Though not a part of mainstream physics , Salam ’ s theory of strong gravity remains a viable effective model for the description of strong interactions in the gauge singlet sector of QCD , capable of producing particle confinement and asymptotic freedom , but not of reproducing interactions involving SU ( 3 ) colour charge .
It may therefore be used to explore the stability and confinement of gauge singlet mesons and baryons , though not to describe scattering processes that require colour interactions .
It is a two-tensor theory of both strong interactions and gravity , in which the strong tensor field is governed by equations formally identical to the Einstein equations , apart from the coupling parameter , which is of order 1 GeV ^ { -1 } .
In this paper , we revisit the strong gravity theory and investigate the strong gravity field equations in the presence of a mixing term which induces an effective strong cosmological constant , \Lambda _ { f } .
This introduces a strong de Sitter radius for strongly interacting fermions , producing a confining bubble , which allows us to identify \Lambda _ { f } with the ‘ bag constant ’ of the MIT bag model , B \simeq 2 \times 10 ^ { 14 } gcm ^ { -3 } .
Assuming a static , spherically symmetric geometry , we derive the strong gravity TOV equation , which describes the equilibrium properties of compact hadronic objects .
From this , we determine the generalised Buchdahl inequalities for a strong gravity ‘ particle ’ , giving rise to upper and lower bounds on the mass/radius ratio of stable , compact , strongly interacting objects .
We show , explicitly , that the existence of the lower mass bound is induced by the presence of \Lambda _ { f } , producing a mass gap , and that the upper bound corresponds to a deconfinement phase transition .
The physical implications of our results for holographic duality in the context of the AdS/QCD and dS/QCD correspondences are also discussed .

Keywords : strong interaction , strong gravity , mass gap , confinement/deconfinement , mass bounds , holography , bag model , AdS/QCD , dS/QCD