### Abstract

The low-lying spectrum of the three-dimensional Ising model is investigated numerically; we made use of an equivalence between the excitation gap and the reciprocal correlation length. In the broken-symmetry phase, the magnetic excitations are attractive, forming a bound state with an excitation gap m2 (<2 m1) (m1: elementary excitation gap). It is expected that the ratio m2 / m1 is a universal constant in the vicinity of the critical point. In order to estimate m2 / m1, we perform a numerical diagonalization for finite clusters with N≤15 spins. In order to reduce the finite-size errors, we incorporated the extended (next-nearest-neighbor and four-spin) interactions. As a result, we estimate the mass-gap ratio as m2 / m1 =1.84 (3).

Original language | English |
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Article number | 051112 |

Journal | Physical Review E - Statistical, Nonlinear, and Soft Matter Physics |

Volume | 77 |

Issue number | 5 |

DOIs | |

Publication status | Published - May 13 2008 |

### ASJC Scopus subject areas

- Statistical and Nonlinear Physics
- Statistics and Probability
- Condensed Matter Physics