Electroweak Precision Data and the Lee-Wick Standard Model
  We investigate the electroweak precision constraints on the recently proposed Lee-Wick Standard Model at tree level. We analyze low energy, Z-pole (LEP1/SLC) and LEP2 data separately. We derive the exact tree level low energy and Z-pole effective Lagrangians from both the auxiliary field and higher derivative formulation of the theory. For the LEP2 data we use the fact that the Lee-Wick Standard Model belongs to the so-called 'universal class' which can be described by seven oblique parameters at leading order in m_W^2/M_{1,2}^2. At tree level we find that the only non-zero oblique parameters are Y = -m_W^2/M_1^2 and W = -m_W^2/M_2^2, where the negative sign is due to the presence of the negative norm states. The Lee-Wick operators do not violate the SU(2)_L or custodial symmetry at tree level implying S=0 and T=0 respectively. Our results differ substantially from a prior analysis in this respect. We show a plot including all three constraints. The LEP1/SLC constraints are slightly stronger than LEP2 and much stronger than the low energy ones. The LEP1/SLC results exclude gauge boson masses of M_1 ~ M_2 ~ 3 TeV at the 99% confidence level. Somewhat lower masses are possible when one of the masses assumes a large value. Loop corrections to the electroweak observables are suppressed by the standard ~1/(4 \pi)^2 factor and are therefore not expected to change the constraints on M_1 and M_2. This assertion is most transparent from the higher derivative formulation of the theory. 
Thomas E.J. Underwood and Roman Zwicky