Transcript PowerPoint

LHC:
Higgs, less Higgs, or more Higgs?
John Ellis, King’s College London (& CERN)
Has the Higgs been Excluded?
Interesting hints around Mh = 125 GeV ?
ATLAS excludes
< 122.5, > 129, < 539 GeV
CMS excludes
> 127.5, < 600 GeV
Has the Higgs been Discovered?
Interesting hints around Mh = 125 GeV ?
CMS prefers
< 125 GeV
ATLAS prefers
> 125 GeV
Unofficial Combination of Higgs
Search Data from March 7th
Is this the
Higgs Boson?
No Higgs here!
No Higgs here!
The Particle Higgsaw Puzzle
Is LHC finding the missing piece?
Is it the right shape?
Is it the right size?
Do we already know the ‘Higgs’
has Spin Zero ?
• Decays into γγ, so cannot have spin 1
• 0 or 2?
• If it decays into ττ or b-bar: spin 0 or 1 or
orbital angular momentum
• Can diagnose spin via
– angular distribution of γγ
– angular correlations of leptons in WW, ZZ decays
• Does selection of WW events mean spin 2?
Does the ‘Higgs’ have Spin Zero ?
• Polar angle distribution: • Azimuthal angle
X2 γγ
distribution: X0 WW
(flat for X0)
JE, Hwang: arXiv:1202.6660
(flat for X2)
Does the ‘Higgs’ have Spin Zero ?
• Polar angle
distribution for
X2 W+W• Polar angle
distribution for
X0 W+W(for φ = π)
JE, Hwang: arXiv:1202.6660
Measuring Higgs Couplings @ LHC
Current LHC hint @ Mh = 125 GeV
Flavour-Changing Couplings?
• Upper limits from FCNC, EDMs, …
• Quark FCNC bounds exclude observability of
quark-flavour-violating h decays
• Lepton-flavour-violating h decays could be large:
BR(τμ) or BR(τe) could be O(10)%
B
Blankenburg, JE, Isidori: arXiv:1202.5704
BR(μe) must be < 2 ✕ 10-5
STANDARD MODE
John Ellis, King’s College London (& CERN)
There
be New
Physics
viXramust
Blogger’s
Combination
March
7th Data Model
Beyondofthe
Standard
Higgs
potential
collapses
Higgs coupling less
than in Standard Model
Precision
Electroweak
data??
Higgs
coupling
blows up!!
Estimates of mH from different
Measurements
Spread looks natural: no significant disagreement
Heretical Interpretation of EW Data
What attitude towards LEP, NuTeV?
Do all the data
tell the same story?
e.g., AL vs AH
Chanowitz
What most
of us think
Elementary Higgs or Composite?
• Higgs field:
<0|H|0> ≠ 0
• Quantum loop problems
• Fermion-antifermion
condensate
• Just like QCD, BCS
superconductivity
Cutoff
Λ = 10 TeV • Top-antitop condensate?
needed mt > 200 GeV
Cut-off Λ ~ 1 TeV with
Supersymmetry?
New technicolour force?
- Heavy scalar resonance?
- Inconsistent with
precision electroweak data?
Interpolating Models
• Combination of Higgs boson and vector ρ
• Two main parameters: mρ and coupling gρ
• Equivalently ratio weak/strong scale:
g ρ / mρ
Grojean, Giudice, Pomarol, Rattazzi
Sum Rule for More or Less Higgs
Models
• What if Higgs-V-V couplings differ from SM?
• Unitarity imposes sum rule on scattering in
different isospin channels:
• If Higgs coupling > Standard Model (a2 > 1),
must have non-zero scattering with I = 2
Fialkowski, Rychkov, Urban: arXiv:1202.1532
Higgs as a
Pseudo-Goldstone
Boson
‘Little Higgs’ models
(breakdown of larger symmetry)
Loop cancellation mechanism
Little Higgs
Supersymmetry
Examples of Higgs as
Pseudo-Goldstone Boson
• Parameterization of effective Lagrangian:
• Examples:
• To be measured!
What if the Higgs is not quite a Higgs?
