Nuclear Theory·nucl-th

Thursday·August 18, 2016

9 papers—4 primary·5 cross-listed

01
Leading-twist distribution amplitudes of scalar- and vector-mesons
Bo-Lin Li🇨🇳 · Lei Chang🇨🇳 · Minghui Ding🇨🇳 · Craig D. Roberts🇺🇸 · Hong-Shi Zong🇨🇳
A symmetry-preserving truncation of the two-body light-quark bound-state problem in relativistic quantum field theory is used to calculate the leading-twist parton distribution amplitudes (PDAs) of scalar systems, both ground-state and radial excitations, and the radial excitations of vector mesons. Owing to the fact that the scale-independent leptonic decay constant of a scalar meson constituted from equal-mass valence-constituents vanishes, it is found that the PDA of a given scalar system possesses one more zero than that of an analogous vector meson. Consequently, whereas the mean light-front relative momentum of the valence-constituents within a vector meson is zero, that within a scalar meson is large, an outcome which hints at a greater role for light-front angular momentum in systems classified as $P$ -wave in quantum mechanical models. Values for the scale-dependent decay constants of ground-state scalar and vector systems are a by-product of this analysis, and they turn out to be roughly equal, viz. $≃ 0.2$ GeV at an hadronic scale. In addition, it is confirmed that the dilation characterising ground-state PDAs is manifest in the PDAs of radial excitations too. The impact of $S U (3)$ -flavour symmetry breaking is also considered. When compared with pseudoscalar states, it is a little stronger in scalar systems, but the size is nevertheless determined by the flavour-dependence of dynamical chiral symmetry breaking and the PDAs are still skewed toward the heavier valence-quark in asymmetric systems.
nucl-thhep-lathep-phnucl-exPRD(2016)·26 citations
02
Pion transverse-momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss interferometry in a viscous granular source model
Jing Yang🇨🇳 · Wei-Ning Zhang🇨🇳 · Yan-Yu Ren🇨🇳
We examine the evolution of quark-gluon plasma (QGP) droplets with viscous hydrodynamics and analyze the pion transverse-momentum spectrum, elliptic flow, and Hanbury-Brown-Twiss (HBT) interferometry in a granular source model consisting of viscous QGP droplets. The shear viscosity of the QGP droplet speeds up and slows down the droplet evolution in the central and peripheral regions of the droplet, respectively. The effect of the bulk viscosity on the evolution is negligible. Although there are viscous effects on the droplet evolution, the pion momentum spectrum and elliptic flow change little for granular sources with and without viscosity. On the other hand, the influence of viscosity on HBT radius $R_{out}$ is considerable. It makes $R_{out}$ decrease in the granular source model. We determine the model parameters of granular sources using the experimental data of pion transverse-momentum spectrum, elliptic flow, and HBT radii together, and investigate the effects of viscosity on the model parameters. The results indicate that the granular source model may reproduce the experimental data of pion transverse-momentum spectrum, elliptic flow, and HBT radii in heavy-ion collisions of Au-Au at $s_{N N} = 200$ GeV and Pb-Pb at $s_{N N} = 2.76$ TeV in different centrality intervals. The viscosity of the droplet leads to an increase in the initial droplet radius and a decrease of the source shell parameter in the granular source model.
nucl-thCPC(2017)·3 citations
03
Impact of Nucleon-Nucleon Bremsstrahlung Rates Beyond One-Pion Exchange
Alexander Bartl · Robert Bollig · Hans-Thomas Janka · Achim Schwenk
Neutrino-pair production and annihilation through nucleon-nucleon bremsstrahlung is included in current supernova simulations by rates that are based on the one-pion-exchange approximation. Here we explore the consequences of bremsstrahlung rates based on a modern nuclear interactions for proto-neutron star cooling and the corresponding neutrino emission. We find that despite a reduction of the bremsstrahlung emission by a factor of 2-5 in the neutrinospheric region, models with the improved treatment exhibit only $≲$ 5% changes of the neutrino luminosities and an increase of $≲$ 0.7 MeV of the average energies of the radiated neutrino spectra, with the largest effects for the antineutrinos of all flavors and at late times. Overall, the proto-neutron star cooling evolution is slowed down modestly by $≲$ 0.5-1 s.
nucl-thastro-ph.HEastro-ph.SRPRD(2016)·38 citations
04
A dynamical $α$ -cluster model of $^{16}$ O
C. J. Halcrow · C. King · N. S. Manton
We calculate the low-lying spectrum of the $^{16}$ O nucleus using an $α$ -cluster model which includes the important tetrahedral and square configurations. Our approach is motivated by the dynamics of $α$ -particle scattering in the Skyrme model. We are able to replicate the large energy splitting that is observed between states of identical spin but opposite parities, as well as introduce states that were previously not found in other cluster models, such as a $0^{-}$ state. We also provide a novel interpretation of the first excited state of $^{16}$ O and make predictions for the energies of $6^{-}$ states that have yet to be observed experimentally.
