Electroweak breaking and supersymmetry breaking

We discuss the clash between the absence of fine tuning in the Higgs potential and a sufficient suppression of flavour changing neutral current transitions in supersymmetric extensions of the standard model. It is pointed out that horizontalU(1) symmetry combined with theD-term supersymmetry breaking provides a realistic framework for solving both problems.     

Metastable supersymmetry breaking without scales

We construct new examples of models of metastable D=4$D=4$N=1$N=1$ supersymmetry breaking in which all scales are generated dynamically. Our models rely on Seiberg duality and on the ISS mechanism of supersymmetry breaking in massive SQCD. Some of the electric quark superfields arise as composites of a strongly coupled gauge sector. This allows us to start with a simple cubic superpotential and an asymptotically free gauge group in the ultraviolet, and end up with an infrared effective theory which breaks supersymmetry dynamically in a metastable state.     

The search for Higgs particles at high-energy colliders: Past,present and future

I briefly review the Higgs sector in the standard model (SM) and its minimal aupersymmetric extension, the MSSM. After summarizing the properties of the Higgs bosons and the present experimental constraints, I will discuss the prospects for discovering these particle at the upgraded Tevatron, the large hadron collider (LHC) and a high-energye ⁺ e ⁻ linear collider. The possibility of studying the properties of the Higgs particles will be then summarized.     

New type of stable Q balls in gauge-mediated supersymmetry breaking

We obtain a new type of a stable Q ball in the context of gauge-mediated supersymmetry breaking in the minimal supersymmetric standard model. It is a so-called gravity-mediation type of Q ball, but stable against the decay into nucleons, since the energy per unit charge is equal to gravitino mass m(3/2), which can be smaller than nucleon mass in the gauge-mediation mechanism. We consider the cosmological consequences in this new Q-ball scenario, and find that this new type of Q ball can be considered as the dark matter and the source for the baryon number of the universe simultaneously.     

B decays and supersymmetry

I discuss how supersymmetry affects various observables in B decays, and point out the interesting channels in the context of B factories.     

TeV能区物理

文章简要介绍研究TeV能区物理的意义、重要性和当前国际上的发展形势,以及清华大学粒子物理理论组为发展TeV能区物理研究所做的工作和取得的成果.     

TeV能区物理

文章简要介绍研究TeV能区物理的意义、重要性和当前国际上的发展形势,以及清华大学粒子物理理论组为发展TeV能区物理研究所做的工作和取得的成果.     

Search for supersymmetry at LEP-2

An extensive effort to search for a hint of a supersymmetric signal was carried out by the four LEP Collaborations. All LEP data, up to centre-of-mass energy of 209 GeV, was carefully analysed with no observed SUSY signal. In an attempt to further increase the sensitivity of the search, the four groups combined some of their searches, to no avail.     

Measuring Higgs CP properties through top quark production at a photon collider

We study resonant effects of heavy Higgs bosons on the top-pair production process at a photon linear collider. Observables which can be obtained by circular polarization of colliding photons and polarization measurement through the angular distribution of the top quark decays are useful not only for measuring the Higgs CP parity but also for resolving degeneracy of Higgs bosons.      

WIMP dark matter in gauge-mediated SUSY breaking models and its phenomenology

We propose an extended version of the gauge-mediated SUSY breaking models where extra SUL₍₂₎$\mathit{SU}{(2)}_L$ doublets and singlet field are introduced. These fields are assumed to be parity-odd under an additional matter parity. In this model, the lightest parity-odd particle among them would be dark matter in the Universe. In this Letter, we discuss direct detection of the dark matter and the collider signatures of the model.     

Physics prospects at a linear e + e − collider

The talk described the prospects of studying standard model parameters as well as scenarios beyond the standard model, like the minimal supersymmetric standard model, theories with extra dimensions and theories with extra neutral gauge bosons, at a future linear e ⁺ e ⁻ collider.     

LHC/ILC/cosmology interplay

There is a strong and growing interplay between particle physics and cosmology. In this talk, I discuss some aspects of this interplay concerning dark matter candidates put forth by theories beyond the standard model. In explaining the requirements for collider tests of such dark matter candidates, I focus in particular on the case of the lightest neutralino in the MSSM.     

Observational constraints on dark matter decaying via gravity portals

Global symmetry can guarantee the stability of dark matter particles (DMps). However, the nonminimal coupling between dark matter (DM) and gravity can break the global symmetry of DMps, which in turn leads to their decay. Under the framework of nonminimal coupling between scalar singlet dark matter (ssDM) and gravity, it is worth exploring the extent to which the symmetry of ssDM is broken. It is suggested that the total number of decay products of ssDM cannot exceed current observational constraints. Along these lines, the data obtained with satellites such as Fermi-LAT and AMS-02 suggest that the scale of ssDM global symmetry breaking can be limited. Because the mass of many promising DM candidates is likely to be in the GeV-TeV range, we determine reasonable parameters for the ssDM lifetime within this range. We find that when the mass of ssDM is around the electroweak scale (246 GeV), the corresponding 3begin{document}$sigma$end{document} lower limit of the lifetime of ssDM is begin{document}$5.3times10^{26}$end{document} s. Our analysis of ssDM around the electroweak scale encompasses the most abundant decay channels of all mass ranges so that the analysis of the behavior of ssDM under the influence of gravity is more comprehensive.     

