Nuclear Theory·nucl-th

Tuesday·January 15, 2019

20 papers—7 primary·13 cross-listed

08
Effects of strong magnetic field on the formation of wakes in thermal QCD
Mujeeb Hasan🇮🇳 · Binoy Krishna Patra🇮🇳
We have investigated how the wakes in the induced charge density and in the potential due to the passage of highly energetic partons through a thermal QCD medium get affected by the presence of strong magnetic field. For that purpose, we wish to analyze first the dielectric responses of the medium both in presence and absence of strong magnetic field. We found that for slow moving partons, the real part of dielectric function is not affected by the magnetic field whereas for fast moving partons, for small $∣ k ∣$ , it becomes very large and approaches towards its counterpart at $B = 0$ , for large $∣ k ∣$ . On the other hand the imaginary part is decreased for both slow and fast moving partons, due to the fact that the imaginary contribution due to quark-loop vanishes. With these ingredients, we found that the oscillation in the (scaled) induced charge density, due to the very fast partons becomes less pronounced in the presence of strong magnetic field whereas for smaller parton velocity, no significant change is observed. For the (scaled) wake potential along the motion of fast moving partons (which is of Lennard-Jones (LJ) type), the depth of negative minimum in the backward region gets reduced drastically, resulting in the reduction of the amplitude of oscillation. On the other hand in the forward region, it remains as the screened Coulomb one, except the screening now becomes much stronger for higher parton velocity. Similarly for the wake potential transverse to the motion of partons in both forward and backward regions, the depth of LJ potential for fast moving partons gets decreased severely, but still retains the forward-backward symmetry. However, for lower parton velocity, the magnetic field does not affect it significantly.
↳ hep-phnucl-thInt.J.Mod.Phys.A(2021)·2 citations
09
Neutrino nucleosynthesis: An overview
Karlheinz Langanke🇩🇪 · Gabriel Martinez-Pinedo🇩🇪 · Andre Sieverding🇩🇪
Neutrinos produced during a supernova explosion induce reactions on abundant nuclei in the outer stellar shells and contribute in this way to the synthesis of the elements in the Universe. This neutrino nucleosynthesis process has been identified as an important contributor to the origin of $^{7}$ Li, $^{11}$ B, $^{19}$ F, $^{138}$ La, and $^{180}$ Ta, but also to the long-lived radionuclides $^{22}$ Na and $^{26}$ Al, which are both key isotopes for $γ$ -ray astronomy. The manuscript summarizes the recent progress achieved in simulations of neutrino nucleosynthesis.
↳ astro-ph.HEnucl-thAAPPS Bulletin, Vol. 28 No. 6, p. 41-48, …·11 citations
10
GW170817 implications on the frequency and damping time of f-mode oscillations of neutron stars
De-Hua Wen🇨🇳 · Bao-An Li🇺🇸 · Hou-Yuan Chen🇨🇳 · Nai-Bo Zhang🇨🇳
Within a minimum model for neutron stars consisting of nucleons, electrons and muons at $β$ -equilibrium using about a dozen Equation of States (EOSs) from microscopic nuclear many-body theories and 40,000 EOSs randomly generated using an explicitly isospin-dependent parametric EOS model for high-density neutron-rich nucleonic matter within its currently known uncertainty range, we study correlations among the f-mode frequency, its damping time and the tidal deformability as well as the compactness of neutron stars. Except for quark stars, both the f-mode frequency and damping time of canonical neutron stars are found to scale with the tidal deformability independent of the EOSs used. Applying the constraint on the tidal deformability of canonical neutron stars $Λ_{1.4} = 19 0_{- 120}^{+ 390}$ extracted by the LIGO+VIRGO Collaborations from their improved analyses of the GW170817 event, the f-mode frequency and its damping time of canonical neutron stars are limited to 1.67 kHz - 2.18 kHz and 0.155 s - 0.255 s, respectively, providing a useful guidance for the ongoing search for gravitational waves from the f-mode oscillations of isolated neutron stars. Moreover, assuming either or both the f-mode frequency and its damping time will be measured precisely in future observations with advanced gravitational wave detectors, we discuss how information about the mass and/or radius as well as the still rather elusive nuclear symmetry energies at supra-saturation densities may be extracted.
