Effect on Higgs Boson Decays from Large Light-Heavy Neutrino Mixing in Seesaw Models

• Main Authors: Jyong-Hao Chen, 陳炯豪
• Other Authors: 何小剛
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/91440011654598061347

碩士 === 國立臺灣大學 === 物理研究所 === 99 === In seesaw models with more than one generation of light and heavy neutrinos, ν and N, respectively, it is possible to have sizable mixing between them for heavy neutrino masses of order 100 GeV or less. We explore this possibility further, taking into account current experimental constraints, and study its effect on Higgs boson decays in the contexts of seesaw models of types I and III. We find that in the type-I case the Higgs decay into a pair of light and heavy neutrinos, h → νN, could increase the total Higgs width in the standard model by up to almost 30% for a relatively light Higgs boson, which would significantly affect Higgs searches at the LHC. The subsequent prompt decay of N into three light fermions makes this Higgs decay effectively a four body decay. We further find that, in the presence of the large light-heavy mixing, these four body Higgs decays can have rates a few times larger than their standard model counterparts and therefore could provide a potentially important window to reveal the underlying seesaw mechanism. However, in type-III seesaw model, due to the stronger experimental constraints on the elements of the mixing matrix U_{νN} and also to the lower limit on the heavy lepton masses, the large light-heavy mixing gives rise to modifications of the SM Higgs total width that are modest, roughly only 5%, much smaller than those in the type-I case. As a consequence, the Higgs decays into four light fermions in this case would be less sensitive for probing the underlying seesaw mechanism than their type-I counterparts.