Nuclear Theory·nucl-th

Friday·October 23, 2020

9 papers—2 primary·7 cross-listed

01
Dyson-Schwinger approach to pion-nucleon scattering using time-ordered perturbation theory
B. Blankleider🇦🇺 · J. L. Wray🇦🇺 · A. N. Kvinikhidze🇬🇪
We present a simple description of pion-nucleon ( $π N$ ) scattering taking into account the full complexity of pion absorption and creation on the nucleon. To do this we solve Dyson-Schwinger equations within the framework of Time-Ordered Perturbation Theory. This enables us to construct partial wave separable $π N$ t matrices that can be useful in models of nuclear processes involving fully dressed nucleons. At the same time, our approach demonstrates features of Quantum Field Theory, like particle dressing, renormalisation, and the use of Dyson-Schwinger equations, in a non-relativistic context that is maximally close to that of Quantum Mechanics. For this reason, this article may also be of pedagogical interest.
nucl-thhep-phAIP Adv.(2021)·1 citation
02
Effective shear and bulk viscosities for anisotropic flow
Fernando G. Gardim🇧🇷 · Jean-Yves Ollitrault🇫🇷
We evaluate the viscous damping of anisotropic flow in heavy-ion collisions for arbitrary temperature-dependent shear and bulk viscosities. We show that the damping is solely determined by effective shear and bulk viscosities, which are weighted averages over the temperature. We determine the relevant weights for nucleus-nucleus collisions at $s_{NN} = 5.02$ TeV and 200 GeV, corresponding to the maximum LHC and RHIC energies, by running ideal and viscous hydrodynamic simulations. The effective shear viscosity is driven by temperatures below $210$ MeV at RHIC, and below $280$ MeV at the LHC, with the largest contributions coming from the lowest temperatures, just above freeze-out. The effective bulk viscosity is driven by somewhat higher temperatures, corresponding to earlier stages of the collision. We show that at a fixed collision energy, the effective viscosity is independent of centrality and system size, to the same extent as the mean transverse momentum of outgoing hadrons. The variation of viscous damping is determined by Reynolds number scaling.
nucl-thhep-phnucl-exPRC(2021)·23 citations
03
The coset construction for particles of arbitrary spin
Michael J. Landry🇺🇸 · Guanhao Sun🇺🇸
When a Poincaré-invariant system spontaneously breaks continuous internal symmetries, Goldstones's theorem demands the existence of massless, spin-zero excitations in a one-to-one correspondence with the broken symmetry generators. When a system spontaneously breaks Poincaré symmetry, however, the kinds of excitations that satisfy Goldstone's theorem can be quite unusual. In particular, they may have any spin and need not be particles or even quasiparticles. The standard coset construction used to formulate effective actions of Goldstones, however, is rather restrictive and is incapable of generating the full spectrum of possibilities allowed by Goldstone's theorem. We propose a (partial) remedy to this problem by postulating a novel coset construction for systems that spontaneously break Poincaré symmetry. This new construction is capable of generating effective actions with a wide range of Goldstone excitations---including fermionic degrees of freedom---even when all symmetries are bosonic. To demonstrate it's utility, we focus on constructing effective actions for point particles of various spins. We recover the known result that a particle of spin $s$ requires an $N = 2 s$ supersymmetric worldline reparameterization gauge symmetry, which we implement at the level of the coset construction. In the process, we discover that massless particles require a novel kind of inverse Higgs constraint that bears some resemblance to the dynamical inverse Higgs constraints that appear in certain fermi liquid effective field theories. We then consider particles that, in addition to quantum spin, have finite spatial extent and are free to rotate. We derive a novel action for such particles and find a `spin-orbital' coupling between the intrinsic quantum spin and the physical-rotation degrees of freedom.
↳ hep-thcond-mat.othergr-qcnucl-th+1JHEP(2021)·5 citations
04
Dispersive $π K \to π K$ and $π π \to K K ˉ$ amplitudes from scattering data, threshold parameters and the lightest strange resonance $κ$ or $K_{0}^{*} (700)$
J.R. Peláez🇪🇸 · A. Rodas🇺🇸
