PAMELA data and leptonically decaying dark matter

TL;DR

The paper analyzes PAMELA's positron fraction in the context of CR propagation modeled with GALPROP, comparing decaying and annihilating DM scenarios. It finds that leptonic final states from a leptonically decaying DM (LDDM) best reconcile the PAMELA data with the antiproton constraints, and that decaying DM is preferred due to the absence of large boost factors required by annihilation. It provides a concrete MSSM realization using tiny LL\bar{E} R-parity violation, with a neutralino mass in the range $m_{\\chi}\\sim 0.6$--$2$ TeV and a lifetime $\\tau_{DM}\\sim 10^{26}$ s, that fits PAMELA (and can accommodate ATIC in some cases). The work highlights multi-messenger predictions including gamma rays and neutrinos and discusses collider implications to test this DM scenario.

Abstract

Recently PAMELA released their first results on the positron and antiproton ratios. Stimulated by the new data, we studied the cosmic ray propagation models and calculated the secondary positron and antiproton spectra. The low energy positron ratio can be consistent with data in the convection propagation model. Above $\sim 10$ GeV PAMELA data shows a clear excess on the positron ratio. However, the secondary antiproton is roughly consistent with data. The positron excess may be a direct evidence of dark matter annihilation or decay. We compare the positron and anti-proton spectra with data by assuming dark matter annihilates or decays into different final states. The PAMELA data actually excludes quark pairs being the main final states, disfavors gauge boson final states. Only in the case of leptonic final states the positron and anti-proton spectra can be explained simultaneously. We also compare the decaying and annihilating dark matter scenarios to account for the PAMELA results and prefer to the decaying dark matter. Finally we consider a decaying neutralino dark matter model in the frame of supersymmetry with R-parity violation. The PAMELA data is well fitted with neutralino mass $600\sim 2000$ GeV and life time $\sim 10^{26}$ seconds. We also demonstrate that neutralino with mass around 2TeV can fit PAMELA and ATIC data simultaneously.

Figures (7)

• Figure 1: Propagated B/C, $^{10}$Be/$^{9}$Be, protons and electrons spectra in the DC and DR models of GALPROP. In each panel of the figure, the thick solid lines represent the results of DC model, while the thin solid lines show results of DR model. For each model the LIS spectrum together with the solar modulated one are plotted. In order to match the low energy data, different modulation potentials are adopted as labeled in the figure. The references of the data are, B/C: Chapell-Webberchapwebb81, Dwyerdwyer78, Maehlmaehl77, HEAOheao90, Voyagervoyager99, ACEace00, Ulyssesulysses96; $^{10}$Be/$^9$Be: Ulyssesconnell98, ACEacebe, Voyagervoyager99, IMP-7/8simpson88, ISEE-3simpson88, ISOMAXHams:2004rz; protons: BESS98Sanuki:2000wh, AMS98Alcaraz:2000vp; electrons: CAPRICEboezio00, HEATbarwick98, SanrikuKobayashi:1999he.
• Figure 2: Left: the calculated positron fraction compared with observations; right: $\bar{p}/p$ ratio. References of the observational data are, positron fraction: TS93Golden:1995sq, CAPRICE94boezio00, AMSAguilar:2007yf, HEAT94+95Barwick:1997ig, HEAT00Coutu:2001jy, PAMELAAdriani:2008zr; $\bar{p}/p$: IMAXMitchell:1996bi, HEATBeach:2001ub, CAPRICE94Boezio:1997ec, CAPRICE98Boezio:2001ac, BESS95+97Orito:1999re, BESS99Asaoka:2001fv, BESS00Asaoka:2001fv, BESS-polarAbe:2008sh, PAMELAAdriani:2008zq.
• Figure 3: The positron and antiproton fraction, $\frac{{\Phi _{\bar{e}} }}{{\Phi _{\bar{e}} + \Phi _e }}$ and $\frac{{\Phi _{\bar{p}} }}{{\Phi _p }}$, as function of energy from DM decaying to gauge boson pairs. The black lines are background for positron and anti-proton. The data points are from the preliminary PAMELA results Adriani:2008zq. The numbers $100$, $300$ and $1000$ GeV refer to the energy of gauge bosons, while the numbers 3.6 and so on refer to the life time of DM in unit of $10^{26} s$. In the title, "DC" and "DR" are the two propagation models discussed in the section II.
• Figure 4: Positron and antiproton fraction as function of energy from DM decaying to quark pairs. The labels are the same as that in Fig. \ref{['gaugeboson']}.
• Figure 5: Positron and antiproton fraction as function of energy from DM decaying to lepton pairs. The labels are the same as that in Fig. \ref{['gaugeboson']}.