26 results on '"Rusetsky, Akaki"'
Search Results
2. Spin structure of the nucleon (theory).
- Author
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Meißner, Ulf-G. and Rusetsky, Akaki
- Subjects
- *
PARTICLES (Nuclear physics) , *EXTRAPOLATION , *NUMERICAL analysis , *INTERPOLATION , *LATTICE dynamics - Abstract
We review the achievements of the project C.3, that dealt with the formulation and application of effective field theories including the Δ and Roper resonances as well as vector mesons. A particular focus was the calculation of finite volume effects and chiral extrapolations for lattice QCD. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
3. Baryon resonances in a finite volume.
- Author
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Meißner, Ulf-G. and Rusetsky, Akaki
- Subjects
- *
HADRON-hadron scattering , *MESON-meson interactions , *ELECTROMAGNETIC coupling , *PERTURBATION theory , *APPROXIMATION theory , *LATTICE dynamics - Abstract
We review the main results obtained in the project A.6, which dealt with hadron-hadron scattering and resonances in a finite volume. These results provide tools for the extraction of the resonance characteristics from lattice QCD simulations. In particular, in this review we focus on the evaluation of the matrix elements of the weak and electromagnetic currents between the states containing at least one resonance, as well as on the description of the three-particle states in a finite volume. We also discuss insights obtained using unitarized chiral perturbation theory in a finite volume. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
4. Three-particle Lellouch-Lüscher formalism in moving frames.
- Author
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Müller, Fabian, Pang, Jin-Yi, Rusetsky, Akaki, and Wu, Jia-Jun
- Abstract
A manifestly relativistic-invariant Lellouch-Lüscher formalism for the decays into three identical particles with no two-to-three transitions is proposed. Similarly to [1], the formalism is based on the use of the non-relativistic effective Lagrangians. Manifest Lorentz invariance is guaranteed, as in [2], by choosing the quantization axis along the total four-momentum of the three-particle system. A systematic inclusion of the higher-order derivative couplings, as well as higher partial waves is addressed. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
5. Lellouch-Lüscher factor for the K → 3π decays.
- Author
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Pang, Jin-Yi, Bubna, Rishabh, Müller, Fabian, Rusetsky, Akaki, and Wu, Jia-Jun
- Subjects
- *
ISOBARIC spin , *RENORMALIZATION (Physics) , *QUANTUM chromodynamics , *EQUATIONS , *ALGORITHMS - Abstract
We derive an explicit expression for the Lellouch-Lüscher (LL) factor in the K → 3π decays at leading order (without derivative couplings). Several important technical details are addressed, like a proper decomposition into the isospin amplitudes, the choice of a minimal set of effective couplings and the renormalization, as well as the algorithm for the solution of the pertinent Faddeev equations in the infinite volume which is based on the contour deformation method. Most importantly, our numerical results demonstrate that the three-body force contributes very little to the LL factor. This result paves the way for the study of the K → 3π decays on the lattice. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
6. Relativistic N-particle energy shift in finite volume.
- Author
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Romero-López, Fernando, Rusetsky, Akaki, Schlage, Nikolas, and Urbach, Carsten
- Abstract
We present a general method for deriving the energy shift of an interacting system of N spinless particles in a finite volume. To this end, we use the nonrelativistic effective field theory (NREFT), and match the pertinent low-energy constants to the scattering amplitudes. Relativistic corrections are explicitly included up to a given order in the 1/L expansion. We apply this method to obtain the ground state of N particles, and the first excited state of two and three particles to order L−6 in terms of the threshold parameters of the two- and three-particle relativistic scattering amplitudes. We use these expressions to analyze the N-particle ground state energy shift in the complex φ4 theory. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
