Large mass hierarchies from strongly-coupled dynamics

Abstract

Besides the Higgs particle discovered in 2012, with mass 125 GeV, recent LHC data show tentative signals for new resonances in diboson as well as diphoton searches at high center-of-mass energies (2 TeV and 750 GeV, respectively). If these signals are confirmed (or other new resonances are discovered at the TeV scale), the large hierarchies between masses of new bosons require a dynamical explanation. Motivated by these tentative signals of new physics, we investigate the theoretical possibility that large hierarchies in the masses of glueballs could arise dynamically in new strongly-coupled gauge theories extending the standard model of particle physics. We study lattice data on non-Abelian gauge theories in the (near-)conformal regime as well as a simple toy model in the context of gauge/gravity dualities. We focus our attention on the ratio R between the mass of the lightest spin-2 and spin-0 resonances, that for technical reasons is a particularly convenient and clean observable to study. For models in which (non-perturbative) large anomalous dimensions arise dynamically, we show indications that this mass ratio can be large, with R > 5. Moreover, our results suggest that R might be related to universal properties of the IR fixed point. Our findings provide an interesting step towards understanding large mass ratios in the non-perturbative regime of quantum field theories with (near) IR conformal behaviour.

Spectrum and mass anomalous dimension of SU(2) adjoint QCD with two Dirac flavors

“…[9] 0.22(6) Ref. [19] 0.50 (26) to note that such smaller values have also been reported in other works, for example, in [43]. Note that the estimates of γ Ã discussed in this work show a remnant dependence on the gauge coupling, and are thus not precisely identical with the universal value at the IR fixed point.…”

“…Even though all masses scale to zero, their ratios can be extrapolated to the conformal limit. It seems that these ratios are a universal characteristic for each (near) IR conformal theory [26].…”

Holographic glueballs from the circle reduction of Romans supergravity

“…On quite general grounds, in a confining theory one expects infinite numbers of such glueballs, that can be classified by quantum numbers of the Poincaré group (mass and spin), possibly supplemented by additional, model-dependent quantum numbers. The literature on the subject includes for instance the reviews in [1,2], and the detailed lattice studies in [3][4][5][6][7][8][9][10][11], besides suggestive ideas on general properties of the glueball spectra (the literature on which is vast, and deserves being reviewed elsewhere, but see for instance [12][13][14][15][16][17][18]). In more general theories, in which gluons couple to matter fields, the physical particles result from mixing between operators made purely of glue and other operators with the same quantum numbers.…”

Glueballs on the baryonic branch of Klebanov-Strassler: dimensional deconstruction and a light scalar particle

“…Their existence is expected on general grounds in large classes of different theories, and their properties capture important information about the underlying dynamics. For example, it has been suggested that the ratio of the masses of the lightest spin-0 and spin-2 particles might highlight the existence of large mass hierarchies in some strongly coupled systems [15].…”