Nuclear Theory·nucl-th

Thursday·January 19, 2017

7 papers—4 primary·3 cross-listed

01
[Submitted on 18 Jan 2017]
Theoretical studies on the impact of point defect on the structures of different uranium silicides
Miao He · Shiyu Du · Heming He · Jiajian Lang · Zhen Liu · Qing Huang · Cheng-Te Lin · Ruifeng Zhang · Dejun Wang
The structures, point defects and impacts of fission products for U3Si (\b{eta}-U3Si and {\gamma}-U3Si) and USi2 ({\alpha}-USi2 and \b{eta}-USi2) are studied by first-principles calculations. The lattice parameters of U3Si and USi2 are calculated and the stability of different types of point defects is predicted by their formation energies. The results show that silicon vacancies are more prone to be produced than uranium vacancies in \b{eta}-USi2 matrix, while uranium vacancies are the most stable defects of other three types of crystallographic structures. The most favorable sites of fission products (strontium, barium, cerium and neodymium) are determined in this work as well. By calculating incorporation energies of fission products, we demonstrate that the uranium site is the most favored for all the fissions products. Comparing the structural changes influenced by different fission products, it is also found that the highest volume change is caused by barium interstitials. According to the current data, rare earth elements cerium and neodymium are found to be more stable than alkaline earth metals strontium and barium in a given nuclear matrix. Finally, it is also determined that in USi2 crystal lattice fission products tend to be stabilized in uranium substitution sites, while they are likely to form precipitates from the U3Si matrix. It is expected that this work may provide new insight into the mechanism for structural evolutions of silicide nuclear fuels in a reactor.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1701.04962 [pdf]
0 citations
02
[Submitted on 18 Jan 2017]
Parametric estimate of the relative photon yields from the Glasma and the Quark-Gluon Plasma in heavy-ion collisions
J. Berges🇩🇪 · K. Reygers🇩🇪 · N. Tanji🇩🇪 · R. Venugopalan🇺🇸
Recent classical-statistical numerical simulations have established the "bottom-up" thermalization scenario of Baier et al. as the correct weak coupling effective theory for thermalization in ultrarelativistic heavy-ion collisions. We perform a parametric study of photon production in the various stages of this bottom-up framework to ascertain the relative contribution of the off-equilibrium "Glasma" relative to that of a thermalized Quark-Gluon Plasma. Taking into account the constraints imposed by the measured charged hadron multiplicities at RHIC and the LHC, we find that Glasma contributions are important especially for large values of the saturation scale at both energies. These non-equilibrium effects should therefore be taken into account in studies where weak coupling methods are employed to compute photon yields.
Comments:
33 pages, 9 figures; version accepted in PRC, title changed
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1701.05064 [pdf]
PRC(2017)·72 citations
03
[Submitted on 18 Jan 2017]
Effect of pre-equilibrium phase on $R_{AA}$ and $v_{2}$ of heavy quarks in heavy ion collisions
Santosh K. Das🇮🇹 · Marco Ruggieri🇨🇳 · Francesco Scardina🇮🇹 · Salvatore Plumari🇮🇹 · Vincenzo Greco🇮🇹
Heavy quark $R_{AA}$ and $v_{2}$ have been calculated at RHIC energy considering initial conditions with and without pre-equilibrium phase to highlight the effect of the latter on heavy quark observables. The momentum evolution of the heavy quark has been studied by means of the Boltzmann transport equation. To model the pre-equilibrium phase we have used the KLN initial condition. We have found that the pre-equilibrium phase impacts the $R_{AA}$ of about 20-25 $%$ whereas the impact on $v_{2}$ is very negligible. We have also calculated heavy quark $R_{AA}$ and $v_{2}$ in the case of initializations with early thermalized quark-gluon plasma. We have checked that the particular form of the initial spectrum is not very important for $R_{AA}$ , the larger energy density being more important. In fact, comparing the results obtained within the two initializations we have found that one can mimic the impact of the pre-equilibrium phase using a early thermalized QGP medium.