nucl-thhep-thPRC(2017)·71 citations
05
Revealing the source of the radial flow patterns in proton--proton collisions using hard probes
Antonio Ortiz🇲🇽 · Gyula Bencédi🇲🇽 · Héctor Bello🇲🇽
In this work, we propose a tool to reveal the origin of the collective-like phenomena observed in proton--proton collisions. We exploit the fundamental difference between the underlying mechanisms, color reconnection (CR) and hydrodynamics, which produce radial flow patterns in \textsc{Pythia}~8 and \textsc{Epos}~3, respectively. Specifically, we proceed by examining the strength of the coupling between the soft and hard components which, by construction, is larger in \textsc{Pythia}~8 than in \textsc{Epos}~3. We study the transverse momentum ( $p_{T}$ ) distributions of charged pions, kaons and (anti)protons in inelastic pp collisions at $s =$ 7\,TeV produced at mid-rapidity. Specific selections are made on an event-by-event basis as a function of the charged particle multiplicity and the transverse momentum of the leading jet ( $p_{T}^{jet}$ ) reconstructed using the \textsc{FastJet} algorithm at mid-pseudorapidity ( $∣ η ∣ < 1$ ). From our studies, quantitative and qualitative differences between \textsc{Pythia}~8 and \textsc{Epos}~3 are found in the $p_{T}$ spectra when (for a given multiplicity class) the leading jet $p_{T}$ is increased. In addition, we show that for low-multiplicity events the presence of jets can produce radial flow-like behavior. Motivated by our findings, we propose to perform a similar analysis using experimental data from RHIC and LHC.
↳ hep-phnucl-thJ.Phys.G(2017)·54 citations
06
Neutrinoless double beta decay from lattice QCD
Amy Nicholson🇺🇸 · Evan Berkowitz🇺🇸 · Chia Cheng Chang🇺🇸 · M. A. Clark🇺🇸 · Balint Joo🇺🇸 · Thorsten Kurth🇺🇸 · Enrico Rinaldi🇺🇸 · Brian Tiburzi🇺🇸 · Pavlos Vranas🇺🇸 · Andre Walker-Loud🇺🇸
While the discovery of non-zero neutrino masses is one of the most important accomplishments by physicists in the past century, it is still unknown how and in what form these masses arise. Lepton number-violating neutrinoless double beta decay is a natural consequence of Majorana neutrinos and many BSM theories, and many experimental efforts are involved in the search for these processes. Understanding how neutrinoless double beta decay would manifest in nuclear environments is key for understanding any observed signals. In these proceedings we present an overview of a set of one- and two-body matrix elements relevant for experimental searches for neutrinoless double beta decay, describe the role of lattice QCD calculations, and present preliminary lattice QCD results.
↳ hep-lathep-phnucl-thPoS(2016)·25 citations
07
Generation of strong magnetic fields in dense quark matter driven by the electroweak interaction of quarks
Maxim Dvornikov (IZMIRAN, Tomsk State University, University of Hamburg)🇷🇺
We study the generation of strong large scale magnetic fields in dense quark matter. The magnetic field growth is owing to the magnetic field instability driven by the electroweak interaction of quarks. We discuss the situation when the chiral symmetry is unbroken in the degenerate quark matter. In this case we predict the amplification of the seed magnetic field $1 0^{12} G$ to the strengths $(1 0^{14} - 1 0^{15}) G$ . In our analysis we use the typical parameters of the quark matter in the core of a hybrid star or in a quark star. We also discuss the application of the obtained results to describe the magnetic fields generation in magnetars.
↳ hep-phastro-ph.HEhep-thnucl-thNPB(2016)·17 citations
08
Relaxation of the chiral imbalance in dense matter of a neutron star
Maxim Dvornikov (IZMIRAN, Tomsk State University, University of Hamburg)🇷🇺
Using the quantum field theory methods, we calculate the helicity flip of an electron scattering off protons in dense matter of a neutron star. The influence of the electroweak interaction between electrons and background nucleons on the helicity flip is examined. We also derive the kinetic equation for the chiral imbalance. The derived kinetic equation is compared with the results obtained by other authors.
↳ hep-phastro-ph.HEnucl-thEPJ Web Conf.(2016)·0 citations
09
Role of medium modifications for neutrino-pair processes from nucleon-nucleon bremsstrahlung - Impact on the protoneutron star deleptonization
Tobias Fischer🇵🇱
In this article the neutrino-pair production from nucleon-nucleon (NN) bremsstrahlung is explored via medium-modifications of the strong interactions at the level of the one-pion exchange approximation. It governs the bulk part of the NN interaction at low densities relevant for the neutrino physics in core-collapse supernova studies. The resulting medium modified one-pion exchange rate for the neutrino-pair processes is implemented in simulations of core collapse supernovae in order to study the impact on the neutrino signal emitted from the deleptonization of the nascent proto-neutron star. Consequences for the nucleosynthesis of heavy elements of the material ejected from the PNS surface are discussed.
↳ astro-ph.HEnucl-thAstron.Astrophys.(2016)·52 citations

Affiliations

first authorsco-authorsvia INSPIRE