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Recent observations of quasars show high line-flux ratios in their broademission lines and the ratios appear to be independent of redshift up to $z\gtrsim 6$, which indicate that the broad-line regions of these early quasarsare surprisingly metal-rich. Here, we revisit the chemical evolution ofhigh-redshift quasars by adding a new ingredient, i.e., the neutrino-dominatedaccretion flows (NDAFs) with outflows, on top of the conventional core-collapsesupernovae (CCSNe). In the presence of the chemical contribution from NDAFswith outflows, the total metal mass (i.e., the summation of the conventionalCCSN and NDAFs with outflows) per CCSN depends weakly upon the mass of theprogenitor star if the mass is in the range of $\sim 25-55~M_{\odot}$. We modelthe chemical evolution by adopting a improved open-box model with three typicalinitial mass functions (IMFs). We find that, with the additional chemicalcontribution from NDAFs with outflows, the quasar metallicity can be enrichedmore rapidly in the very early Universe ($z \sim 10$) and reaches highersaturation than the no-NDAF case at $z \sim 8$, after which they evolve slowlywith redshift. The quasar metallicity can reach $\sim 20~Z_{\odot}$ ($Z_\odot$denotes the metallicity of the Sun; and $\sim 20\%$ of which is produced byNDAF outflows) at $z \sim 8$ for the ``top-heavy'' IMF model in\citet{Toyouchi2022}, which readily explains the quasar observations on thesuper-solar metal abundance and redshift-independent evolution.

Nucleosynthesis Contribution of Neutrino-dominated Accretion Flows to the Chemical Evolution of Active Galactic Nuclei