arXiv subjects

A. Rusetsky

Publications and source records attributed to A. Rusetsky.

53 records · Page 3Linked to original sources

arXiv2002

Including virtual photons in strong interactions

In the perturbative field-theoretical models we investigate the inclusion of the electromagnetic interactions into the purely strong theory that describes hadronic processes. In particular, we study the convention for splitting electromagnetic and strong interactions and the ambiguity of such a splitting. The issue of the interpretation of the parameters of the low-energy effective field theory in the presence of electromagnetic interactions is addressed, as well as the scale and gauge dependence of the effective theory couplings. We hope, that the results of these studies are relevant for the electromagnetic sector of ChPT.

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arXiv2002

Ground-state energy of pionic hydrogen to one loop

We investigate the ground-state energy of the pi- p atom (pionic hydrogen) in the framework of QCD+QED. In particular, we evaluate the strong energy-level shift. We perform the calculation at next-to-leading order in the low-energy expansion in the framework of the relevant effective field theory. The result provides a relation between the strong energy shift and the pion-nucleon S-wave scattering lengths - evaluated in pure QCD - at next-to-leading order in isospin breaking and in the low-energy expansion. We compare our result with available model calculations.

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arXiv2001

HadAtom01

These are the proceedings of the workshop "HadAtom01", held at the Institut fuer Theoretische Physik, Universitaet Bern, October 11 - 12, 2001. 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.

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arXiv2001

Hadronic potentials from effective field theories

We construct the potentials that describe the spectrum and decay of electromagnetic bound states of hadrons, and are consistent with ChPT. These potentials satisfy the matching condition which enables one to express the parameters of the potential through the threshold scattering amplitudes calculated in ChPT. We further analyze the ambiguity in the choice of the short-range hadronic potentials, which satisfy this matching condition.

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arXiv2001

Decays of the pi+ pi- atom

We construct an effective non-relativistic quantum field theory that describes bound states of pi+ pi- pairs and their hadronic decays. We then derive a general expression for the lifetime of the ground state at next-to-leading order in isospin breaking. Chiral perturbation theory allows one to relate the decay rate to the two S-wave pi pi scattering lengths and to several low-energy constants that occur in the chiral Lagrangian. Recent predictions for the scattering lengths give tau = (2.9 \pm 0.1) * 10^{-15} sec. This result may be confronted with pi+ pi- lifetime measurements, like the one presently carried out at CERN.

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arXiv2000

Theory of Hadronic Atoms

A review of the modern theory of hadronic atoms based on the non-relativistic effective Lagrangian approach and ChPT, is given. As an application of the general framework, we consider the decay of the pi+pi- atom into two neutral pions, and the energy-level shift of the pi-p atom. The analysis of the decay width of the pi+pi- atom has been carried out at the first non-leading order in isospin breaking, and at O(e^2p^2) in ChPT, that results in an accurate theoretical prediction for this quantity. The study of the pi-p atom energy-level shift within the same approach clearly demonstrates the necessity to critically reaccess the values of the pi N scattering lengths, extracted from the energy-level shift measurement by means of the potential model-based theoretical analysis. The construction of short-range hadronic potentials from field theory is also discussed.

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arXiv2000

Effective theories and hadronic bound states

Recent progress in the description of the properties of hadronic atoms on the basis of non-relativistic effective Lagrangian approach and Chiral Perturbation Theory (ChPT) is reported. For the case of the pi(+)pi(-) atom decay, the problem is completely solved, both conceptually and numerically. For the pi(-)p atom, a general expression for the ground-state energy is obtained in the first non-leading order in isospin breaking, and the numerical analysis is carried out at O(p^2) in ChPT. We briefly consider a possible solution of the "potential model puzzle" in the hadronic atom problem, providing a constructive algorithm for the derivation of the isospin-breaking part of the short-range hadronic potential from field theory.

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arXiv2000

pi(-)p atom in ChPT: strong energy-level shift

The general formula of the pi(-)p atom strong energy-level shift in the 1s state is derived in the next-to-leading order in the isospin breaking, and in all orders in chiral expansion. Isospin-breaking corrections to the level shift are explicitly evaluated at order p^2 in ChPT. The results clearly demonstrate the necessity to critically reaccess the values of the piN scattering lengths, extracted from the energy-level shift measurement by means of the potential model-based theoretical analysis.

