Superstring theory tries to describe everything in the world as vibrations of unimaginably tiny threads. But even these threads have their own bookkeeping. When physicists calculate the energy of empty space, they have to go through all possible string states, like a cashier who must scan every item in a huge hypermarket. Some items are later returned, but first they must be accounted for.

That is exactly what the authors of the new work did for the closed type IIB string. They built rules that allow one to carefully sum contributions from all 'spin sectors' (different ways the string can spin) before the final filter, the GSO projection, kicks in. Previously, the filter was applied immediately, and some information was lost. Now, they managed to preserve the full picture.

The main tool here is special mathematical integrals. There has always been a problem with them: they diverge, giving infinite answers. The authors used a regularization method previously proposed by Manschot and Wang. Infinities are carefully subtracted according to strict rules, leaving a finite, meaningful result. This approach allowed them to independently cross-check the results via another technique — the Lorentzian inversion, developed by the Baccianti group.

All this work is not just an exercise in higher mathematics. It is a step toward understanding what the vacuum is actually made of. If we know exactly all the 'expenses' and 'incomes' of the void, we better understand why our world is the way it is and not otherwise.