Antiprotons in cosmic rays from neutralino annihilation

TL;DR

We compute the antiproton flux from relic neutralino annihilation within a two-zone diffusion framework, calibrated to stable and radioactive cosmic-ray data. The production term is factored into a supersymmetric flux factor Υ and a per-annihilation spectrum g(T_pbar) with a DM density profile ρ_DM, across two SUSY schemes (eMSSM and mSUGRA) and DM halo variations. The study finds the primary flux uncertainty spans about two orders of magnitude at low energy, dominated by the halo height L, while DM density profiles (e.g., NFW vs isothermal) modify the flux by at most ~20%. With optimistic propagation parameters (L ≈ 4 kpc) some low-mass neutralino configurations near m_χ ≈ 100 GeV could be excluded, and halo clumps or higher local density could further tighten constraints. The results underscore the need for improved propagation physics and halo modeling to leverage antiproton data for indirect SUSY searches.

Abstract

We calculate the antiproton flux due to relic neutralino annihilations, in a two-dimensional diffusion model compatible with stable and radioactive cosmic ray nuclei. We find that the uncertainty in the primary flux induced by the propagation parameters alone is about two orders of magnitude at low energies, and it is mainly determined by the lack of knowledge on the thickness of the diffusive halo. On the contrary, different dark matter density profiles do not significantly alter the flux: a NFW distribution produces fluxes which are at most 20% higher than an isothermal sphere. The most conservative choice for propagation parameters and dark matter distribution normalization, together with current data on cosmic antiprotons, cannot lead to any definitive constraint on the supersymmetric parameter space, neither in a low-energy effective MSSM, or in a minimal SUGRA scheme. However, if the best choice for propagation parameters - corresponding to a diffusive halo of L=4 kpc - is adopted, some supersymmetric configurations with the neutralino mass of about 100 GeV should be considered as excluded. An enhancement flux factor - due for instance to a clumpy dark halo or to a higher local dark matter density - would imply a more severe cut on the supersymmetric parameters.

Figures (19)

• Figure 1: Scatter plot of the supersymmetric flux factor $\Upsilon \equiv \xi^2\langle \sigma_{\rm ann} v \rangle_0/m_\chi^2$ as a function of the neutralino mass $m_\chi$, calculated in the eMSSM. Panel (a) refers to supersymmetric configurations with the neutralino as a dominant dark matter component ( i.e.$0.05 \leq \Omega_\chi h^2 \leq 0.3$, and therefore a rescaling factor $\xi=1$). The light (green) circles show the eMSSM configurations for which the neutralino relic abundance lies in the preferred range for CDM, as determined by the combined wmap+2d fgrs+Lyman--$\alpha$ analysis: $0.095 \leq \Omega_{CDM} h^2 \leq 0.131$cmb. Panel (b) refers to the neutralino as a subdominant dark matter particle ($\Omega_\chi h^2 < 0.05$).
• Figure 2: The same as in Fig. \ref{['fig:mssm_y_mchi']}, calculated in the mSUGRA scheme. Panels (a) and (c) refer to cosmologically dominant neutralinos ($0.05 \leq \Omega_\chi h^2 \leq 0.3$); panels (b) and (d) to subdominant neutralinos ($\Omega_\chi h^2 < 0.05$). The upper row (panels (a) and (b)) is obtained for the universal soft--scalar mass $m_0$ smaller than 1 TeV (for these models, the neutralino is mostly a bino state); the lower row (panels (c) and (d)) refers to values of $m_0$ in excess of 1 TeV (in this case the neutralino may have a substantial higgsino component). The light (green) circles in panel (a) and (c) show the mSUGRA configurations for which the neutralino relic abundance lies in the preferred range for CDM, as determined by the combined wmap+2d fgrs+Lyman--$\alpha$ analysis: $0.095 \leq \Omega_{CDM} h^2 \leq 0.131$cmb.
• Figure 3: Antiproton differential energy distribution for pure annihilation channels as a function of the reduced kinetic energy $x_{\bar{p}}\equiv T_{\bar{p}}/m_\chi$. Panel (a) refers to annihilation into a $b \bar{b}$ pair, for neutralino masses of: $m_\chi=10,60,100,300,500,1000$ GeV (from bottom to top); panel (b) refers to annihilation into a $ZZ$ pair, for $m_\chi=100,300,500,1000$ GeV (from top to bottom); panel (c) refers to annihilation into a scalar+pseudoscalar higgs pair $hA$, for $m_\chi=300,500,1000$ GeV (from top to bottom), and for: $m_h=120$ GeV, $m_A=200$ GeV, tan$\beta=10$ (ratio of higgs vev's) and $\alpha=0$ (higgs mixing parameter); panel (d) refers to annihilation into a $hZ$ pair, for $m_\chi=300,500,1000$ GeV (from top to bottom), and for: $m_h=120$ GeV, tan$\beta=10$ and $\alpha=0$.
• Figure 4: Branching ratios for the neutralino self--annihilation cross section in the eMSSM. Panel (a) shows the amount of the branching ratio for the annihilation into a fermion--antifermion final state ($\chi\chi\rightarrow f\bar{f}$). Panels (b), (c) and (d) show the amount, relative to the $f\bar{f}$ final state, of the annihilation into higgs bosons, gauge bosons and the mixed higgs-gauge bosons final state. Dark (red) points denote configuration with $0.05\leq \Omega_\chi h^2 \leq 0.3$ (dominant relic neutralinos). Light (green) circles indicate configuration with $\Omega_\chi h^2 < 0.05$ (subdominant relic neutralinos).
• Figure 5: The same as in Fig. \ref{['fig:mssm_branching']}, calculated in the mSUGRA scheme. Dark (red) points denote configuration with $0.05\leq \Omega_\chi h^2 \leq 0.3$ (dominant relic neutralinos). Light (green) circles indicate configuration with $\Omega_\chi h^2 < 0.05$ (subdominant relic neutralinos). Crosses (in blue) indicate the mSUGRA configurations with $m_0>1$ TeV.