Browsing by Author "Vadacchino, Davide"

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Color dependence of tensor and scalar glueball masses in Yang-Mills theories
(2020-07-20)
Bennett, Ed
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Holligan, Jack
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Hong, Deog Ki
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Lee, Jong-Wan
;
Lin, C. -J. David
We report the masses of the lightest spin-0 and spin-2 glueballs obtained in an extensive lattice study of the continuum and infinite volume limits of Sp(N-c) gauge theories for N-c = 2, 4, 6, 8. We also extrapolate the combined results toward the large-N-c limit. We compute the ratio of scalar and tensor masses, and observe evidence that this ratio is independent of N-c. Other lattice studies of Yang-Mills theories at the same space-time dimension provide a compatible ratio. We further compare these results to various analytical ones and discuss them in view of symmetry-based arguments related to the breaking of scale invariance in the underlying dynamics, showing that a constant ratio might emerge in a scenario in which the 0(++) glueball is interpreted as a dilaton state.
Sp(4) gauge theories on the lattice: N-f=2 dynamical fundamental fermions
(2019-12-05)
Bennett, Ed
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Hong, Deog Ki
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Lee, Jong-Wan
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Lin, C. -J. David
;
Lucini, Biagio
We perform lattice studies of the gauge theory with Sp(4) gauge group and two flavours of (Dirac) fundamental matter. The global SU(4) symmetry is spontaneously broken by the fermion condensate. The dynamical Wilson fermions in the lattice action introduce a mass that breaks the global symmetry also explicitly. The resulting pseudo-Nambu-Goldstone bosons describe the SU(4)/Sp(4) coset, and are relevant, in the context of physics beyond the Standard Model, for composite Higgs models. We discuss scale setting, continuum extrapolation and finite volume effects in the lattice theory. We study mesonic composite states, which span representations of the unbroken Sp(4) global symmetry, and we measure masses and decay constants of the (flavoured) spin-0 and spin-1 states accessible to the numerical treatment, as a function of the fermion mass. With help from the effective field theory treatment of such mesons, we perform a first extrapolation towards the massless limit. We assess our results by critically comparing to the literature on other models and to the quenched results, and we conclude by outlining future avenues for further exploration. The results of our spectroscopic analysis provide new input data for future phenomenological studies in the contexts of composite Higgs models, and of dark matter models with a strongly coupled dynamical origin.
Sp(4) gauge theories on the lattice: Quenched fundamental and antisymmetric fermions
(2020-04-27)
Bennett, Ed
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Hong, Deog Ki
;
Lee, Jong-Wan
;
Lin, C-J David
;
Lucini, Biagio
We perform lattice studies of meson mass spectra and decay constants of the Sp(4) gauge theory in the quenched approximation. We consider two species of (Dirac) fermions as matter field content, transforming in the 2-index antisymmetric and the fundamental representation of the gauge group, respectively. All matter fields are formulated as Wilson fermions. We extrapolate to the continuum and massless limits and compare to each other the results obtained for the two species of mesons. In the case of two fundamental and three antisymmetric fermions, the long-distance dynamics is relevant for composite Higgs models. This is the first lattice study of this class of theories. The global SU(4) x SU(6) symmetry is broken to the Sp(4) x SO(6) subgroup, and the condensates align with the explicit mass terms present in the lattice formulation of the theory. The main results of our quenched calculations are that, with fermions in the 2-index antisymmetric representation of the group, the masses squared and decay constant squared of all the mesons we considered are larger than the corresponding quantities for the fundamental representation, by factors that vary between similar to 1.2 and similar to 2.7. We also present technical results that will be useful for future lattice investigations of dynamical simulations, of composite chimera baryons, and of the approach to large N in the Sp(2N) theories considered. We briefly discuss their high-temperature behavior, where symmetry restoration and enhancement are expected.
Sp(4) gauge theory on the lattice: towards SU(4)/Sp(4) composite Higgs (and beyond)
(2018-03-29)
Bennett, Ed
;
Hong, Deog Ki
;
Lee, Jong-Wan
;
Lin, C. -J. David
;
Lucini, Biagio
The Sp(4) gauge theory with two Dirac fundamental flavours provides a candidate for the microscopic origin of composite-Higgs models based on the SU(4)/Sp(4) coset. We employ a combination of two different, complementary strategies for the numerical lattice calculations, based on the Hybrid Monte Carlo and on the Heat Bath algorithms. We perform pure Yang-Mills, quenched computations and exploratory studies with dynamical Wilson fermions. We present the first results in the literature for the spectrum of glueballs of the pure Sp(4) Yang-Mills theory, an EFT framework for the interpretation of the masses and decay constants of the lightest pion, vector and axial-vector mesons, and a preliminary calculation of the latter in the quenched approximation. We show the first numerical evidence of a bulk phase transition in the lattice theory with dynamical Wilson fermions, and perform the technical steps necessary to set up future investigations of the mesonic spectrum of the full theory.