Nuclear Theory·nucl-th

Friday·March 8, 2019

18 papers—7 primary·11 cross-listed

01
Universal behavior of $p$ -wave proton-proton fusion near threshold
Bijaya Acharya🇩🇪 · Lucas Platter🇺🇸 · Gautam Rupak🇺🇸
We calculate the $p$ -wave contribution to the proton-proton fusion $S$ factor and its energy derivative in pionless effective field theory (EFT) up to next-to-leading order. The leading contributions are given by a recoil piece from the Gamow-Teller and Fermi operators, and from relativistic $1/ m$ suppressed weak interaction operators. We obtain the value of $(2.5 \pm 0.3) \times 1 0^{- 28} MeV f m^{2}$ for the $S$ factor and $(2.2 \pm 0.2) \times 1 0^{- 26} f m^{2}$ for its energy derivative at threshold. These are smaller than the results of a prior study that employed chiral EFT by several orders of magnitude. We conclude that, contrary to what has been previously reported, the $p$ -wave contribution does not need to be considered in a high-precision determination of the $S$ factor at astrophysical energies. Combined with the chiral EFT calculation of Acharya {\it et al.} [Phys. Lett. B \bf{760}, 584 (2016)] for the $s$ -wave channel, this gives a total threshold $S$ factor of $S (0) = (4.04 7_{- 0.032}^{+ 0.024}) \times 1 0^{- 23} MeV fm^{2}$ .
nucl-thastro-ph.SRhep-phPRC(2019)·8 citations
02
Scattering matrix pole expansions & invariance with respect to R-matrix parameters
Pablo Ducru🇺🇸 · Vladimir Sobes🇺🇸 · Gerald Hale🇺🇸 · Mark Paris🇺🇸 · Benoit Forget🇺🇸
Nuclear data libraries (ENDF, JEFF, JENDL, CENDL, etc.) document our phenomenological knowledge of nuclear cross sections as interpreted by R-matrix theory. The R-matrix scattering model can parameterize the energy dependence of the scattering matrix in different ways. This article establishes new results on three such sets of parameters: the Wigner-Eisenbud, the Brune, and the Siegert-Humblet parameters. We show how the latter two arise from invariance to the arbitrary boundary condition, and how they can trade-off more complex parameters for a simpler energy dependence parameterization: the scattering matrix pole expansion of Humblet and Rosenfeld. We establish that the scattering matrix's invariance to channel radius sets a partial differential equation on the widths of the Kapur-Peierls operator, which enables us to derive an explicit transformation of the Siegert-Humblet radioactive residue widths under a change of channel radius. Considering the continuation of the scattering matrix to complex wavenumbers, several new results are established. We unveil there exist more Brune parameters than previously thought, depending on the way the scattering matrix is continued to complex energies. This points to a broader conundrum in the field: how to analytically continue the scattering matrix while closing sub-threshold channels. We argue that, contrary to the Lane and Thomas legacy of force-closing sub-threshold channels which introduces spurious poles, analytic continuation is the physically correct way of defining the scattering matrix for complex wave numbers. To back this claim we establish thee results: analytic continuation cancels spurious poles, enforces the generalized unitarity conditions of Eden and Taylor, and closes massive particle channels below threshold by both quantum tunneling and from the definition of the cross section as the ratio of probability currents.
nucl-thPRC(2021)·4 citations
03
Photoproduction of charged final states in ultra-peripheral collisions and electroproduction at an electron-ion collider
Spencer. R. Klein🇺🇸 · Ya-Ping Xie🇨🇳
Ultra-peripheral collisions (UPCs) of relativistic ions are an important tool for studying photoproduction at high energies. Vector meson photoproduction is an important tool for nuclear structure measurements and other applications. A future electron-ion collider (EIC) will allow additional studies, using virtual photons with a wide range of $Q^{2}$ . We propose a significant expansion of the UPC and EIC photoproduction physics programs to include charged final states which may be produced via Reggeon exchange. We consider two examples: $a_{2}^{+} (1320)$ , which is a conventional $q q$ meson, and the exotic $Z_{c}^{+} (4430)$ state (modeled here as a tetraquark). The $Z_{c}^{+} (4430)$ cross-section depends on its internal structure, so photoproduction can test whether the $Z_{c}^{+} (4430)$ is a tetraquark or other exotic object. We calculate the rates and kinematic distributions for $γ p \to X^{+} n$ in $p A$ UPCs and $e p$ collisions at an EIC and in UPCs. The rates are large enough for detailed studies of these final states. Because the cross-section for Reggeon exchange is largest near threshold, the final state rapidity distribution depends on the beam energies. At high-energy colliders like the proposed LHeC or $p A$ collisions at the LHC, the final states are produced at far forward rapidities. For lower energy colliders, the systems are produced closer to mid-rapidity, within reach of central detectors.
