Enhanced global symmetries and the chiral phase transition - art. no. 116007

We examine the possibility that the physical spectrum of a vectorlike gauge field theory exhibits an enhanced global symmetry near a chiral phase tran sition. A transition from the Goldstone phase to the symmetric phase is exp ected as the number of fermions N-f is increased to some critical value. Va rious investigations have suggested that a parity-doubled spectrum develops as the critical value is approached. Using an effective Lagrangian as a gu ide, we note that parity doubling is associated with the appearance of an e nhanced global symmetry in the spectrum of the theory. The enhanced symmetr y would develop as the spectrum splits into two sectors, with the first exh ibiting the usual pattern of a spontaneously broken chiral symmetry, and th e second exhibiting an additional, unbroken symmetry and parity doubling. T he first sector includes the Goldstone bosons and other states such as mass ive scalar partners. The second includes a parity-degenerate vector and axi al vector along with other possible parity partners. We note that if such a near-critical theory describes symmetry breaking in the electroweak theory , the additional symmetry suppresses the contribution of the parity-doubled sector to the S parameter. [S0556-2821(99)01421-6].