Cosmology And High-energy Collider Physical Phenomenological Study

The standard model(SM),including the strong and electroweak interactions,is the SU(3)_c(?)SU(2)_L(?)U(1)_Y gauge model which has been extensively tested during the past 30 years.The discovery of the weak neutral current brought the Nobel Prize of physics to S.Weinberg and Salam in 1979.Rubbia and Van der Meer were awarded with the Nobel Prize for physics in 1984 because of the experimentally detecting the intermediate vector bosons(W^±and Z₀) and then David J.Gross,H.David Politzer and Frank Wilczek obtained their Nobel Prize for physics in 2004 because of the asymptotical freedom.The predictions of the SM are in accordance with the data coming from all the experiments within the error tolerance so far.All the facts indeed strengthen our confidence in the SM.However,there are still some problems existing in the framework of SM.For example,the exits the famous hierarchy problem,and etc.But the most troublesome problem is that the Higgs particle which is crucial in the Higgs mechanism hasn't been found in the experiments.This indicate that the explanation provided by the SM should not be the end of the story and it will let a little room for the new physics beyond the standard model.There are many new physics models have been proposed,such as:Technicolor(TC),Little Higgs,etc.Technicolor is a theory without the Higgs particle,the basic idea of it is introduce a new strong force that similar of the asymptotically free QCD and the new TC fermions.At a rather high scale,the condensation is formed between two TC fermions.This phenomenon could be taken the function of the SM Higgs boson.So the electro-weak symmetry is broken to the electromagnetic symmetry dynamically.Technicolor has solved the problems of the SM naturally.However,there are also some problems with the original Technicolor model.In order to explain the masses of ordinary quarks and leptons without leading large falvor-changing neutral current(FCNC),people have built the walking Technicolor model(WTC).Accommodating the top quark mass without large corrections to△Γ_b and T leads us to consider topcolor-assisted Technicolor(TC2) model.Despite the great progress that has been made,no complete and consistent model exists.The ex- perimental instruction is needed to make further progress on these dynamical theories.The top-pion(Π^0,±) and top-Higgs(H_TC) are the typical particles predicted by the topcolor-assisted techinicolor(TC2) model,the observation of these particles can be regarded as the direct evidence of the TC2 model.In our work,we study two onelooplevel pair production processes of these typical particles,i.e.,e⁺e^-→H_TCΠ⁰ and e⁺e^-→Π⁺Π^-[1,2].The cross sections of these processes can reach the level of a few fb at most of the parameter spaces.At the same time,the NLO corrections of these processes are obvious.One the other hand,we also study the process of gg→H_TC at the LHC,the results show that the production rate is much higher than the similar gg→h of the SM.We also find that the production rate of gg→H_TC also larger than another neutral scalar particle(top-pion:Π⁰) production rate in the process of gg→Π⁰ [3].So we believe that this production process is worth expecting at the imminent LHC detection.We know that another flaw of SM is it can't provide a appropriate candidate of the dark matter,but the Little Higgs model with T parity could sovle the problem successfully.In the Littlest Higgs model with T parity,there is a neutral minimum weight particle: heavy photon A_H and it has an odd T parity,if the T parity was conservation, it would be stable and not decay.So the heavy photon could be regarded as an ideal candidate of the WIMP cold dark matter.In this paper,we have calculated the relic abundance of the heavy photon in terms of the Boltzman-Lee-Weinberg time-evolution equation[4].Our calculations show that when Higgs mass M_H taken to be 300 GeV and don't consider T-parity violation,only two narrow ranges 133＜M_AH＜135 GeV and 167＜M_AH＜169 GeV are tolerable with the current astrophysical observation and if 135＜M_AH＜167 GeV,there must at least exist another species of heavy particle contributing to the cold dark matter. The effects of the T-parity violation is also considered in our work.If the T-parity can be violated,the heavy photon can decay into regular standard model particles and would affect the dark matter abundance in the universe,we discuss the constraint on the T-parity violation parameter based on the present data.Direct detection prospects of earth-base are also discussed in some detail in our work.