Comments:
10 pages, 2 figures, Accepted for publication in Journal of Physics G
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1701.05123 [pdf]
J.Phys.G(2017)·66 citations
04
[Submitted on 18 Jan 2017]
Electromagnetic scaling functions within the Green's Function Monte Carlo approach
N. Rocco🇪🇸 · L. Alvarez-Ruso🇪🇸 · A. Lovato🇺🇸 · J. Nieves🇪🇸
We have studied the scaling properties of the electromagnetic response functions of $^{4}$ He and $^{12}$ C nuclei computed by the Green's Function Monte Carlo approach, retaining only the one-body current contribution. Longitudinal and transverse scaling functions have been obtained in the relativistic and non relativistic cases and compared to experiment for various kinematics. The characteristic asymmetric shape of the scaling function exhibited by data emerges in the calculations in spite of the non relativistic nature of the model. The results are consistent with scaling of zeroth, first and second kinds. Our analysis reveals a direct correspondence between the scaling and the nucleon-density response functions.
Comments:
11 pages, 15 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex)
arXiv:
1701.05151 [pdf]
PRC(2017)·17 citations
05
[Submitted on 16 Jan 2017] (cross-list from hep-lat)
The QCD Equation of State to $O (μ_{B}^{6})$ from Lattice QCD
A. Bazavov🇺🇸 · H.-T. Ding🇨🇳 · P. Hegde🇮🇳 · O. Kaczmarek🇨🇳 · F. Karsch🇩🇪 · E. Laermann🇩🇪 · Y. Maezawa🇯🇵 · S. Mukherjee🇺🇸 · H. Ohno🇺🇸 · P. Petreczky🇺🇸 · H. Sandmeyer🇩🇪 · P. Steinbrecher🇺🇸 and 4 other authors
We calculated the QCD equation of state using Taylor expansions that include contributions from up to sixth order in the baryon, strangeness and electric charge chemical potentials. Calculations have been performed with the Highly Improved Staggered Quark action in the temperature range $T \in [135 MeV, 330 MeV]$ using up to four different sets of lattice cut-offs corresponding to lattices of size $N_{σ}^{3} \times N_{τ}$ with aspect ratio $N_{σ} / N_{τ} = 4$ and $N_{τ} = 6 - 16$ . The strange quark mass is tuned to its physical value and we use two strange to light quark mass ratios $m_{s} / m_{l} = 20$ and $27$ , which in the continuum limit correspond to a pion mass of about $160$ MeV and $140$ MeV espectively. Sixth-order results for Taylor expansion coefficients are used to estimate truncation errors of the fourth-order expansion. We show that truncation errors are small for baryon chemical potentials less then twice the temperature ( $μ_{B} \leq 2 T$ ). The fourth-order equation of state thus is suitable for the modeling of dense matter created in heavy ion collisions with center-of-mass energies down to $s_{N N} \sim 12$ GeV. We provide a parametrization of basic thermodynamic quantities that can be readily used in hydrodynamic simulation codes. The results on up to sixth order expansion coefficients of bulk thermodynamics are used for the calculation of lines of constant pressure, energy and entropy densities in the $T$ - $μ_{B}$ plane and are compared with the crossover line for the QCD chiral transition as well as with experimental results on freeze-out parameters in heavy ion collisions. These coefficients also provide estimates for the location of a possible critical point. We argue that results on sixth order expansion coefficients disfavor the existence of a critical point in the QCD phase diagram for $μ_{B} / T \leq 2$ and $T / T_{c} (μ_{B} = 0) > 0.9$ .
Comments:
Updated to correspond to journal version. The ancillary files, which contain tables of the basic thermodynamic observables calculated for baryon chemical potentials \mu_B/T < 2.2 in the temperature range 135 MeV < T < 280 MeV and for the cases \mu_Q = \mu_S = 0 and n_S=0, n_Q/n_B=0.4, can be found in version v1
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1701.04325 [pdf]
PRD(2017)·586 citations
06
[Submitted on 17 Jan 2017] (cross-list from hep-ph)
$K π$ $I = 1/2$ $S$ -wave from $η_{c}$ decay data at BaBar and classic Meson-Meson scattering from LASS
A. Palano🇺🇸 · M.R. Pennington🇺🇸