↳ gr-qcastro-ph.HEastro-ph.SRnucl-ex+1PRC(2019)·69 citations
11
Revisit to electrical and thermal conductivities, Lorenz number and Knudsen number in thermal QCD in a strong magnetic field
Shubhalaxmi Rath🇮🇳 · Binoy Krishna Patra🇮🇳
We have explored how the electrical ( $σ_{el}$ ) and thermal ( $κ$ ) conductivities in a thermal QCD medium get affected in weak-momentum anisotropies arising either due to a strong magnetic field or due to asymptotic expansion. This study facilitates to understand the longevity of strong magnetic field through $σ_{e l}$ , Lorenz number in Wiedemann-Franz law, and the validity of equilibrium by the Knudsen number. We calculate the conductivities by solving relativistic Boltzmann transport equation in relaxation-time approximation within quasiparticle model at finite T and strong B. We have found that $σ_{e l}$ and $κ$ get enhanced in a magnetic field-driven anisotropy, but $σ_{e l}$ decreases with temperature, opposite to its faster increase in expansion-driven anisotropy. Whereas $κ$ increases slowly with temperature, contrary to its rapid increase in expansion-driven anisotropy. The above findings are broadly attributed to three factors: the stretching and squeezing of distribution function in anisotropies generated by the magnetic field and asymptotic expansion, respectively, the dispersion relation and resulting phase-space factor, the relaxation-time in absence and presence of strong magnetic field. So $σ_{el}$ extracts the time-dependence of magnetic field, which decays slower than in vacuum but expansion-driven anisotropy makes the decay faster. The variation in $κ$ transpires that Knudsen number decreases with T but expansion-driven anisotropy reduces its value and magnetic field-driven anisotropy raises its value but to less than one, thus the system can still be in equilibrium. The ratio, $κ / σ_{e l}$ in magnetic field-driven anisotropy increases linearly with temperature but with a value smaller than in expansion-driven anisotropy. Thus the Lorenz number can make the distinction between different anisotropies.
↳ hep-phhep-thnucl-thPRD(2019)·55 citations
12
Precision Analysis of the $^{136}$ Xe Two-Neutrino $β β$ Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements
KamLAND-Zen Collaboration
We present a precision analysis of the $^{136}$ Xe two-neutrino $β β$ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino $β β$ rate allows us to measure the ratio of the leading and subleading $2 ν β β$ nuclear matrix elements (NMEs), $ξ_{31}^{2 ν} = - 0.2 6_{- 0.25}^{+ 0.31}$ . Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consistent with the experimental limit. However, part of the $ξ_{31}^{2 ν}$ range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted $ξ_{31}^{2 ν}$ values are sensitive to the quenching of NMEs and the competing contributions from low- and high-energy states in the intermediate nucleus. Since these aspects are also at play in neutrinoless $β β$ decay, $ξ_{31}^{2 ν}$ provides new insights towards reliable neutrinoless $β β$ NMEs.
↳ hep-exnucl-exnucl-thPRL(2019)·97 citations
13
Pion Valence Quark Distribution from Matrix Element Calculated in Lattice QCD
Raza Sabbir Sufian🇺🇸 · Joseph Karpie🇺🇸 · Colin Egerer🇺🇸 · Kostas Orginos🇺🇸 · Jian-Wei Qiu🇺🇸 · David G. Richards🇺🇸
We present the first exploratory lattice QCD calculation of the pion valence quark distribution extracted from spatially separated current-current correlations in coordinate space. We show that an antisymmetric combination of vector and axial-vector currents provides direct information on the pion valence quark distribution. Using the collinear factorization approach, we calculate the perturbative tree-level kernel for this current combination and extract the pion valence distribution. The main goal of this article is to demonstrate the efficacy of this general lattice QCD approach in the reliable extraction of parton distributions. With controllable power corrections and a good understanding of the lattice systematics, this method has the potential to serve as a complementary to the many efforts to extract parton distributions in global analyses from experimentally measured cross sections. We perform our calculation on an ensemble of 2+1 flavor QCD using the isotropic-clover fermion action, with lattice dimensions $3 2^{3} \times 96$ at a lattice spacing \mbox{ $a = 0.127$ fm} and the quark mass equivalent to a pion mass $m_{π} ≃ 416$ MeV.
