Infrared Bound and Mean-Field Behaviour in the Quantum Ising Model

• We prove an infrared bound for the transverse field Ising model. This bound is stronger than the previously known infrared bound for the model, and allows us to investigate mean-field behaviour. As an application we show that the critical exponent gamma for the susceptibility attains its mean-field value gamma = 1 in dimension at least 4 (positive temperature), respectively 3 (ground state), with logarithmic corrections in the boundary cases.

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