Hidden particles can help explain many hints for new physics, but the large variety of viable hidden sector models is a challenge for model-independent interpretations of new particle searches. Effective field theories (EFTs) that add higher dimensional operators to the standard model (SM) model-independently describe the impact heavy new particles, but do not capture light ones. Adapting the EFT approach, we propose a method to streamline the computation of light hidden particle production rates by factorizing them into i) a model-independent SM contribution, and ii) a observable-independent hidden sector contribution. This factorization uses portal effective theories (PETs) that list all operators coupling SM fields to generic hidden particles. We developed a framework to construct such PETs, and used it to derive portal chiral perturbation theories that couple the light pseudoscalar mesons to a single generic spin 0, 1/2, or 1 particle. Showcasing the formalism, we present master formulae for hidden particle production in charged Kaon decays.
Ankita Budhraja, Juraj Klaric, Johannes Michel, Tanjona R. Rabemananjara