Nuclear Theory·nucl-th

Wednesday·November 11, 2015

8 papers—4 primary·4 cross-listed

01
[Submitted on 10 Nov 2015]
Generator coordinate method for hypernuclear spectroscopy with a covariant density functional
H. Mei🇯🇵 · K. Hagino🇯🇵 · J.M. Yao🇯🇵
We apply the generator coordinate method (GCM) to single- $Λ$ hypernuclei in order to discuss the spectra of hypernuclear low-lying states. To this end, we use the same relativistic point-coupling energy functional both for the mean-field and the beyond-mean-field calculations. This relativistic GCM approach provides a unified description of low-lying states in ordinary nuclei and in hypernuclei, and is thus suitable for studying the $Λ$ impurity effect. We carry out an illustrative calculation for the low-lying spectrum of $_{Λ}^{21}$ Ne, in which the interplay between the hypernuclear collective excitations and the single-particle excitations of the unpaired $Λ$ hyperon is taken into account in a full microscopic manner.
Comments:
5 pages, 3 eps figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1511.02957 [pdf]
PRC(2016)·27 citations
02
[Submitted on 10 Nov 2015]
Magnetic moments in odd-A Cd isotopes and coupling of particles with zero-point vibrations
S. Mishev · V. V. Voronov
Background: The coupling of the last nucleon with configurations in the ground state of the even-even core is known to augment the single quasiparticle fragmentation pattern. In a recent experimental study by Yordanov \emph{et al.} the values of the magnetic dipole and electric quadrupole moments of the $11/ 2^{-}$ state in a long chain of Cd isotopes were found to follow a simple trend which we try to explain by means of incorporating long-range correlations in the ground state. Purpose: Our purpose is to study the influence of the ground-state correlations (GSC) on the magnetic moments and compare our results with the data for the odd-A Cd isotopes. Method: In order to evaluate if the additional correlations have bearing on the magnetic moments we employ an extension to the quasiparticle-phonon model (QPM) which takes into account quasiparticle $\otimes$ phonon configurations in the ground state of the even-even core to the structure of the odd-A nucleus wave function. Results: It is shown that the values for the magnetic moments which the applied QPM extension yields deviate further from the Schmidt values. The latter is in agreement with the measured values for the Cd isotopes. Conclusions: The GSC exert significant influence on the magnetic dipole moments and reveal a potential for reproducing the experimental values for the studied cadmium isotopes.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.03013 [pdf]
PRC(2015)·7 citations
03
[Submitted on 10 Nov 2015]
Electromagnetic recombination spectra at the quark-hadron phase transition
Clint Young🇺🇸 · Scott Pratt🇺🇸
When quarks hadronize, they accelerate. Because they carry electric charge, they must radiate light as they accelerate and hadronize. This is true not only in jets but also in heavy ion collisions, where a thermalized plasma of quarks and gluons cools into a gas of hadrons. First, direct emission of photons from two quarks coalescing into pions is calculated using the quark-meson model. The yield of final-state photons to pions is found to be about $e^{2} / g_{π q q}^{2}$ , which is on the order of a percent. Second, the yield of photons from the decay of highly excited color singlets, which may exist ephemerally during hadronizaton, is estimated. Because these contributions occur late in the reaction, they should carry significant elliptic flow, which may help explain the large observed flow of direct photons at RHIC by the PHENIX Collaboration at the Relativistic Heavy Ion Collider (RHIC). The enhanced emission also helps explain PHENIX's surprisingly large observed $γ / π$ ratio.
Comments:
18 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1511.03147 [pdf]
PRC(2016)·7 citations
04
[Submitted on 10 Nov 2015]
Numerical assessment of post-prior equivalence for inclusive breakup reactions
Jin Lei🇪🇸 · Antonio M. Moro🇪🇸
We address the problem of the post-prior equivalence in inclusive breakup reactions induced by weakly-bound nuclei. The problem is studied within the DWBA model of Ichimura, Austern, Vincent [Phys. Rev. C32, 431 (1985)]. The post and prior formulas obtained in this model are briefly recalled, and applied to several breakup reactions induced by deuterons and $^{6}$ Li projectiles, to test their actual numerical equivalence. The different contributions of the prior-form formula are also discussed. A critical comparison with the prior-form distorted-wave Born approximation (DWBA) model of Udagawa and Tamura [Phys. Rev. C24, 1348 (1981)] is also provided.
Comments:
6 pages, 2 figures, submitted to PRC
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.03214 [pdf]
PRC(2015)·55 citations
05
[Submitted on 10 Nov 2015] (cross-list from hep-lat)
(2+1)-flavor QCD Thermodynamics from the Gradient Flow
Etsuko Itou🇯🇵 · Hiroshi Suzuki🇯🇵 · Yusuke Taniguchi🇯🇵 · Takashi Umeda🇯🇵
Recently, we proposed a novel method to define and calculate the energy-momentum tensor (EMT) in lattice gauge theory on the basis of the Yang-Mills gradient flow [1]. In this proceedings, we summarize the basic idea and technical steps to obtain the bulk thermodynamic quantities in lattice gauge theory using this method for the quenched and $(2 + 1)$ -flavor QCD. The revised results of integration measure (trace anomaly) and entropy density of the quenched QCD with corrected coefficients are shown. Furthermore, we also show the flow time dependence of the parts of EMT including the dynamical fermions. This work is based on a joint-collaboration between FlowQCD and WHOT QCD.
