Nuclear Theory·nucl-th

Friday·January 27, 2017

7 papers—3 primary·4 cross-listed

01
Kubo formulae for the shear and bulk viscosity relaxation times and the scalar field theory shear $τ_{π}$ calculation
Alina Czajka🇨🇦 · Sangyong Jeon🇨🇦
In this paper we provide a quantum field theoretical study on the shear and bulk relaxation times. First, we find Kubo formulas for the shear and the bulk relaxation times, respectively. They are found by examining response functions of the stress-energy tensor. We use general properties of correlation functions and the gravitational Ward identity to parametrize analytical structures of the Green functions describing both sound and diffusion mode. We find that the hydrodynamic limits of the real parts of the respective energy-momentum tensor correlation functions provide us with the method of computing both the shear and bulk viscosity relaxation times. Next, we calculate the shear viscosity relaxation time using the diagrammatic approach in the Keldysh basis for the massless $λ ϕ^{4}$ theory. We derive a respective integral equation which enables us to compute $η τ_{π}$ and then we extract the shear relaxation time. The relaxation time is shown to be inversely related to the thermal width as it should be.
nucl-thPRC(2017)·41 citations
02
Few-body approach to structure of $K ˉ$ -nuclear quasi-bound states
Shota Ohnishi🇯🇵 · Wataru Horiuchi🇯🇵 · Tsubasa Hoshino🇯🇵 · Kenta Miyahara🇯🇵 · Tetsuo Hyodo🇯🇵
Structure of light antikaon-nuclear quasi-bound states, which consist of an antikaon $(K ˉ = K^{-}, K ˉ^{0})$ and a few nucleons $(N = p, n)$ such as $K ˉ N N$ , $K ˉ N N N$ , $K ˉ N N N N$ and $K ˉ N N N N N N$ systems, is studied with full three- to seven-body calculations. Employing a realistic $K ˉ N$ potential based on the chiral SU(3) effective field theory with the SIDDHARTA constraint, we show that the central nucleon densities of these systems increases when the antikaon is injected, by about factor of two at maximum. The $K ˉ N N N N$ system shows the largest central density, about 0.74 fm $^{- 3}$ even with the phenomenological $K ˉ N$ potential, which are not as high as those suggested in previous studies with approximate treatments of the few-body systems. We find the spin of the ground state of the $K ˉ N N N N N N$ system depends on the strength of the $K ˉ N$ attraction. Thus, the quantum number of the ground state can be another constraint on the $K ˉ N$ interaction.
nucl-thhep-phPRC(2017)·43 citations
03
Ab initio calculations for non-strange and strange few-baryon systems
Winfried Leidemann🇮🇹
Concerning the non-strange particle systems the low-energy excitation spectra of the three- and four-body helium isotopes are studied. Objects of the study are the astrophysical $S$ -factor $S_{12}$ of the radiative proton deuteron capture $d (p, γ)^{3}$ He and the width of the $^{4}$ He isoscalar monopole resonance.Both observables are calculated using the Lorentz integral transform (LIT) method. The LIT equations are solved via expansions of the LIT states on a specifically modified hyperspherical harmonics (HH) basis. It is illustrated that at low energies such a modification allows to work with much higher LIT resolutions than with an unmodified HH basis. It is discussed that this opens up the possibility to determine astrophysical $S$ -factors as well as the width of low-lying resonances with the LIT method. In the sector of strange baryon systems binding energies of the hypernucleus $_{Λ}^{3}$ H are calculated using a nonsymmetrized HH basis. The results are compared with those calculated by various other groups with different methods. For all the considered non-strange and strange baryon systems it is shown that high-precision results are obtained.
nucl-thJ.Phys.Conf.Ser.(2018)·0 citations
04
Subtracting IR Renormalons from Wilson Coefficients: Uniqueness and power dependences on $Λ_{QCD}$
Go Mishima🇩🇪 · Yukinari Sumino🇯🇵 · Hiromasa Takaura🇯🇵
In the context of OPE and using the large- $β_{0}$ approximation, we propose a method to define Wilson coefficients free from uncertainties due to IR renormalons. We first introduce a general observable $X (Q^{2})$ with an explicit IR cutoff, and then we extract a genuine UV contribution $X_{UV}$ as a cutoff-independent part. $X_{UV}$ includes power corrections $\sim (Λ_{QCD}^{2} / Q^{2})^{n}$ which are independent of renormalons. Using the integration-by-regions method, we observe that $X_{UV}$ coincides with the leading Wilson coefficient in OPE and also clarify that the power corrections originate from UV region. We examine scheme dependence of $X_{UV}$ and single out a specific scheme favorable in terms of analytical properties. Our method would be optimal with respect to systematicity, analyticity and stability. We test our formulation with the examples of the Adler function, QCD force between $Q Q ˉ$ , and $R$ -ratio in $e^{+} e^{-}$ collision.
↳ hep-phhep-thnucl-thPRD(2017)·11 citations
05
Relating the finite-volume spectrum and the two-and-three-particle $S$ matrix for relativistic systems of identical scalar particles
