The Exceptional Set in Goldbach's Problem with two Chen Primes

We show that all natural numbers $n\equiv 4\pmod 6$ are the sum of two Chen primes (primes $p$ such that $p+2$ has at most two prime factors), apart from a power-saving set of exceptions. This improves on various previous results and is optimal, barring substantial progress on the twin prime or binary Goldbach conjectures. The proof is based on constructing a non-negative model for the Chen primes in a suitable approximate sense. To do this, we develop an efficient sieving strategy that makes use of a power-saving variant of the Bombieri--Vinogradov theorem. Furthermore, we show that the primes are well approximated in additive problems by the Cramér model (rough numbers) with a sifting parameter of power size.