7. Relativistic-invariant formulation of the NREFT three-particle quantization condition.
- Author
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Müller, Fabian, Pang, Jin-Yi, Rusetsky, Akaki, and Wu, Jia-Jun
- Subjects
- *
LATTICE field theory , *QUANTUM field theory , *BOUND states - Abstract
A three-particle quantization condition on the lattice is written down in a manifestly relativistic-invariant form by using a generalization of the non-relativistic effective field theory (NREFT) approach. Inclusion of the higher partial waves is explicitly addressed. A partial diagonalization of the quantization condition into the various irreducible representations of the (little groups of the) octahedral group has been carried out both in the center-of-mass frame and in moving frames. Furthermore, producing synthetic data in a toy model, the relativistic invariance is explicitly demonstrated for the three-body bound state spectrum. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
8. Testing a new method for scattering in finite volume in the ϕ4 theory.
- Author
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Garofalo, Marco, Romero-López, Fernando, Rusetsky, Akaki, and Urbach, Carsten
- Subjects
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FINITE volume method , *TEST methods - Abstract
We test an alternative proposal by Bruno and Hansen (J High Energy Phys 2021(6), https://doi.org/10.1007/JHEP06(2021)043, 2021) to extract the scattering length from lattice simulations in a finite volume. For this, we use a scalar ϕ 4 theory with two mass nondegenerate particles and explore various strategies to implement this new method. We find that the results are comparable to those obtained from the Lüscher method, with somewhat smaller statistical uncertainties at larger volumes. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
9. Multi-particle systems on the lattice and chiral extrapolations: a brief review.
- Author
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Mai, Maxim, Döring, Michael, and Rusetsky, Akaki
- Subjects
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CHIRAL perturbation theory , *SCATTERING amplitude (Physics) , *S-matrix theory , *EXTRAPOLATION , *WAGES , *QUANTUM chromodynamics - Abstract
The extraction of two- and three-body hadronic scattering amplitudes and the properties of the low-lying hadronic resonances from the finite-volume energy levels in lattice QCD represents a rapidly developing field of research. The use of various modifications of the Lüscher finite-volume method has opened a path to calculate infinite-volume scattering amplitudes on the lattice. Many new results have been obtained recently for different two- and three-body scattering processes, including the extraction of resonance poles and their properties from lattice data. Such studies, however, require robust parametrizations of the infinite-volume scattering amplitudes, which rely on basic properties of S-matrix theory and—preferably—encompass systems with quark masses at and away from the physical point. Parametrizations of this kind, provided by unitarized Chiral Perturbation Theory, are discussed in this review. Special attention is paid to three-body systems on the lattice, owing to the rapidly growing interest in the field. Here, we briefly survey the formalism, chiral extrapolation, as well as finite-volume analyses of lattice data. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
10. Solving integral equations in η→3π.
- Author
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Gasser, Jürg and Rusetsky, Akaki
- Subjects
- *
PARTICLE decays , *NUMERICAL solutions to integral equations , *DEFORMATIONS (Mechanics) , *NAKED singularities (Cosmology) , *PARTICLE physics - Abstract
A dispersive analysis of η→3π decays has been performed in the past by many authors. The numerical analysis of the pertinent integral equations is hampered by two technical difficulties: (i) The angular averages of the amplitudes need to be performed along a complicated path in the complex plane. (ii) The averaged amplitudes develop singularities along the path of integration in the dispersive representation of the full amplitudes. It is a delicate affair to handle these singularities properly, and independent checks of the obtained solutions are demanding and time consuming. In the present article, we propose a solution method that avoids these difficulties. It is based on a simple deformation of the path of integration in the dispersive representation (not in the angular average). Numerical solutions are then obtained rather straightforwardly. We expect that the method also works for ω→3π. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
11. Three-particle quantization condition in a finite volume: 1. The role of the three-particle force.
- Author
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Hammer, Hans-Werner, Pang, Jin-Yi, and Rusetsky, Akaki
- Subjects
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QUANTIZATION (Physics) , *FINITE volume method , *LAGRANGIAN functions , *BOUND states , *BOSONS , *FIELD theory (Physics) - Abstract
Using non-relativistic effective Lagrangians in the particle-dimer picture, we rederive the expression for the energy shift of a loosely bound three-particle bound state of identical bosons in the unitary limit. The effective field theory formalism allows us to explicitly investigate the role of the three-particle force. Moreover, we discuss relaxing the unitary limit of infinite scattering length and demonstrate a smooth transition from the weakly bound three-particle state to a two-particle bound state of a particle and a deeply bound dimer. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
