Muon anomalous magnetic dipole moment in supersymmetric theories

Abstract

We study the muon anomalous magnetic dipole moment in supersymmetric theories. The impact of the recent Brookhaven E821 experimental measurement on both model-independent and model-dependent supersymmetric parameter spaces is discussed in detail. We find that values of tanβas low as 3 can be obtained while remaining within the E821 one-sigma bound. This requires a light smuon; however, we show that, somewhat surprisingly, no model-independent bound can be placed on the mass of the lightest chargino for any tanβgreater than or equal to 3. We also show that the maximum contributions to the anomalous magnetic moment are insensitive to CP-violating phases. We provide analyses of the supersymmetric contribution to the muon anomalous magnetic moment in dilaton-dominated supergravity models and gauge-mediated supersymmetry-breaking models. Finally, we discuss how other phenomena, such as $B(b\to sγ)$, relic abundance of the lightest superpartner, and the Higgs mass may be correlated with the anomalous magnetic moment, but do not significantly impact the viability of a supersymmetric explanation, or the mass limits obtainable on smuons and charginos.

Figures (8)

• Figure 1: The maximum possible values for the supersymmetric contribution to the muon anomalous magnetic moment, as a function of the lighter chargino mass and the lighter smuon mass. Gaugino mass unification conditions have not been imposed. All charged superpartners are required to be heavier than 100 GeV, and the lightest neutralino is required to be heavier than 50 GeV. The maximum allowed value for $|\mu|$ is taken to be 1000 GeV. The contours are shown from bottom to top for $\tan\beta =$ 2, 3, 6, 10, 20, 30, 40, 50. The red bars on the right vertical axes indicate the 1-$\sigma$ and 2-$\sigma$ allowed regions from the Brookhaven E821 experiment.
• Figure 2: Effects of larger allowed $|\mu |$: the maximum possible values for the supersymmetric contribution to the muon anomalous magnetic moment, as a function of the lighter chargino mass and the lighter smuon mass, for $\tan\beta=3$ and different values (2000 GeV, 1000 GeV, 500 GeV from top to bottom) of the allowed maximum $|\mu|$. Gaugino mass unification conditions have not been imposed. All charged superpartners are required to be heavier than 100 GeV, and the lightest neutralino is required to be heavier than 50 GeV. The red bars on the right vertical axes indicate the 1-$\sigma$ and 2-$\sigma$ allowed regions from the Brookhaven E821 experiment.
• Figure 3: Effects of a gaugino mass unification requirement: the maximum possible values for the supersymmetric contribution to the muon anomalous magnetic moment, as a function of the lighter chargino mass. The solid lines are the general results as before for $\tan\beta = 3,6,10,30$, while the dashed lines are obtained with the additional condition $M_1 = (5/3) \tan^2\theta_W M_2$ imposed. The maximum allowed value of $|\mu|$ is 1000 GeV. All charged superpartners are required to be heavier than 100 GeV, and the lightest neutralino is required to be heavier than 50 GeV. The red bars on the right vertical axis indicate the 1-$\sigma$ and 2-$\sigma$ allowed regions from the Brookhaven E821 experiment. (The corresponding plot as a function of the lighter smuon mass is essentially unaffected by the gaugino mass unification condition.)
• Figure 4: Effects of phases: the contribution to the muon anomalous magnetic moment as a function of the lighter chargino mass, with magnitudes of all parameters held fixed. The dashed lines enclose the region obtained as the phases of all parameters are varied over all possible values. The circles at the corners of the regions are obtained when all parameters are required to be real. The graph on the left is obtained for a model close to a dilaton-dominated supergravity model, while the graph on the right is the same but with $|\mu|$ adjusted to equal $|M_2|$.
• Figure 5: Predictions for $a_\mu^{\rm SUSY} - a_\mu^{\rm SM}$ in dilaton-dominated supergravity models with various $\tan\beta=2,3,6,10,20,30,40$ (from bottom to top), as a function of the lighter chargino mass and the lighter smuon mass. All charged superpartners are required to have mass above $100\hbox{\rm,GeV}$. The solid lines indicate where the lightest Higgs scalar boson mass $m_h$ exceeds its approximate LEP2 bound of 114 GeV, while the dashed lines indicate where $m_h < 114$ GeV. The red bars on the right vertical axes indicate the 1-$\sigma$ and 2-$\sigma$ allowed regions from the Brookhaven E821 experiment.