Top-flavored dark matter and the forward-backward asymmetry

Abstract

We propose a simple model where dark matter (DM) carries top flavor and couples to the Standard Model through the top quark within a framework of minimal flavor violation (MFV).Top-flavored DM can explain the anomalous top forward-backward asymmetry observed at the Tevatron, while remaining consistent with other top observables at colliders. By virtue of its large coupling to top, DM acquires a sizable loop coupling to the Z boson, and the relic density is set by annihilation through the Z. We also discuss contraints from current direct detection searches, emphasizing the role of spin-dependent searches to probe this scenario. * Electronic address: abhishek@triumf.ca † Electronic address: tulin@umich.edu

Signatures of top flavored dark matter

“…[6]. In figure 3 we plot our results in the form of the LUX bound on the coupling λ with and without taking the box diagram into account, confirming the conclusions derived in ref.…”

“…The leading such process is shown in figure 15. At first sight, this process may appear to be of the same size as the tree level decay in the five-body region 6 . However, a closer inspection reveals this to be incorrect: both quark propagators in the loop are attached to an FDM vertex on one end and to a W boson on the other.…”

“…In figure 3 we plot our results in the form of the LUX bound on the coupling λ with and without taking the box diagram into account, confirming the conclusions derived in ref. [6] that the direct detection bounds are dominated by the effective γ/Z coupling. For the rest of this paper, we will use only this dominant contribution in calculating the bounds from direct detection experiments on the parameter space of the top FDM model.…”

“…These contributions were all calculated in ref. [6], with the conclusion that the γ/Z exchange diagram dominates over the four-point coupling to u-ū, the remaining diagrams being negligible compared to these two. Let us start by focusing on the diagrams of figure 1.…”

“…If one pursues the alternative guiding principle of looking for a connection between DM and matter particles in the SM, one is then led to the possibility that DM itself may transform nontrivially under flavor symmetries. It is therefore worthwhile to consider classes of models with "Flavored Dark Matter" (FDM) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18], to look for universal features of such models, and to study whether there exist experimental signatures that may be used to distinguish FDM from more traditional models of DM, such as a neutralino in a supersymmetric setup. It is even possible that this line of inquiry may yield new insights in searching for the origin of the SM flavor structure.…”