Little Higgs Models and Electroweak Measurements

Using effective field theory approach, we study the constraints from electroweak data on the SU(5)/SO(5), SU(6)/SP(6), SU(3)xU(1) little Higgs models and their variations. We construct an effective theory valid above the electroweak symmetry breaking scale in these models that includes dimension-six operators induced by integrating out heavy fields. We calculate the constraints on the models using the results of hep-ph/0412166, where bounds on arbitrary linear combinations of flavor and CP conserving dimension-six operators are given. We present the constraints in terms of the bounds on the masses of heavy fermions and heavy gauge bosons. The constraints are often stringent, but in some regions of the parameter space the constraints are mild enough and do not imply significant fine-tuning.Comment: Small changes to the plots due to the change in numerical results in hep-ph/0412166, text unchange

Duality in Sp and SO Gauge Groups from M Theory

We describe fivebrane configurations in M theory whose 4-d spacetime contains N=1 supersymmetric Sp or SO gauge fields and fundamentals of these groups. We show how field-theory dualities for Sp and SO groups can be derived using these fivebrane configurations in M theory.Comment: 12 pages, LaTeX, four embedded figure

Disguising the Oblique Parameters

We point out a set of operator identities that relate the operators corresponding to the oblique corrections to operators that modify fermion couplings to the gauge bosons as well as operators that modify triple gauge boson couplings. Such identities are simple consequences of the equations of motion. Therefore the contributions from new physics to the oblique parameters can be disguised as modifications of triple gauge boson couplings provided the fermion couplings to the gauge bosons are suitably modified by higher dimensional operators. Since the experimental constraints on triple gauge boson couplings are much weaker than the constraints on the oblique parameters this observation allows extra room for model building. We derive operator relations in effective theories of the Standard Model with the electroweak symmetry either linearly or nonlinearly realized and discuss applications of our results.Comment: 12 pages. v2: two references adde