Phenomenology of Scalar Singlet Dark Matter in BSM Models

Approximately 85% of the mass of the universe is classified as dark matter, a type of matter outside the framework of the Standard Model.This thesis studies the phenomenology of three models that incorporate dark matter.Firstly, a singlet scalar dark matter candidate is added to two previously established models: the Higgslike dilaton and the Georgi-Machacek models.The parameters of these models are constrained using experimental results such as dark matter direct detection measurements, Higgs signal strengths, Higgs invisible width and the measured relic abundance of dark matter in the universe.The notion of self-interacting dark matter, derived from measurements of galaxy cluster Abell 3827, is also studied for SSDM extensions of both the Standard Model and the Two Higgs Doublet model.The parameters of these models are in each case tightly constrained by experiment.iv Preface vTable of Contents vi List of Tables ix List of Figures x List of Figures 2.1 Elementary particles of the Standard Model . . . . . . . . . . . . . . 4 2.2 An elementary vertex for QED . . . . . . . . . . . . . . . . . . . . . . 5 2.3 The composition of the universe, according to percentage by mass. . . 10 3.1 Feynman vertex for invisible Higgs decay . . . . . . . . . . . . . . . .12 3.2 The Feynman diagram for DM direct detection through DM/nucleon scattering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 4.1 Parameter space of c gg and c γγ , where the allowed region is χ 2 < 5.9.20 4.2 The branching ratio for the dilaton decay to invisible particles, with c gg = 0.67 and c γγ = -6.5.The horizontal line is the ATLAS upper bound [19]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21 4.3 A contour plot of the m S and c gg .The contours are the values for the branching ratio, with an experimental cutoff of 0.28.The value of c gg is clearly not sensitive to the value of m S -no new information is gained concerning these parameters. . . . . . . . . . . . . . . . . . .22 4.4 The Feynman diagrams for the processes SS→xx, where x is a SM particle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 4.5 The Feynman diagrams for the process SS→ σσ. . . . . . . . . . . . .24 4.6 The DM relic abundance as a function of the DM mass.The λ = 3 case corresponds to the black line, and the λ = 4π case corresponds to the lower grey line.The horizontal grey line is the experimental value [21]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 4.7 The DM direct detection cross section as a function of the DM mass.The cases for λ = 3 and λ = 4π are shown in black and dark grey, respectively.The experimental limits are, starting from bottom: DEAP projection (black), LUX (grey), and XENON (light grey). . . . . . .27 5.1 Feynman diagram for SS → A + B where A, B are SM particles . . .32 5.2 Feynman diagram for SS → H 3 V ( * ) . . . . . . . . . . . . . . . . . . .33 x 5.3 Feynman diagrams for SS → h 1 h 2 . . . . . . . . . . . . . . . . . . . .34 5.4 The average and standard deviation of critical parameters . . . . . .35 5.5 Feynman diagram for direct detection . . . . . . . . . . . . . . . . . .37 5.6 Direct detection cross section as a function of m S .The left plot is a zoom of the low-m S region while the right plot shows the full m S range scanned.Experimental bounds include LUX (magenta), XENON10 (purple), XENON1T (brown), DEAP3600 (green), and the neutrino floor (yellow). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38 5.7 Constraint from invisible decays of the Higgs for a dark matter mass range between 0 GeV and 125/2 GeV.The blue points are allowed while the red points are excluded by either direct detection constraints, b → sγ constraints, constraints on the invisible decays of the Higgs, dwarf spheroidal galaxy constraints, or mass constraints on the triplet and fiveplet.Anything above the blue line is excluded. . . . . . . . .39 5.8 Parameter space of κ f and κ V .The blue points are allowed by all previously imposed constraints. . . . . . . . . . . . . . . . . . . . . .41 6.1 Abell 3827 HST image from Reference [42], showing the F160W (red), F160W (green) and F336W (blue) optical bands on a logarithmic colour scale.Labels N1 through N4 are the four bright central galaxies, while N5 is a star. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 6.2 Feynman diagrams for the interaction SS → SS . . . . . . . . . . . .45 6.3 Feynman diagrams for the annihilation of DM into SM particles in the real singlet scalar extension of the SM. . . . . . . . . . . . . . . . . .46 6.4 The allowed region for m S and |λ ef f | to obtain the desired range in Equation 6.8.This includes the constraints from perturbative unitarity and thresholds for DM annihilation to electrons, muons, and neutral pions. . . . . . . . . . . . . . . . . . . . .

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