arXiv subjects
Publications and source records attributed to Juho Salmensuu.
In this paper, we study a density version of Waring's problem. We prove that a positive density subset of $k$th-powers forms an asymptotic additive basis of order $O(k^2)$ provided that the relative lower density of the set is greater than $(1 - \mathcal{Z}_k^{-1}/2)^{1/k}$, where $\mathcal{Z}_k$ is certain constant depending on $k$ for which it holds that $\mathcal{Z}_k > 1$ for every $k$ and $\lim_{k \rightarrow \infty} \mathcal{Z}_k = 1$.
We prove that, for almost all $r \leq N^{1/2}/\log^{O(1)}N$, for any given $b_1 \mod r$ with $(b_1, r) = 1$, and for almost all $b_2 \mod r$ with $(b_2, r) = 1$, we have that almost all natural numbers $2n \leq N$ with $2n \equiv b_1 + b_2 \mod r$ can be written as the sum of two prime numbers $2n = p_1 + p_2$, where $p_1 \equiv b_1 \mod r$ and $p_2 \equiv b_2 \mod r$. This improves the previous result which required $r \leq N^{1/3}/\log^{O(1)}N$ instead of $r \leq N^{1/2}/\log^{O(1)}N$. We also improve some other results concerning variations of the problem.
We use transference principle to show that whenever $s$ is suitably large depending on $k \geq 2$, every sufficiently large natural number $n$ satisfying some congruence conditions can be written in the form $n = p_1^k + \dots + p_s^k$, where $p_1, \dots, p_s \in [x-x^θ, x + x^θ]$ are primes, $x = (n/s)^{1/k}$ and $θ= 0.525 + ε$. We also improve known results for $θ$ when $k \geq 2$ and $s \geq k^2 + k + 1$. For example when $k \geq 4$ and $s \geq k^2 + k + 1$ we have $θ= 0.55 + ε$. All previously known results on the problem had $θ> 3/4$.