This doctoral thesis addresses aspects of Supersymmetry (Susy) phenomenology. In addition to previously published work, it contains introductions to the following topics: from classical mechanics to quantum field theory for the more casual reader, electroweak naturalness, the Higgs as a pseudo-Nambu-Goldstone boson, the MSSM and NMSSM, simple and less simple models of gauge-mediated Susy breaking (GMSB), collider searches for Susy and other new theories, transverse mass observables with missing energy, and Brazil-band plots. The previously published work is as follows.
The optimally natural Higgs-stop sector in the MSSM in light of the 2012 discovery of a Higgs boson is derived, namely that of almost maximal mixing, with the scalar top partners almost as light as can be. The discovery is also interpreted numerically in the NMSSM, with greater emphasis placed on the visibility of the Higgs boson at the observed mass, i.e. on signal strengths. I investigate the role played by the mediation scale of GMSB: this is found to be as a control of the extent to which Yukawa couplings de-tune flavour-blind relations set by gauge couplings. Finally, issues relating to the discovery or exclusion of Susy at colliders are discussed. Bounds are derived for the masses of new particles from LHC searches for excesses of jets and missing energy without leptons, and compared to constraints arising from Higgs boson searches, for models of GMSB and the Constrained Minimal Supersymmetric Standard Model. I present a novel search strategy for new physics signatures with two neutral, stable particles, when such particles are produced by boosted decays. (Susy motivations include models with light gravitinos, pseudo-goldstinos, singlinos or new photinos.) The method is shown to produce sharp mass peaks that enhance the visibility of the signal, with mass reconstruction to 5% from O(100) events.
We propose to accommodate economically the type-II neutrino seesaw mechanism in (G)NMSSM from GMSB and AMSB, respectively. The heavy triplets within neutrino seesaw mechanism are identified to be the messengers. Therefore, the $μ$-problem, the neutrino mass generation, LFV as well the soft SUSY breaking parameters can be economically combined in a non-trivial way. General features of such extensions are discussed. The type-II neutrino seesaw-specific interactions can give additional Yukawa deflection contributions to the soft SUSY breaking parameters of NMSSM, which are indispensable to realiz…
This study provides a brief overview of low-energy supersymmetry (SUSY) in light of current experimental constraints, such as collider searches, dark matter searches, and muon $g-2$ measurements. In addition, we survey a variety of low energy supersymmetric models: the phenomenological minimal supersymmetric model (MSSM); the supersymmetric models with cut-off-scale boundary conditions, i.e., the minimal supergravity (mSUGRA) or the constrained MSSM (CMSSM), the gauge mediation of SUSY breaking (GMSB), and the anomaly mediation of SUSY breaking (AMSB), as well as their extensions. The conclusi…
Higgs mass and muon anomalous magnetic moment in the U(1) extended MSSM
我们研究了具有额外U（1）规范对称性的MSSM的唯象问题。我们发现，最轻的希格斯玻色子玻色子的质量可以增加到125 GeV，而不引入一个大的超对称尺度或大的A项，在CMSSM和规范介导的超对称破缺（GMSB）模型的框架。这一方案可以同时解释U（1）-扩展的CMSSM/GMSB模型中μ子异常磁矩（μ on g-2）在1 σ水平上的差异。在CMSSM的情况下，暗物质丰度也可以解释。
