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Recently developed renormalization-group techniques are summarized and exploited to yield a renormalization-group analysis of bicritical and tetracritical points (which arise in antiferromagnets and boson systems). For n3 an isotropic or Heisenberg fixed point dominates and gives bicritical behavior; but for n4 a new "biconical" fixed point with irrational ε-expansion coefficients appears. This describes a tetracritical point and may be relevant to displacive phase transitions.
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Nelson et al. (1974) studied this question.
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