gauge interactions be unified?

• Why such an hierarchy of gauge fields?

EnergyTemperature

10 GeV

10 K 100 GeV

10 eV

10 K

10 K 10 GeV

Quantum Gravity Era

Present time

Neutrino transparency

EW scale

GUT scale

Quark confinement

Planck scale

Inflation

Tim

e (s

eco

nd

s)

Ele

ctr

om

ag

ne

tic

Gra

vity

Str

on

g

We

ak

32

27

15

14

19

−4

1010

1010

1010

101

1020

−40

−30

−20

−50

−10

2.7 K

Big Bang

Light transparency

Ele

ctr

ow

ea

k

Cosmological Problems

• What is dark matter?

• What is dark energy?

Attempts to Solve the Problems of the Standard Model

Many attemps going in different directions

• Extended gauge symmetries• New mechanisms of symmetry breaking

• More fundamental fields• Extra dimensions

• . . .

Radiative Corrections to Higgs Mass

• Higgs Self-energy corrections in perturbation theory: M2H = M2H,bare + ∆M

2H

Have to integrate over all particle momenta in loops⇒ Loop corrections to Higgs mass rise with UV cut-off Λ2

t

H Ht−

H HW,Z,γ

H HH

∆M2H,1 = −3

8π2g2fΛ

2

∆M2H,2 =1

16π2g2Λ2

∆M2H,3 =1

16π2λ2Λ2 V(φ) = −µ2|φ†φ| + λ|φ†φ|2

• Fine tuning to precision ∼ M2H/Λ2 is needed

For Λ = MPlanck, MH ∼ 100 GeV: (Λ/MH)2 ∼ 1034 – gauge field scale hierarchy

M2H = M2H,bare +

116π2

(−6g2t + g2+ λ2) · 1034M2H

︸ ︷︷ ︸

− . . .︸ ︷︷ ︸

≃ (130 GeV)2

SM New Physics

“Fine Tuning” Argument

• Current exp. limits on Higgs mass:114.4 < MH < 144 GeV

direct searches EW fits

• If SM is valid up to MPlanck, theor. limits:135< MH < 175 GeV

EW vacuum Triviality

EW vacuum stability: Higgs mass cannot be toolight or the potential will not have a Mexican hat

shape and will turn negative at large values

V(φ) = −µ2|φ†φ| + λ|φ†φ|2

Triviality: if the Higgs mass is too large, the Higgs

self-coupling drives the mass to infinity above cer-tain scale

Triviality and Vacuum Instability

with MH ∝ "(#2) #2

"(q)

q!q0

MH q

Upper bound: q! < !

Lower bound: q0 < ![Triviality, Landau Pole]

[Vacuum Instability]

Must be larger than scale ! at which SM breaks down}

From RGEand MH ∝ "(#2)

Higgsself coupling

depends on MH

scale[#: vacuum expectation value]

[Running self coupling]

Even if new physics appears atΛ = 10 TeV, fine tuning is significant

tree

top

gauge

Higgsm2

H

However: SM can be valid up to the Plank scale!Fine tuning is just a “stomach problem”.

Anthropic principle: properties of the universe are so specialbecause we happen to exist and be able to ask these very questions

Electron in Classical Electrodynamics

• E.m. self-energy

∆ECoulomb=1

4πǫ0

e2

rere − “size”

must be a part of the electron mass:

(mec2)observed= (mec

2)bare+ ∆ECoulomb

• From experiments: re < 10−17 cm =⇒ ∆ECoulomb& 10 GeV

0.511= −9999.489+ 10000.000 MeV

◮◮ Classical e.m. is not valid for scales where ∆ECoulomb& mec2:

d <e2

4πǫ0mec2= 2.8 · 10−13 cm

Quantum Effect – e+e− Pair Production

• Self-energy e− e−e−γ ←

←

the same diagram in QED

• Positron exists. e+e− pair production

+ee−

e−γ

Vacuum fluctuations at ∆t ∼~

∆E∼

~

2mec2(Heisenberg’s uncertainty)

modify physics at d ∼ c∆t ∼ 200· 10−13 cm

∆Epair = −1

4πǫ0

e2

re+ . . . =⇒ ∆E = ∆ECoulomb+ ∆Epair =

3α4π

mec2log

~

mecre

• Mass correction

(mec2)observed= (mec

2)bare

[

1+3α4π

log~

mecre

]

Even for re ∼ 1/MPlank ∼ 10−33 cm mass increases by 9%

◮◮ Doubling d.o.f. + symmetry =⇒ divergency cancellation

Higgs Self-Energy

t

H Ht−

∆M2H,top = −3

8π2g2tΛ

2+ . . .

