Density versions of the binary Goldbach problem

Abstract

Let $\delta > 1/2$. We prove that if $A$ is a subset of the primes such that the relative density of $A$ in every reduced residue class is at least $\delta$, then almost all even integers can be written as the sum of two primes in $A$. The constant $1/2$ in the statement is best possible. Moreover we give an example to show that for any $\varepsilon > 0$ there exists a subset of the primes with relative density at least $1 - \varepsilon$ such that $A+A$ misses a positive proportion of even integers.