Distribution of products of shifted primes in arithmetic progressions with increasing difference
Zarullo Rakhmonov
TL;DR
This work extends Karatsuba's method for ternary multiplicative problems to the distribution of products of shifted primes in arithmetic progressions with growing difference. It proves an asymptotic formula for the count of pairs $(p_1,p_2)$ with $p_1\le x_1$, $p_2\le x_2$ such that $p_1(p_2+a) \equiv l \pmod q$, under $q \le x^{\kappa_0}$ with $\kappa_0 = \frac{1}{2.5+\theta+\varepsilon}$ and $\theta=\frac{1}{2}$ if $q$ is cube-free (otherwise $\theta=\frac{5}{6}$). The main term is $\frac{1}{\varphi(q)} \prod_{p|q}(1-\frac{1}{p-1}) \mathrm{Li}(x_1)\mathrm{Li}(x_2)$ with a power-saving error, derived from average Chebyshev sums over Dirichlet characters and short sums of nonprincipal characters in shifted primes, together with Bombieri–Vinogradov and Brun–Titchmarsh-type bounds. The result generalizes Karatsuba's formula and tightens previous bounds by allowing a broader range for $q$ and more general moduli, highlighting the role of cube-free vs non-cube-free moduli via the parameter $\theta$.
Abstract
We obtain an asymptotic formula for the number of primes $p\leq x_1$, $p\leq x_2$ such that $p_1(p_2+a)\equiv l \pmod q$ with $(a,q)=(l,q)=1$, $q\leq x^{κ_0}$, $x_1\geq x^{1-α}$, $x_2\geq x^α$, $$ κ_0=\frac{1}{2.5+θ+\varepsilon}, \quad α\in \left[(θ+\varepsilon)\frac{\ln q}{\ln x}, 1-2.5\frac{\ln q}{\ln x}\right], $$ where $θ=1/2$, if $q$ is a cube free and $θ=\frac{5}{6}$ otherwise. This is the refinement and generalization of the well-known formula of A.~A.~Karatsuba.\\ Keywords: {Dirichlet character, shifted primes, short sum of characters with primes}\\ Bibliography: 39 references
