Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/109233
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Type: Journal article
Title: Constraining fine tuning in composite Higgs models with partially composite leptons
Author: Barnard, J.
Murnane, D.
White, M.
Williams, A.
Citation: The Journal of High Energy Physics, 2017; 2017(9):049-1-049-31
Publisher: Springer
Issue Date: 2017
ISSN: 1126-6708
1029-8479
Statement of
Responsibility: 
James Barnard, Daniel Murnane, Martin White, Anthony G. Williams
Abstract: Minimal Composite Higgs Models (MCHM) have long provided a solution to the hierarchy problem of the Standard Model, yet suffer from various sources of fine tuning that are becoming increasingly problematic with the lack of new physics observations at the LHC. We develop a new fine tuning measure that accurately counts each contribution to fine tuning (single, double, triple, etc) that can occur in a theory with np parameters, that must reproduce no observables. We then use a novel scanning procedure to perform a comprehensive study of three different two-site, 4D, SO(5) → SO(4) MCHMs with all third generation fermions included, distinguished by the choice of the lepton embeddings. These are the MCHM5 − 5 − 55 − 5 − 5, MCHM14 − 14 − 105 − 5 − 5 and MCHM14 − 1 − 105 − 5 − 5, where MCHMl − τ − νq − t − b has the lepton doublet partner in representation l, tau partner in representation τ, and so on. We find that embedding at least one massive lepton in the symmetric 14 of SO(5) moderately reduces the tuning for the case of low top partner masses (in line with previous results), but that this is balanced against the increased complexity of the model when one properly accounts for all sources of fine tuning. We study both the current relative fine-tuning of each scenario, and the future prospects. Noting that the different scenarios behave differently with respect to future improvements in collider measurements, we find that the MCHM14 − 1 − 105 − 5 − 5 enjoys a relatively low increase in fine tuning even for a future lower bound on the top partner masses of 3.4 TeV (or equivalently a maximum Higgs-fermion or Higgs-gluon coupling deviation of 2%).
Keywords: Technicolor and composite models; beyond standard model; effective field theories
Rights: © 2017, The Author(s). Published in cooperation with JHEP is an open-access journal funded by SCOAP3 and licensed under CC BY 4.0
DOI: 10.1007/JHEP09(2017)049
Grant ID: http://purl.org/au-research/grants/arc/FT140100244
http://purl.org/au-research/grants/arc/CE1101004
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Physics publications

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