Patterns of deviation from the standard model

Abstract

Eective Lagrangians can be used to parametrize the eects of physics beyond the standard model. Assuming the complete theory is a gauge theory, w e determine which eective operators may be generated at tree level, and which are only generated at loop level. The latter are be suppressed by factors of 1=16 2 and will therefore be quite dicult to detect. In particular, all operators changing the Standard-Model structure of the triple-gauge-vector couplings fall into this category. W e also point out that in certain cases, dimension-eight operators may be more important than dimension-six operators. We discuss both the linear and non-linear representation of the Higgs sector.

Observable effects of general new scalar particles

“…[57]. (See [58][59][60][61][62] for a related discussion of dimension-six physics in different operator bases.) The only differences (apart from changes in the names) are the use of different normalization factors in several operators, and the trade of their operators…”

Higgs-Higgs bound state due to new physics at a TeV

“…[36] As such, these operators need not be suppressed by loop factors of 1/16π 2 or proportional to a small custodial symmetry breaking parameter. For these reasons these operators are expected to have the dominant effects on the higgs self couplings and we take their coefficients to be O(1).…”

Effective-field-theory approach to top-quark production and decay

“…There is an argument that can be used to neglect some of the new operators [17]. Some new operators can be generated at tree level from an underlying gauge theory, while others must be generated at loop order.…”