In the first moments, the Universe expanded at an enormous rate. This process is called inflation, and its driving force is the inflaton field. Its energy pushed space apart, like yeast raising dough. But physicists suspect that the dough might have left 'bubbles'—superheavy particles born from the expansion itself.
The authors considered models where the inflaton is coupled to an extra dimension. As it rolls down its energy slope, it creates an electric field in that hidden direction. The field pulls charged particles out of the vacuum, just like the Schwinger effect in strong fields. Neutral particles appear through nonstandard interactions with the same field. The big surprise: even particles with masses greater than the Hubble scale (the energy limit of inflation) are produced. Usually such giants are suppressed by the Boltzmann factor, but here the mechanism works without a thermal brake — a cold start.
Such a 'cold' collider leaves imprints in the cosmic microwave background and large-scale structure. If the signal is found, we'll glimpse physics at energies unattainable on Earth. Density fluctuations arising from quantum fluctuations carry the fingerprint of those heavy visitors from the beginning of time.
The Schwinger effect predicts that an electric field of about 10¹⁸ V/m can 'pull' an electron-positron pair straight out of the vacuum. Such a field hasn't been created in the lab yet, but inflation in the early Universe could have been a natural generator.
In Carl Sagan's novel 'Contact', a superintelligent civilization encodes a message in the very fabric of spacetime — much like heavy particles leave an imprint in the cosmic microwave background.