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Comment on ``Bicritical and Tetracritical Phenomena and Scaling Properties of the SO(5) Theory,'' [X. Hu, Phys. Rev. Lett. 87, 057004 (2001)]

Pasquale Calabrese, Andrea Pelissetto, Ettore Vicari

cond-mat.supr-conarXiv:cond-mat/0203533

Abstract

We show that, in the most general N-component theory with symmetry O(n1)+O(n2), N=n1+n2≥ 3, the O(N)-symmetric fixed point has (at least) three unstable directions: the temperature, the quadratic anisotropy, and the spin-4 quartic perturbation. This implies that in the SO(5) theory of high-Tc superconductivity an additional tuning is required to obtain an enlarged SO(5) symmetry. This is in contrast with the recent numerical results reported by Hu, Phys. Rev. Lett. 87, 057004 (2001). \

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