AbstractA general appearance of two-pole structures is exhibited in a relativistic Friedrichs–Lee model combined with a relativistic quark pair creation model in a consistent manner. This kind of two-pole structure could be found when a $$q\bar{q}$$
q
q
¯
state couples to the open-flavor continuum state in the S partial wave. We found that many enigmatic states, such as $$f_0(500)/\sigma $$
f
0
(
500
)
/
σ
, $$K_0^*(700)/\kappa $$
K
0
∗
(
700
)
/
κ
, $$a_0(980)$$
a
0
(
980
)
, $$f_0(980)$$
f
0
(
980
)
, $$D_0^*(2300)$$
D
0
∗
(
2300
)
, $$D_{s0}^*(2317)$$
D
s
0
∗
(
2317
)
, and X(3872), together with another higher state for each, all result from this kind of two-pole structures. Furthermore, an interesting observation is that this kind of two-pole structure will contribute roughly a total of $$180^\circ $$
180
∘
phase shift for the scattering process in a single channel approximation. This relativistic scheme may provide more insights into the understanding of the properties of non-$$q\bar{q}$$
q
q
¯
state. It is also suggested that such two-pole structure could be a common phenomenon which deserves studying both from theoretical and experimental perspectives.
Two-pole structures in a relativistic Friedrichs–Lee-QPC scheme
