Tensor networks for QCD in the strong-coupling expansion

We present the order-separated Grassmann higher-order tensor renormalization group (OS-GHOTRG) method for QCD with staggered quarks in the strong-coupling expansion. Themethod allows us to determine the expansion coefficients of the partition function, from which we can obtain the strong-coupling expansions of thermodynamical observables. We use the method in two dimensions to compute the free energy, the particle-number density, and the chiral condensate as a function of the chemical potential up to third order in the inverse coupling 𝛽. Although the expansion itself is only a good approximation to the full theory at small 𝛽, we show that in the vicinity of the phase transition the range of applicability can be greatly extended by fits to judiciously chosen transition functions. These fits also yield a valuable expansion of the critical chemical potential in 𝛽.

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