12. Three-body resonances in the φ4 theory.
- Author
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Garofalo, Marco, Mai, Maxim, Romero-López, Fernando, Rusetsky, Akaki, and Urbach, Carsten
- Abstract
We study the properties of three-body resonances using a lattice complex scalar φ4 theory with two scalars, with parameters chosen such that one heavy particle can decay into three light ones. We determine the two- and three-body spectra for several lattice volumes using variational techniques, and then analyze them with two versions of the three-particle finite-volume formalism: the Relativistic Field Theory approach and the Finite-Volume Unitarity approach. We find that both methods provide an equivalent description of the energy levels, and we are able to fit the spectra using simple parametrizations of the scattering quantities. By solving the integral equations of the corresponding three-particle formalisms, we determine the pole position of the resonance in the complex energy plane and thereby its mass and width. We find very good agreement between the two methods at different values of the coupling of the theory. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
13. Resonance form factors from finite-volume correlation functions with the external field method.
- Author
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Lozano, Jonathan, Meißner, Ulf-G., Romero-López, Fernando, Rusetsky, Akaki, and Schierholz, Gerrit
- Abstract
A novel method for the extraction of form factors of unstable particles on the lattice is proposed. The approach is based on the study of two-particle scattering in a static, spatially periodic external field by using a generalization of the Lüscher method in the presence of such a field. It is shown that the resonance form factor is given by the derivative of the resonance pole position in the complex plane with respect to the coupling constant to the external field. Unlike the standard approach, this proposal does not suffer from problems caused by the presence of the triangle diagram. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
14. Spurious poles in a finite volume.
- Author
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Pang, Jin-Yi, Ebert, Martin, Hammer, Hans-Werner, Müller, Fabian, Rusetsky, Akaki, and Wu, Jia-Jun
- Subjects
- *
FINITE, The , *QUANTUM chromodynamics - Abstract
Using effective-range expansion for the two-body amplitudes may generate spurious sub-threshold poles outside of the convergence range of the expansion. In the infinite volume, the emergence of such poles leads to the inconsistencies in the three-body equations, e.g., to the breakdown of unitarity. We investigate the effect of the spurious poles on the three-body quantization condition in a finite volume and show that it leads to a peculiar dependence of the energy levels on the box size L. Furthermore, within a simple model, it is demonstrated that the procedure for the removal of these poles, which was recently proposed in ref. [1] in the infinite volume, can be adapted to the finite-volume calculations. The structure of the exact energy levels is reproduced with an accuracy that systematically improves order by order in the EFT expansion. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
15. Spectrum of Three-Body Bound States in a Finite Volume.
- Author
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Meißner, Ulf-G., Ríos, Guillermo, and Rusetsky, Akaki
- Subjects
- *
FINITE volume method , *BOUND states , *COEFFICIENTS (Statistics) , *WAVE functions , *NUMERICAL analysis - Abstract
The spectrum of a bound state of three identical particles with a mass m in a finite cubic box is studied. It is shown that in the unitary limit, the energy shift of a shallow bound state is given by ΔE = c(k2/m)(xL)-3/2∣A∣2 exp(-2xL/√3), where k is the bound-state momentum, L is the box size, ∣∣A2 denotes the three-body analog of the asymptotic normalization coefficient of the bound state wave function, and c is a numerical constant. The formula is valid for kL ⪢ 1. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
