I. INTRODUCTION Recently, the PAMELA satellite experiment has observed an excess in the positron frac- tion from 10 to 100 GeV [1], which confirmed the previous hints from HEAT [2], CAPRICE [3] and AMS-01 [4]. The reports from ATIC balloon experiment showed a rapid rise of the total electron and positron flux at a range 300-800 GeV[5] with a peak at around 600 GeV, which agreed with the PPB-BETS results[6]. More recently, the Fermi-LAT [7] and the HESS [8] Cherenkov experiments have released their results for the sum of electron and positron flux. Although they did not fully confirm the previous results reported by the ATIC experiment, both the measurements indicated excesses over the expected background, which suggests the presence of extra sources for the e ± spectra. Besides the astrophysical explanations for e ± anomalies by some nearly sources like pulsars and supernova remnants, the dark matter (DM) annihilation or decay is one of the most interesting explanation from particle physics. The PAMELA, ATIC, and Fermi-LAT anomalies may be a consequence of DM particle annihilating mainly into lepton final states. However, if the dark matter is generated ther- mally, the annihilation cross section obtained from the observed relic density is significantly lower than that required by the current data. One has to resort to a large boost factor (about 100 − 1000) to explain the observed large positron flux. Note that the most probable boost factor from the clumpiness of DM structures is estimated to be less than ∼ 10 − 20 [9]. The large boost factor may come from nonperturbative Sommerfeld enhancement [10] or Breit-Wigner enhancement [11–13]. An other possibility is that the DM particle may slightly decay, and dominantly decay into leptons [14]. In this case the bound from the DM relic density is relaxed. The current data require that the lifetime of DM particle should be of the order O (10 $^{26}$s). If the mass of DM particle is very heavy, it may first decay into some lighter intermediate states rather than directly into standard model (SM) particles. An interesting intermediate state might be SU (2)$_{L}$ triplets, as it is known in many models that they may carry nonzero lepton numbers, and do not couple to quarks directly. This leptophilic feature can naturally account for the PAMELA results on both the excesses of positrons and the absence of large anti-proton flux. The stability of the DM particle is usually protected by imposing extra discrete sym- 2