Search results for "renormalization"
showing 10 items of 470 documents
Probing chiral interactions up to next-to-next-to-next-to-leading order in medium-mass nuclei
2019
We study ground-state energies and charge radii of closed-shell medium-mass nuclei based on novel chiral nucleon-nucleon (NN) and three-nucleon (3N) interactions, with a focus on exploring the connections between finite nuclei and nuclear matter. To this end, we perform in-medium similarity renormalization group (IM-SRG) calculations based on chiral interactions at next-to-leading order (NLO), N$^2$LO, and N$^3$LO, where the 3N interactions at N$^2$LO and N$^3$LO are fit to the empirical saturation point of nuclear matter and to the triton binding energy. Our results for energies and radii at N$^2$LO and N$^3$LO overlap within uncertainties, and the cutoff variation of the interactions is w…
A CRITICAL VIEW ON THE PERTURBATIVE RG METHOD
2012
The perturbative renormalization group (RG) treatment of the Ginzburg–Landau model is reconsidered based on the Feynman diagram technique. We derive RG flow equations, exactly calculating all vertices appearing in the perturbative RG transformation of the φ4 model up to the ε3 order of the ε-expansion. The Fourier-transformed two-point correlation function G(k) has been considered. Although the ε-expansion of X(k) = 1/G(k) is well defined on the critical surface, we have revealed an inconsistency with the exact rescaling of X(k), represented as an expansion in powers of k at k →0. This new result can serve as a basis to challenge the correctness of the ε-expansion-based perturbative RG met…
Improving the ultraviolet behavior in baryon chiral perturbation theory
2004
We introduce a new formulation of baryon chiral perturbation theory which improves the ultraviolet behavior of propagators and can be interpreted as a smooth cutoff regularization scheme. It is equivalent to the standard approach, preserves all symmetries and therefore satisfies the Ward identities. Our formulation is equally well defined in the vacuum, one- and few-nucleon sectors of the theory. The equations (Bethe-Salpeter, Lippmann-Schwinger, etc.) for the scattering amplitudes of the few-nucleon sector are free of divergences in the new approach. Unlike the usual cutoff regularization, our 'cutoffs' are parameters of the Lagrangian and do not have to be removed.
Recent developments in effective field theory
2007
We will give a short introduction to the one-nucleon sector of chiral perturbation theory and will address the issue of a consistent power counting and renormalization. We will discuss the infrared regularization and the extended on-mass-shell scheme. Both allow for the inclusion of further degrees of freedom beyond pions and nucleons and the application to higher-loop calculations. As applications we consider the chiral expansion of the nucleon mass to order O(q^6) and the inclusion of vector and axial-vector mesons in the calculation of nucleon form factors.
Infrared regularization of baryon chiral perturbation theory reformulated
2003
We formulate the infrared regularization of Becher and Leutwyler in a form analogous to our recently proposed extended on-mass-shell renormalization. In our formulation, IR regularization can be applied straightforwardly to multi-loop diagrams with an arbitrary number of particles with arbitrary masses.
Extraction of K --> pi pi matrix elements with Wilson fermions
2001
We present the status of a lattice calculation for the K-->pipi matrix elements of the (delta S=1) effective weak Hamiltonian, directly with two pion in the final state. We study the energy shift of two pion in a finite volume both in the I=0 and I=2 channels. We explain a method to avoid the Goldstone pole contamination in the computation of renormalization constants for (delta I=3/2) operators. Finally we show some preliminary results for the matrix elements of (delta I=1/2) operators. Our quenched simulation is done at beta=6.0, with Wilson fermions, on a (24^3 X 64) lattice.
Asymptotic properties of Born-improved amplitudes with gauge bosons in the final state
1999
For processes with gauge bosons in the final state we show how to continuously connect with a single Born-improved amplitude the resonant region, where resummation effects are important, with the asymptotic region far away from the resonance, where the amplitude must reduce to its tree-level form. While doing so all known field-theoretical constraints are respected, most notably gauge-invariance, unitarity and the equivalence theorem. The calculations presented are based on the process $f\bar{f}\to ZZ$, mediated by a possibly resonant Higgs boson; this process captures all the essential features, and can serve as a prototype for a variety of similar calculations. By virtue of massive cancel…
Nonperturbative effective model for the Higgs sector of the standard model
2010
A nonperturbative effective model is derived for the Higgs sector of the Standard Model which is described by a simple scalar theory. The renormalized couplings are determined by the derivatives of the Gaussian effective potential that are known to be the sum of infinite bubble graphs contributing to the vertex functions. A good agreement has been found with strong coupling lattice simulations when a comparison can be made.
Displacement Operator Formalism for Renormalization and Gauge Dependence to All Orders
2005
We present a new method for determining the renormalization of Green functions to all orders in perturbation theory, which we call the displacement operator formalism, or the D-formalism, in short. This formalism exploits the fact that the renormalized Green functions may be calculated by displacing by an infinite amount the renormalized fields and parameters of the theory with respect to the unrenormalized ones. With the help of this formalism, we are able to obtain the precise form of the deformations induced to the Nielsen identities after renormalization, and thus derive the exact dependence of the renormalized Green functions on the renormalized gauge-fixing parameter to all orders. As…
One-loop Renormalization of Resonance Chiral Theory with Scalar and Pseudoscalar Resonances
2005
The divergent part of the generating functional of the Resonance Chiral Theory is evaluated up to one loop when one multiplet of scalar an pseudoscalar resonances are included and interaction terms which couple up to two resonances are considered. Hence we obtain the renormalization of the couplings of the initial Lagrangian and, moreover, the complete list of operators that make this theory finite, at this order.