Bosons and fermions produce different signs in loops =⇒

Introduce “superpartner” for top = scalar top = “stop” = t̃

H Ht~−

t~

∆M2H,stop= +3

8π2g2tΛ

2+ . . .

Total correction

∆M2H,top + ∆M2H,stop= −

38π2

g2t (m2t̃ − m

2t )log

Λ2

m2t̃

◮◮ “Naturalness” argument: mt̃ should be not much larger than mt mt̃ ∼ TeV???

Supersymmetry (SUSY)

SUSY Particles

sleptons, squarks =sfermions = bosons

. . . -inos = fermionshiggsinos, gauginos

(photino, wino, . . . )= neutralinos,

charginos

Searches for New PhysicsStandard Model FermionsStandard Model FermionsStandard Model BosonsStandard Model BosonsCosmological ProblemsAttempts to Solve the Problems of the Standard ModelRadiative Corrections to Higgs Mass``Fine Tuning'' ArgumentTriviality and Vacuum InstabilityElectron in Classical ElectrodynamicsQuantum Effect -- e+e- Pair ProductionHiggs Self-EnergySupersymmetry (SUSY)SUSY ParticlesSUSY ModelsmSUGRATypical mSUGRA SpectrumR-ParityGrand Unification Theory (GUT)SUSY Production at LHCMissing ETSimulation: SUSY Event in ATLASSUSY Signatures at the LHCDiscovery Potential -- Example mSUGRADiscovery Potential -- Adding LeptonsSUSY Particle Mass ReconstructionSUSY Particle Mass ReconstructionSUSY Particle Mass Reconstruction(Quasi-)Stable Coloured Hadrons: R-Hadrons(Quasi-)Stable Coloured Hadrons: R-HadronsForest SketchArguments for SUSYChallenges for Low Energy SUSYScenarios for SUSY at the LHCExtradim SketchCompactified Extra DimensionsLarge Extra DimensionsNew Fundamental Planck ScalePossible Sizes of Extra DimensionsMotivation by the String TheoryKaluza--Klein Gravitons in ADDMonojetsMonojets -- Standard Model BackgroundsMonojets -- Standard Model BackgroundsMonojets @ Tevatron and LHCVirtual Graviton Exchange in ADDVirtual Graviton Exchange in ADD @ LHCLarge Extra Dimensions at LEPBlack HolesBlack Hole Formation @ Hadron CollidersBlack Hole Production @ LHCBlack Hole FactoryHawking RadiationBlack Hole Event Simulation @ ATLASBlack Hole Event SelectionBlack Hole Mass ReconstructionBlack Hole Discovery PotentialDemocratic Particle DistributionBlack Holes vs. SUSYExtraction of Model ParametersFurther AlternativesAdditional InformationWino Dark MatterProton Decay -- Higher OrdersAstrophysical Limits in ADD ModelsAstrophysical Limits in ADD ModelsWarped Extra DimensionsWarped Extra DimensionsKaluza--Klein Gravitons in RSRemark on RS Model ParametersRS Gravitons: Expectations for Tevatron and LHCKK Gravitons in RS: Reconstruction @ TevatronKK Gravitons in RS @ TevatronKK Gravitons in RS: Reach @ LHCKK Gravitons in RS: Reach @ LHCBlack Hole DecayCHARYBDIS MC Event GeneratorTriggering Black HolesHiggs in Black Hole DecaysBlack Holes in Cosmic RaysCosmic Ray Bounds in ADDFuture Bounds in ADDFuture Bounds in RSBlack Holes -- The End of The WorldBlack Holes as Energy Source