Where do the electron and antineutrino come from in beta decay? [duplicate]

I was studying about nuclear reactions and similar stuff, but stumbled upon this doubt

In the process of beta decay, where a neutron transforms into a proton, a positron and an antineutrino, where do the electron and antineutrino come from ( do they already exist within the neutron or like? )

I do not believe that this is a duplicate of In nuclear chemistry, how does a neutron split to form a proton and an electron?