↳ hep-lathep-phnucl-thPRD(2019)·168 citations
14
Roles of $^{7}$ Be $(n, p)^{7}$ Li resonances in big bang nucleosynthesis with time-dependent quark mass and Li reduction by a heavy quark mass
Kanji Mori🇯🇵 · Motohiko Kusakabe🇨🇳
Big bang nucleosynthesis (BBN) has been used as a probe of beyond-standard physics in the early Universe, which includes a time-dependent quark mass m_q. We investigate effects of a quark mass variation delta m_q on the cross sections of the 7Be(n, p)7Li reaction and primordial light element abundances taking into account roles of 8Be resonances in the reaction during BBN. This resonant reaction has not been investigated although behaviors of low-lying resonances are not trivial. It is found that a resonance at the resonance energy E_r=0.33 MeV enhances the reaction rate and lowers the 7Li abundance significantly when the quark mass variation is negative. Based upon up-to-date observational limits on primordial abundances of D, 4He and Li, the quark mass variation in the BBN epoch are derived. In a model in which the resonance energies of the reactions 3He(d, p)4He and 3H(d, n)4He are insensitive to the quark mass, we find that the Li abundance can be consistent with observations for delta m_q/m_q = (4--8) times 10^{-3}.
↳ astro-ph.COhep-phnucl-thPRD(2019)·15 citations
15
Chromopolarizability of charmonium and $π π$ final state interaction revisited
Yun-Hua Chen🇨🇳
The chromopolarizability of a quarknonium describes the quarknonium's interaction with soft gluonic fields and can be measured in the heavy quarkonium decays. Within the framework of dispersion theory which consider the $π π$ final state interaction (FSI) model-independently, we analyze the transition $ψ^{'} \to J / ψ π^{+} π^{-}$ and obtain the chromopolarizability $α_{ψ^{'} ψ}$ and the parameter $κ$ . It is found that the $π π$ FSI plays an important role in extracting the chromopolarizability from the experimental data. The obtained chromopolarizability with the FSI is reduced to about 1/2 of that without the FSI. With the FSI, we determine the chromopolarizability $∣ α_{ψ^{'} ψ} ∣ = (1.44 \pm 0.02)$ GeV $^{- 3}$ and the parameter $κ = 0.139 \pm 0.005.$ Our results could be useful in studying the interactions of charmonium with light hadrons.
↳ hep-phhep-exhep-latnucl-thAdv.High Energy Phys.(2019)·9 citations
16
Impact of magnetic-field fluctuations on measurements of the chiral magnetic effect in collisions of isobaric nuclei
Xin-Li Zhao🇨🇳 · Guo-Liang Ma🇨🇳 · Yu-Gang Ma🇨🇳
We investigate the properties of electromagnetic fields in isobaric $_{44}^{96} Ru +_{44}^{96} Ru$ and $_{40}^{96} Zr +_{40}^{96} Zr$ collisions at $s$ = 200 GeV by using a multiphase transport model, with special emphasis on the correlation between magnetic field direction and participant plane angle $Ψ_{2}$ (or spectator plane angle $Ψ_{2}^{SP}$ ), i.e. $⟨ cos 2 (Ψ_{B} - Ψ_{2})⟩$ [or $⟨ cos 2 (Ψ_{B} - Ψ_{2}^{SP})⟩$ ]. We confirm that the magnetic fields of $_{44}^{96} Ru +_{44}^{96} Ru$ collisions are stronger than those of $_{40}^{96} Zr +_{40}^{96} Zr$ collisions due to their larger proton fraction. We find that the deformation of nuclei has a non-negligible effect on $⟨ cos 2 (Ψ_{B} - Ψ_{2})⟩$ especially in peripheral events. Because the magnetic-field direction is more strongly correlated with $Ψ_{2}^{SP}$ than with $Ψ_{2}$ , the relative difference of the chiral magnetic effect observable with respect to $Ψ_{2}^{SP}$ is expected to be able to reflect much cleaner information about the chiral magnetic effect with less influences of deformation.
