We study the relation between chiral and U
A
(1) symmetries in quark-meson model. While quarks and mesons are described in mean field approximation, the topological susceptibility characterizing the U
A
(1) breaking contains two components, the condensate controlled one and the meson fluctuation one. The U
A
(1) restoration is governed by their competition. In hot medium the condensates are melted but the fluctuation is enhanced, the U
A
(1) symmetry can therefore not be restored by temperature effect alone. The baryon density, however, reduces both the condensates and fluctuation, the U
A
(1) symmetry can only be restored in dense or dense and hot mediums. The strange condensate plays a weak role in the susceptibility, the chiral and U
A
(1) symmetry restoration happen at almost the same critical point. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.
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