When CoGeNT met PAMELA

arXiv:1010.1774v2 [hep-ph] 22 Dec 2010 When CoGeNT met PAMELA Wai-Yee Keung a, Ian Low b,c, Gabe Shaughnessy b,c a Department of Physics, University of Illinois, Chicago, IL 60607 bHigh Energy Physics Division, Argonne National Laboratory, Argonne, IL 60439 cDepartment of Physics and Astronomy, Northwestern University, Evanston, IL 60208 Abstract If the excess events from the CoGeNT experiment arise from elastic scatterings of a light dark matter offthe nuclei, crossing symmetry implies non-vanishing annihilation cross-sections of the light dark matter into hadronic final states inside the galactic halo, which we confront with the anti-proton spectrum measured by the PAMELA collaboration. We consider two types of effective interactions between the dark matter and the quarks: 1) contact interactions from integrating out heavy particles and 2) long-range interactions due to the electromagnetic properties of the dark matter. The lack of excess in the anti-proton spectrum results in tensions for a scalar and, to a less extent, a vector dark matter interacting with the quarks through the Higgs portal. 1 I. INTRODUCTION In recent years we have witnessed a plethora of experimental anomalies in both direct and indirect detection experiments in search of the dark matter (DM). For example, the direct detection experiment DAMA [1] observed signals of annual modulations consistent with that expected from dark matter scattering offthe nuclei, while the CDMS collaboration announced two candidate events for detection of dark matter [2]. More recently, the CoGeNT experiment [3] released results containing signal events suggestive of a light dark matter in the range of 7 – 12 GeV. On the other hand, several collaborations in indirect detections reported excessive fluxes of electrons/positrons and photons, such as the PAMELA [4], the ATIC [5], the Fermi LAT [6], the HESS [7], and the WMAP [8], which may not be explained away easily by conventional astrophysical sources. In order to understand whether these experimental excesses are indeed the prelude to a discovery of the dark matter, it is crucial to cross-check dark matter interpretations of these empirical anomalies against one another. One possibility is to construct a unified theory explaining all these signal events [9]. Another is to confront the events with constraints from measurements which do not see any excess, one example of which is the anti-proton spectrum measured also by the PAMELA [10]. While this has been generally been studied for Dirac DM with a contact interaction [11] and specifically for 10 GeV DM [12], In this work we propose to study the consistency of the CoGeNT signals with the anti-proton spectrum of PAMELA within the context of generic effective interactions between DM and quarks. If the signal events in various direct detection experiments are due to elastic scatterings of the dark matter offthe nuclei, which arise from the dark matter interaction with the quarks, then crossing symmetry implies the same interactions must also give rise to annihilations of dark matter into quarks. This argument has been used to constrain the boost factor [13] necessary to explain the electron/positron excess in the PAMELA, using the updated limits from the CDMS [11]. Another example studied the implication of various direct detection bounds on the anti-deuteron flux from hadronic annihilations of the dark matter [14]. Theoretically, the light ( 7 – 12 GeV) dark matter interpretation of the CoGeNT offers a unique opportunity for a model-independent study. Since such a mass scale is far below the electroweak scale, it seems reasonable to assume that any degrees of freedom mediating the dark matter interactions with the standard model particles have masses much heavier 2 than that of the dark matter.1 Hence at energy scales relevant for the elastic scattering of dark matter with the nucleons and the dark matter annihilations into quarks, these “mediator particles” can be integrated out and the interactions could be approximated by higher dimensional operators. The resulting effective interactions can be either contact interactions, when the mediator particle interacts with the quarks, or long range in nature, when the mediator particle interacts with the photon. By combining the PAMELA anti-proton spectrum and the putative CoGeNT signal, we find that contact interactions of a scalar or vector dark matter, arising from a heavy mediator particle with Yukawa-like interactions with quarks, is the most severely constrained. These constraints apply to models with a light scalar dark matter which interacts with the standard model through the Higgs portal [16]. Cases of fermionic dark matter with an electromagnetic charge form factor coupling or magnetic moment coupling also exhibit tension with these data, but to a lesser degree. Previous studies on properties of the dark matter using higher dimensional contact interactions can be found in Refs. [17, 18]. This work is organized as f

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