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.
Highlights
We perform lattice field theory simulations of QCD with different numbers of light fermions to study the spectrum of bound states in the scalar and pseudoscalar channel, in particular focusing on particles that have no flavor charge
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
Our lattice simulations aim at filling this gap and at providing data with which phenomenological models could be benchmarked. This is relevant for the understanding of strongly interacting theories like QCD, and for physics Beyond the Standard Model (BSM)—in particular extensions of the Standard Model based on strong dynamics
Summary
We perform lattice field theory simulations of QCD with different numbers of light (massless) fermions to study the spectrum of bound states in the scalar and pseudoscalar channel, in particular focusing on particles that have no flavor charge (flavor singlets). Previous lattice numerical simulations indicate that these 3 different values of N f correspond to rather different type of dynamics: while N f = 4 is expected to show the same features of QCD with N f = 2, namely confinement and spontaneous chiral symmetry breaking, the theory with N f = 12 is expected to have conformal dynamics, with ratios of mass scales that stay constant toward the massless limit This points to QCD with N f = 8 as a candidate for near-conformal dynamics, with several lattice studies confirming the presence of a flavor-singlet scalar state much lighter than the vector state, in contrast with QCD with smaller number of flavors. We leave the interpretation of the results in terms of composite Higgs models, or walking technicolor theories, to future and more thorough investigations
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