分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： In the minimal supersymmetric standard model extended by including right-handed neutrinos with seesaw mechanism, the neutrino Yukaka couplings can be as large as the top-quark Yukawa couplings and thus the neutrino/sneutrino may cause sizable effects in Higgs boson self-energy loops. Our explicit one-loop calculations show that the neutrino/sneutrino effects may have an opposite sign to top/stop effects and thus lighten the lightest Higgs boson. If the soft-breaking mass of the right-handed neutrino is very large (at the order of Majorana mass scale), such as in the split-supersymmetry (SUSY) scenario, the effects can lower the lightest Higgs boson mass by a few tens of GeV. So the Higgs mass bound of about 150 GeV in split-SUSY may be lowered significantly if right-handed neutrinos come into play with seesaw mechanism.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： The topcolor-assisted technicolor (TC2) theory predicts tree-level flavor-changing neutral-current (FCNC) top quark Yukawa couplings with top-pions. Such FCNC interactions will induce like-sign top quark pair productions at CERN Large Hadron Collider (LHC). While these rare productions are far below the observable level in the Standard Model and other popular new physics models such as the Minimal Supersymmetric Model, we find that in a sound part of parameter space the TC2 model can enhance the production cross sections to several tens of fb and thus may be observable at the LHC due to rather low backgrounds. Searching for these productions at the LHC will serve as an excellent probe for the TC2 model.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： The top-charm associated productions via e(+)e(-), e(-)gamma and gamma gamma collisions at linear colliders, which are extremely suppressed in the standard model ( SM), could be significantly enhanced in some extensions of the SM. In this article we calculate the full contribution of the top-color-assisted technicolor ( TC2) to these productions and then compare the results with the existing predictions of the SM, the general two-Higgs-doublet model and the minimal supersymmetric model. We find that the TC2 model predicts much larger production rates than other models and the largest-rate channel is gamma gamma -> t (c) over bar, which exceeds 10 fb for a large part of the parameter space. From the analysis of the observability of such productions at the future linear colliders, we find that the predictions of the TC2 model can reach the observable level for a large part of the parameter space while the predictions of other models are hardly accessible.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： We propose to probe the top-color-assisted technicolor (TC2) model from the top-charm associated production at the CERN LHC, which is highly suppressed in the standard model. Because of the flavor-changing couplings of the top quark with the scalars (top-pions and top-Higgs-bosons) in the TC2 model, the top-charm associated production can occur via both the s-channel and t-channel parton processes by exchanging a scalar field at the LHC. We examine these processes through Monte Carlo simulation and find that they can reach the observable level at the LHC in quite a large part of the parameter space of the TC2 model.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： The Higgs boson production pp(p (p) over bar)-->bh+X via bg-->bh at hadron colliders, which may be an important channel for testing the bottom quark Yukawa coupling, is subject to large supersymmetric quantum corrections. In this work the one-loop supersymmetric (SUSY) QCD corrections to this process are evaluated and are found to be quite sizable in some parameter space. We also study the behavior of the corrections in the limit of heavy SUSY masses and find the remnant effects of SUSY QCD. These remnant effects, which are left over in the Higgs sector by the heavy sparticles, are found to be so sizable (for a light CP-odd Higgs boson and large tan beta) that they might be observable in future experiments. The exploration of such remnant effects is important for probing SUSY, especially in the case that the sparticles are too heavy (above TeV) to be directly discovered in future experiments.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： Recently the ATLAS collaboration reported a 3 sigma excess in the leptonic-Z + jets + E-T(miss) channel. This may be interpreted in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) by gluino pair production with the decay chain (g) over tilde -> q (q) over bar(chi) over tilde (0)(2) -> q (q) over barZ (chi) over tilde (0)(1), where (chi) over tilde (0)(1) and (chi) over tilde (0)(2) denote the lightest and the next-to-lightest neutralinos with singlino and bino as their dominant components respectively. After exploring the relevant parameter space of the NMSSM by considering the constraints from the ATLAS searches for jets + E-T(miss) signals, we conclude that the NMSSM is able to explain the excess at 1 sigma level with the number of the signal events reaching its measured central value in optimal cases, and the best explanation comes from a compressed spectrum such as m((g) over tilde) similar or equal to 650 GeV, m((chi) over tilde2)(0) similar or equal to 565 GeV and m((chi) over tilde1)(0) similar or equal to 465 GeV. We also check the consistency of the ATLAS results with the null result of the CMS on-Z search. We find that under the CMS limits at 95% C.L., the event number of the ATLAS on-Z signal can still reach 11 in our scenario, which is about 1.2 sigma away from the measured central value.
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