Renormalization Group¶and the Melnikov Problem for PDE's

We give a new proof of persistence of quasi-periodic, low dimensional elliptic tori in infinite dimensional systems. The proof is based on a renormalization group iteration that was developed recently in [BGK] to address the standard KAM problem, namely, persistence of invariant tori of maximal dimension in finite dimensional, near integrable systems. Our result covers situations in which the so called normal frequencies are multiple. In particular, it provides a new proof of the existence of small-amplitude, quasi-periodic solutions of nonlinear wave equations with periodic boundary conditions. Received: 29 January 2001 / Accepted: 8 March 2001     

On the Renormalization of the One–Pion Exchange Potential and the Consistency of Weinberg’s Power Counting

Nogga, Timmermans and van Kolck recently argued that Weinberg’s power counting in the few–nucleon sector is inconsistent and requires modifications. Their argument is based on the observed cutoff dependence of the nucleon–nucleon scattering amplitude calculated by solving the Lippmann–Schwinger equation with the regularized one–pion exchange potential and the cutoff Λ varied in the range Λ = 2 . . . 20 fm^?1. In this paper we discuss the role the cutoff plays in the application of chiral effective field theory to the two–nucleon system and study carefully the cutoff–dependence of phase shifts and observables based on the one–pion exchange potential. We show that (i) there is no need to use the momentum–space cutoff larger than Λ ~ 3 fm^?1; (ii) the neutron–proton low–energy data show no evidence for an inconsistency of Weinberg’s power counting if one uses Λ ~ 3 fm^?1.     

Generalized Central Limit Theorem and Renormalization Group

We introduce a simple instance of the renormalization group transformation in the Banach space of probability densities. By changing the scaling of the renormalized variables we obtain, as fixed points of the transformation, the Lévy strictly stable laws. We also investigate the behavior of the transformation around these fixed points and the domain of attraction for different values of the scaling parameter. The physical interest of a renormalization group approach to the generalized central limit theorem is discussed.     

Renormalization of the Chapman–Enskog Expansion: Isothermal Fluid Flow and Rosenau Saturation

This paper continues the author's study of procedures for rewriting the well-known Chapman–Enskog expansion used in the kinetic theory of gases. The usual Chapman–Enskog expansion, when used in isothermal fluid motion, will introduce nonlinear instability at super-Burnett order O(³) truncation. The procedure given here eliminates the truncation instability and produces the desired dissipation inequality.     

Renormalization and Periodic Orbits¶for Hamiltonian Flows

We consider a renormalization group transformation for analytic Hamiltonians in two or more dimensions, and use this transformation to construct invariant tori, as well as sequences of periodic orbits with rotation vectors approaching that of the invariant torus. The construction of periodic and quasiperiodic orbits is limited to near-integrable Hamiltonians. But as a first step toward a non-perturbative analysis, we extend the domain of to include any Hamiltonian for which a certain non-resonance condition holds. Received: 5 October 1999 / Accepted: 2 February 2000     

Renormalization group treatment of the quantum nonlinear σ-model

The quantum nonlinear -model in (d+1)-dimensional space-time is investigated by a renormalization group approach. The beta-functions for the couplingg and the temperaturet are given. The renormalisation group equations of theN-point functions are derived for finite coupling and finite temperature. It is known that the model shows a phase transition at zero temperature at some critical couplingg _c . The behaviour near this critical point is investigated. The crossover exponent , describing the crossover between different regimes near the critical point is calculated, verifying a conjecture by Chakravarty, Halperin and Nelson, who have argued that ind dimensions should have the same value as the critical exponent of the correlation length in a (d+1)-dimensional classical system. A subtraction scheme appropriate to calculate the renormalisation factors and from these the beta-functions at finite temperature and finite coupling constant will be introduced. Using this method the beta-functions will be calculated to order two loops. The exponents obtained this way are in good agreement with the values found on other ways.     

