Analysis of a possible explanation of the positron anomaly in terms of dark matter
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EMENTARY PARTICLES AND FIELDS Theory
Analysis of a Possible Explanation of the Positron Anomaly in Terms of Dark Matter V. V. Alekseev1) , K. M. Belotsky2), Yu. V. Bogomolov1) , R. I. Budaev2)* , O. A. Dunaeva1) , A. A. Kirillov1), 2) , A. V. Kuznetsov1) , A. D. Lukyanov1), V. V. Malakhov2), A. G. Mayorov1), 2) , M. A. Mayorova2), A. F. Mosichkin1), A. A. Okrugin1), S. A. Rodenko2) , and A. M. Shitova1) Received October 5, 2016
Abstract—The possibility of explaining the positron anomaly on the basis of models involving the darkmatter annihilation or decay is being widely discussed at the present time. However, such models are severely constrained by data on cosmic gamma radiation. Two different procedures that rely on the χ2 criterion and which permit taking this constraint into account are considered in the present study. In one case, the use of positron data alone in searches for a minimum value of χ2 via varying model parameters is followed by a comparison with gamma-radiation data. In the second case, the χ2 functional is minimized by simultaneously employing positron and gamma-radiation data, whereby a more lenient (more “flexible”) constraint is obtained. Nevertheless, either procedure rules out the possibility of explaining the positron anomaly in terms of unstable dark matter distributed over the whole halo. The assumption that the dark-matter component undergoing annihilation (decay) is concentrated within the galactic disk makes it possible to remove the constraint in either case. DOI: 10.1134/S1063778817040020
1. INTRODUCTION Starting from the first studies on the subject in [1– 6], an analysis of cosmic-ray data is a widespread means for testing dark-matter models. At the present time, particular attention is being given to attempts at explaining an excess of high-energy cosmic positrons that was discovered in the PAMELA [7] and AMS02 [8] experiments and which was called a “positron anomaly.” At the same time, it was found (see, for example, [9–14]) that any dark-matter model that purports to explain the positron anomaly produces high-energy photons, with the result that it inevitably comes in conflict with data from the Fermi-LAT experiment [15, 16] on the isotropic diffuse gamma-ray background (IGRB). An analysis of models in the majority of earlier studies was performed via optimizing parameters with the aim of obtaining a better description of the positron fraction, and the IGRB-induced constraint was imposed on a model independently, the parameter values being preliminarily fixed. This approach excluded many models. However, the simultaneous 1)
Demidov Yaroslavl State University, Sovetskaya ul. 14, Yaroslavl, 150000 Russia. 2) National Research Nuclear University MEPhI, Kashirskoe sh. 31, Moscow, 115409 Russia. * E-mail: [email protected]
inclusion of cosmic-positron and IGRB data at the optimization stage will lead to a different result on the level of agreement with data. In the present study, we compare the two methods in question by employing the χ2 criterion. The results are presented for two cases
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