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.
Highlights
Non-perturbative methods are needed to test this broadly defined scenario
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, 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 want to find appropriate physical observables that allow such an identification to be assessed in a clean, unambiguous way distinctive from simple arguments formulated at weak coupling on the basis of internal symmetries
Summary
The SU(2) gauge theory with two Dirac fermions in the adjoint representation of the gauge group is the first that has been shown to be infrared (IR) conformal in the context of lattice studies of the conformal window. In QCD, for which the mass of the vector is above the threshold of the two pion system, unless the corresponding weighting coefficient k1 is suppressed for dynamical reasons or by an appropriate choice of the probe operators used in the calculation, in general with this technique one would extract the invariant mass associated to the scattering of two pions with J = 1, and the mass of the resonance will only manifest as an excitation [79] The latter discussion about this somewhat technical aspect of the calculation will be relevant when analysing the numerical results obtained for the investigated lattice theories. Further technical details on how glueball masses are extracted using this method are provided for instance in [27]
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