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Magnetic catalysis effect kills neutral pion superfluidity and vacuum superconductivity in strong magnetic field

Not scheduled
15m
Hualongcheng Hotel

Hualongcheng Hotel

469 Shizhou Road Enshi, Hubei,China

Speaker

Dr Gaoqing Cao (Sun Yat-sen University)

Summary

In the chiral effective Nambu--Jona-Lasinio (NJL) model with two- and three-flavor quarks, we demonstrate that the naively expected neutral pion ($\pi^0$) superfluidity (NPSF) and vacuum superconductivity (VSC) in constant magnetic field ${\bf B}=B\hat z$ are both disfavored, due to the well-known magnetic catalysis effect (MCE) to chiral symmetry breaking. Based on the simple two-flavor NJL model, we illuminate in the lowest Landau level approximation the similar origins of $\pi^0$ and $\bar{\rho}^+_1$ (${\rho}^+$ meson with spin $S_z=1$) mass reductions with $B$ and thus of NPSF and VSC tendencies. With the full Landau levels, the two-flavor NJL model is found to be invalid to study the magnetic field effect to $\bar{\rho}^+_1$ meson with physical vacuum mass $775~{\rm MeV}$. Then, restricted to $\rho$ meson mass below two-quark threshold in vacuum, that is $m_\rho^v<2m_q^v$, it is found that $\pi^0$ mass decreases and then increases with $B$ slowly, and $\bar{\rho}^+_1$ mass vanishing point is delayed to larger $B$ compared to the point particle result. In the more realistic three-flavor NJL model, all the quark masses split in strong magnetic field as a combinatorial result of their different current masses and electric charges. By choosing a vacuum mass closer to the physical one, $\bar{\rho}^+_1$ meson mass is found to be consistent with the LQCD results semi-quantitatively in smaller $B$ region but increase in larger $B$ region. These features are mainly outcomes of the interplay between the $S_z-B$ coupling effect and splitting MCE to the composite $u$ and $d$ quarks, which definitely disfavors VSC when the latter dominates. Furthermore, mesonic flavor mixing is modified by $B$ among the neutral pseudoscalars: $\pi^0,\eta_0$ and $\eta_8$, which is very important to suppress the mass enhancement of the effective mass eigenstates at large $B$.

Primary author

Dr Gaoqing Cao (Sun Yat-sen University)

Presentation materials

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