Functional Truncations for the Solution of the Nonperturbative RG Equations
Journal of Physics A: Mathematical and Theoretical 2022
Jevgenijs Kaupužs, R.V.N. Melnik

We consider the Wetterich exact renormalization group (RG) equation. Approximate closed equations are obtained from it, applying certain truncation schemes for the effective average action. These equations are solved either purely numerically or by certain extra truncations for the potential and related quantities, called the functional truncations. Traditionally, the functional truncations consist of truncated expansions in powers of ρ ˜ − ρ ˜ 0 , where ρ ˜ ∝ ϕ 2 , φ is the averaged order parameter, and ρ ˜ 0 corresponds to the minimum of the dimensionless potential u k ( ρ ˜ ) , depending on the infrared cut-off scale k. We propose a new approach of functional truncations, using the expansion u k ( ρ ˜ ) − u k ( 0 ) = ( 1 − s ) − μ u 1 , k s + u 2 , k s 2 + ⋯ , where s = ρ ˜ / ( ρ ˜ 0 + ρ ˜ ) , ρ ˜ 0 is an optimization parameter and µ is the exponent, describing the ρ ˜ → ∞ asymptotic. The newly developed method provides accurate estimates of the critical exponents η, ν and also ω. In the case of the local potential approximation (LPA), the discrepancy with the purely numerical solution is 0.000 15 for ν and 0.0012 for ω at the s 13 order of truncation. We show that this method is advantageous for estimations beyond the LPA, especially, for the critical exponent ω. In particular, we have obtained η = 0.0454 ( 1 ) , ν = 0.6292 ( 2 ) , and ω = 0.8606 ( 30 ) for the equation originally derived in 2020 J. Phys. A: Math. Theor. 53 415002 within a new truncation scheme for the effective action. The approach can also be used for the solution of other nonperturbative RG models that have a broad range of applications.


Atslēgas vārdi
exact renormalization group equations | functional renormalization | functional truncations | non-perturbative approaches | quantum and statistical field theories | strongly interacting systems | Wetterich equation
DOI
10.1088/1751-8121/ac9f8c
Hipersaite
https://iopscience.iop.org/article/10.1088/1751-8121/ac9f8c

Kaupužs, J., Melnik, R. Functional Truncations for the Solution of the Nonperturbative RG Equations. Journal of Physics A: Mathematical and Theoretical, 2022, Vol. 55, No. 46, Article number 465002. ISSN 1751-8113. Available from: doi:10.1088/1751-8121/ac9f8c

Publikācijas valoda
English (en)
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