The metric theory of the pair correlation function of real-valued lacunary sequences

Let $\{ a(x) \}_{x=1}^{\infty}$ be a positive, real-valued, lacunary sequence. This note shows that the pair correlation function of the fractional parts of the dilations $\alpha a(x)$ is Poissonian for Lebesgue almost every $\alpha\in \mathbb{R}$. By using harmonic analysis, our result - irrespective of the choice of the real-valued sequence $\{ a(x) \}_{x=1}^{\infty}$ - can essentially be reduced to showing that the number of solutions to the Diophantine inequality $$\vert n_1 (a(x_1)-a(y_1))- n_2(a(x_2)-a(y_2)) \vert < 1$$ in integer six-tuples $(n_1,n_2,x_1,x_2,y_1,y_2)$ located in the box $[-N,N]^6$ with the ``excluded diagonals'', that is $$x_1\neq y_1, \quad x_2 \neq y_2, \quad (n_1,n_2)\neq (0,0),$$ is at most $N^{4-\delta}$ for some fixed $\delta>0$, for all sufficiently large $N$.