Effective-dimension theory of critical phenomena above upper critical dimensions

Phase transitions and critical phenomena are among the most intriguing phenomena in nature and the renormalization-group theory for them is one of the greatest achievements of theoretical physics. However, the predictions of the theory above an upper critical dimension d ( c ) seriously disagree with reality. In addition to its fundamental significance, the problem is also of practical importance because both complex classical systems with long-range spatial or temporal interactions and quantum phase transitions with long-range interactions can substantially lower d ( c ). The extant scenarios built on a dangerous irrelevant variable (DIV) to resolve the problem introduce two sets of critical exponents and even two sets of scaling laws whose origin is obscure. Here, we consider the DIV from a different perspective and clearly unveil the origin of the two sets of exponents and hence the intrinsic inconsistency in those scenarios. We then develop an effective-dimension theory in which critical fluctuations and system volume are fixed at an effective dimension by the DIV. This enables us to account for all the extant results consistently. A novel asymptotic finite-size scaling behavior for a correlation function together with a new anomalous dimension and its associated scaling law is also predicted. We also apply the theory to quantum phase transitions.

Automated summary

Phase transitions and critical phenomena are fascinating phenomena in nature, and the renormalization-group theory is a great achievement in theoretical physics for describing them. However, the theory fails to accurately predict above a critical dimension, leading to a discrepancy with reality. In this study, we offer a different perspective on the problem and reveal the origin of the inconsistencies in the existing scenarios. We also develop an effective-dimension theory that can account for all the existing results and predict new scaling behaviors.