arXiv subjects

A. Rusetsky

Publications and source records attributed to A. Rusetsky.

At least 37 records · Page 2Linked to original sources

arXiv2012

Scalar mesons moving in a finite volume and the role of partial wave mixing

Phase shifts and resonance parameters can be obtained from finite-volume lattice spectra for interacting pairs of particles, moving with nonzero total momentum. We present a simple derivation of the method that is subsequently applied to obtain the pi pi and pi K phase shifts in the sectors with total isospin I=0 and I=1/2, respectively. Considering different total momenta, one obtains extra data points for a given volume that allow for a very efficient extraction of the resonance parameters in the infinite-volume limit. Corrections due to the mixing of partial waves are provided. We expect that our results will help to optimize the strategies in lattice simulations, which aim at an accurate determination of the scattering and resonance properties.

hep-lat↗

arXiv2012

Matrix elements of unstable states

Using the language of non-relativistic effective Lagrangians, we formulate a systematic framework for the calculation of resonance matrix elements in lattice QCD. The generalization of the Lüscher-Lellouch formula for these matrix elements is derived. We further discuss in detail the procedure of the analytic continuation of the resonance matrix elements into the complex energy plane and investigate the infinite-volume limit.

hep-lat↗

arXiv2011

Dynamical coupled-channel approaches on a momentum lattice

Dynamical coupled-channel approaches are a widely used tool in hadronic physics that allow to analyze different reactions and partial waves in a consistent way. In such approaches the basic interactions are derived within an effective Lagrangian framework and the resulting pseudo-potentials are then unitarized in a coupled-channel scattering equation. We propose a scheme that allows for a solution of the arising integral equation in discretized momentum space for periodic as well as twisted boundary conditions. This permits to study finite size effects as they appear in lattice QCD simulations. The new formalism, at this stage with a restriction to S-waves, is applied to coupled-channel models for the sigma(600), f0(980), and a0(980) mesons, and also for the Lambda(1405) baryon. Lattice spectra are predicted.

hep-lat↗

arXiv2011

Unitarized Chiral Perturbation Theory in a finite volume: scalar meson sector

We develop a scheme for the extraction of the properties of the scalar mesons f0(600), f0(980), and a0(980) from lattice QCD data. This scheme is based on a two-channel chiral unitary approach with fully relativistic propagators in a finite volume. In order to discuss the feasibility of finding the mass and width of the scalar resonances, we analyze synthetic lattice data with a fixed error assigned, and show that the framework can be indeed used for an accurate determination of resonance pole positions in the multi-channel scattering.

hep-lat↗

arXiv2011

Chiral unitary theory of scalar mesons in a finite volume

We develop a scheme for the extraction of the properties of the scalar mesons $f_0(600)$, $f_0(980)$, and $a_0(980)$ from lattice QCD data. This scheme is based on a two-channel chiral unitary approach with fully relativistic propagators in a finite volume. In order to discuss the feasibility of finding the mass and width of the scalar resonances, we analyze synthetic lattice data with a fixed error assigned, and show that the framework can be indeed used for an accurate determination of resonance pole positions in the multi-channel scattering.

hep-lat↗

arXiv2010

Scalar mesons in a finite volume

Using effective field theory methods, we discuss the extraction of the mass and width of the scalar mesons f0(980) and a0(980) from the finite-volume spectrum in lattice QCD. In particular, it is argued that the nature of these states can be studied by invoking twisted boundary conditions, as well as investigating the quark mass dependence of the spectrum.

hep-lat↗

arXiv2010

Resonances in an external field: the 1+1 dimensional case

Using non-relativistic effective field theory in 1+1 dimensions, we generalize Luescher's approach for resonances in the presence of an external field. This generalized approach provides a framework to study the infinite-volume limit of the form factor of a resonance determined in lattice simulations.

hep-lat↗

arXiv2009

The nucleon recoil effect in antikaon-deuteron scattering at threshold

We investigate the role of the nucleon recoil for antikaon-deuteron scattering using EFT. In particular, we show that the leading correction to the static term that appears at order $ξ^{1/2}$ (where $ξ=m_K/M_N$) cancels completely in the double scattering process. We calculate the higher order recoil corrections and study the pattern of convergence of the expansion method. We find that the recoil correction to the double scattering process is of order of 10-15% of the static contribution.