Renormalization of quantum discord and Bell nonlocality in the XXZ model with Dzyaloshinskii–Moriya interaction

In this paper, we have investigated the dynamical behaviors of the two important quantum correlation witnesses, i.e. geometric quantum discord (GQD) and Bell–CHSH inequality in the XXZ model with DM interaction by employing the quantum renormalization group (QRG) method. The results have shown that the anisotropy suppresses the quantum correlations while the DM interaction can enhance them. Meanwhile, using the QRG method we have studied the quantum phase transition of GQD and obtained two saturated values, which are associated with two different phases: spin-fluid phase and the Néel phase. It is worth mentioning that the block–block correlation is not strong enough to violate the Bell–CHSH inequality in the whole iteration steps. Moreover, the nonanalytic phenomenon and scaling behavior of Bell inequality are discussed in detail. As a byproduct, the conjecture that the exact lower and upper bounds of Bell inequality versus GQD can always be established for this spin system although the given density matrix is a general X state.     

Renormalization of Möbius infinities and partition function representation for the string theory effective action

We show that subtraction of the Möbius group volume in the open string massless amplitudes can be realized as a renormalization of linear 2D ultraviolet divergences in the generating functional (“partition function”). This implies that the vector field effective action can be represented as a renormalized partition function (i.e. as a path integral of the “Wilson factor”). We check this by computing several leading terms in the non-abelian effective action.     

Renormalization of the Asymptotically Expanded Yang–Mills Spectral Action

We study renormalizability aspects of the spectral action for the Yang–Mills system on a flat 4-dimensional background manifold, focusing on its asymptotic expansion. Interpreting the latter as a higher-derivative gauge theory, a power-counting argument shows that it is superrenormalizable. We determine the counterterms at one-loop using zeta function regularization in a background field gauge and establish their gauge invariance. Consequently, the corresponding field theory can be renormalized by a simple shift of the spectral function appearing in the spectral action.     

Renormalization and Asymptotic Expansion of Dirac’s Polarized Vacuum

We perform rigorously the charge renormalization of the so-called reduced Bogoliubov-Dirac-Fock (rBDF) model. This nonlinear theory, based on the Dirac operator, describes atoms and molecules while taking into account vacuum polarization effects. We consider the total physical density ρ _ph including both the external density of a nucleus and the self-consistent polarization of the Dirac sea, but no ‘real’ electron. We show that ρ _ph admits an asymptotic expansion to any order in powers of the physical coupling constant α _ph, provided that the ultraviolet cut-off behaves as L ~ e^{3p(1-Z₃)/2a_ph} >> 1{\Lambda\sim e^{3\pi(1-Z_3)/2\alpha_{\rm ph}} \gg 1}. The renormalization parameter 0 < Z ₃ < 1 is defined by Z ₃ = α _ph/α, where α is the bare coupling constant. The coefficients of the expansion of ρ _ph are independent of Z ₃, as expected. The first order term gives rise to the well-known Uehling potential, whereas the higher order terms satisfy an explicit recursion relation.     

Philosophical Implications of Kadanoff’s Work on the Renormalization Group

This paper investigates the consequences for our understanding of physical theories as a result of the development of the renormalization group. Kadanoff’s assessment of these consequences is discussed. What he called the “extended singularity theorem” (that phase transitons only can occur in infinite systems) poses serious difficulties for philosophical interpretation of theories. Several responses are discussed. The resolution demands a philosophical rethinking of the role of mathematics in physical theorizing.     

Refined Chiral Slavnov–Taylor Identities: Renormalization and Local Physics

We study the quantization of chiral QED with one family of massless fermions and the Stueckelberg field in order to give mass to the Abelian gauge field in a BRST-invariant way. We show that an extended Slavnov–Taylor (ST) identity can be introduced and fulfilled to all orders in perturbation theory by a suitable choice of the local actionlike counterterms, order by order in the loopwise expansion. This ST identity incorporates the Adler–Bardeen anomaly and involves the introduction of a doublet (K, c), where K is an external source of dimension 0 and c is the ghost field. By a purely algebraic argument we show that the introduction of the source K trivializes the cohomology of the extended linearized classical ST operator S ₀ in the Fadeev–Popov (FP) charge + 1 sector.We discuss the physical content of the extended ST identity and prove that the cohomology classes associated with S ₀ are modified with respect to the ones of the classical BRST differential s in the FP neutral sector (physical observables). This provides a counterexample showing that the introduction of a doublet can modify the cohomology of the model, as a consequence of the fact that the counting operator for the doublet (K, c) does not commute with S ₀ .We explicitly check that the physical states defined by s are no more physical states of the full quantized theory by showing that the subspace of the physical states corresponding to s is not left-invariant under the application of the S matrix, as a consequence of the extended ST identity.     