A recent analysis of data on the two photon production of the $η_{c}$ and its decay to $K (K π)$ has determined the $K π$ $S$ -wave amplitude in a "model-independent" way assuming primarily that the additional kaon is a spectator in this decay. The purpose of this paper is to fit these results, together with classic $K π$ production data from LASS, within a formalism that implements unitarity for the di-meson interaction. This fixes the $I = 1/2$ $K π \to K π$ $S$ -wave amplitude up to 2.4 GeV. This resolves the Barrelet ambiguity in the original LASS analysis, and constrains the amount of inelasticity in $K π$ scattering, highlighting that this becomes significant beyond 1.8 GeV. This result needs to be checked by experimental information on the many inelastic channels, in particular $K η^{'}$ and $K π π π$ . Our analysis provides a single representation for the $K π$ $S$ -wave from threshold, controlled by Chiral Perturbation Theory, through the broad $κ$ , $K_{0}^{*} (1430)$ and $K_{0}^{*} (1950)$ resonances. There is no arbitrary sum of Breit-Wigner forms and random backgrounds for real $K π$ masses. Rather the form provides a representation that can be translated to other processes with $K π$ interactions with their own coupling functions, while automatically maintaining consistency with the chiral dynamics near threshold, with the LASS data and the new results on $η_{c}$ decay.
Comments:
A new analysis superceding this earlier version is under way and will be submitted to the arXiv once complete. (original version 8 pages, 6 figures)
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1701.04881 [pdf]
5 citations
07
[Submitted on 18 Jan 2017] (cross-list from cond-mat.soft)
The relation between stretched-exponential relaxation and the vibrational density of states in glassy disordered systems
B. Cui · R. Milkus · A. Zaccone
Amorphous solids or glasses are known to exhibit stretched-exponential decay over broad time intervals in several of their macroscopic observables: intermediate scattering function, dielectric relaxation modulus, time-elastic modulus etc. This behaviour is prominent especially near the glass transition. In this Letter we show, on the example of dielectric relaxation, that stretched-exponential relaxation is intimately related to the peculiar lattice dynamics of glasses. By reformulating the Lorentz model of dielectric matter in a more general form, we express the dielectric response as a function of the vibrational density of states (DOS) for a random assembly of spherical particles interacting harmonically with their nearest-neighbours. Surprisingly we find that near the glass transition for this system (which coincides with the Maxwell rigidity transition), the dielectric relaxation is perfectly consistent with stretched-exponential behaviour with Kohlrausch exponents $0.56 < β < 0.65$ , which is the range where exponents are measured in most experimental systems. Crucially, the root cause of stretched-exponential relaxation can be traced back to soft modes (boson-peak) in the DOS.
Subjects:
cond-mat.soft (cond-mat.soft); cond-mat.dis-nn (cond-mat.dis-nn); cond-mat.mtrl-sci (cond-mat.mtrl-sci); Statistical Mechanics (cond-mat.stat-mech); Nuclear Theory (nucl-th)
arXiv:
1701.05037 [pdf]
PLA(2017)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Theoretical studies on the impact of point defect on the structures of different uranium silicides

Parametric estimate of the relative photon yields from the Glasma and the Quark-Gluon Plasma in heavy-ion collisions

Effect of pre-equilibrium phase on RAA​ and v2​ of heavy quarks in heavy ion collisions

Electromagnetic scaling functions within the Green's Function Monte Carlo approach

The QCD Equation of State to O(μB6​) from Lattice QCD

Kπ I=1/2 S-wave from ηc​ decay data at BaBar and classic Meson-Meson scattering from LASS

The relation between stretched-exponential relaxation and the vibrational density of states in glassy disordered systems

Affiliations

Effect of pre-equilibrium phase on $R_{AA}$ and $v_{2}$ of heavy quarks in heavy ion collisions

The QCD Equation of State to $O (μ_{B}^{6})$ from Lattice QCD

$K π$ $I = 1/2$ $S$ -wave from $η_{c}$ decay data at BaBar and classic Meson-Meson scattering from LASS