| Weakly Interacting Massive Particle(WIMP)has been one of the most promising dark matter candidates and been widely studied in the supersymmetric theoretical framework during the last three decades.However,recent dark matter detection experiments reveal that the interaction between dark matter particles and nucleons is very feeble instead of weak,which deviates from the essential assumption of the WIMP particle.Since the Minimal Supersymmetric Standard Model(MSSM)and Next-to Minimal Supersymmetric Standard Model(NMSSM)are based on the original idea of the WIMP dark matter,they are questioned by more and more physicists.During the last three years,our team analyzed various experimental constraints on the MSSM and NMSSM from the search for sparticles at the Large Hadron Collider(LHC)and the dark matter detection experiments and concluded the conditions that the WIMP dark matter should satisfy to be consistent with these experiments.More importantly,we pointed out that the dark matter-nucleon scattering cross-section can be suppressed naturally if the super-partner of the neutrino,namely,sneutrino,acts as the dark matter candidate.In spirits of this idea,we construct the most economical and natural supersymmetric theory,i.e.,the NMSSM extended by the seesaw mechanism.This kind of theory can explain the neutrino oscillation phenomenon and naturally generate the electroweak symmetry breaking under the premise to be consistent with the experimental constraints.No other teams are focusing on this idea currently to solve the significant problem that the MSSM and NMSSM are facing.According to our study,the sneutrino dark matter in the NMSSM with the seesaw mechanism has the following primary properties:ˇTogether with the singlet-dominated Higgs bosons and the sterile neutrinos,it may form a self-contained theoretical structure secluded from the Standard Model in particle physics.In this structure,the dark matter annihilated into a pair of the Higgs bosons or the neutrinos,which can naturally account for its experimentally measured density.ˇDue to the interaction mediated by the singlet-dominated Higgs bosons,the sneutrino dark matter and the higgsino kept in a thermal-bath in the early universe.In this case,the annihilation of the higgsino pair ensured the correct abundance without tuning the theoretical input parameters.ˇIn either case,the sneutrino dark matter couples very weakly to the Standard Model particles,which naturally makes the dark matter-nucleon scattering suppressed.ˇ Because the sneutrino dark matter and the traditional neutralino dark matter are very different,the decay pattern of massive supersymmetric particles and its signal on the collider can be very different from the predictions of MSSM and NMSSM.This property effectively weakens the constraints of the LHC experiments on supersymmetric particles.Regarding the NMSSM with the seesaw mechanism,our team has completed six works,of which three papers committed to studying the essential characteristics of the theory[1-3],two papers discussed the applications of the theory[4,5],and another paper investigated the dark matter-nucleon scattering deeply in different supersymmetric theories[61.This dissertation will focus on the first three works to introduce the theory's essential features,and it is organized as follows:ˇIn the fourth chapter of the paper,we consider the lightest sneutrino as the dark matter candidate in the NMSSM with Type-I seesaw mechanism(from now on referred to as Type-I NMSSM)and carry out a global fit of the theory[1].We use the Multinest algorithm to perform a very detailed scan of the model's parameter space by constructing a likelihood function.This function includes the LHC's measurement of the property for 125GeV Higgs boson,Planck satellite's measurement of dark matter residual density,and the results of the dark matter direct detection experiment XENON1T-2018,the Fermi-LAT satellite search for dwarf galaxy and B physical measurement.Through Bayesian and frequency theory analysis of the scan results,we obtain a series of characteristics of the theory(due to the consideration of many latest experimental results,these characteristics are entirely different from the previous research conclusions).Our work is currently the only one that performed the global fit of the Type-I NMSSM.With the help of the team's advanced computing cluster,we spent about 1 million core-hours to complete the relevant calculations.ˇGiven the unnatural smallness of the neutrino Yukawa coupling in the Type-I NMSSM,we incorporate the NMSSM with the inverse seesaw mechanism in Chapter 5 of this thesis[2]and abbreviate the resulting theory as ISS-NMSSM hereafter.Compared with the Type-I NMSSM,we introduced an additional type of sterile neutrino field X in the ISS-NMSSM.The advantage of this doing is that the masses of the sneutrino dark matter and the sterile neutrinos are naturally located around the electroweak scale,the theory is consistent with the existing experimental results more flexibly and naturally,and meanwhile,its phenomenology becomes very rich[2].In the second section of Chapter 5 in this thesis,we analyze the annihilation of the sneutrino dark matter and its scattering with the nucleons through analytical formulas and point out the characteristics of the theory.Besides,we also use the Markov chain algorithm to scan the model parameter space and consider the constraints of various experiments on the theory.We confirm our speculations about these characteristics by numerical results[2].Recently we have realized that the above research needs a more dedicated study,and meanwhile,it neglects the impacts of neutrino unitarity on the theory[3].In the third section of Chapter 5,we focus on the constraint of the unitarity and obtain the cross-section formula for the dark matter-nucleon scattering in a very concise form.We verify the validity of these formulas through numerical calculations,and systematically demonstrated the effect of the unitarity and the direct detection experiments on the general characteristics.This research deepens our understanding of ISS-NMSSM and lays the foundation for a global fitting study~2. |
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