We present results for pseudo-critical temperatures of QCD chiral crossovers at zero and non-zero values of baryon (B), strangeness (S), electric charge (Q), and isospin (I) chemical potentials <math><msub><mrow><mi>μ</mi></mrow><mrow><mi>X</mi><mo>=</mo><mi>B</mi><mo>,</mo><mi>Q</mi><mo>,</mo><mi>S</mi><mo>,</mo><mi>I</mi></mrow></msub></math>. The results were obtained using lattice QCD calculations carried out with two degenerate up and down dynamical quarks and a dynamical strange quark, with quark masses corresponding to physical values of pion and kaon masses in the continuum limit. By parameterizing pseudo-critical temperatures as <math><msub><mrow><mi>T</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>(</mo><msub><mrow><mi>μ</mi></mrow><mrow><mi>X</mi></mrow></msub><mo>)</mo><mo>=</mo><msub><mrow><mi>T</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>(</mo><mn>0</mn><mo>)</mo><mrow><mo>[</mo><mn>1</mn><mo>−</mo><msubsup><mrow><mi>κ</mi></mrow><mrow><mn>2</mn></mrow><mrow><mi>X</mi></mrow></msubsup><msup><mrow><mo>(</mo><msub><mrow><mi>μ</mi></mrow><mrow><mi>X</mi></mrow></msub><mo>/</mo><msub><mrow><mi>T</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>(</mo><mn>0</mn><mo>)</mo><mo>)</mo></mrow><mrow><mn>2</mn></mrow></msup><mo>−</mo><msup><mrow><msub><mrow><mi>κ</mi></mrow><mrow><mn>4</mn></mrow></msub></mrow><mrow><mi>X</mi></mrow></msup><msup><mrow><mo>(</mo><msub><mrow><mi>μ</mi></mrow><mrow><mi>X</mi></mrow></msub><mo>/</mo><msub><mrow><mi>T</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>(</mo><mn>0</mn><mo>)</mo><mo>)</mo></mrow><mrow><mn>4</mn></mrow></msup><mo>]</mo></mrow></math>, we determined <math><msubsup><mrow><mi>κ</mi></mrow><mrow><mn>2</mn></mrow><mrow><mi>X</mi></mrow></msubsup></math> and <math><msubsup><mrow><mi>κ</mi></mrow><mrow><mn>4</mn></mrow><mrow><mi>X</mi></mrow></msubsup></math> from Taylor expansions of chiral observables in <math><msub><mrow><mi>μ</mi></mrow><mrow><mi>X</mi></mrow></msub></math>. We obtained a precise result for <math><msub><mrow><mi>T</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>(</mo><mn>0</mn><mo>)</mo><mo>=</mo><mo>(</mo><mn>156.5</mn><mo>±</mo><mn>1.5</mn><mo>)</mo></math> MeV. For analogous thermal conditions at the chemical freeze-out of relativistic heavy-ion collisions, i.e., <math><msub><mrow><mi>μ</mi></mrow><mrow><mi>S</mi></mrow></msub><mo>(</mo><mi>T</mi><mo>,</mo><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub><mo>)</mo></math> and <math><msub><mrow><mi>μ</mi></mrow><mrow><mi>Q</mi></mrow></msub><mo>(</mo><mi>T</mi><mo>,</mo><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub><mo>)</mo></math> fixed from strangeness-neutrality and isospin-imbalance, we found <math><msup><mrow><msub><mrow><mi>κ</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow><mrow><mi>B</mi></mrow></msup><mo>=</mo><mn>0.012</mn><mo>(</mo><mn>4</mn><mo>)</mo></math> and <math><msubsup><mrow><mi>κ</mi></mrow><mrow><mn>4</mn></mrow><mrow><mi>B</mi></mrow></msubsup><mo>=</mo><mn>0.000</mn><mo>(</mo><mn>4</mn><mo>)</mo></math>. For <math><msub><mrow><mi>μ</mi></mrow><mrow><mi>B</mi></mrow></msub><mo>≲</mo><mn>300</mn></math> MeV, the chemical freeze-out takes place in the vicinity of the QCD phase boundary, which coincides with the lines of constant energy density of <math><mn>0.42</mn><mo>(</mo><mn>6</mn><mo>)</mo><mspace width="0.25em"></mspace><msup><mrow><mtext>GeV/fm</mtext></mrow><mrow><mn>3</mn></mrow></msup></math> and constant entropy density of <math><mn>3.7</mn><mo>(</mo><mn>5</mn><mo>)</mo><mspace width="0.25em"></mspace><msup><mrow><mtext>fm</mtext></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math>.

United States