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arXiv2000

Effective Lagrangians in bound state calculations

In order to investigate specific aspects of bound state calculations in a non-relativistic framework, we consider the energy-levels of a massive scalar particle, which moves in an external field and interacts in addition with a massless scalar particle. The discussion includes the following topics: dimensionally regularized bound-state calculations, ultraviolet finiteness of bound-state observables and their independence of the off-mass-shell behavior of Green functions, non-renormalizable interactions, structure of the non-relativistic two-point function, power counting and matching.

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arXiv1999

Report of Working Group on Electromagnetic Corrections

The talks delivered by M. Knecht, H. Neufeld, V.E. Lyubovitskij, A. Rusetsky and J. Soto during the session of the working group of electromagnetic corrections to hadronic processes at the Eight International Symposium MENU99, cover a wide range of problems. In particular, those include: construction of the effective Lagrangians that then are used for the evaluation of electromagnetic corrections to the decays of K mesons; evaluation of some of the low-energy constants in these Lagrangians, using sum rules and the large-N_c arguments; complete calculations of electromagnetic corrections to the pi pi scattering amplitude at O(e^2p^2); the general theory of electromagnetic bound states of hadrons in the Standard Model.

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arXiv1999

HadAtom99

These are the proceedings of the workshop "HadAtom99", held at the Institut fuer Theoretische Physik, Universitaet Bern, October 14-15, 1999. The main topics discussed at the workshop were the physics of hadronic atoms and in this context recent results from Chiral Perturbation Theory. Included here are the program, the list of participants and a short summary provided by the speakers.

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arXiv1999

Spectrum and Decays of Hadronic Atoms

Using non relativistic effective Lagrangian techniques, we analyze the hadronic decay of the pi+pi- atom and the strong energy-level shift of pionic hydrogen in the ground state. We derive general formulae for the width and level shift, valid at next-to-leading order in isospin breaking. The result is expressed in terms of hadronic threshold amplitudes that include isospin-breaking effects. In order to extract isospin symmetric scattering lengths from the data, we invoke chiral perturbation theory, that allows one to relate the scattering lengths to the threshold amplitudes.

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arXiv1999

Hadronic Atoms in QCD

We propose a non relativistic effective Lagrangian approach to study hadronic atom observables in the framework of QCD (including photons). We apply our formalism to derive a general expression for the width of the pi+pi- atom decaying into two neutral pions. It contains all terms at leading and next-to-leading order in isospin breaking. The result allows one to evaluate the combination a0-a2 of pi-pi S-wave scattering lengths from pi+pi- atom lifetime measurements, like the one presently performed by the DIRAC expeiment at CERN.

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arXiv1999

Numerical analysis of the pi+pi- atom lifetime in ChPT

We apply Chiral Perturbation Theory at one loop to analyze the general formula for the pi+pi- atom lifetime derived recently in the framework of QCD. The corresponding analytic expression is investigated numerically, and compared with recent work in the literature.

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arXiv1999

On the Lifetime of the pi+pi- Atom

The pi+pi- atom decays -in the ground state - predominantly into two neutral pions. We present a general expression for the corresponding decay width in the framework of QCD (including photons). It contains all terms at leading and next-to-leading order in isospin breaking. The result allows one to evaluate the combination |a_0-a_2| of pi-pi S-wave scattering lengths from pi+pi- lifetime measurements, like the one presently performed by the DIRAC experiment at CERN.

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arXiv1997

Working group on $ππ$ and $π$N interactions - Summary

This is the summary of the working group on $ππ$ and $π$N interactions of the Chiral Dynamics Workshop in Mainz, September 1-5, 1997. Each talk is represented by an extended one page abstract. Some additional remarks by the convenors are added

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arXiv1997

The Spin Structure of the qq Interaction and the Mass Spectra of Bound q\bar q Systems: Different Versions of the 3-Dimensional Reductions of the Bethe-Salpeter Equation

Bound q\bar q -systems are considered in the framework of three different versions of the 3-dimensional reduction of the Bethe-Salpeter equation, all having the correct one-body limit when one of the constituent quark masses tends to infinity, and in the framework of the Salpeter equation. The spin structure of confining qq interaction potential is taken in the form xγ_{1}^{0}γ_{2}^{0}+(1-x)I_{1}I_{2}, with 0 \leq x \leq 1. The problem of existence (nonexistence) of stable solutions of 3-dimensional relativistic equations for bound q\bar q systems is studied for different values of x from this interval. Some other aspects of this problem are discussed.

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