• Tree-level Higgs couplings ~ masses
– Coefficient ~ 1/v
• Couplings ~ dilaton of scale invariance
• Broken by Higgs mass term –μ2, anomalies
– Cannot remove μ2 (Coleman-Weinberg)
– Anomalies give couplings to γγ, gg
• Generalize to pseudo-dilaton of new (nearly)
conformal strongly-interacting sector
• Pseudo-Goldstone boson of scale symmetry
Effective Lagrangian Framework
•
•
•
•
Standard Model Higgs sector = linear σ model
Replace by nonlinear chiral Lagrangian
Assume ~ scale (conformal) symmetry
Realized via (pseudo-)dilaton field χ
JE 1970
• Effective χ potential à la Coleman-Weinberg,
with small coefficient B:
• Large <0|χ|0> = V >> electroweak scale v
A Phenomenological Profile of a
Pseudo-Dilaton
• Universal suppression of couplings to Standard
Model particles: a = c = v/V
• Effective potential:
• Self-couplings:
Compilation
Updated
1000
900
of
with
constraints
Dec. 11
constraints
800
• Γ(gg) may be enhanced
• Γ(γγ) may be suppressed
V (GeV)
700
Pseudo-baryons as dark matter?
Campbell, JE, Olive: arXiv:1111.4495
600
500
400
precision data
300
N =3
g
200
100
200
300
400
m (GeV)
500
600
700
General Analysis of ‘Less Higgs’
Models
• Parameterization of effective Lagrangian:
• Fits
a≠c
Azatov, Contino, Galloway: arXiv:1202.3415
Espinosa, Grojean, Muhlleitner, Trott: arXiv:1202.3697
Analysis of ‘Less Higgs’ Models
• Rescale couplings:
to bosons by a
to fermions by c
• Standard Model:
a=c=1
JE & Tevong You
Electroweak Pseudo-Baryons
• Chiral Lagrangian has soliton solutions
whenever higher-order term present (generic):
• Have non-zero topological quantum number
• B is integer, can be identified with baryon #
• Underlying SU(N) gauge theory: bosons
(fermions) with I = J = 0 (1/2) if N even (odd)
– SO(N) gauge theory: B is Z2 quantum number
– Sp(N) gauge theory: baryons decay to mesons
Campbell, JE, Olive: arXiv:1111.4495
Behaviour at Finite Temperature
• Corrections to nonlinear effective theory:
• Correction to effective dilaton potential:
• Critical temperature when
equal free energies
• More degrees of freedom in confined phase:
Campbell, JE, Olive: arXiv:1111.4495
Cosmological Phase Transition
• Critical temperature with <0|χ|0> ~ V:
• But supercooling to nucleation temperature:
• First-order phase transition
• Percolation ~ immediate
• Short phase of non-adiabatic
expansion
Campbell, JE, Olive: arXiv:1111.4495
Evolution of the Universe
• Universe supercoools
• Expansion briefly
dominated by field energy
• Growth in entropy by
factor ~ 7 to 200
• Identify confinement,
appearance of electroweak
‘baryons’ with transition to
<0|χ|0> ≠ 0
Campbell, JE, Olive: arXiv:1111.4495
Baryon-to-Entropy Ratio
• ‘Kibble’ estimate would be large
• But thermal equilibrium thought to be restored
• Expect smaller density:
: freeze-out
• Density
smaller than required for
cold dark matter:
• Need electroweak ‘pseudo-baryon’ asymmetry
Campbell, JE, Olive: arXiv:1111.4495
Electroweak baryons ?
Can we look for
them with the
LHC?
Electroweak Baryons as Dark Matter
• Fermions with I = J = ½?
• Expect mass of charged partner > neutral:
• Estimate mass difference ~ GeV
– β-decay lifetime ~ 10-11 sec
– thermal equilibrium down to T ~ MeV
– Small abundance of charged state
• BUT some might be trapped in stable charged
‘pseudo-nuclei’ ✕ experiment
Campbell, JE, Olive: arXiv:1111.4495
Pseudo-Baryonic Dark Matter?
• No problem if I = J = 0 bosons
• Estimate scattering cross section:
where:
with
• Within range of future experiments
Campbell, JE, Olive: arXiv:1111.4495
Dark mattter
Scattering rate
Classic Supersymmetric Signature
Missing transverse energy
carried away by dark matter particles
Limits on Heavy MSSM Higgses
Gluino mass
--- pre-Higgs
___ Higgs @ 125
… H@125, no g-2
Buchmueller, JE et al: arXiv:1112.3564
Favoured values of gluino mass significantly
above pre-LHC, > 2 TeV
The Stakes in the Higgs Search
• How is gauge symmetry broken?
• Is there any elementary scalar field?
• Would have caused phase transition in the Universe when
it was about 10-12 seconds old
• May have generated then the matter in the Universe:
electroweak baryogenesis
• A related inflaton might have expanded the Universe
when it was about 10-35 seconds old
• Contributes to today’s dark energy: 1060 too much!
Conversation with Mrs Thatcher: 1982
What do you do?
Think of things for the
experiments to look
for, and hope they find
something different
Then we would not
learn anything!
Wouldn’t it be
better if they
found what
you predicted?