16. Finite-volume energy shift of the three-pion ground state.
- Author
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Müller, Fabian, Yu, Tiansu, and Rusetsky, Akaki
- Subjects
- *
ISOBARIC spin , *PIONS - Abstract
Using the framework of nonrelativistic effective field theory, the finite-volume ground-state energy shift is calculated up to and including O(L-6) for the system of three pions in the channel with the total isospin I=1. The relativistic corrections are included perturbatively, up to the same order in the inverse of the box size L. The obtained explicit expression, together with the known result for the system with maximal isospin I=3, can be used for the extraction of two independent effective three-body couplings from the measured ground-state spectrum of three pions. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
17. Nucleon in a periodic magnetic field: Finite-volume aspects.
- Author
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Agadjanov, Andria, Meißner, Ulf-G., and Rusetsky, Akaki
- Subjects
- *
MAGNETIC fields , *COMPTON scattering , *PARTICLES (Nuclear physics) , *EXTRACTION techniques - Abstract
The paper presents an extension and a refinement of our previous work on the extraction of the doubly virtual forward Compton scattering amplitude on the lattice by using the background field technique [1]. The zero frequency limit for the periodic background field is discussed, in which the well-known result is reproduced. Further, an upper limit for the magnitude of the external field is established for which the perturbative treatment is still possible. Finally, the framework is set for the evaluation of the finite-volume corrections allowing for the analysis of upcoming lattice results. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
18. Recoil corrections in antikaon-deuteron scattering.
- Author
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Mai, Maxim, Baru, Vadim, Epelbaum, Evgeny, and Rusetsky, Akaki
- Subjects
- *
DEUTERON scattering , *QUANTUM perturbations , *LOW energy electron diffraction , *QUANTUM theory , *FIELD theory (Physics) - Abstract
Using the non-relativistic effective field theory approach for K-d scattering, it is demonstrated that a systematic perturbative expansion of the recoil corrections in the parameter ξ = MK/mN is possible in spite of the fact that K-d scattering at low energies is inherently non-perturbative due to the large values of the K̄N scattering lengths. The first order correction to the K-d scattering length due to single insertion of the retardation term in the multiple-scattering series is calculated. The recoil effect turns out to be reasonably small even at the physical value of MK/mN ≃ 0.5. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
19. Resonance matrix elements on the lattice.
- Author
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Agadjanov, Andria, Bernard, Véronique, Meißner, Ulf-G., and Rusetsky, Akaki
- Subjects
- *
LATTICE theory , *PION production , *PIONS , *PHOTOELECTRONS , *PHYSICS research - Abstract
The notion of resonance matrix elements is discussed. The analogue of the Lellouch-Lüscher formula for the pion photo(electro)production amplitude in the Δ(1232) resonance region is given. A prescription for the pole extraction of the ΔNγ* transition form factors is provided. Theoretical prospects on the lattice calculation of B → K*(892)l+l- form factors are briefly summarized. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
20. Radiative decays of resonances on the lattice.
- Author
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Agadjanov, Andria, Bernard, Véronique, Meißner, Ulf-G., and Rusetsky, Akaki
- Subjects
- *
RESONANCE , *LATTICE dynamics , *MATRICES (Mathematics) , *PHASE transitions , *FORM factor (Nuclear physics) - Abstract
We discuss a generalization of the Lüscher approach to the calculation of the matrix elements of the unstable states. A theoretical framework for the lattice extraction of the ΔNγ* transition form factors is formulated. The procedure to measure the form factors at the resonance pole is given. The current theoretical progress on the B→K*γ* decays is briefly summarized. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
21. Radiative decays of resonances on the lattice.
- Author
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Agadjanov, Andria, Bernard, Véronique, Meiβner, Ulf-G., and Rusetsky, Akaki
- Subjects
- *
RADIOACTIVE decay , *LATTICE gauge theories , *QUANTUM states , *QUANTUM chromodynamics , *QUANTUM theory - Abstract
We discuss a generalization of the Lüscher approach to the calculation of the matrix elements of the unstable states. A theoretical framework for the lattice extraction of the ΔNγ ∗ transition form factors is formulated. The procedure to measure the form factors at the resonance pole is given. The current theoretical progress on the B→K∗γ ∗ decays is briefly summarized. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
