Quark-meson-diquark model for two-color QCD

TL;DR

This paper develops a two-flavor quark-meson-diquark model for two-color QCD, highlighting the importance of baryonic degrees of freedom in accurately capturing phase structure and critical phenomena.

Contribution

It introduces a novel model incorporating baryonic degrees of freedom and extends it with gauge-field dynamics, analyzed using mean-field and functional renormalization group methods.

Findings

Baryonic degrees of freedom are crucial for correct phase diagram features.

Omission of baryons leads to a phase diagram similar to QCD models with a critical endpoint.

Functional renormalization group captures the interplay of mesonic and baryonic fluctuations.

Abstract

We introduce a two-flavor quark-meson-diquark model for two-color QCD and its extensions to include gauge-field dynamics as described by the Polakov loop. Grand potential and phase structure are being studied both in mean-field approximation and with the functional renormalization group. The model provides an explicit example for the importance of baryonic degrees of freedom: When they are omitted, the phase diagram closely resembles that of the corresponding (Polyakov)-quark-meson models for QCD, in particular including their critical endpoint. In order to reproduce the well established main features based on the symmetries and breaking patterns of two-color QCD, however, they must be included and there is no critical endpoint. The competing dynamics of collective mesonic and baryonic fluctuations is well described by the functional renormalization group equation in lowest order derivative expansion for the effective potential which we solve numerically on a two-dimensional grid in field space.