Raúl A. Briceño🇺🇸 · Maxwell T. Hansen🇩🇪 · Stephen R. Sharpe🇺🇸
Working in relativistic quantum field theory, we derive the quantization condition satisfied by coupled two- and three-particle systems of identical scalar particles confined to a cubic spatial volume with periodicity $L$ . This gives the relation between the finite-volume spectrum and the infinite-volume $2 \to 2$ , $2 \to 3$ and $3 \to 3$ scattering amplitudes for such theories. The result holds for relativistic systems composed of scalar particles with nonzero mass $m$ , whose center of mass energy lies below the four-particle threshold, and for which the two-particle $K$ matrix has no singularities below the three-particle threshold. The quantization condition is exact up to corrections of the order $O (e^{- m L})$ and holds for any choice of total momenta satisfying the boundary conditions.
↳ hep-latnucl-thPRD(2017)·209 citations
06
Möbius domain-wall fermions on gradient-flowed dynamical HISQ ensembles
Evan Berkowitz🇩🇪 · Chris Bouchard🇬🇧 · Chia Cheng Chang🇺🇸 · M. A. Clark🇺🇸 · Balint Joo🇺🇸 · Thorsten Kurth🇺🇸 · Christopher Monahan🇺🇸 · Amy Nicholson🇺🇸 · Kostas Orginos🇺🇸 · Enrico Rinaldi🇺🇸 · Pavlos Vranas🇺🇸 · Andre Walker-Loud🇺🇸
We report on salient features of a mixed lattice QCD action using valence Möbius domain-wall fermions solved on the dynamical $N_{f} = 2 + 1 + 1$ HISQ ensembles generated by the MILC Collaboration. The approximate chiral symmetry properties of the valence fermions are shown to be significantly improved by utilizing the gradient-flow scheme to first smear the HISQ configurations. The greater numerical cost of the Möbius domain-wall inversions is mitigated by the highly efficient QUDA library optimized for NVIDIA GPU accelerated compute nodes. We have created an interface to this optimized QUDA solver in Chroma. We provide tuned parameters of the action and performance of QUDA using ensembles with the lattice spacings $a ≃ {0.15, 0.12, 0.09}$ fm and pion masses $m_{π} ≃ {310, 220, 130}$ MeV. We have additionally generated two new ensembles with $a \sim 0.12$ fm and $m_{π} \sim {400, 350}$ MeV. With a fixed flow-time of $t_{g f} = 1$ in lattice units, the residual chiral symmetry breaking of the valence fermions is kept below 10\% of the light quark mass on all ensembles, $m_{r es} ≲ 0.1 \times m_{l}$ , with moderate values of the fifth dimension $L_{5}$ and a domain-wall height $M_{5} \leq 1.3$ . As a benchmark calculation, we perform a continuum, infinite volume, physical pion and kaon mass extrapolation of $F_{K^{\pm}} / F_{π^{\pm}}$ and demonstrate our results are independent of flow-time, and consistent with the FLAG determination of this quantity at the level of less than one standard deviation.
↳ hep-lathep-phnucl-thPRD(2017)·33 citations
07
On Lattice Calculation of Electric Dipole Moments and Form Factors of the Nucleon
M. Abramczyk🇺🇸 · S. Aoki🇯🇵 · T. Blum🇺🇸 · T. Izubuchi🇺🇸 · H. Ohki🇺🇸 · S. Syritsyn🇺🇸
We analyze commonly used expressions for computing the nucleon electric dipole form factors (EDFF) $F_{3}$ and moments (EDM) on a lattice and find that they lead to spurious contributions from the Pauli form factor $F_{2}$ due to inadequate definition of these form factors when parity mixing of lattice nucleon fields is involved. Using chirally symmetric domain wall fermions, we calculate the proton and the neutron EDFF induced by the CP-violating quark chromo-EDM interaction using the corrected expression. In addition, we calculate the electric dipole moment of the neutron using background electric field that respects time translation invariance and boundary conditions, and find that it decidedly agrees with the new formula but not the old formula for $F_{3}$ . Finally, we analyze some selected lattice results for the nucleon EDM and observe that after the correction is applied, they either agree with zero or are substantially reduced in magnitude, thus reconciling their difference from phenomenological estimates of the nucleon EDM.
↳ hep-latnucl-thPRD(2017)·102 citations

Affiliations

first authorsco-authorsvia INSPIRE

Kubo formulae for the shear and bulk viscosity relaxation times and the scalar field theory shear τπ​ calculation

Few-body approach to structure of Kˉ-nuclear quasi-bound states

Ab initio calculations for non-strange and strange few-baryon systems

Subtracting IR Renormalons from Wilson Coefficients: Uniqueness and power dependences on ΛQCD​

Relating the finite-volume spectrum and the two-and-three-particle S matrix for relativistic systems of identical scalar particles

Möbius domain-wall fermions on gradient-flowed dynamical HISQ ensembles

On Lattice Calculation of Electric Dipole Moments and Form Factors of the Nucleon

Affiliations

Kubo formulae for the shear and bulk viscosity relaxation times and the scalar field theory shear $τ_{π}$ calculation

Few-body approach to structure of $K ˉ$ -nuclear quasi-bound states

Subtracting IR Renormalons from Wilson Coefficients: Uniqueness and power dependences on $Λ_{QCD}$

Relating the finite-volume spectrum and the two-and-three-particle $S$ matrix for relativistic systems of identical scalar particles