Parallel Talk presented at the XX International Workshop on Neutrino Telescopes - Venice 23-27 October 2023 Abstract: Solar nuclear reactions can occasionally produce feebly interacting particles (FIPs) X that escape the solar interior without further interactions. In this talk, we focus on the second stage of the solar proton-proton chain and evaluate the fluxes of monochromatic 5.49 MeV FIPs produced by the p(d, He3)X reaction, analyzing the potential to detect them with the forthcoming large underground neutrino oscillation experiment Jiangmen Underground Neutrino Observatory (JUNO). In particular, we forecast the JUNO sensitivity on different combinations of the axion couplings and on hidden vectors, identifying the regions of the parameter space where current terrestrial bounds will be improved. This project has received funding /support from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860881-HIDDeN.