On the Rankin-Selberg problem in short intervals

If $Δ(x) \;:=\; \sum_{n\leqslant x}c_n - Cx\qquad(C>0)$ denotes the error term in the classical Rankin-Selberg problem, then we obtain a non-trivial upper bound for the mean square of $Δ(x+U) - Δ(x)$ for a certain range of $U = U(X)$. In particular, under the Lindelöf hypothesis for $ζ(s)$, it is shown that $$ \int_X^{2X} \Bigl(Δ(x+U)-Δ(x)\Bigr)^2\,{\roman d} x \;\ll_ε\; X^{9/7+ε}U^{8/7}, $$ while under the Lindelöf hypothesis for the Rankin-Selberg zeta-function the integral is bounded by $X^{1+ε}U^{4/3}$. An analogous result for the discrete second moment of $Δ(x+U)-Δ(x)$ also holds.

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