M. Golterman, W. I. Jay, E. T. Neil, Y. Shamir, and B. SvetitskyThe low-energy constant L10 in a two-representation lattice theory, arXiv:2010.01920 [hep-lat], October 2020. Submitted to Physical Review D.
We calculate the low-energy constant L10 in a two-representation SU(4) lattice gauge theory that is close to a composite-Higgs model. From this we obtain the contribution of the new strong sector to the S parameter. This leads to an upper bound on the vacuum misalignment parameter ΞΎ which is similar to current estimates of this bound. Our result agrees with large-Nc scaling expectations, within large systematic uncertainties.
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B. Svetitsky, V. Ayyar, T. DeGrand, M. Golterman, D. Hackett, W. I. Jay, E. T. Neil, and Y. ShamirTowards a composite Higgs and a partially composite top quark, talk given at Lattice 2019, the 37th International Symposium on Lattice Field Theory, Wuhan, China, June 2019, published in proceedings Proc. Sci. (LATTICE2019) 241 (arXiv:1911.10867 [hep-lat], November 2019).
We have calculated quantities of interest to a theory of compositeness. The lattice model, approximating the candidate theory, is the SU(4) gauge theory coupled to fermions in two color representations. For the composite Higgs, a current correlator gives one of the ingredients of the effective Higgs potential. For the partially composite top quark, we have hyperbaryon matrix elements that govern mixing of the fundamental quark with its heavy composite partner. The matrix elements turn out to be so small that the theory is disfavored as a source of a realistic top mass.
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V. AyyarM. Golterman, D. Hackett, W. I. Jay, E. T. Neil, Y. Shamir, and B. SvetitskyRadiative contribution to the composite-Higgs potential in a two-representation lattice model, Phys. Rev. D 99 (2019) 094504 (arXiv:1903.02535 [hep-lat], March 2019).
Working in a two-representation lattice gauge theory that is close to a composite Higgs model, we calculate the low-energy constant CLR which controls the contribution of the electroweak gauge bosons to the Higgs potential. In QCD, the corresponding low-energy constant governs the mass splitting of the pion multiplet. Taking the continuum and chiral limits, we find that CLR, in units of the pseudoscalar decay constant, is roughly of the same size as its QCD counterpart.
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V. Ayyar, T. DeGrand, D. Hackett, W. I. Jay, E. T. Neil, Y. Shamir, and B. SvetitskyPartial compositeness and baryon matrix elements on the lattice, Phys. Rev. D 99 (2019) 094502 (arXiv:1812.02727 [hep-lat], December 2018).
Partial compositeness is a mechanism for the generation of fermion masses which replaces a direct Higgs coupling to the fermions by a linear mixing with heavy composite partners. We present the first calculation of the relevant matrix element in a lattice model which is very close to a candidate theory containing a composite Higgs boson and a partially composite top quark. Specifically, our model is an SU(4) gauge theory coupled to dynamical fermions in the fundamental and two-index antisymmetric (sextet) representations. The matrix element we obtain is small and hence our result disfavors the scenario of obtaining a realistic top mass in this model.
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B. SvetitskyLooking behind the Standard Model with lattice gauge theory, plenary lecture given at Lattice 2017, the 35th International Symposium on Lattice Field Theory, Granada, Spain, June 2017, published in proceedings, EPJ Web Conf. 175, 01017 (2018) (arXiv:1708.04840 [hep-lat], August 2017).
Models for what may lie behind the Standard Model often require non-perturbative calculations in strongly coupled field theory. This creates opportunities for lattice methods, to obtain quantities of phenomenological interest as well as to address fundamental dynamical questions. I survey recent work in this area.
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