Flavor-singlet spectrum in multi-flavor QCD

¹ Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
² RIKEN BNL Research Center, Brookhaven National Laboratory, Upton, NY, 11973, USA
³ Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan
⁴ College of Science, Swansea University, Singleton Park, Swansea, SA2 8PP, UK
⁵ Research and Education Center for Natural Sciences, Keio University, Hiyoshi 4-1-1, Yokohama, Kanagawa 223-8521, Japan
⁶ Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602, Japan
⁷ Centre de Physique Theorique(CPT), Aix-Marseille University, Campus de Luminy, Case 907, 163 Avenue de Luminy, 13288 Marseille cedex 9, France
⁸ Department of Physics, Nara Women’s University, Nara 630-8506, Japan
⁹ Computing Research Center, High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
¹⁰ Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
¹¹ Center for Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
¹² Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA

^* Speaker, e-mail: erinaldi@bnl.gov Acknowledgements: We thank the Lattice Strong Dynamics (LSD) collaboration for sharing their plots and their preliminary unpublished results for the flavor-singlet scalar mass on their ensembles. Numerical calculations have been carried out on the high-performance computing systems at KMI, at the ITC in Nagoya University, and at the Research Institute for Information Technology in Kyushu University through the HPCI System Research Projects (Project ID: hp140152, hp150157, hp160153). This work is supported in part by the JSPS KAKENHI Grant No. 16K05320.

Published online: 26 March 2018

Abstract

Studying SU(3) gauge theories with increasing number of light fermions is relevant both for understanding the strong dynamics of QCD and for constructing strongly interacting extensions of the Standard Model (e.g. UV completions of composite Higgs models). In order to contrast these many-flavors strongly interacting theories with QCD, we study the flavor-singlet spectrum as an interesting probe. In fact, some composite Higgs models require the Higgs boson to be the lightest flavor-singlet scalar in the spectrum of a strongly interacting new sector with a well defined hierarchy with the rest of the states. Moreover, introducing many light flavors at fixed number of colors can influence the dynamics of the lightest flavor-singlet pseudoscalar. We present the on-going study of these flavor-singlet channels using multiple interpolating operators on high-statistics ensembles generated by the LatKMI collaboration and we compare results with available data obtained by the Lattice Strong Dynamics collaboration. For the theory with 8 flavors, the two collaborations have generated configurations that complement each others with the aim to tackle the massless limit using the largest possible volumes.