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Flavor Beyond Standard Model
G.G. Devidze
High Energy Physics Institute of Tbilisi State University
1.Introduction
2.Flavor beyond the standard model
3.Heavy quarks and leptons rare decays
4. Conclusion
5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
Nanouniverse
10-9 m
Femtouniverse
10-15 m
Attouniverse
10-18 m
10-20 m
Zeptouniverse
10-21 m
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
Exciting time is for fundamental physics, after the LHC experiments announced about discovery of
neutral Higgs particle on July the 4th. Many in the community expect a new paradigm to emerge
around the TeV scale, be it some variant of SUSY or of Technicolour or something even more radical,
like extra (space) dimensions. Those novel structures can manifest themselves directly through the
production of new quanta or the topology of events or indirectly by inducing forces that modify
rare weak decays. Such indirect searches are not a luxury. We consider it likely that to differentiate
between different scenarios of New Physics, one needs to analyze their impact on flavor dynamics.
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
Processes, which are highly suppressed in the Standard Model (SM), such as
decays mediated by flavour changing neutral currents (FCNC) allow stringent tests
of our current understanding of particle physics. These transitions are forbidden at
tree level in the SM, as all electrically neutral particles have only diagonal
couplings in the flavor space.
FCNC processes are therefore only allowed through loop contributions and probe
the underlying fundamental theory at the quantum level, where they are sensitive to
masses much higher than that of the b-quark.
Historically, many observations have first been indicated by FCNC processes,
examples include the existence of the charm quark or the high top quark mass.
Enhancements of the decay rates of these FCNC decays are predicted in a variety of
different New Physics models.
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
The fundamental Lagrangian of the SM consists of four pieces
LSM = Lgauge+Lfermion+LHiggs+LYukawa,
• What is the dynamical origin of the observed electroweak symmetry breaking, of related
fermion masses and the reason for their hierarchy and hierarchy of their flavour-changing
interactions?
•
•
•
•
Will the dynamics of electroweak symmetry breaking be driven by an elementary Higgs and
be calculable within perturbation theory?
Will these dynamics be related to a new strong force with a composite Higgs or without
Higgs at all?
Could these dynamics help us to explain the amount of matter-antimatter asymmetry and
the amount of dark matter observed in the universe?
Will these dynamics help us to explain various anomalies observed recently in the flavour
data?
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
•
What is the fundamental dynamics behind the electroweak symmetry breaking that very
likely plays also an important role in flavour physics?
•
Are there any new flavour symmetries that could help us to understand the existing hierarchies
of fermion masses and the hierarchies in the quark and lepton flavour violating interactions?
Are they local or global? Are they continuous or discrete?
Are there any flavour violating interactions that are not governed by the SM Yukawa couplings?
In other words, is the Minimal Flavour Violation (MFV) the whole story?
•
Are there any additional flavour violating and CP-violating (CPV) phases that could explain
certain anomalies present in the flavour data and simultaneously play a role in the explanation
of the observed baryon-antibaryon asymmetry in the universe (BAU)?
•
Are there any flavour conserving CPV phases that could also help in explaining the flavour
anomalies in question and would be signalled in this decade through enhanced electric dipole
moments (EDMs) of the neutron, the electron and of other particles?
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
•
Are there any new sequential heavy quarks and leptons of the 4th generation and/or new
fermions with exotic quantum numbers like vector-like fermions?
•
Are there any elementary neutral and charged scalar particles with masses below 1 TeV and
having a significant impact on flavour physics?
•
Are there any new heavy gauge bosons representing an enlarged gauge symmetry group?
•
Are there any relevant right-handed (RH) weak currents that would help us to make our
fundamental theory parity conserving at short distance scales well below those explored by
the LHC?
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
In order to identify new physics through flavour physics and generally
through high precision experiments we need:
• Many high precision measurements of many observables and precise
theory,
• Identification of patterns of flavour violation in various NP models, in
particular correlations between many flavour observables that could
distinguish between various NP scenarios,
• Identification of correlations between low energy flavour observables
and observables measured in high energy collisions.
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
• Heavy quarks rare decays.
• Lepton flavour violating decays like μ →eg, t →eg , t →mg , decays with three
leptons in the final state and m −e conversion in nuclei.
• Electric dipole moments of the neutron, the electron, atoms and leptons.
• Anomalous magnetic moment of the muon
Having experimental results on these decays and observables with sufficient precision
accompanied by improved theoretical calculations will exclude several presently studied
models reducing thereby our exploration of short distance scales to a few avenues.
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
• Heavy quarks rare decays.
Br(t →cg)=5 ∙10-11, Br(t →cg)=5 ∙10-13, Br(t →cZ)=1.3 ∙10-11 , Br(t →ch)= 10-13 ,
Even single experimental observation for any top rare processes could be
breakthrough beyond the SM physics.
• Lepton flavour violating decays like μ →eg, t →eg , t →mg , decays with three
leptons in the final state and m −e conversion in nuclei.
Br(μ →eg)SM < 10-54, Br(μ →eg)exp < 10-12
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
COMET (COherent Muon to Electron Transition), to search for coherent neutrino-less conversion of
muons to electrons (μ−−e− conversion), in the presence of a nucleus, μ− + N(A,Z) → e− + N(A,Z),
with a single event sensitivity B(μ−N → e−N) < 10−16.
Currently, the search for possible flavor violation of the muon is considered to be a powerful and the
most sensitive tool to reveal or restrict a new physics beyond the SM.
μ− + N(A,Z) → e − + N(A,Z),
The muon system is considered to be the best system in which to study cLFV experiments because of
following reasons:
• Intense muon beam can be obtained at meson factories
• Muon life time is rather long .
• Final states are very simple and can be precisely measured.
• Observation of cLFV would indicate a clear signal of physics beyond the SM.
• Search cLFV is especially promising to probe the Tev-scale physics.
m-e conversion at level 10-16-18
The big challenge and great discovery petential!
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
We have studied manifestation of NP in rare processes. Our attention was devoted to lepton
flavour violation processes, top quark and neutral B-meson rare decays.
Numerical estimates show that in case of B-meson double radiative decays we can get a
difference from SM-result as much as ~40%.
We have estimated lepton flavour violation processes rates and concluded that three body
decays and m −e conversion seem more favourable then radiative decays.
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5th Georgian –German School and Workshop in Basic Science, Tbilisi 2012
G.G. Devidze
We are at the beginning of a new era which certainly will bring us first
more detailed insights into the physics at short distance scales.
The interplay of high energy collider results with the flavour precision
experiments will allow us to make important steps towards a New
Standard Model.
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