2023/06/26 by Jens O. Andersen, Qing Yu, Andersen, Jens O. +3
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Nuclear Theory (nucl-th) #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #Quantum Gases (cond-mat.quant-gas)
paper · pdf · doi:10.48550/arxiv.2306.14472
openalex publication_date 2023/06/26 · openalex created_date 2023/06/28 · openalex updated_date 2026/07/28
We consider pion condensation in QCD at finite isospin density μI and zero temperature using two-flavor chiral perturbation theory (χPT). The pressure is calculated to next-to-leading order (NLO) in the low-energy expansion. In the nonrelativistic limit, we recover the classic result by Lee, Huang, and Yang for the energy density of a dilute Bose gas with an s-wave scattering length that includes loop corrections from χPT. In the chiral limit, higher-order calculations are tractable. We calculate the pressure to next-to-next-to-leading order (NNLO) in the low-energy expansion, which is an expansion in powers of μI2/(4π)2f2, where f is the (bare) pion decay constant. The spontaneous breakdown of the global internal symmetry U(1)I3 gives rise to a massless Goldstone boson or phonon. We discuss the properties of the low-energy effective theory describing this mode. Finally, we compare our results for the pressure and the speed of sound with recent lattice simulations with 2+1 flavors. The agreement is very good for isospin chemical potentials up to 180-200 MeV, depending on the physical quantity.