nucl-th↗

arXiv2009

The role of nucleon recoil in low-energy antikaon-deuteron scattering

The effect of the nucleon recoil for antikaon-deuteron scattering is investigated in the framework of effective field theory. In particular, we concentrate on the calculation of the nucleon recoil effect for the double-scattering process. It is shown that the leading correction to the static term that emerges at order xi^{1/2} with xi=M_K/m_N vanishes due to a complete cancellation of individually large contributions. The resulting recoil effect in this process is found to be of order of 10-15% as compared to the static term. We also briefly discuss the application of the method in the calculations of the multiple-scattering diagrams.

nucl-th↗

arXiv2009

Hadronic Atoms

We review the theory of hadronic atoms in QCD+QED. The non-relativistic effective Lagrangian approach, used to describe this type of bound states, is illustrated with the case of pi+pi- atoms. In addition, we discuss the evaluation of isospin-breaking corrections to hadronic atom observables by invoking chiral perturbation theory.

hep-ph↗

arXiv2009

Hadronic atoms in QCD + QED

We review the theory of hadronic atoms in QCD + QED, based on a non-relativistic effective Lagrangian framework. We first provide an introduction to the theory, and then describe several applications: meson-meson, meson-nucleon atoms and meson-deuteron compounds. Finally, we compare the quantum field theory framework used here with the traditional approach, which is based on quantum-mechanical potential scattering.

hep-ph↗

arXiv2009

The mass of the Delta resonance in a finite volume: fourth-order calculation

We calculate the self-energy of the Delta (1232) resonance in a finite volume, using chiral effective field theory with explicit spin-3/2 fields. The calculations are performed up-to-and-including fourth order in the small scale expansion and yield an explicit parameterization of the energy spectrum of the interacting pion-nucleon pair in a finite box in terms of both the quark mass and the box size L. It is shown that finite-volume corrections can be sizeable at small quark masses.

hep-lat↗

arXiv2008

Predictions for the cusp in eta->3pi0 decay

A realistic estimate of the cusp effect in the eta->3pi0 decay is required for the forthcoming high precision experiments. The predictions for the size of this effect are given within the framework of nonrelativistic effective field theory.

hep-ph↗

arXiv2008

Radiative corrections in K --> 3 pi decays

We investigate radiative corrections to K --> 3 pi decays. In particular, we extend the non-relativistic framework developed recently to include real and virtual photons and show that, in a well-defined power counting scheme, the results reproduce corrections obtained in the relativistic calculation. Real photons are included exactly, beyond the soft-photon approximation, and we compare the result with the latter. The singularities generated by pionium near threshold are investigated, and a region is identified where standard perturbation theory in the fine structure constant alpha may be applied. We expect that the formulae provided allow one to extract S-wave pi pi scattering lengths from the cusp effect in these decays with high precision.

hep-ph↗

arXiv2007

Cusps in K_L --> 3 pi decays

The pion mass difference generates a pronounced cusp in K --> 3 pi decays, the strength of which is related to the pi pi S-wave scattering lengths. We apply an effective field theory framework developed earlier to evaluate the amplitudes for K_L --> 3 pi decays in a systematic manner, where the strictures imposed by analyticity and unitarity are respected automatically. The amplitudes for the decay eta --> 3 pi are also given.

hep-ph↗

arXiv2004

HadAtom03

These are the proceedings of the workshop "HadAtom03," held at the European Centre for Theoretical Nuclear Physics and Related Studies (ECT*), Trento (Italy), October 13 - 17, 2003. The main topics discussed at the workshop were the physics of hadronic atoms and in this context recent results in experiment and theory. Included here are the list of participants, the scientific program and a short contribution from each speaker.

hep-ph↗

arXiv2003

Electromagnetic corrections in hadronic processes

In quantum field theory, the splitting of the Hamiltonian into a strong and an electromagnetic part cannot be performed in a unique manner. We propose a convention for disentangling these two effects: one matches the parameters of two theories -- with and without electromagnetic interactions -- at a given scale mu_1, referred to as the matching scale. This procedure enables one to analyze the separation of strong and electromagnetic contributions in a transparent manner. We illustrate the method -- in the framework of the loop expansion -- in a Yukawa model, as well as in the linear sigma model, where we also investigate the corresponding low-energy effective theory.

hep-ph↗

arXiv2003

Chiral Perturbation Theory in a Nuclear Background

We propose a novel way to formulate Chiral Perturbation Theory in a nuclear background, characterized by a static, non-uniform distribution of the baryon number that describes the finite nucleus. In the limiting case of a uniform distribution, the theory reduces to the well-known zero-temperature in-medium ChPT. The proposed approach is used to calculate the self-energy of the charged pion in the background of the heavy nucleus at O(p^5) in the chiral expansion, and to derive the leading terms of the pion-nucleus optical potential.

hep-ph↗