22. The B → K⁎ form factors on the lattice.
- Author
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Agadjanov, Andria, Bernard, Véronique, Meißner, Ulf-G., and Rusetsky, Akaki
- Subjects
- *
LATTICE theory , *FACTORS (Algebra) , *RELATIVITY (Physics) , *FIELD theory (Physics) , *FINITE volume method - Abstract
The extraction of the B → K ⁎ transition form factors from lattice data is studied, applying non-relativistic effective field theory in a finite volume. The possible mixing of πK and ηK states is taken into account. The two-channel analogue of the Lellouch–Lüscher formula is reproduced. Due to the resonance nature of the K ⁎ , an equation is derived, which allows to determine the form factors at the pole position in a process-independent manner. The infinitely-narrow width approximation of the results is discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
23. Nucleon in a periodic magnetic field.
- Author
-
Agadjanov, Andria, Meißner, Ulf-G., and Rusetsky, Akaki
- Subjects
- *
PARTICLES (Nuclear physics) , *MAGNETIC fields , *COMPTON scattering - Abstract
The energy shift of a nucleon in a static periodic magnetic field is evaluated at second order in the external field strength in perturbation theory. It is shown that the measurement of this energy shift on the lattice allows one to determine the unknown subtraction function in the forward doubly virtual Compton scattering amplitude. The limits of applicability of the obtained formula for the energy shift are discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
24. A framework for the calculation of the ΔNγ* transition form factors on the lattice.
- Author
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Agadjanov, Andria, Bernard, Véronique, Meißner, Ulf-G., and Rusetsky, Akaki
- Subjects
- *
LATTICE theory , *KINEMATICS , *FIELD theory (Physics) , *RELATIVITY (Physics) , *MATRICES (Mathematics) , *INVARIANTS (Mathematics) - Abstract
Using the non-relativistic effective field theory framework in a finite volume, we discuss the extraction of the ΔNγ* transition form factors from lattice data. A counterpart of the Lüscher approach for the matrix elements of unstable states is formulated. In particular, we thoroughly discuss various kinematic settings, which are used in the calculation of the above matrix element on the lattice. The emerging Lüscher-Lellouch factor and the analytic continuation of the matrix elements into the complex plane are also considered in detail. A full group-theoretical analysis of the problem is made, including the partial-wave mixing and projecting out the invariant form factors from data. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
25. Recoil corrections in antikaon-deuteron scattering.
- Author
-
Mai, Maxim, Baru, Vadim, Epelbaum, Evgeny, and Rusetsky, Akaki
- Subjects
- *
DEUTERON scattering , *PERTURBATION theory , *KAONS , *DEUTERIUM , *QUANTUM chromodynamics - Abstract
The recoil retardation effect in the K-d scattering length is studied. Using the nonrelativistic effective field theory approach, it is demonstrated that a systematic perturbative expansion of the recoil corrections in the parameter ξ = MK/mN is possible in spite of the fact that K-d scattering at low energies is inherently nonperturbative due to the large values of the KN scattering lengths. The first-order correction to the K-d scattering length due to single insertion of the retardation term in the multiple-scattering series is calculated. The recoil effect turns out to be reasonably small even at the physical value of MK/mN ≃ 0.5. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
26. Energy shift of the three-particle system in a finite volume.
- Author
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Jin-Yi Pang, Jia-Jun Wu, Hammer, Hans-Werner, Meißner, Ulf-G., and Rusetsky, Akaki
- Subjects
- *
SHIFT systems , *FINITE, The - Abstract
Using the three-particle quantization condition recently obtained in the particle-dimer framework, the finite-volume energy shift of the two lowest three-particle scattering states is derived up to and including order L-6. Furthermore, assuming that a stable dimer exists in the infinite volume, the shift for the lowest particle-dimer scattering state is obtained up to and including order L-3. The result for the lowest three-particle state agrees with the results from the literature, and the result for the lowest particle-dimer state reproduces the one obtained by using the Lüscher equation. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
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