Effects of a Family Non-universal Z' Boson in B_d → μ~+μ~-and B~-→ π~-μ~+μ~-,ρ~-μ~+μ~-Decays

Motivated by the recently updated experimental measurement on Bˉd →μ+μ and B →πμ+μ decays by CDF and Belle collaborations,we revisit these decays,as well as B →ρμ+μ decay,within the Standard Model,and evaluate the effects of a family non-universal Z' boson.Under the constraint from B(B →πμ+μ),we find the ranges of the Z' couplings SμLμR 5.2 × 10 2 or DμLμR 8.1 × 10 2 are excluded.Within the allowed Z' parameters spaces,comparing with the SM predictions,we find that B(Bˉd →μ+μ),B(B →πμ+μ),and B(B →ρμ+μ) could be enhanced by a factor about 226%,245%,and 254%,respectively,by Z' contributions.However,they are hardly to be reduced.Furthermore,the zero crossing in the normalized forward-backward asymmetry spectrum of B →ρμ+μ decay at low dimuon mass always exists.     

Equivalence of stochastic quantization to field theories from supersymmetry

Using the Ward-Takahashi identities from the hidden supersymmetry in Langevin equation we present a very simple proof of the equivalence of stochastic quantization to field theories.     

Higgs physics at LHC

The large hadron collider (LHC) and its detectors, ATLAS and CMS, are being built to study TeV scale physics, and to fully understand the electroweak symmetry breaking mechanism. The Monte-Carlo simulation results for the standard model and minimal super symmetric standard model Higgs boson searches and parameter measurements are discussed. Emphasis is placed on recent investigations of Higgs produced in association with top quarks and in vector boson fusion channels. These results indicate that Higgs sector can be explored in many channels within a couple of years of LHC operation, i.e.,L = 30 fb⁻¹. Complete coverage including measurements of Higgs parameters can be carried out with full LHC program.     

Associted Production of Z Boson and a Pair of New Quarks at LHC

The associated production of Z boson and a pair of new quarks at the Large Hadron Collider （LHC） is studied. The cross sections for both sequential fermions and vector-like fermions are presented. It is found that for sequential fermions the cross sections can reach 1 - 10^2 /b for heavy quark mass mQ from 1000 GeV to 200 GeV. For vector-like quarks, the cross sections are suppressed by mixing parameter sin OL. Focusing on process pp → b＇b＇, we investigate the possibility of detecting the 6l 4- 2j signal. For a b＇ with light mass and a large branching ratio of b＇ → bZ, it is found that only several signal events （ parton level ） can be produced with 1000 fb^-1 integrated luminosity. Although the signal events are rare, all the final states are produced centrally and multi lepton final states are clear at hadron collider, which could be easily detected.     

Symmetries of the standard model without and with a right-handed neutrino

Given the particle content of the standard model without and with a right-handed neutrino, the requirement that all anomalies cancel singles out a set of possible global symmetries which can be gauged. I review this topic and propose a new gauge symmetryB — 3L _T in the context of the minimal standard model consisting of the usual three families of quarks and leptons plus just onev _R. The many interesting phenomenological consequences of this hypothesis are briefly discussed.     

Effects of a Family Non-universal Z' Boson in \bar{B}_d→μ+μ- and B- →π-μ+μ-,ρ-μ+μ- Decays

Motivated by the recently updated experimental measurement on \bar{B}_d→μ⁺μ^- and B^-→π^-μ⁺μ^- decays by CDF and Belle collaborations, we revisit these
decays, as well as B^-→ρ^-μ⁺μ^- decay, within the Standard Model, and evaluate the effects of a family non-universal Z' boson. Under the constraint from {\cal B}(B^-→π^-μ⁺μ^-), we find the ranges of the Z' couplings S^LR_μμ< -5.2×10^-2 or D^LR_μμ < -8.1× 10^-2 are excluded. Within the allowed Z' parameters spaces, comparing with the SM predictions, we find that {\cal B}(\bar{B}_d→ μ⁺μ^-, {\cal B}(B^-→ π^-μ⁺μ^-), and {\cal B}(B^-→ρ^-μ⁺μ^-) could be enhanced by a factor about
226%, 245%, and 254%, respectively, byZ' contributions. However, they are hardly to be reduced. Furthermore, the zero crossing in the normalized forward-backward asymmetry spectrum of B^- →ρ^-μ⁺μ^- decay at low dimuon mass always exists.