Supersymmetric Electroweak Baryogenesis Via Resonant Sfermion Sources

Abstract

We calculate the baryon asymmetry produced at the electroweak phase transition by quasi-degenerate third generation sfermions in the minimal supersymmetric extension of the Standard Model. We evaluate constraints from Higgs searches, from collider searches for supersymmetric particles, and from null searches for the permanent electric dipole moment (EDM) of the electron, of the neutron and of atoms. We find that resonant sfermion sources can in principle provide a large enough baryon asymmetry in various corners of the sfermion parameter space, and we focus, in particular, on the case of large $\tanβ$, where third-generation down-type (s)fermions become relevant. We show that in the case of stop and sbottom sources, the viable parameter space is ruled out by constraints from the non-observation of the Mercury EDM. We introduce a new class of CP violating sources, quasi-degenerate staus, that escapes current EDM constraints while providing large enough net chiral currents to achieve successful "slepton-mediated" electroweak baryogenesis.

Figures (9)

• Figure 1: Supergauge equilibration time scales for the RH (s)tops (Left) and LH (s)quarks (Right), where $M_{\tilde{Q}_3}$ ($M_{\tilde{U}_3}$) $=1000$ GeV in computing the RH (LH) stop rates and $M_1=100$ GeV, $M_2=200$ GeV. Also shown is the diffusion time-scale $\tau_{\rm diff}$ in both cases. The superequilibrium timescale is longer than $\tau_{\rm diff}$ only in kinematically forbidden regions and for heavy squarks, where the baryon asymmetry is suppressed.
• Figure 2: Regions of the stop soft supersymmetry breaking mass parameter space consistent with the observed value of the baryon asymmetry resulting from stop sources for $\mu=1000$ GeV, $\left|A_t\right|=250$ GeV (Left) and $\left|A_t\right|=100$ GeV (Right). Regions shaded blue (green) correspond to $Y_B\geq Y_{Obs}$ with $Y_B<0$ ($Y_B>0$) for maximal CP-violating phase. The dotted blue contour on the left marks the region that would be consistent with stop-sourced EWB if the vev-insertion approximation had underestimated $Y_B$ by a factor of 10 (we omit this curve in subsequent plots). On the left we also show, by the darker shaded regions, the parameter space compatible with $10\times$ the observed BAU, i.e. the allowed regions if the vev-insertion approximation overestimated $Y_B$ by a factor of 10. Black shaded regions are excluded by stop mass direct searches; regions to the left of the thick red line are excluded by LEP Higgs mass bounds in both cases. Current constraints on the electron, neutron, and $^{199}$Hg EDMs are represented by the black dashed-dot, dashed, and dashed-double-dot lines, respectively, with regions to the left of each line ruled out by null results; the projected future reaches for $d_e$, $d_n$, and $d_{Hg}$ measurements are shown in magenta (where applicable). In both cases here, both the $d_e$ and $d_n$ future sensitivities lie above the plane shown. For the $\left|A_t\right|=250$ GeV case, the Mercury EDM future sensitivity also lies above the plane shown.
• Figure 3: Same as Fig. \ref{['fig:stop_sources1']}, but for $\left|A_t\right|=250$ GeV, $\mu=200$ GeV (Left) and $\left|A_t\right|=1000$ GeV, $\mu=1000$ GeV (Right). For $\left|A_t\right|=250$ GeV, the $Y_B>0$ curve falls beneath the black shaded region and future measurements of the neuron EDM are expected to probe all parameter space shown. For $\left|A_t\right|=1000$ GeV, the expected reaches of $d_e$, $d_n$, and $d_{Hg}$ future measurements lie above the plane shown here.
• Figure 4: Neutron EDMs for $M_{\tilde{U}_3} = 800$ GeV, $\tan \beta = 10$, $\mu = 1000$ GeV and $\left|A_t\right| = 250$ GeV. Red denotes negative values. Left: the three independent calculations of the neutron EDM. Right: EDM subcomponents using QCD sum rules. By far the largest contribution comes from the down-quark chromo-EDM $d^C_d$, followed by the down-quark EDM $d^E_d$.
• Figure 5: Left: a breakdown of the Mercury EDM, using the same parameters as in figure \ref{['fig:neutEDM']}. Almost the entire contribution comes from the down-quark chromo-EDM (multiplied by a constant factor). Right: a further breakdown of the down-quark chromo-EDM.