About the Higgs boson - Istituto Nazionale di Fisica Nucleare · About the Higgs boson (On June...

About the Higgs boson (On June 2012)

Naples, June 14, 2012

Riccardo BarbieriSNS and INFN, Pisa

Majorana Lectures

giovedì 14 giugno 2012

Il modello di Higgs del Modello Standard

Soluzioni di minima energia:

φT = (φ1(x),φ2(x),φ3(x),φ4(x)) x = (x, t)

V (φ) = −µ2|φ|2 +λ

2(|φ|2)2

|φ|2 = φ21 + φ2

2 + φ23 + φ2

4

φ→ R(4)φ

| < φ > |2 = Σi(φ0i )

2 = v2 =µ2

λ< φi >= φ0

i

dell’elettromagnetismo e’ intatta ⇒ la carica elettrica e’ conservata1 - Esiste una simmetria residua intatta: la simmetria R(3)

2 - La degenerazione del “vuoto” e’ descritta da 3 angoli (6-3)θi

3 - Delle 4 particelle che corrispondono alle vibrazioni quantistiche

la quarta, il bosone di Higgs ha massa mh = λv del campo , tre (i ) “spariscono” dallo spettro, mentreθiφ

E =12Σi[(

dφi

dt)2 + (∇φi)2] + V (φ)

W±, Z


Interpretazione fisica: Una condensazione di BE di particellescalari, che riempie tutto lo spazio in una configurazione costante, lo stato di minima energia del sistema

Rottura spontanea della simmetria ElettroDebole

Conseguenze fisiche:

L (EWSB) = |Dµφ|2−V (φ)

⇒ L’elettromagnetismo e le interazioni deboli sono distinti

SU(2)× U(1)⇒ U(1)em

⇒ Viaggiando in questo mezzo, i “bosoni intermedi” e i fermioni acquistano massa

⇒ Nel Modello “minimo”, con 4 campi scalari per partire,esiste una particella scalare, il “bosone di Higgs”, conaccoppiamenti ai bosoni di gauge e ai fermionideterminati dalle masse rispettive


Particle Physics in one page

The gauge sector (1)

The flavor sector (2)

The EWSB sector (3)

The ν-mass sector (4)(if Majorana)

+|Dµh|2−V (h)

+NiMi jNj

L∼SM =−14

FaµνFaµν + iψ �Dψ

+ψiλi jψ jh+h.c.

Una pagina di qualche tempo fa(una pagina di qualche tempo fa!)


Higgs boson searches after 2011

(compiled by Gigi Rilandi)

Let’s be patient

Yes, but....

σobs − σbk

σSMAs case study, accept “125 GeV discovery”


Standard/Non-standard Higgs couplings (at 125 GeV)

Tree Level

Loop Level

⇒ Not an elementary particle (other parameters for LHC14 only)

⇒ mixing with other scalars

⇒ New missed final states

⇒ with new virtual particles: t,W ; t, T, ρ±,0µ , etc

E.g.: ghbb (↑↓ with SU(2) singlets, doublets or even triplets)

E.g.: h→ χDMχDM

aSM = cfSM ≈ 1L = a(

2m2W

vW+

µ W−µ +

m2Z

vZ2

µ)h + cf mf

vffh

Can have large effects, δa/a, δc/c = O(1), if new physics nearby

Leff = cγ α

πvF 2

µνh + cg αS

12πvG2

µνh cγSM = 2/9, cg

SM ≈ 1


Higgs widths⇒ Relative to the SM, the Higgs widths scales

get approximately modified as

≡ |a|2

where, taking into account the W loopcγ ≈ cγ − cV cγ,SM ≈ −0.8


Higgs rates⇒ For the total width scales asmh = 125 GeV

and, as long as dominates Higgs widthsh→ bb


Examples of preparatory gymnastics (at 125 GeV)

full 2011 data

Carmi, Falkowski, Kuflik, Volansky

end of 2012 projection

a

c

Azatov, Contino et al

loop effects tree level


Is it the SM up to very high energies?

ATLAS example forSUSY searches

Very surprising if this were the case! Nevertheless...M(TeV )

7 TeV

6≈ 1.2 TeV

(See tomorrow)


The SM unchanged up to very high energies

most accurate calculation to date

largest couplings Higgs self-coupling

Degrassi et al


A special meaning for λ≈0 at MPl?

Degrassi et alAssume SM unchanged up to MPl

Mt

Mh

Absolute stability at not quiteMPl(λ(MPl) � 0)achieved for current “best” values of andMt Mh

Speculations about possible meaning of all this not lackinggiovedì 14 giugno 2012

is possibly coupled

The Fine Tuning problem of the Fermi scale

SMδm2H

= + New

knows about ΛNPi.e. any higher physical scaleto which the Higgs boson

is possibly coupledyou name itMPl,MGUT . . .

in isolation grows like Λ2

where Λ ≡ the “cutoff”i.e. the highest scale at

which the theory is valid:a signal of the sensitivity of mH

δm2H≈ λ2

16π2Λ2

NP

The ElectroWeak scale determined by the Higgs massWhy ?G−1/2

F << ΛNP Why ?G−1/2F << G−1/2

N


We only know of approximate symmetries that can explain this

⇒ What are and where are they?

−−−−

}SM

h

In all explicit examples, without unwarranted cancellations,

There are infinitely many theories at short distances, that give the same physics of the

Standard Model, as long as their “low energy” spectrum coincides with the one of the SM

including the Higgs boson

Another look at the FT problem

new phenomena required at a scale not far fromΛNP mh


The (many) reactions to the FT problem

0. Ignore it and view the SM in isolation(if no other short distance scale, what about gravity?)

1. Cure it by symmetries: SUSY, Higgs boson as PGB

2. A new strong interaction nearby

3. A new strong interaction not so nearby: quasi-CFT

5. Warp space-time: RS

4. Saturate the UV nearby: extra-dimensions around the corner

Anything else?

6. Accept it: anthropic selection, the multiverse, 10120 the vacua of string theory


About the Higgs boson - Istituto Nazionale di Fisica Nucleare · About the Higgs boson (On June...

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