On the Second Hardy-Littlewood Conjecture

Abstract: The second Hardy-Littlewood conjecture asserts that the prime counting function $\pi(x)$ satisfies the subadditive inequality \begin{align*} \pi(x+y)\leqslant \pi(x)+\pi (y) \end{align*} for all integers $x,y\geqslant 2$. By linking the subadditivity of $\pi(x)$ to the error term in the Prime Number Theorem, we obtain unconditional improvements on the range of $y$ for which $\pi(x)$ is known to be subadditive. Moreover, assuming the Riemann Hypothesis, we show that for all $\epsilon>0$, there exists $x_{\epsilon} \geqslant 2$ such that for all $x\geqslant x_\epsilon$ and $y$ in the range \begin{align*} \frac{(2+\epsilon)\sqrt{x}\log^2x}{8\pi}\leqslant y\leqslant x, \end{align*} the inequality $\pi(x+y)\leqslant \pi(x) + \pi(y)$ holds.