Nuclear Theory Publications (50)

Search

Nuclear Theory Publications

Background The nuclear structure of the cluster bands in $^{20}$Ne presents a challenge for different theoretical approaches. It is especially difficult to explain the broad 0$^+$, 2$^+$ states at 9 MeV excitation energy. Simultaneously, it is important to obtain more reliable experimental data for these levels in order to quantitatively assess the theoretical framework. Read More


We study the fission yield of recently predicted thermally fissile neutron-rich uranium and thorium nuclei using statistical model. The level density parameters needed for the study are evaluated from the excitation energies of temperature dependent relativistic mean field formalism. The excitation energy and the level density parameter for a given temperature are employed in the convolution integral method to obtain the probability of the particular fragmentation. Read More


Systems of Bose particles with both repulsive and attractive interactions are studied using the Skyrme-like mean-field model. The phase diagram of such systems exhibits two special lines in the chemical potential-temperature plane: one line which represents the first-order liquid-gas phase transition with the critical end point, and another line which represents the onset of Bose-Einstein condensation. The calculations are made for strongly-interacting matter composed of alpha particles. Read More


Background: The Skyrme energy density functional is widely used in mean-field calculations of nuclear structure and dynamics. However, its reliance on phenomenology may compromise its isovector properties and its performance for exotic nuclear systems. Purpose: This work investigates the possibility of removing some phenomenology from the density functional by drawing on the high-energy degrees-of-freedom of the quark-meson coupling (QMC) model. Read More


The objective of this paper is to assess the current theoretical understanding of the extensive set of quarkonium observables (for both charmonia and bottomonia) that have been attained in ultrarelativistic heavy-ion collisions over two orders of magnitude in center-of-mass energy. We briefly lay out and compare the currently employed theoretical frameworks and their underlying transport coefficients, and then analyze excitation functions of quarkonium yields to characterize the nature of the varying production mechanisms. We argue that an overall coherent picture of suppression and regeneration mechanisms emerges which enables to deduce insights on the properties of the in-medium QCD force from SPS via RHIC to LHC, and forms a basis for future quantitative studies. Read More


The reduced magnetic dipole and electric quadrupole transition probabilities for the radiative decay of the $^{229}$Th 7.8~eV isomer to the ground state are predicted within a detailed nuclear-structure model approach. We show that the presence and decay of this isomer can only be accounted for by the Coriolis mixing emerging from a remarkably fine interplay between the coherent quadrupole-octupole motion of the nuclear core and the single-nucleon motion within a reflection-asymmetric deformed potential. Read More


We study the equation of state of QCD using an improved version of the three-flavor Polyakov-Nambu-Jona-Lasinio model beyond the mean-field approximation. It incorporates the effects of unquenched quarks into the Polyakov-loop effective potential, as well as mesonic contributions to the grand-canonical potential. We study in full detail the calculation of the thermodynamical potential in this approach and compare the resulting pressure and entropy density with the most-recent lattice-QCD calculations at zero baryochemical potential. Read More


Photons and dileptons are emitted throughout the evolution of the deconfined nuclear medium produced in heavy ion collisions. As such they can provide valuable information about the different phases of the medium, and complement hadronic measurements and other observables. In this work, recent developments related to electromagnetic emissions at early time, in the cross-over region, and at late times are reviewed. Read More


As the calorimetric method of neutrino-energy reconstruction is generally considered to be largely insensitive to nuclear effects, its application seems to be an effective way for reducing systematic uncertainties in oscillation experiments. To verify the validity of this opinion, we quantitatively study the sensitivity of the calorimetric energy reconstruction to the effect of final-state interactions in an ideal detector and in a realistic scenario. We find that when particles escaping detection carry away a non-negligible fraction of neutrino energy, the calorimetric reconstruction method becomes sensitive to nuclear effects which, in turn, affects the outcome of the oscillation analysis. Read More


