Critical exponents from optimised renormalisation group flows

TL;DR

This paper uses optimized renormalization group flows to accurately compute critical exponents in O(N) scalar theories, demonstrating rapid convergence and analyzing scheme dependence across different N values.

Contribution

It introduces an optimized flow method within the exact renormalization group framework to precisely determine critical exponents and their corrections for all N in scalar theories.

Findings

Optimized flows lead to rapid convergence of critical exponents.

The scheme dependence of the leading critical exponent is bounded for all N.

Polynomial truncations are reliable when combined with proper regulator choices.

Abstract

Within the exact renormalisation group, the scaling solutions for O(N) symmetric scalar field theories are studied to leading order in the derivative expansion. The Gaussian fixed point is examined for d>2 dimensions and arbitrary infrared regularisation. The Wilson-Fisher fixed point in d=3 is studied using an optimised flow. We compute critical exponents and subleading corrections-to-scaling to high accuracy from the eigenvalues of the stability matrix at criticality for all N. We establish that the optimisation is responsible for the rapid convergence of the flow and polynomial truncations thereof. The scheme dependence of the leading critical exponent is analysed. For all N > 0, it is found that the leading exponent is bounded. The upper boundary is achieved for a Callan-Symanzik flow and corresponds, for all N, to the large-N limit. The lower boundary is achieved by the optimised flow and is closest to the physical value. We show the reliability of polynomial approximations, even to low orders, if they are accompanied by an appropriate choice for the regulator. Possible applications to other theories are outlined.