Abstract
We present a framework for the construction of portal effective theory (PETs) that couple effective field theories of the Standard Model (SM) to light hidden messenger fields. Using this framework we construct electroweak and strong scale PETs that couple the SM to messengers carrying spin zero, one half, or one. The electroweak scale PETs encompass all portal operators up to dimension five, while the strong scale PETs additionally contain all portal operators of dimension six and seven that contribute at leading order to quark-flavour violating transitions. Using the strong scale PETs, we define a set of portal currents that couple hidden sectors to QCD, and construct portal chiral perturbation theory (χPTs) that relate these currents to the light pseudoscalar mesons. We estimate the coefficients of the portal χPT Lagrangian that are not fixed by SM observations using non-perturbative matching techniques and give a complete list of the resulting one- and two-meson portal interactions. From those, we compute transition amplitudes for three golden channels that are used in hidden sector searches at fixed target experiments: i) charged kaon decay into a charged pion and a spin zero messenger, ii) charged kaon decay into a charged lepton and a spin one half messenger, and iii) neutral pion decay into a photon and a spin one messenger. Finally, we compare these amplitudes to specific expressions for models featuring light scalar particles, axion-like particles, heavy neutral leptons, and dark photons.
Highlights
The search for physics beyond the Standard Model (BSM) is one of the most pursued research avenues in modern high-energy physics
We present a framework for the construction of portal effective theory (PETs) that couple effective field theories of the Standard Model (SM) to light hidden messenger fields
At the electroweak (EW) scale, there are two Effective field theories (EFTs) that encompass the entire SM and that are commonly used to include heavy new physics (NP) [27]: Standard Model effective field theory (SMEFT), which is composed of all the SM fields including the Higgs doublet and restricted by the SM gauge group [28,29,30,31,32], and Higgs effective field theory (HEFT), which lifts the restriction on the Higgs boson to be part of a doublet [33,34,35,36]
Summary
The search for physics beyond the Standard Model (BSM) is one of the most pursued research avenues in modern high-energy physics. The hidden sector can in general contain an arbitrary number of secluded fields that do not couple directly to the SM but interact among themselves and with the messenger fields This setup, which is illustrated, describes both heavy and light new particles, since heavy particles with masses well above the characteristic energy of the EFT are captured by infinite towers of SM, portal, and hidden operators. In order to supply a complete toolkit for the computation of hidden sector induced meson transitions, we construct portal χPTs, which couple the light pseudoscalar mesons to a messenger of spin 0, 1, and match them to the corresponding portal For this matching, we adapt to our framework a number of well-established non-perturbative techniques used to match χPT to QCD in the SM, as in e.g. In the following list we summarise the main new results that we present throughout this paper
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
