the top quark is the heaviest quark. the current theory is its invariant mass is based solely on its interactions with the higgs field. in absence of the higgs field, fermions, quarks and leptons are massless, and in the presence of the higgs field, they acquire mass. the reason the top quark is the heaviest quark is that it couples to the higgs field more strongly than an electron or up or down quark. is there any theory that explains why a top quark interacts with the higgs more strongly than up or down quark, or electron? is there any research into the possibility that fundamental particles can gain additional mass, through say the color force or electromagnetic force? i.e the reason the top quark quark is so massive is it couples to both the higgs and color force and electromagnetic force where as electrons do not couple to the color force.