PAMELA Positron Excess as a Signal from the Hidden Sector

Abstract

The recent positron excess observed in the PAMELA satellite experiment strengthens previous experimental findings. We give here an analysis of this excess in the framework of the Stueckelberg extension of the standard model which includes an extra $U(1)_X$ gauge field and matter in the hidden sector. Such matter can produce the right amount of dark matter consistent with the WMAP constraints. Assuming the hidden sector matter to be Dirac fermions it is shown that their annihilation can produce the positron excess with the right positron energy dependence seen in the HEAT, AMS and the PAMELA experiments. Further test of the proposed model can come at the Large Hadron Collider. The predictions of the $\bar p/p$ flux ratio also fit the data.

Figures (3)

• Figure 1: (Left Panel): Positron spectrum including the monochromatic source and continuum flux for various halo/diffusion models with $(\epsilon= 0.006,\delta =0.00)$ and $\rho= 0.35~\rm GeV/cm^3$ with $M_{Z'}= 298$ GeV, $M_D=150$ GeV, $\tau_E = 3 \times 10^{16} \rm s$Longair:1994wu, and B=10; and $\Omega h^2 = 0.13$ (calculated by integration over the Breit-Wigner pole). Also plotted is the just released PAMELA data Adriani:2008zr, along with the AMS-01 and HEAT data Barwick:1997igAguilar:2007yf. The background flux ratio is the decaying solid (blue) lower curve. (Right Panel): An exhibition of the dependence of $\langle \sigma v\rangle$ on temperature for Stueckelberg models as given in the figure with $M_D/\rm GeV \in [150,153]$ in steps of 1.5 and $M_{Z'}$ fixed as in the left panel of Fig(\ref{['1']}). The annihilation near a pole generates a significant enhancement of $\langle \sigma v\rangle_{H}$ in the halo relative to $\langle \sigma v\rangle_{X_f}$ at freezeout. The natural Breit-Wigner enhancement of $\langle \sigma v\rangle_H$ obviates the necessity of using very large boost factors.
• Figure 2: The $\bar{p}/p$ flux ratio including the TOA correction to the IS spectrum Bottino:1994xs, and with $B_{\bar{p}} \in (1-10)$. The green (darker) curves (NFW min) are insensitive to the boost in the ratio, while the yellow (lighter) curves (NFW med) allow a boost as large as 5 or even larger.
• Figure 3: Fit to the PAMELA and ATIC:2008zzr data for a heavy Dirac dark matter mass of $688.8$ GeV with the Breit-Wigner enhancement. The curves in descending order are for the cases for the halo profiles listed on the top right hand corner.