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Flavourful new physics for precision observables Innes Bigaran, Raymond Volkas
@innesbigaran11
Frontiers in Quantum Matter Workshop: Electric Dipole Moments, November 25-27 2019
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Overview
1. Standard Model and CP symmetry 2. CPV + flavour to extend the SM 3. Example models: scalar LQs 4. Current and future work
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The SM and CP symmetry
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The Standard Model• Quarks combine to produce
mesons and baryons • Leptons and quarks interact via
gauge bosons • Leptons and quarks exist in
different flavours, with different masses
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?
X
1. No direct lepton-quark interaction2. Neutrino masses 3. Dark matter and dark energy4. Matter/antimatter asymmetry (req. CPV)
Notable absences
The Standard Model
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▪︎ Similarities and differences between different types of quarks and leptons
▪︎ Flavours have different Higgs couplings: ▪︎ different particle masses
▪︎ The flavour puzzle:▪︎ Why so many “free-parameters”?▪︎ Why only 3 families?▪︎ Relationships between masses,
couplings etc for different generations
Up-type quarks
u ds
c b
t
e 𝜇𝜏
Down-type quarks
Charged leptons
Flavour Physics in the SM
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By delving into flavour, we aim to understand the connections between SM and a more complete picture of nature, including CPV
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BSM and CPV
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C and CP and their violationState A ! State B
State A ! State B
��A ! B
�6= � (A ! B)
� (A ! L) 6= ��A ! R
�
C action
CP violation
C violation
Where L and R are the left- and right-handed projections of the same field (mix via the Higgs)
L � gABL+ g0ABR+ h.c.
hHi
Example:
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g
g0⇤
iM / 116⇡
gg0⇤
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C and CP and the CKM
We have some of this in the SM, via the complex terms in the quark CKM mixing matrices— which allow for quark-flavour changing interactions
Not enough to explain matter/antimatter asymmetry
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(See other talks i.e Csaba Balasz)
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CPV in the SM: Strong CP problem
L � ✓ g2
32⇡2✏µ⌫↵�G
aµ⌫G
a↵�
▪︎ CP-odd, total-derivative term in the QCD Lagrangian
▪︎ Derivative terms don’t enter the equations of motion, within PT regime
▪︎ This term has non-perturbative effects
/ ✓ [@µJµ]
Coupling phase mismatch in the chiral EFT Lagrangian —> EDM of the neutron! From experimental constraints on this, SM needs a very small theta ~~10^(-11)
Very fine-tuned, or see work by others on Axions, massless quarks etc….
WHY?
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eEDMs as a probe of NP
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Very broad sub-categories which are “indicative” but also can be quite disheartening for model-builders
Google images: “sad electron”
Sauer, Devlin 2017
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Scalar LQ Models
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Scalar LQ models in context
• Direct coupling between SM quarks and leptons
• Flavour violation in BSM theories ✴ Flavour anomalies? ✴ Neutrino mass?
• CPV possible with complex Yukawa couplings (recall earlier example)
LQ
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Q
L
Q
L
LQ
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Scalar LQ: EDM generation
• Having 2 leptoquark interactions allow for a coupling phase difference —> CPV
• Focus on single-loop specific model constraints for this arXiv:1804.01137
• Revisit with leading-order EDM constraints on the set of scalar LQ models
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https://arxiv.org/pdf/1407.1064.pdf
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Reference for phenomenology
Chupp, Ramsey-Musolf ArXiv:1407.1064
General
More specific
Aim to provide a clear reference on EDM contributions from each of the Scalar LQ models
Thank you to Sacha Davidson and Jordy de Vries for useful discussion on this
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Related precision observable: lepton (g-2)
Bigaran, Volkas , arXiv 1912.xxxx Manuscript in preparation
A bit simpler than the eEDM calculations
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Problem: • Deviation between SM and experiment, • 2.5 sigma for electron, 3.6 sigma for muon but opposite sign —> flavour specific BSM?
Solution:
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Summary
1. Flavour physics has useful applications on the precision frontier
2. Scalar LQs are very neat BSM models 3. (g-2) is a good way to start exploring these models 4. EDM summary tables, developed by
phenomenologists, can help experimentalists make useful conclusions
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