AbstractBased on an equivalence relation that was established recently on exponential sums, in this paper we study the class of functions that are equivalent to the Riemann zeta function in the half-plane $$\{s\in {\mathbb {C}}:\mathrm{Re}\, s>1\}$$
{
s
∈
C
:
Re
s
>
1
}
. In connection with this class of functions, we first determine the value of the maximum abscissa from which the images of any function in it cannot take a prefixed argument. The main result shows that each of these functions experiments a vortex-like behavior in the sense that the main argument of its images varies indefinitely near the vertical line $$\mathrm{Re}\, s=1$$
Re
s
=
1
. In particular, regarding the Riemann zeta function $$\zeta (s)$$
ζ
(
s
)
, for every $$\sigma _0>1$$
σ
0
>
1
we can assure the existence of a relatively dense set of real numbers $$\{t_m\}_{m\ge 1}$$
{
t
m
}
m
≥
1
such that the parametrized curve traced by the points $$(\mathrm{Re} (\zeta (\sigma +it_m)),\mathrm{Im}(\zeta (\sigma +it_m)))$$
(
Re
(
ζ
(
σ
+
i
t
m
)
)
,
Im
(
ζ
(
σ
+
i
t
m
)
)
)
, with $$\sigma \in (1,\sigma _0)$$
σ
∈
(
1
,
σ
0
)
, makes a prefixed finite number of turns around the origin.
Special values of the Riemann zeta function capture all real numbers