nucl-thhep-phPRC(2019)·29 citations
04
On formal scattering theory for differential Faddeev equations
S.L. Yakovlev
The formal scattering theory is developed for the three-particle differential Faddeev equations. The theory is realised along the same line as in the standard two-body case. The solution of the scattering problem is expressed in terms of the matrix T-operator constructed from the matrix resolvent of the differential Faddeev equations. The relationships of the matrix T-operator with elements of transition operators and Faddeev T-matrix components have been established.
nucl-thFew Body Syst.(2019)·0 citations
05
Hybrid Stars in the Framework of the Local Nambu - Jona-Lasinio Model for Quark Matter
G. B. Alaverdyan🇦🇲 · Yu. L. Vartanyan🇦🇲
The integral parameters of neutron stars are studied taking into account the hadron-quark phase transition, which leads to the formation of a core of quark matter in the central part of a star. The quark matter is described using the local Nambu - Jona-Lasinio (NJL) model. The thermodynamic characteristics of the hadron matter are calculated in the framework of an extended version of the relativistic mean field (RMF) model that includes the contribution of the scalar-isovector $δ$ -meson effective field. A Maxwell construction is used to determine the parameters of the phase transition. It is shown that for the equation of state examined here, stable hybrid stars correspond to a narrow range of values for the central density. In our model hybrid stars lie on the same branch as neutron stars, so that a branch with a third family is not formed. It is shown that for the equation of state examined here, stable hybrid stars correspond to a narrow range of values for the central density $ρ_{c} \in (1.71 \div 1.73] \cdot 1 0^{15}$ g/cm $^{3}$ . In our model hybrid stars lie on the same branch as neutron stars, so that a branch with a third family is not formed. The maximum mass of a stable hybrid star is found to be $M_{ma x} = 2.05 M_{⊙}$ . The configuration with the maximum mass has a quark core with mass $M_{cor e} \approx 1 0^{- 3} M_{⊙}$ and radius $R_{cor e} \approx 0.6$ km.
nucl-thAstrophysics(2018)·5 citations
06
Effect of in-medium mass-shift on transverse-momentum spectrum and elliptic anisotropy of $ϕ$ meson
Yong Zhang🇨🇳 · Jing Yang🇨🇳 · Weihua Wu🇨🇳
We study the effect of in-medium mass-shift on transverse-momentum spectrum and elliptic anisotropy of $ϕ$ meson. It is found that the mass-shift enhances the $ϕ$ yields and suppresses the elliptic flow $v_{2}$ in large momentum region, and the effects increase with the increasing mass-shift. The effects are various for different sources and decrease with the increasing expanding velocity. We further study the effects for parts of all $ϕ$ meson with mass-shift, and the effects decrease with the decreasing probability of $ϕ$ meson with mass-shift. Since the different mass-shift lead to different transverse-momentum spectrum and $v_{2}$ , our study may provide a way to restrict the ranges of in-medium mass-shift of $ϕ$ meson in high-energy heavy-ion collisions.
nucl-thIJMPE(2020)·5 citations
07
Pairing effects on neutron matter equation of state and symmetry energy at subsaturation densities
Zhen Zhang · Lie-Wen Chen
Within the framework of BCS theory and Skyrme-Hartree-Fock model, we employ various microscopic pairing gaps and effective pairing interactions to study pairing effects on the equation of state (EOS) of neutron matter and the symmetry energy at subsaturation densities. We find pairing effects may have considerable contributions to the EOS of neutron matter at very low densities ( $≲ 0.02 fm^{- 3}$ ), while only have a small impact on the symmetry energy at subsatruation densities. In addition, the reliability of the parabolic approximation for the isospin asymmetry dependence of nuclear matter EOS with pairing correlations included is also discussed.
nucl-thPRC(2019)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE

Universal behavior of p-wave proton-proton fusion near threshold

Scattering matrix pole expansions & invariance with respect to R-matrix parameters

Photoproduction of charged final states in ultra-peripheral collisions and electroproduction at an electron-ion collider

On formal scattering theory for differential Faddeev equations

Hybrid Stars in the Framework of the Local Nambu - Jona-Lasinio Model for Quark Matter

Effect of in-medium mass-shift on transverse-momentum spectrum and elliptic anisotropy of ϕ meson

Pairing effects on neutron matter equation of state and symmetry energy at subsaturation densities

Affiliations

Universal behavior of $p$ -wave proton-proton fusion near threshold

Effect of in-medium mass-shift on transverse-momentum spectrum and elliptic anisotropy of $ϕ$ meson