The SUSY contributions $Δa_μ$ to muon $g-2$ anomaly can not even reach $3σ$ in ordinary gauge mediated SUSY breaking (GMSB) scenarios because of the strong correlations between the colored sparticle masses and the uncolored EW sparticle masses. An interesting extension to GMSB is the (Extra)Ordinary Gauge Mediation (EOGM), which can relax the correlations between squarks and sleptons with non-universal choices for $N_{eff,3}$ and $N_{eff,2}$. We find that EOGM scenarios with $N_{eff,3}\ll N_{eff,2}$ can explain the muon $g-2$ anomaly within $3σ$ range, however can not explain the new W-boson m…
The new FNAL result of the muon $g-2$, combined with the BNL result, shows a 4.2$σ$ deviation from the SM. We use the new data of the muon $g-2$ to revisit several GUT-scale constrained SUSY models with the constraints from the LHC searches, the dark matter detection, the flavor data and the electroweak vacuum stability. We first demonstrate the tension between the muon $g-2$ and other experimental measurements in the CMSSM/mSUGRA. Then after discussing the possible ways to alleviate such a tension and showing the muon $g-2$ in pMSSM under relevant experimental constraints, we survey several e…
By extending a previously proposed conformal gauge mediation model, we construct a gauge-mediated SUSY breaking (GMSB) model where a SUSY-breaking scale, a messenger mass, the $μ$-parameter and the gravitino mass in a minimal supersymmetric (SUSY) Standard Model (MSSM) are all explained by a single mass scale, a R-symmetry breaking scale. We focus on a low scale SUSY-breaking scenario with the gravitino mass $m_{3/2}=\mathcal{O}(1){\rm eV}$, which is free from the cosmological gravitino problem and relaxes the fine-tuning of the cosmological constant. Both the messenger and SUSY-breaking secto…
Higgs, di-Higgs and tri-Higgs production via SUSY processes at the LHC with 14 TeV
我们系统地研究了超对称粒子在唯象MSSM（pMSSM）中衰变产生质量约为$125$ GeV的希格斯玻色子.我们发现区域的参数空间是一致的，与所有的世界数据，并预测在14 TeV的LHC的异常希格斯粒子，双希格斯粒子，甚至三希格斯粒子事件的相当大的速度。所有相关的超对称性生产过程进行了调查。我们发现，希格斯玻色子可以产生在各种各样的超对称过程中，导致在一个大范围的不同的检测器签名包含丢失的横向动量。这样的希格斯事件是新物理学的杰出标志，已经为早期的14 TeV LHC数据。超对称过程对于消除即将到来的标准模型希格斯和双希格斯生产测量中发现的偏差也很重要。
We have studied the SUSY scale dependence of supersymmetric radiative corrections to bottom quark mass on the branching ratio of $B_s^0 \to μ^+μ^-$ and its impact on the cMSSM parameter space. The supersymmetric radiative corrections to bottom quark mass is in general evaluated at the SUSY scale, which is normally considered to be the geometric mean of stop masses. Then, the running of bottom quark mass is considered from the SUSY scale to the matching scale $M_W$ of the effective Hamiltonian which describes this decay. It is found that the branching ratio varies drastically with the SUSY scal…
The like-sign dimuon charge asymmetry in SUSY models
我们研究了新的物理（NP）的影响，最近报道的3.2西格玛标准模型（SM）的偏差在Tevatron的同号双μ子不对称性。假设新物理只进入B（s）混合振幅，我们探讨了一般新物理，一般超对称（SUSY）模型和SUSY SU（5）的含义。在超对称SU（5）的情况下，我们利用大统一理论尺度之间的关系slepton和夸克软质量预测率轻子味破坏（LFV）。预测率tau -> mu +伽马被发现是可检测的，在未来的超级B工厂。
We examine production and decay of heavy neutral SUSY Higgs bosons pp-> H,\ A -> τ\barτ within the hMSSM and compare against a perhaps more plausible natural supersymmetry scenario dubbed m_h^{125}({\rm nat}) which allows for a natural explanation for m_{weak}\simeq m_{W,Z,h}\sim 100 GeV while maintaining m_h\simeq 125 GeV. We evaluate signal against various Standard Model backgrounds from γ,Z ->τ\barτ, t\bar{t} and vector boson pair production VV. We combine the transverse mass method for back-to-back (BtB) taus along with the ditau mass peak m_{ττ} method for acollinear taus as our signal ch…
Indirect heavy SUSY signals in Higgs and top decays
本文综述了在最小超对称标准模型和超重超对称粒子退耦极限条件下，在单圈水平上，Higgs和顶夸克衰变的超对称QCD辐射修正的最新结果.特别注意的是特殊的衰变$h^0\to b \bar b$，$H^+\to t \bar b$，$H^0\to b \bar b$，$A^0\to b \bar b$和$t \to H^+\bar b$的辐射校正重方和重胶子不去耦，并在大$\tan β$增强。一些有趣的现象学后果也简要总结。
