Level Unitarity Research Articles

Does unitarity imply finiteness of electroweak oblique corrections at one loop? Constraining extra neutral Higgs bosons

Introducing an arbitrary number of neutral Higgs bosons in the electroweak symmetry breaking sector, we derive a set of conditions among Higgs couplings which need to be satisfied to maintain the unitarity of the high energy scattering amplitudes of weak gauge bosons at the tree level (unitarity sum rules). It is shown that the unitarity sum rules require the tree level $\ensuremath{\rho}$ parameter to be 1, without explicitly invoking the custodial symmetry arguments. The one loop finiteness of the electroweak oblique corrections is automatically guaranteed once these unitarity sum rules are imposed among Higgs couplings. Severe constraints on the lightest Higgs coupling (125 GeV Higgs coupling) and the mass of the second lightest Higgs boson are obtained from the unitarity and the results of the electroweak precision tests (oblique parameter measurements). These results are compared with the effective theory of the light Higgs boson, and we find simple relationships between the mass of the second lightest Higgs boson in our framework and the ultraviolet cutoff in the effective theory framework.

How well do we know the three-gluon vertex?

Deviations from the QCD prediction for the three-gluon vertex can be parameterised in terms of the dimension-6 operator Tr( G μ v G v p G p μ ) in a gauge invariant way.Tree level unitarity considerations for the gg→gg elastic scattering process severely constrain the signal for an anomalous three-gluon vertex in dijet production at hadron colliders. This leaves four-jet events at e +e − colliders as a very competitive way to study the three-gluon vertex.