Comments:
7 pages, Proceedings for the 33rd International Symposium on Lattice Field Theory 14 -18 July 2015 Kobe International Conference Center, Kobe, Japan
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.03009 [pdf]
PoS(2016)·9 citations
06
[Submitted on 10 Nov 2015] (cross-list from hep-ph)
The effect of the chiral chemical potential on the chiral phase transition in the NJL model with different regularization schemes
Lang Yu🇨🇳 · Hao Liu🇨🇳 · Mei Huang🇨🇳
We study the chiral phase transition in the presence of the chiral chemical potential $μ_{5}$ using the two-flavor Nambu--Jona-Lasinio model. In particular, we analyze the reason why one can obtain two opposite behaviors of the chiral critical temperature as a function of $μ_{5}$ in the framework of different regularization schemes. We compare the modifications of the chiral condensate and the critical temperature due to $μ_{5}$ in different regularization schemes, analytically and numerically. Finally, we find that, for the conventional hard-cutoff regularization scheme, the increasing dependence of the critical temperature on the chiral chemical potential is an artifact, which is caused by the fact that it does not include complete contribution from the thermal fluctuations. When the thermal contribution is fully taken into account, the chiral critical temperature should decrease with $μ_{5}$ .
Comments:
11 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1511.03073 [pdf]
PRD(2016)·69 citations
07
[Submitted on 10 Nov 2015] (cross-list from hep-ph)
Di-hadron fragmentation and mapping of the nucleon structure
Silvia Pisano🇮🇹 · Marco Radici🇮🇹
The fragmentation of a colored parton directly into a pair of colorless hadrons is a non-perturbative mechanism that offers important insights into the nucleon structure. Di-hadron fragmentation functions can be extracted from semi-inclusive electron-positron annihilation data. They also appear in observables describing the semi-inclusive production of two hadrons in deep-inelastic scattering of leptons off nucleons or in hadron-hadron collisions. When a target nucleon is transversely polarized, a specific chiral-odd di-hadron fragmentation function can be used as the analyzer of the net density of transversely polarized quarks in a transversely polarized nucleon, the so-called transversity distribution. The latter can be extracted through suitable single-spin asymmetries in the framework of collinear factorization, thus in a much simpler framework with respect to the traditional one in single-hadron fragmentation. At subleading twist, the same chiral-odd di-hadron fragmentation function provides the cleanest access to the poorly known twist-3 parton distribution $e (x)$ , which is intimately related to the mechanism of dynamical chiral symmetry breaking in QCD. When sensitive to details of transverse momentum dynamics of partons, the di-hadron fragmentation functions for a longitudinally polarized quark can be connected to the longitudinal jet handedness to explore possible effects due to $C P -$ violation of the QCD vacuum. In this review, we outline the formalism of di-hadron fragmentation functions, we discuss different observables where they appear and we present measurements and future worldwide plans.
Comments:
19 pages, 18 figures. Contribution to the EPJA Special Issue on "3D Structure of the Nucleon"
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1511.03220 [pdf]
EPJA(2016)·21 citations
08
[Submitted on 10 Nov 2015] (cross-list from nucl-ex)
The pi0, eta, eta' -> gamma gamma*(Q^2) Decay Rates and Radii
A.M.Bernstein🇺🇸
The low $Q^{2}$ slopes of the the transition form factors provide a unique method to measure the sizes of the neutral pseudo-scalar mesons, since they do not have electromagnetic form factors. From the slope one obtains the "axial transition RMS radius" $R_{P S, A} = < r^{2} >$ for each PS meson. The present status of theory and experiment for these quantities are presented. A comparison of the $R_{P S, A}$ is presented along with the electromagnetic and scalar radii of the $π^{\pm}$ mesons and the proton. We observe the striking similarity of the values of axial transition radii of all of the pseudoscalar mesons to each other and to the charge radius of the $π^{\pm}$ . In the $Q^{2}$ = 0 limit the transition form factor is a measure of the pseudo-scalar meson radiative width (lifetime) and is a possible fourth (unexploited) method to perform such a measurement. The $π^{0} \to γ γ$ decay rate is a test of QCD at the confinement scale. There is a firm QCD prediction with a theoretical uncertainty of $≃$ 1 \% which calls for an experimental test at the same level of accuracy. There are three methods that have been utilized to perform this measurement and the present status of the experimental tests are outlined. The current accuracy is significantly less than the theoretical uncertainty. The efforts to improve this are briefly summarized.
Comments:
6 pages, 2 figures: Internation Workshop on Chiral Dynamics, 29June-3July 2015, Pisa, Italy
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.03242 [pdf]
PoS(2016)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE