Dark Matter Sees The Light

📝 Abstract

We construct a Dark Matter (DM) annihilation module that can encompass the predictions from a wide array of models built to explain the recently reported PAMELA and ATIC/PPB-BETS excesses. We present a detailed analysis of the injection spectrums for DM annihilation and quantitatively demonstrate effects that have previously not been included from the particle physics perspective. With this module we demonstrate the parameter space that can account for the aforementioned excesses and be compatible with existing high energy gamma ray and neutrino experiments. However, we find that it is relatively generic to have some tension between the results of the HESS experiment and the ATIC/PPB-BETS experiments within the context of annihilating DM. We discuss ways to alleviate this tension and how upcoming experiments will be able to differentiate amongst the various possible explanations of the purported excesses.

💡 Analysis

We construct a Dark Matter (DM) annihilation module that can encompass the predictions from a wide array of models built to explain the recently reported PAMELA and ATIC/PPB-BETS excesses. We present a detailed analysis of the injection spectrums for DM annihilation and quantitatively demonstrate effects that have previously not been included from the particle physics perspective. With this module we demonstrate the parameter space that can account for the aforementioned excesses and be compatible with existing high energy gamma ray and neutrino experiments. However, we find that it is relatively generic to have some tension between the results of the HESS experiment and the ATIC/PPB-BETS experiments within the context of annihilating DM. We discuss ways to alleviate this tension and how upcoming experiments will be able to differentiate amongst the various possible explanations of the purported excesses.

📄 Content

Dark Matter Sees The Light Patrick Meade, Michele Papucci and Tomer Volansky Institute for Advanced Study Princeton, NJ 08540 Abstract We construct a Dark Matter (DM) annihilation module that can encompass the predic- tions from a wide array of models built to explain the recently reported PAMELA and ATIC/PPB-BETS excesses. We present a detailed analysis of the injection spectrums for DM annihilation and quantitatively demonstrate effects that have previously not been included from the particle physics perspective. With this module we demonstrate the parameter space that can account for the aforementioned excesses and be compat- ible with existing high energy gamma ray and neutrino experiments. However, we find that it is relatively generic to have some tension between the results of the HESS exper- iment and the ATIC/PPB-BETS experiments within the context of annihilating DM. We discuss ways to alleviate this tension and how upcoming experiments will be able to differentiate amongst the various possible explanations of the purported excesses. arXiv:0901.2925v1 [hep-ph] 20 Jan 2009 1 Introduction Recently there has been a series of experimental results suggesting that we may have indi- rectly detected dark matter (DM) within our Galaxy. The combination of the positron frac- tion measured by the PAMELA experiment [1] and the ATIC/PPB-BETS experiments [2,3], have led to a compelling picture of DM being responsible for a new population of positrons at high energies. These excesses, if confirmed, could in principle have alternative explana- tions through either refining our understanding of charged particle propagation within our Galaxy, or by identifying new astrophysical sources of positrons coming, for instance, from pulsars [4]. It is intriguing therefore, that new experimental data expected in the near future could not only confirm or contradict those results, but also allow us to possibly determine the physics behind these excesses. Furthermore, in the case of DM, such experiments could strongly constrain the various DM models. Broadly speaking, the plethora of DM models bifurcate into either annihilating [5,6] or decaying [7] DM. In this paper we choose to focus on the former possibility as being the source of the electronic excesses. The above experiments then place strong restrictions on the models, so we adopt the following phenomenological inputs as constraints: • There is an excess in the flux ratio Φe+/Φe++e−observed by the PAMELA experiment extending to at least 100 GeV [1]. • There is an excess in the ATIC/PPB-BETS experiments for the flux of charged elec- trons and positrons, Φe++e−, extending to energies of ∼700 GeV [2,3]. • There is no excess observed by the PAMELA experiment in the antiproton flux [8]. • In the absence of large local overdensity in the DM distribution (boost factor), the annihilation cross section in our galaxy needs to be O(100) times larger than a standard thermal WIMP. These facts are not easily reconciled. The last of these assumptions follows from the large measured rates combined with the higher mass scale indicated by the ATIC/PPB- BETS anomaly. For the case of a WIMP DM, a large enhancement of the cross section is needed [9–11]. Alternatively, a large boost factor (BF) is required. However, such a pos- sibility seems unlikely in light of the results from N-body simulations [12]. Furthermore, a model must prefer annihilation into leptonic final states so that the antiproton fraction is not overpopulated. There has been a recent explosion in model building that attempts to incorporate the necessary ingredients to explain these excesses. Typically, these models explain the electronic activity by either assuming a symmetry that forbids hadronic production, or otherwise pos- tulating an intermediate light state that can only decay into light leptons due to kinematics. Most of these studies have either stopped at the heuristic level of explanation, or attempted quantitatively only to postdict certain experiments. It is therefore desirable to consider a larger set of experimental data in order to better establish the correct model-building direction. 1 We attempt to address the following questions: • Given a model that can explain the PAMELA and ATIC/PPB-BETS data, what are the experimental bounds arising from other experiments? • What are the viable classes of models? • For these models, what are the implications for upcoming experiments? The most logical additional signature which has not been entirely explored is the one coming from photons. Whenever there are charged particles in the final state there will be additional photons radiated, leading to a model independent signature [13]. Additional sources of photons may contribute depending on the specific details of the model. Recently there have been a few papers [14–16] that have studied the bounds from high energy photons in models that explain the excesses. The authors of [15,16] reached the conclusion that for most dark matter

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