A pseudoscalar at the LHC: technicolor vs a fourth family

Condensates of colored fermions driving electroweak symmetry breaking could give rise to a light pseudoscalar that would show up in the Higgs search at the LHC. The branching ratios of its decay will distinguish it from the Higgs and illuminate its origin. In particular the colored fermions may be the techniquarks of a one family technicolor theory or the quarks of a strongly interacting fourth family. The former has more difficulties in this context. Electroweak symmetry breaking is intrinsically natural if it is due to the condensation of strongly interacting fermions. It is also noteworthy that the condensing fermions need not be exotic fermions; a family of fermions with standard model quantum numbers is quite ad-equate. One family technicolor models were extensively studied very early [1, 2]. Although the interest in such models have ebbed and waned over the years, they have not been conclu-sively eliminated by experimental data. Electroweak precision constraints along with recent constraints from the LHC [3] point towards the minimal number of technicolors, NTC = 2. An even more minimal model of electroweak symmetry breaking occurs when the strong gauge interaction responsible for the condensation is itself broken. Then it is possible that the con-densing fermions are no more than a standard (although strongly interacting) fourth family [4, 5, 6, 7]. The one family technicolor model and the strong fourth family model are similar in many respects. They both predict that the lightest states of the new strong sector are neutral color singlet pseudoscalar mesons that arise naturally as pseudo-Goldstone bosons of the symmetry breaking. The masses of such states are difficult to predict. Meanwhile a light scalar meson with the properties of the Higgs particle is not expected in such theories in the absence of fin