Renormalization Group Analysis of the Self-Avoiding Paths on the d-Dimensional Sierpiński Gaskets

Notion of the renormalization group dynamical system, the self-avoiding fixed point and the critical trajectory are mathematically defined for the set of self-avoiding walks on the d-dimensional pre-Sierpiski gaskets (n-simplex lattices), such that their existence imply the asymptotic behaviors of the self-avoiding walks, such as the existence of the limit distributions of the scaled path lengths of canonical ensemble, the connectivity constant (exponential growth of path numbers with respect to the length), and the exponent for mean square displacement. We apply the so defined framework to prove these asymptotic behaviors of the restricted self-avoiding walks on the 4-dimensional pre-Sierpiski gasket.     

Renormalization of the contribution of the electron—electron interaction to the conductivity of two-dimensional electron systems

The contribution of the electron—electron interaction to the conductivity of the two-dimensional electron gas in an In_x Ga_1-x As single quantum well with different disorder strengths was experimentally studied. It is shown that the data are described well within the framework of the one-loop approximation of the renormalization group theory so long as the conductivity of the system remains higher than around 15e ²/μh.     

Renormalization group fixed points in the local potential approximation ford≧3

In the Local Potential Approximation, renormalization group equations reduce to a semilinear parabolic partial differential equation. Felder [8] has derived this equation and has constructed a family of non-trivial fixed pointsu _2n ^* (n=2,3,4,...) which have the form ofn-well potentials and exist in the ranges of dimensions 2<d<2+2/n–1. In this paper we show that ifd4, then these non-trivial fixed points disappear, and if 3d<4 then we have only theu ₄ ^* fixed point.Research supported by CNPq, Brazil     

Renormalization in the Hénon Family, I: Universality But Non-Rigidity

In this paper geometric properties of infinitely renormalizable real Hénon-like maps F in are studied. It is shown that the appropriately defined renormalizations R ⁿ F converge exponentially to the one-dimensional renormalization fixed point. The convergence to one-dimensional systems is at a super-exponen- tial rate controlled by the average Jacobian and a universal function a(x). It is also shown that the attracting Cantor set of such a map has Hausdorff dimension less than 1, but contrary to the one-dimensional intuition, it is not rigid, does not lie on a smooth curve, and generically has unbounded geometry Dedicated to Mitchell Feigenbaum on the occasion of his 60th birthday     

Renormalization of the electron spectrum by confined and interface phonons in a spherical nanoheterosystem (β-HgS/CdS)

The mechanisms of the electron spectrum renormalization by confined (L) and interface (I) phonons in a spherical quantum dot (QD) embedded in a semiconducting sphere are studied for the specific case of the β-HgS/CdS nanosystem. It is shown that, in view of the absence of interaction between an electron in spherically symmetric states and interface phonons forming only one bound state in a small-size QD, the shift Δ of this single level is formed only by confined phonons. As the size of the QD increases, the contribution of L and I phonons to Δ changes accordingly (L phonons slightly dominate), and the shift varies from Δ _CdS ^3D to Δ _HgS ^3D .     

Renormalization group equation and QCD coupling constant in?the?presence of?SU(3) chromo-electric field

We solve the renormalization group equation in QCD in the presence of a SU(3) constant chromo-electric field E ^a with arbitrary color index a=1,2,…,8 and find that the QCD coupling constant α _s depends on two independent Casimir/gauge invariants C ₁=[E ^a E ^a ] and C ₂=[d _abc E ^a E ^b E ^c ]² instead of one gauge invariant C ₁=[E ^a E ^a ]. The β function is derived from the one-loop effective action. This coupling constant may be useful to study hadron formation from color flux tubes/strings at high energy colliders and to study quark–gluon plasma formation at RHIC and LHC.