Expectations for LHC from naturalness: Modified vs. SM Higgs sector

Common lore has it that naturalness of electroweak breaking in the SM requires new physics (NP) at Lambda less than or similar to 2-3 TeV, hopefully within the reach of LHC. Moreover the Higgs should be light (m(h) less than or similar to 219 GeV) to pass electroweak precision tests (EWPT). However one should be prepared for "unexpected" (although admittedly unpleasant) results at LHC, i.e. no NP and/or a heavy Higgs. We revisit recent attempts to accommodate this by modifying the SM Higgs sector (using 2-Higgs-doublet models). We find that generically these models do not improve significantly the naturalness of the SM, and so they do not change the expectations of observing NP at LHC. We also stress that a heavy SM Higgs would not be evidence in favor of a modified Higgs sector, provided certain higher order operators influence EWPT. On the other hand, we show that NP can escape LHC detection without a naturalness price, and with the pure SM as the effective theory valid at LHC energies, simply if the cut-off for top loops is slightly lower than for Higgs loops. (C) 2007 Elsevier B.V. All rights reserved.