Fat brane, dark matter and localized kinetic terms in six dimensions

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Regular Article - Theoretical Physics

Fat brane, dark matter and localized kinetic terms in six dimensions Ricardo G. Landima Physik Department T70, Technische Universität München, James-Franck-Straße 1, 85748 Garching, Germany

Received: 12 November 2019 / Accepted: 29 January 2020 © The Author(s) 2020

Abstract Extra dimensions (ED) have been used as attempts to explain several phenomena in particle physics over the years. In this paper we investigate the role of an abelian gauge field as mediator of the interaction between dark matter (DM) and Standard Model (SM) particles, in a model with two flat and transverse ED compactified on the chiral square. DM is confined in a thin brane, localized at the origin of the chiral square, while the SM is localized in a finite width brane, lying in the opposite corner of the square. A brane-localized kinetic term is present in the DM brane, while in the fat brane it is not allowed. In this model the kinetic mixing is not required because we assume that the SM particles couple to the mediator through their B − L charges, while DM couples to it via a dark charge. Assuming a complex scalar field as DM candidate it is possible to obtain the observed DM relic abundance and avoid direct detection constraints for some parameter choices.

1 Introduction Weakly interacting massive particles (WIMPs) have been the most well-known dark matter (DM) candidates [1] for decades, but the absence of any trace encourage us to look for different scenarios, both experimentally and theoretically. One promising way to chase DM would be if it interacts with the standard model (SM) particles through a new mediator. A relatively recent and very explored idea is the possible interaction between DM and SM via a new dark U (1) D gauge field, arising in turn from a kinetic mixing term between this new vector mediator (called dark photon, DP) and the hypercharge U (1)Y field [2–19]. Among other theoretical alternatives, extra dimensions (ED) have been considered over the decades as tools to address a wide range of issues in particle physics, such as the hierarchy [20–27] and flavor problems [28–30]. Moda e-mail:

els employing two ED, for example, may provide explanations for proton stability [31], origin of electroweak symmetry breaking [32–35], breaking of grand unified gauge groups [36–39] and the number of fermion generations [40– 45]. Many extensions of the SM appear by employing ED as well; indeed even the SM itself can be embedded in ED, whose fields propagate in the compact ED. In 4-D, the zero mode of each Kaluza–Klein (KK) tower of states is identified with the correspondent SM particle. These so-called Universal Extra Dimension (UED) models were build either with one [46] or two ED [47–50], for example, and current results from LHC [51,52] impose bounds on the UED compactification radius L for one (L −1 > 1.4 − 1.5 TeV) [53–55] (for ΛL ∼ 5 − 35, where Λ is the cutoff scale) or two ED (L −1 > 900 GeV) [56]. In the context of ED, the DP model was embedded in a flat, single ED, along with DM cand