Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Triangle Singularities and XYZ Quarkonium Peaks   We discuss analytical properties of partial waves derived from projection of
a 4-legged amplitude with crossed-channel exchanges in the kinematic region of
the direct channel that corresponds to the XYZ peaks in charmonium and
bottomonium. We show that in general partial waves can develop anomalous branch
points in the vicinity of the direct channel physical region. In a specific
case, when these branch points lie on the opposite side of the unitary cut they
pinch the integration contour in a dispersion relation and if the pinch happens
close to threshold, the normal threshold cusp is enhanced. We show that this
effect only occurs if masses of resonances in the crossed channel are in a
specific, narrow range. We estimate the size of threshold enhancements
originating from these anomalous singularities in reactions where the Zc(3900)
and the Zb(10610) peaks have been observed.

6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
16
The categories of this paper are: stat
27
The categories of this paper are: comp-gas
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an
21
The categories of this paper are: adap-org