Define the infimal exponent μζ by
μζ := inf{θ≥0: ∣ζ(1/2+it)∣≪ε(1+∣t∣)θ+ε for all ε>0}.
We define
C62a := μζ,
the Lindelof (pointwise growth) exponent for ζ(1/2+it).
The Lindelof hypothesis is the conjecture that ∣ζ(1/2+it)∣≪tε for every ε>0, which is equivalent to C62a=0.
[Har2019-lindelof]
Unconditionally, convexity gives C62a≤1/4.
[Har2019-convexity-1-4]
Hardy-Littlewood proved the bound C62a≤1/6.
[Har2019-hl-1-6]
Bourgain proved the sharper bound C62a≤13/84.
[Bou2017-13-84]
The best established range currently is
0 ≤ C62a ≤ 8413.