We discuss the simultaneous dispersive analyses of $π K \to π K$ and $π π \to K K ˉ$ scattering data and the $κ / K_{0}^{*} (700)$ resonance. The unprecedented statistics of present and future Hadron Experiments, modern Lattice QCD calculations, and the wealth of new states and decays, require such precise and model-independent analyses to describe final state interactions. We review the existing and often conflicting data and explain in detail the derivation of the relevant dispersion relations, maximizing their applicability range. Next, we review and extend the caveats on some data, showing their inconsistency with dispersion relations. Our main result is the derivation and compilation of precise amplitude parameterizations constrained by several $π K \to π K$ and $π π \to K K ˉ$ dispersion relations. These constrained parameterizations are easily implementable and provide the rigor and accuracy needed for modern experimental and phenomenological Hadron Physics. As applications, after reviewing their status and interest, we will provide new precise threshold and subthreshold parameters and review our dispersive determination of the controversial $κ / K_{0}^{*} (700)$ resonance and other light-strange resonances.
↳ hep-phhep-exhep-latnucl-thPhys.Rept.(2022)·99 citations
05
Aspects of model dependence of eta'-eta complex treated by going beyond the isospin limit
Davor Horvatic🇭🇷 · Dubravko Klabucar🇭🇷 · Dalibor Kekez🇭🇷
Exploring the extent of model dependence, we study effects of certain Ansaetze for the T-dependence of the correction term in the QCD topological susceptibility. The one producing unwanted effects on results at T > 0 in the eta'-eta complex in the usual limit of isospin symmetry, is largely cured from its peculiar behavior and brought into agreement with the other, when breaking of isospin symmetry is allowed and the realistic quark mass ratio m_u/m_d = 0.50 is adopted.
↳ hep-phnucl-thEPJA(2020)·1 citation
06
Access to the kaon radius with kaonic atoms
Niklas Michel🇩🇪 · Natalia S. Oreshkina🇩🇪
We put forward a method for determination of the kaon radius from the spectra of kaonic atoms. We analyze the few lowest transitions and their sensitivity to the size of the kaon for ions in the nuclear charge range Z = 1 - 100, taking into account finite-nuclear-size, finite-kaon-size, recoil and leading-order quantum-electrodynamic effects. Additionally, the opportunities of extracting the kaon mass and nuclear radii are demonstrated by examining the sensitivity of the transition energies in kaonic atoms.
↳ physics.atom-phnucl-thquant-phAnnalen Phys.(2022)·1 citation
07
Relativistic $N$ -particle energy shift in finite volume
Fernando Romero-López🇪🇸 · Akaki Rusetsky🇩🇪 · Nikolas Schlage🇩🇪 · Carsten Urbach🇩🇪
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 $φ^{4}$ theory.
↳ hep-latnucl-thJHEP(2021)·58 citations
08
The subtraction contribution to the muonic-hydrogen Lamb shift: a point for lattice QCD calculations of the polarizability effect
Franziska Hagelstein (PSI)🇨🇭 · Vladimir Pascalutsa (JGU Mainz)🇩🇪
The proton-polarizability contribution to the muonic-hydrogen Lamb shift is a major source of theoretical uncertainty in the extraction of the proton charge radius. An empirical evaluation of this effect, based on the proton structure functions, requires a systematically improvable calculation of the "subtraction function", possibly using lattice QCD. We consider a different subtraction point, with the aim of accessing the subtraction function directly in lattice calculations. A useful feature of this subtraction point is that the corresponding contribution of the structure functions to the Lamb shift is suppressed. The whole effect is dominated by the subtraction contribution, calculable on the lattice.
↳ hep-phhep-latnucl-thphysics.atom-phNPA(2021)·16 citations
09
Self-learning Monte-Carlo for non-abelian gauge theory with dynamical fermions
Yuki Nagai🇯🇵 · Akinori Tanaka🇯🇵 · Akio Tomiya🇺🇸
In this paper, we develop the self-learning Monte-Carlo (SLMC) algorithm for non-abelian gauge theory with dynamical fermions in four dimensions to resolve the autocorrelation problem in lattice QCD. We perform simulations with the dynamical staggered fermions and plaquette gauge action by both in HMC and SLMC for zero and finite temperature to examine the validity of SLMC. We confirm that SLMC can reduce autocorrelation time in non-abelian gauge theory and reproduces results from HMC. For finite temperature runs, we confirm that SLMC reproduces correct results with HMC, including higher-order moments of the Polyakov loop and the chiral condensate. Besides, our finite temperature calculations indicate that four flavor QC $_{2}$ D with $m^= 0.5$ is likely in the crossover regime in the Colombia plot.
↳ hep-latnucl-thPRD(2023)·19 citations

Affiliations

first authorsco-authorsvia INSPIRE