↳ hep-phnucl-exnucl-thPRC(2019)·40 citations
17
Novel mechanism for electric quadrupole moment generation in relativistic heavy-ion collisions
Xin-Li Zhao🇨🇳 · Guo-Liang Ma🇨🇳 · Yu-Gang Ma🇨🇳
We present the spatial distributions of electromagnetic fields ( $E$ and $B$ ) and electromagnetic anomaly $E \cdot B$ in Au+Au collisions at the RHIC energy $s$ =200 GeV based on a multi-phase transport model. A dipolar distribution of $E \cdot B$ is observed in non-central collisions. We find that the coupling of the $E \cdot B$ dipole and magnetic field $B$ can induce an electric quadrupole moment which can further lead to the difference in elliptic flows between positive charged particles and negative charged particles through final interactions. The centrality dependence of the density of $E \cdot B$ is similar to the trend of the slope parameter $r$ measured from the difference in elliptic flows between positive pions and negative pions by the STAR collaboration. Therefore, the novel mechanism for electric quadrupole moment generation can offer a new interpretation of the observed charge-dependent elliptic flow of pions, but without the formation of chiral magnetic wave.
↳ hep-phnucl-exnucl-thPLB(2019)·30 citations
18
On the kinematic limit of the charm production in fixed-target experiments with the intrinsic charm from the target
Stefan Groote🇪🇪 · Sergey Koshkarev🇪🇪
In this note we provide a detailed derivation of the kinematic limit of the charm production in fixed-target experiments with the intrinsic charm coming from the target. In addition, we discuss the first measurement of charm quark production in the fixed-target configuration at the LHC.
↳ hep-phnucl-th0 citations
19
The Bethe-Salpeter approach to bound states: from Euclidean to Minkowski space
A. Castro🇧🇷 · E. Ydrefors🇧🇷 · W. de Paula🇧🇷 · T. Frederico🇧🇷 · J.H. de Alvarenga Nogueira🇧🇷 · P. Maris🇺🇸
The challenge to obtain from the Euclidean Bethe--Salpeter amplitude the amplitude in Minkowski is solved by resorting to un-Wick rotating the Euclidean homogeneous integral equation. The results obtained with this new practical method for the amputated Bethe--Salpeter amplitude for a two-boson bound state reveals a rich analytic structure of this amplitude, which can be traced back to the Minkowski space Bethe--Salpeter equation using the Nakanishi integral representation. The method can be extended to small rotation angles bringing the Euclidean solution closer to the Minkowski one and could allow in principle the extraction of the longitudinal parton density functions and momentum distribution amplitude, for example.
↳ hep-phnucl-thJ.Phys.Conf.Ser.(2019)·6 citations
20
Scattering cross-section under external magnetic field using the optical theorem
Snigdha Ghosh🇮🇳 · Vinod Chandra🇮🇳
The cross-section for the lowest order $2 \to 2$ elastic scattering between two charged scalars under external magnetic field mediated via a neutral scalar, has been computed in strong as well as weak magnetic field limits. This has been done by applying the optical theorem where the cross-section is expressed in terms of the imaginary parts of different one-loop graphs contributing to the forward scattering amplitudes. The modification in the amplitudes due to the external magnetic field has been done by means of replacing the charged scalar propagators with the Schwinger proper-time ones. Significant modifications of the cross-sections with respect to the vacuum cross-section are observed due to the external magnetic field.
↳ hep-phnucl-thEPJA(2020)·5 citations

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