Nuclear Theory·nucl-th

Monday·August 21, 2017

9 papers—5 primary·4 cross-listed

01
Primordial lithium abundance problem of BBN and baryonic density in the universe
Vinay Singh🇮🇳 · Joydev Lahiri🇮🇳 · Debasis Bhowmick🇮🇳 · D. N. Basu🇮🇳
Prediction of the primordial abundances of elements in the big-bang nucleosynthesis (BBN) is one of the three strong evidences for the big bang model. Precise knowledge of the baryon-to-photon ratio of the Universe from observations of the anisotropies of cosmic microwave background radiation has made the Standard BBN a parameter-free theory. Although, there is a good agreement over a range of nine orders of magnitude between abundances of light elements deduced from observations and calculated in primordial nucleosynthesis, there remains a yet-unexplained discrepancy of $^{7}$ Li abundance higher by a factor of $\sim 3$ when calculated theoretically. The primordial abundances depend on the astrophysical nuclear reaction rates and on three additional parameters, the number of light neutrino flavours, the neutron lifetime and the baryon-to-photon ratio in the universe. The effect of the modification of thirty-five reaction rates on light element abundance yields in BBN was investigated earlier by us. In the present work we have incorporated the most recent values of neutron lifetime and the baryon-to-photon ratio and further modified $^{3}$ He( $^{4}$ He, $γ$ ) $^{7}$ Be reaction rate which is used directly for estimating the formation of $^{7}$ Li as a result of $β^{+}$ decay as well as the reaction rates for t( $^{4}$ He, $γ$ ) $^{7}$ Li and d( $^{4}$ He, $γ$ ) $^{6}$ Li. We find that these modifications reduce the theoretically calculated abundance of $^{7}$ Li by $\sim 12%$ .
nucl-thastro-ph.SRJ.Exp.Theor.Phys.(2019)·16 citations
02
Quantum van der Waals and Walecka models of nuclear matter
R. V. Poberezhnyuk · V. Vovchenko · D. V. Anchishkin · M. I. Gorenstein
A comparable study of the quantum van der Waals and Walecka models of nuclear matter is presented. Each model contains two parameters which characterize the repulsive and attractive interactions between nucleons. These parameters are fixed in order to reproduce the known properties of the nuclear ground state. Both models predict a first-order liquid-gas phase transition and a very similar behavior in the vicinity of the critical point. Critical exponents of the quantum van der Waals model are studied both analytically and numerically. There are important differences in the behavior of the thermodynamical functions of the considered models at large values of the nucleon number density. At the same time both models fall into the universality class of mean-field theory.
nucl-thIJMPE(2017)·17 citations
03
Enhancement of elliptic flow can signal a first order phase transition in high energy heavy ion collisions
Yasushi Nara🇯🇵 · Harri Niemi🇩🇪 · Akira Ohnishi🇯🇵 · Jan Steinheimer🇩🇪 · Xiaofeng Luo🇨🇳 · Horst Stoecker🇩🇪
The beam energy dependence of the elliptic flow, $v_{2}$ , is studied in mid-central Au+Au collisions in the energy range of $3 \leq s_{N N} \leq 30$ GeV within the microscopic transport model JAM. The results of three different modes of JAM are compared; cascade-,hadronic mean field-, and a new mode with modified equations of state, with a first order phase transition (1.O.P.T.) and with a crossover transition. The standard hadronic mean field suppresses $v_{2}$ , while the inclusion of the effects of a 1.O.P.T. (and also of a crossover transition) does enhance $v_{2}$ at $s_{N N} < 30$ GeV. The enhancement or suppression of the scaled energy flow, dubbed "elliptic flow"is understood as being due to out of plane- flow, i.e. $v_{2} < 0$ , dubbed out of plane - "squeeze-out", which occurs predominantly in the early, compression stage. Subsequently, the in-plane flow dominates, in the expansion stage, $v_{2} > 0$ . The directed flow, dubbed "bounce- off", is an independent measure of the pressure, which quickly builds up the transverse momentum transfer in the reaction plane. When the spectator matter leaves the participant fireball region, where the highest compression occurs, a hard expansion leads to larger $v_{2}$ . A combined analysis of the three transverse flow coefficients, radial $v_{0}$ -, directed $v_{1}$ - and elliptic $v_{2}$ - flow, in the beam energy range of $3 \leq s_{N N} \leq 10$ GeV, distinguishes the different compression and expansion scenarios: a characteristic dependence on the early stage equation of state is observed. The enhancement of both the elliptic and the transverse radial flow and the simultaneous collapse of the directed flow of nucleons offers a clear signature if 1.O.P.T. is realized at the highest baryon densities created in high energy heavy-ion collisions.
nucl-thhep-phnucl-exEPJA(2018)·29 citations
04
Bulk viscosity from hydrodynamic fluctuations with relativistic hydro-kinetic theory
Yukinao Akamatsu🇯🇵 · Aleksas Mazeliauskas🇩🇪 · Derek Teaney🇺🇸
Hydro-kinetic theory of thermal fluctuations is applied to a non-conformal relativistic fluid. Solving the hydro-kinetic equations for an isotropically expanding background we find that hydrodynamic fluctuations give ultraviolet divergent contributions to the energy-momentum tensor. After shifting the temperature to account for the energy of non-equilibrium modes, the remaining divergences are renormalized into local parameters, e.g. pressure and bulk viscosity. We also confirm that the renormalization of the pressure and bulk viscosity is universal by computing them for a Bjorken expansion. The fluctuation-induced bulk viscosity reflects the non-conformal nature of the equation of state and is modestly enhanced near the QCD deconfinement temperature.
nucl-thhep-thPRC(2018)·52 citations
05
Analysis of Spectroscopic Factors in 11Be and 12Be in the Nilsson Strong Coupling Limit
A.O. Macchiavelli · H.L. Crawford · C.M. Campbell · R.M. Clark · M. Cromaz · P. Fallon · M.D. Jones · I.Y. Lee · M. Salathe
Spectroscopic factors in 10Be, 11Be and 12Be, extracted from (d,p), one neutron knockout, and (p,d) reactions are interpreted within the rotational model. Assuming that the ground state and first excited state of 11Be can be associated with the 1/2[220] and 1/2[101] Nilsson levels, the strong coupling limit gives simple expressions that relate the amplitudes of these wavefunctions (in the spherical basis) with the measured cross-sections and derived spectroscopic factors. We obtain good agreement with both the measured magnetic moment of the ground state in 11Be and the reaction data.
nucl-thPRC(2018)·22 citations
06
Quantifying finite-momentum effects in meson quasi-PDFs
T. J. Hobbs🇺🇸
The recently proposed large momentum effective theory (LaMET) of Ji has led to a burst of activity among lattice practitioners to perform and control the first pioneering calculations of the quasi-PDFs of the nucleon. These calculations represent approximations to the standard PDFs defined as correlation functions of fields with lightlike separation, being instead correlations along a longitudinal direction of the operator $γ^{z}$ ; as such, they differ from standard PDFs by power-suppressed $1 / p_{z}^{2}$ corrections, becoming exact in the limit $p_{z} \to \infty$ . Investigating the systematics of this behavior thus becomes crucial to understanding the validity of LaMET calculations. While this has been done using models for the nucleon, an analogous dedicated study has not been carried out for the $π$ and $ρ$ quark distribution functions. Using a constituent quark model, a systematic calculation is performed to estimate the size and $x$ dependence of the finite- $p_{z}$ effects in these quasi-PDFs, finding them to be potentially tamer for lighter mesons than for the collinear quasi-PDFs of the nucleon.
↳ hep-phhep-latnucl-thPRD(2018)·38 citations
07
Nonequilibrium thermodynamics with binary quantum correlations
Klaus Morawetz
The balance equations for thermodynamic quantities are derived from the nonlocal quantum kinetic equation. The nonlocal collisions lead to molecular contributions to the observables and currents. The corresponding correlated part of the observables is found to be given by the rate to form a molecule multiplied with its lifetime which can be considered as collision duration. Explicit expressions of these molecular contributions are given in terms of the scattering phase shifts. The two-particle form of the entropy is derived. This extends the Landau quasiparticle picture by two-particle molecular contributions. There is a continuous exchange of correlations into kinetic parts condensing into the rate of correlated variables for energy and momentum. For the entropy, an explicit gain remains and Boltzmann's H-theorem is proved including the molecular parts of the entropy.
↳ cond-mat.stat-mechcond-mat.str-elnucl-thphysics.plasm-phPRE(2017)·9 citations
08
Nuclear Structure Functions at a Future Electron-Ion Collider
E. C. Aschenauer (1)🇺🇸 · S. Fazio (1)🇺🇸 · M. A. C. Lamont (1)🇺🇸 · H. Paukkunen (2 and 3)🇫🇮 · Pia Zurita (1) ((1) Brookhaven National Laboratory, (2) University of Jyvaskyla, (3) Helsinki Institute of Physics)🇺🇸
The quantitative knowledge of heavy nuclei's partonic structure is currently limited to rather large values of momentum fraction $x$ -- robust experimental constraints below $x \sim 1 0^{- 2}$ at low resolution scale $Q^{2}$ are particularly scarce. This is in sharp contrast to the free proton's structure which has been probed in deep inelastic scattering (DIS) measurements down to $x \sim 1 0^{- 5}$ at perturbative resolution scales. The construction of an Electron-Ion Collider (EIC) with a possibility to operate with a wide variety of nuclei, will allow one to explore the low- $x$ region in much greater detail. In the present paper we simulate the extraction of the nuclear structure functions from measurements of inclusive and charm reduced cross sections at an EIC. The potential constraints are studied by analyzing simulated data directly in a next-to-leading order global fit of nuclear parton distribution functions based on the recent EPPS16 analysis. A special emphasis is placed on studying the impact an EIC would have on extracting the nuclear gluon PDF, the partonic component most prone to non-linear effects at low $Q^{2}$ . In comparison to the current knowledge, we find that the gluon PDF can be measured at an EIC with significantly reduced uncertainties.
↳ nucl-exhep-exnucl-thPRD(2017)·77 citations
09
Strongly-coupled anisotropic gauge theories and holography
Dimitrios Giataganas🇹🇼 · Umut Gürsoy🇳🇱 · Juan F. Pedraza🇳🇱
We initiate a non-perturbative study of anisotropic, non-conformal and confining gauge theories that are holographically realized in gravity by generic Einstein-Axion-Dilaton systems. In the vacuum our solutions describe RG flows from a conformal field theory in the UV to generic scaling solutions in the IR with generic hyperscaling violation and dynamical exponents $θ$ and $z$ . We formulate a generalization of the holographic c-theorem to the anisotropic case. At finite temperature, we discover that the anisotropic deformation reduces the confinement-deconfinement phase transition temperature suggesting a possible alternative explanation of inverse magnetic catalysis solely based on anisotropy. We also study transport and diffusion properties in anisotropic theories and observe in particular that the butterfly velocity that characterizes both diffusion and growth of chaos transverse to the anisotropic direction, saturates a constant value in the IR which can exceed the bound given by the conformal value.
↳ hep-thhep-phnucl-thPRL(2018)·143 citations

Affiliations

first authorsco-authorsvia INSPIRE