Chiral properties of (2+1)-flavor QCD in strong magnetic fields at zero temperature

We present lattice QCD results for masses and magnetic polarizabilities of light and strange pseudo-scalar mesons, chiral condensates, decay constants of neutral pion and neutral kaon in the presence of background magnetic fields with $eB$ ranging up to around 3.35 GeV$^2$ ($\sim70~M_\pi^2$) in the vacuum. The computations were carried out in (2+1)-flavor QCD on $32^3 \times 96$ lattices using the Highly Improved Staggered Quarks (HISQ) action with $M_{\pi} \approx $ 220 MeV at zero temperature. We find that the masses of neutral pseudo-scalar mesons monotonously decrease as the magnetic field strength grows and then saturate at a nonzero value, while there exists a non-monotonous behavior of charged pion and kaon masses in the magnetic field. We observe a $qB$ scaling of the up and down quark flavor components of neutral pion mass, neutral pion decay constant as well as the quark chiral condensates at 0.05 $\lesssim eB\lesssim$ 3.35 GeV$^2$. We show that the next-to-leading order chiral correction to the Gell-Mann-Oakes-Renner relation involving neutral pion is less than 6% and the correction for the relation involving neutral kaon is in the range of (56-72)% at $eB\lesssim$ 3.35 GeV$^2$. We also derive the Ward-Takahashi identities for QCD in the magnetic field in the continuum formulation including the relation between neutral pseudo-scalar meson correlators and chiral condensates.