Charginos and Neutralinos in the Light of Radiative Corrections: Sealing the Fate of Higgsino Dark Matter

TL;DR

This work incorporates one-loop radiative corrections to chargino and neutralino masses into LEP-based MSSM analyses, revealing shifts in the μ–$M_2$ mapping and modest reductions in the inferred lightest neutralino mass by about 1 GeV. With LEP data up to 183 GeV and universal scalar masses, the authors update the lower limit on the neutralino mass to roughly $m_{ ilde{ ext{χ}}} \,\gtrsim\, 42$ GeV and raise the tanβ bounds to about $\tanβ \gtrsim 2.0$ for $μ<0$ and $\tanβ \gtrsim 1.65$ for $μ>0$, while cosmological relic-density constraints push $m_{ ilde{ ext{χ}}}$ higher in certain regions. The viability of Higgsino dark matter is shown to be strongly constrained, existing only in a very restricted region of parameter space (and largely disfavored for $μ>0$) when radiative corrections and co-annihilations are accounted for, with $m_{ ilde{ ext{χ}}}$ typically above ~71 GeV in the remaining Higgsino region. Overall, the study demonstrates that radiative corrections and LEP data jointly seal much of the Higgsino DM parameter space, guiding future collider searches toward the remaining gaugino-dominated scenarios and higher-energy LEP runs.

Abstract

We analyze the LEP constraints from searches for charginos $χ^{\pm}$ and neutralinos $χ_i$, taking into account radiative corrections to the relations between their masses and the underlying Higgs-mixing and gaugino-mass parameters $μ, m_{1/2}$ and the trilinear mass parameter $A_t$. Whilst radiative corrections do not alter the excluded domain in $m_{χ^{\pm}}$ as a function of $m_{χ^{\pm}} - m_χ$, its mapping into the $μ, m_{1/2}$ plane is altered. We update our previous lower limits on the mass of gaugino dark matter and on tan$β$, the ratio of Higgs vacuum expectation values, in the light of the latest LEP data and these radiative corrections. We also discuss the viability of Higgsino dark matter, incorporating co-annihilation effects into the calculation of the Higgsino relic abundance. We find that Higgsino dark matter is viable for only a very limited range of $μ$ and $m_{1/2}$, which will be explored completely by upcoming LEP runs.

Figures (7)

• Figure 1: The effects of one-loop radiative corrections in the $\mu,M_2$ plane, calculated for tan$\beta = 2$, $m_0 = 200$ GeV, $m_A = 1$ TeV and $A_t = 2 m_{1/2}$. The thick lines are one-loop-corrected contours corresponding to fixed values of chargino and neutralino masses, and the thin lines are tree-level contours. The continuous lines are for $m_{\chi^{\pm}} = 91{\rm \, Ge V}$, the dashed lines for $m_{\chi^{\pm}} = 86{\rm \, Ge V}$, the dash-dotted lines for the bound on associated neutralino production, and the dotted lines for $m_{\chi} = 40{\rm \, Ge V}$.
• Figure 2: (a) The experimental limit on $m_{\chi^{\pm}}$ as function of $M_2$ and as a function of $\Delta M \equiv m_{\chi^{\pm}} - m_{\chi}$, for fixed $m_0 = 200{\rm \, Ge V}$ and $\tan\beta = 2$. The value of $\mu$ is determined by the combination $m_{\chi^{\pm}}$ and $M_2$.The drop at large $M_2$ is due to the loss in experimental efficiency as $\chi^{\pm}$ decays into $\chi$ involve softer leptons. The dotted line comes from a tree-level analysis, and the solid line is obtained using an ad hoc parameterization of the experimental efficiency, in conjunction with the radiatively-corrected mass formulae. Note that the lines separate significantly when $M_2$ is large. (b) The experimental limit on $m_{\chi^{\pm}}$ is now plotted as a function of $\Delta M \equiv m_{\chi^{\pm}} - m_{\chi}$. Note that the tree-level and radiatively-corrected curves are almost coincident.
• Figure 3: Plots of the radiative correction to the lower limit on the neutralino mass, in the case that $m_{\chi^{\pm}} = 85{\rm \, Ge V}$, tan$\beta = 2$ and $\mu = - 140{\rm \, Ge V}$. The plots are obtained by varying $-500{\rm \, Ge V} \le A_t \le 500{\rm \, Ge V}$ and $50{\rm \, Ge V} \le m_0 \le 1000{\rm \, Ge V}$. The solid line in the second panel is for the fixed-point value $A_t = 2 m_{1/2}$. We see that the limit on $m_{\chi}$ is reduced by about 1 GeV if we assume this value of $A_t$ and take $m_0 = 80{\rm \, Ge V}$, corresponding to the tree-level lower limit on $m_{\chi}$.
• Figure 4: Contours of neutralino purity: 99%, 97% and (for $\mu < 0$) 75%, and chargino and neutralino masses (solid lines). The long-dashed lines are contours of high bino purity, the dotted lines are contours of high photino purity, the dashed lines are contours of high ${\tilde{H}}_{12}$ Higgsino purity, and the dash-dotted lines are contours of high ${\tilde{S}}_0$ Higgsino purity. The radiative corrections to $m_{\chi}$ are calculated for tan$\beta = 2$ and $m_0 = 100$ GeV.
• Figure 5: Survey of experimental and cosmological constraints in the $\mu, M_2$ plane, focusing on Higgsino dark matter for tan$\beta = 2$ and (a) $\mu < 0$ and (b) $\mu > 0$. We plot the radiatively-corrected contours for $m_{\chi^{\pm}} = 91{\rm \, Ge V}$, for $m_{\chi} + m_{\chi'_H} = 182{\rm \, Ge V}$, for selected values of $m_h$ and the Higgsino purity $p$, and for $\Omega_{\chi} h^2 = 0.1$. The shaded regions yield a Higgsino which satisfies the mass and relic density constraints described in the text.