Reconciling GR and QCD

An ambitious new paper demonstrates in a brief ten pages how to generalize lattice quantum chromodynamics (QCD) (an approach to calculating strong force interactions using the actual equations of the Standard Model in a discrete approximation that is not scale dependent) to incorporate curved space-times, such as the classical version of general relativity.

Reconciling the Standard Model to General Relativity is a Holy Grail of fundamental physics.  And, even if one can't accomplish this result for both electro-weak interactions and strong force interaction, doing so with the strong force part of the Standard Model is an impressive accomplishment.

The ordinary assumption is that GR and the Standard Model can be reconciled only by formulating a new theory of quantum gravity.  But, in the case of lattice QCD models, the authors show that QCD and GR can be reconciled using ordinary classical general relativity's equations.

As a corollary of this new approach, the authors demonstrate analytically (rather than merely by numerical approximation) for all curved space-times, that QCD does not permit free gluons even in the intense gravitational fields of neutron stars and black holes, contrary to numerous previous speculations that deconfinement (i.e. the existence of particles that are not part of a color charge neutral composite particle) might occur in those circumstances. 

This paper also paves the way for determining definitively using numerical approximations, if free quarks can exist in strong gravitational fields, and confirms that a quirk of lattice QCD calculations called the double fermion problem is also present in curved space-times.  But, the authors reserve resolution of this issue for further resolution.