PAMELA and dark matter

Abstract

Assuming that the positron excess in PAMELA satellite data is a consequence of annihilations of cold dark matter, we consider from a model-independent perspective if the data show a preference for the spin of dark matter. We then perform a general analysis of annihilations into two-body final states to determine what weighted combination of channels best describes the data.

Figures (9)

• Figure 1: Annhilations of DM directly into $e^+e^-$ give the $e^+$ line at about $M_{DM}=150$ GeV. The secondary positron spectrum from decays into $e^+\nu$ of longitudinal (transverse) $W$ bosons is labeled $W_L W_L$ ($W_T W_T$); the soft component of the spectra are neglected for illustration. Including the soft component (with spin-correlations neglected) results in a much softer spectrum labelled $WW$ that does not fit the PAMELA data above 10 GeV. The solid curve is the expected background. The Med set of propagation parameters is used with a cored isothermal profile for the DM halo.
• Figure 2: Positron fraction from DM annihilation into $e^+e^-$, $\mu^+\mu^-$, $\tau^+\tau^-$, $W^+W^-$, $ZZ$, $c\bar{c}$, $b\bar{b}$, and $hh$, with a Standard Model Higgs boson $h$ of mass 120 GeV for the Med set of propagation parameters. We have assumed that the DM annihilates into each mode with a 100% branching fraction. Accounting for the smaller boost factor, the $e^+e^-$ mode is somewhat preferred; see Table \ref{['table3']}. The Max set yields spectra very similar to the Med set.
• Figure 3: Same as Fig. \ref{['fig:2']}, but for the Min set of propagation parameters. The $\mu^+\mu^-$, $\tau^+\tau^-$ and $W^+W^-$ modes are preferred; see Table \ref{['table3']}.
• Figure 4: The probability distribution of the weight of each channel $f$ for the Med and Min sets. The medians, and $1\sigma$ and $2\sigma$ C. L. ranges are indicated in the lower panels.
• Figure 5: A graphical representation of the correlations between modes for the Med (upper triangle) and Min (lower triangle) propagation sets. The cells along the diagonal show the probability distribution of $f$ corresponding to the mode labeled. The contour plots show the $2\sigma$ allowed regions in planes of weights, with $f$ of the column (row) mode along the x-axis (y-axis). No two modes are significantly correlated with each other.