46 research outputs found
Extra Families, Higgs Spectrum and Oblique Corrections
The standard model accommodates, but does not explain, three families of
leptons and quarks, while various extensions suggest extra matter families. The
oblique corrections from extra chiral families with relatively light
(weak-scale) masses, , are analyzed and used to constrain the
number of extra families and their spectrum. The analysis is motivated, in
part, by recent N = 2 supersymmetry constructions, but is performed in a
model-independent way. It is shown that the correlations among the
contributions to the three oblique parameters, rather than the contribution to
a particular one, provide the most significant bound. Nevertheless, a single
extra chiral family with a constrained spectrum is found to be consistent with
precision data without requiring any other new physics source. Models with
three additional families may also be accommodated but only by invoking
additional new physics, most notably, a two-Higgs-doublet extension. The
interplay between the spectra of the extra fermions and the Higgs boson(s) is
analyzed in the case of either one or two Higgs doublets, and its implications
are explored. In particular, the precision bound on the SM-like Higgs boson
mass is shown to be significantly relaxed in the presence of an extra
relatively light chiral family.Comment: 20 pages, 8 figures, version for PR