# Recent selected theory developments for NICA

## TL;DR

This paper reviews recent theoretical advances relevant to the NICA facility, including QCD phase diagram insights, event simulation developments, and signals of deconfinement, with a focus on experimental observables and model improvements.

## Contribution

It introduces new theoretical perspectives on the QCD phase diagram, presents progress in the THESEUS event simulator, and explores signals of deconfinement and strangeness in heavy-ion collisions at NICA energies.

## Key findings

- Analysis of the QCD critical endpoint and deconfinement pressure.
- First results from the THESEUS event simulator including hadronic interactions.
- Investigation of deconfinement signals like baryon-stopping and antiflow in Au+Au collisions.

## Abstract

In this contribution I present a few selected topics of recent theoretical developments of relevance for the NICA facility under construction. In a first part, I discuss new aspects of the QCD phase diagram like the possible existence of a critical endpoint of first-order phase transitions from the perspective of generalizations of the 3-flavor PNJL model including the conjecture of a universal pressure for the onset of deconfinement in heavy-ion collisions and astrophysics. A second part is devoted to first results of the newly constructed event simulator (THESEUS) which is based on the particlization of the former three-fluid hydrodynamics code by Ivanov, Russkikh and Toneev that allows also to study the role of hadronic final state interactions. Possible signals of the mixed phase accessible at NICA are considered. In particular, the robustness of the baryon-stopping signal of deconfinement and the occurrence of antiflow for protons have been investigated for Au+Au collisions in the range of the NICA-MPD energy scan for $\sqrt{s} \sim 6 \dots 8$ GeV. This signal is reflected also in the flow pattern of light nuclear clusters, in particular deuterons. The sharp peak for the $K^+/\pi^+$ ratio at $\sqrt{s} \sim 8$ GeV (the "horn" effect) is not obtained in the present version of THESEUS and calls for improvement of the equation of state input. I report the recent progress in developing a generalized Beth-Uhlenbeck approach to a unified description of quark-hadron matter which includes now strangeness and reveals a new mechanism for explaining the $K^+/\pi^+$ ratio due to the pronounced occurrence of an anomalous mode in the $K^+$ at finite baryochemical potentials.