arXiv subjects

H. Sonoda

Publications and source records attributed to H. Sonoda.

14 recordsLinked to original sources

arXiv2022

Wilson Action for the $O(N)$ Model

In this paper the fixed-point Wilson action for the critical $O(N)$ model in $D=4-\eps$ dimensions is written down in the $\eps$ expansion to order $\eps^2$. It is obtained by solving the fixed-point Polchinski Exact Renormalization Group equation (with anomalous dimension) in powers of $\eps$. This is an example of a theory that has scale and conformal invariance despite having a finite UV cutoff. The energy-momentum tensor for this theory is also constructed (at zero momentum) to order $\eps^2$. This is done by solving the Ward-Takahashi identity for the fixed point action. It is verified that the trace of the energy-momentum tensor is proportional to the violation of scale invariance as given by the exact RG, i.e., the $β$ function. The vanishing of the trace at the fixed point ensures conformal invariance. Some examples of calculations of correlation functions are also given.

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arXiv2021

The Operator Algebra at the Gaussian Fixed-Point

We consider the multiple products of relevant and marginal scalar composite operators at the Gaussian fixed-point in $D=4$ dimensions. This amounts to perturbative construction of the $ϕ^4$ theory where the parameters of the theory are momentum dependent sources. Using the exact renormalization group (ERG) formalism, we show how the scaling properties of the sources are given by the short-distance singularities of the multiple products.

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arXiv2020

Products of Current Operators in the Exact Renormalization Group Formalism

Given a Wilson action invariant under global chiral transformations, we can construct current composite operators in terms of the Wilson action. The short distance singularities in the multiple products of the current operators are taken care of by the exact renormalization group. The Ward-Takahashi identity is compatible with the finite momentum cutoff of the Wilson action. The exact renormalization group and the Ward-Takahashi identity together determine the products. As a concrete example, we study the Gaussian fixed-point Wilson action of the chiral fermions to construct the products of current operators.

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arXiv2020

Operator product expansion coefficients in the exact renormalization group formalism

We study how to compute the operator product expansion coefficients in the exact renormalization group formalism. After discussing possible strategies, we consider some examples explicitly, within the $ε$-expansions, for the Wilson-Fisher fixed points of the real scalar theory in $d=4-ε$ dimensions and the Lee-Yang model in $d=6-ε$ dimensions. Finally we discuss how our formalism may be extended beyond perturbation theory.

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arXiv2019

Holographic Wilson's RG

In an earlier paper (arXiv:1706.03371) a holographic form of the Exact Renormalization Group (ERG) evolution operator for a (perturbed) free scalar field (CFT) in D dimensions was formulated. It was shown to be equivalent, after a change of variables, to a free scalar field action in AdS_{D+1} space time. We attempt to extend this result to a theory where the scalar field has an anomalous dimension. Instead of the ERG evolution operator, we examine the generating functional with an infrared cutoff, and derive the prescription of alternative quantization by using the change of variables introduced in the previous paper. The anomalous dimension is thus related in the usual way to the mass of the bulk scalar field. Computation of higher point functions remains difficult in this theory, but should be tractable in the large N version.

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arXiv2018

On the geometry of the theory space in the ERG formalism

We consider the theory space as a manifold whose coordinates are given by the couplings appearing in the Wilson action. We discuss how to introduce connections on this theory space. A particularly intriguing connection can be defined directly from the solution of the exact renormalization group (ERG) equation. We advocate a geometric viewpoint that lets us define straightforwardly physically relevant quantities invariant under the changes of a renormalization scheme.

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arXiv2017

The generating functional of correlation functions as a high momentum limit of a Wilson action

It is well known that a Wilson action reduces to the generating functional of connected correlation functions as we take the momentum cutoff to zero. For a fixed point Wilson action, this implies that for momenta large compared with the cutoff, the action reduces to the generating functional. We elaborate on this simple observation.

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arXiv2017

Products of composite operators in the exact renormalization group formalism

We discuss a general method of constructing the products of composite operators using the exact renormalization group formalism. Considering mainly the Wilson action at a generic fixed point of the renormalization group, we give an argument for the validity of short distance expansions of operator products. We show how to compute the expansion coefficients by solving differential equations, and test our method with some simple examples.

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arXiv2016

On the wave function renormalization for Wilson actions and their 1PI actions

We clarify the relation between the wave function renormalization for Wilson actions and that for the 1PI actions in the exact renormalization group formalism. Our study depends crucially on the use of two independent cutoff functions for the Wilson actions. We relate our results to those obtained previously by Bervillier, Rosten, and Osborn & Twigg.

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arXiv2015

Equivalence of Wilson Actions

We introduce the concept of equivalence among Wilson actions. Applying the concept to a real scalar theory on a euclidean space, we derive the exact renormalization group transformation of K. G. Wilson, and give a simple proof of universality of the critical exponents at any fixed point of the exact renormalization group transformation. We also show how to reduce the original formalism of Wilson to the simplified formalism by J. Polchinski.

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arXiv2015

Construction of the Energy-Momentum Tensor for Wilson Actions

Given an arbitrary Wilson action of a real scalar field, we discuss how to construct the energy-momentum tensor of the theory. Using the exact renormalization group, we can determine the energy-momentum tensor implicitly, but we are short of obtaining an explicit formula in terms of the Wilson action.

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arXiv2014

Renormalization for free harmonic oscillators

We introduce a model of free harmonic oscillators that requires renormalization. The model is similar to but simpler than the soluble Lee model. We introduce two concrete examples: the first, resembling the three dimensional $ϕ^4$ theory, needs only mass renormalization, and the second, resembling the four dimensional $ϕ^4$ theory and the Lee model, needs additional renormalization of a coupling and a wave function.

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arXiv2013

Solving RG equations with the Lambert W function

It has been known for some time that 2-loop renormalization group (RG) equations of a dimensionless parameter can be solved in a closed form in terms of the Lambert W function. We apply the method to a generic theory with a Gaussian fixed point to construct RG invariant physical parameters such as a coupling constant and a physical squared mass. As a further application, we speculate a possible exact effective potential for the O(N) linear sigma model in four dimensions.

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arXiv1993

Connections on the State-Space over Conformal Field Theories

Motivated by the problem of background independence of closed string field theory we study geometry on the infinite vector bundle of local fields over the space of conformal field theories (CFT's). With any connection we can associate an excluded domain $D$ for the integral of marginal operators, and an operator one-form $ω_μ$. The pair $(D, ω_μ)$ determines the covariant derivative of any correlator of local fields. We obtain interesting classes of connections in which $ω_μ$'s can be written in terms of CFT data. For these connections we compute their curvatures in terms of four-point correlators, $D$, and $ω_μ$. Among these connections three are of particular interest. A flat, metric compatible connection $\HG$, and connections $c$ and $\bar c$ having non-vanishing curvature, with $\bar c$ being metric compatible. The flat connection cannot be used to do parallel transport over a finite distance. Parallel transport with either $c$ or $\bar c$, however, allows us to construct a CFT in the state space of another CFT a finite distance away. The construction is given in the form of perturbation theory manifestly free of divergences.

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