Extra U(1), effective operators, anomalies and dark matter

Abstract

A general analysis is performed on the dimension-six operators mixing an almost hidden Z to the Standard Model (SM), when the Z communicates with the SM via heavy mediators. These are fermions charged under both Z and the SM, while all SM fermions are neutral under Z . We classify the operators as a function of the gauge anomalies behaviour of mediators and explicitly compute the dimension-six operators coupling Z to gluons, generated at one-loop by chiral but anomaly-free, sets of fermion mediators. We prove that only one operator contribute to the couplings between Z charged matter and on-shell gluons. We then make a complete phenomenological analysis of the scenario where the lightest fermion charged under Z is the dark matter candidate. Combining results from WMAP/PLANCK data, mono-jet searches at LHC, and direct/indirect dark matter detections restrict considerably the allowed parameter space.

LHC signatures of a Z ′ mediator between dark matter and the SU(3) sector

“…On the other hand, string inspired models propose an anomaly cancellation a la Green-Schwarz [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] where a very light U(1) X mediator is generated with the use of axionic couplings and generalized ChernSimons terms, or via Stueckelberg realization of the Z boson [8,[42][43][44]. Another option is to consider neutral Standard Model fermions under the new gauge group U(1) X [11].…”

“…Such scenarios have already been studied in the context of Dark Matter (DM) model building [11,[48][49][50]. In such framework, dimension six operators are suppressed by a factor M 2 (M being the mass of heavy fermions integrated out) and the dark matter sector, charged under U(1) X , couples with the weak or coloured sector of the Standard Model.…”

“…In such framework, dimension six operators are suppressed by a factor M 2 (M being the mass of heavy fermions integrated out) and the dark matter sector, charged under U(1) X , couples with the weak or coloured sector of the Standard Model. An interaction with the weak SM sector was shown to have possible astrophysical signatures [48,49], while a coupling to the coloured SM sector was constrained [11] using mono-jets events at the LHC [52], as well as indirect detection constraints arising from astrophysical measurements. Such couplings had been studied, together with couplings to the top quarks in [53] but only in the context JHEP03(2016)006 Figure 1.…”

“…Z'coupling to colored sector of the Standard Model. The heavy mediators are suppressed when integrating over all considered heavy states [11].…”

“…The presence of such a feeble coupling has interesting features in the quark physics which may be discoverable during the Run-2 ( √ s = 13 TeV) of the LHC. Therefore, this study aims to show what sensitivity can be reached for the theoretical model developed in [11] given the latest LHC Run-1 ( √ s = 7 or 8 TeV) experimental results. For completeness, the dark matter constraints and prospect studies for the LHC Run-2 are also included.…”