Background: 12C has been and is still widely used in neutrino-nucleus scattering and oscillation experiments. More recently, 40Ar has emerged as an important nuclear target for current and future experiments. Liquid argon time projection chambers (LArTPCs) possess various advantages in measuring electroweak neutrino-nucleus cross sections. Read More


Using a Bayesian model-to-data analysis, we estimate the temperature dependence of the heavy quark diffusion coefficients by calibrating to the experimental data of $D$-meson $R_{\mathrm{AA}}$ and $v_2$ in AuAu collisions ($\sqrt{s_{NN}}=200$ GeV) and PbPb collisions ($\sqrt{s_{NN}}=2.76$ TeV)~\cite{Xie:2016iwq}. The spatial diffusion coefficient $D_s2\pi T$ is found to be mostly constraint around $(1. Read More


Starting from the semi-analytic construction of a equation of state (EoS) which takes into account nuclear and quark matter at finite temperature, we study the possibility that proto-neutron stars, be proto-hybrid stars whose cores are composed of quark matter. We obtain the mass-radius relationship and discuss the latest constraints on masses and radii of neutron stars, considering the pulsars PSR J1614-2230 and PSR J0348 + 0432. Read More


We study the possibility of a hadron-quark phase transition in the interior of neutron stars, taking into account different schematic evolutionary stages at finite temperature. Furthermore, we analyze the astrophysical properties of hot and cold hybrid stars, considering the constraint on maximum mass given by the pulsars J1614-2230 and J1614-2230. We obtain cold hybrid stars with maximum masses $\geq 2$ M$_{\odot}$. Read More


The quality of data taken at RHIC and LHC as well as the success and sophistication of computational models for the description of ultra-relativistic heavy-ion collisions have advanced to a level that allows for the quantitative extraction of the transport properties of the Quark-Gluon-Plasma. However, the complexity of this task as well as the computational effort associated with it can only be overcome by developing novel methodologies: in this paper we outline such an analysis based on Bayesian Statistics and systematically compare an event-by-event heavy-ion collision model to data from the Large Hadron Collider. We simultaneously probe multiple model parameters including fundamental quark-gluon plasma properties such as the temperature-dependence of the specific shear viscosity $\eta/s$, calibrate the model to optimally reproduce experimental data, and extract quantitative constraints for all parameters simultaneously. Read More


We calculate momentum distributions of neutrons and protons in $^3$He in the framework of a model which includes 3N interactions together with 2N interactions. It is shown that contribution of 3N interactions becomes essential in comparison with contribution coming from 2N interaction for internal momentum in $^3$He $k>$~250~MeV/c. We also compare calculated momentum distribution of protons with so-called empirical momentum distribution of protons extracted from A$(^3\mathrm{He},p)$ breakup cross-sections measured for protons emitted at zero degree. Read More


In this work, we study the odd-even effect in binding energies and charge radii, and systematic behavior of differential radii, to identify the underlying components of the effective nuclear interaction. We apply nuclear density functional theory using a family of Fayans and Skyrme energy density functionals fitted to similar datasets but using different optimization protocols. We inspect various correlations between differential charge radii, odd-even staggering in energies and radii, and nuclear matter properties. Read More


We introduce an effective theory which extends hydrodynamics into a regime where the critical slowing down would otherwise make hydrodynamics inapplicable. Read More


Path integrals describing quantum many-body systems can be calculated with Monte Carlo sampling techniques, but average correlation functions and other observables are subject to signal-to-noise ratios that degrade exponentially in time. Following up on our previous work, it is found that reweighting correlation functions by a phase determined from the same correlation function at an earlier time can eliminate this exponential signal-to-noise degradation. This method of phase reweighting introduces a bias that vanishes in a well-defined limit, and which can be systematically removed through extrapolation. Read More


We study the implications of the heavy-quark spin symmetry for the possible spin partners of the exotic states $Z_b(10610)$ and $Z_b(10650)$ in the spectrum of bottomonium. We formulate and solve numerically the coupled-channel equations for the $Z_b$ states that allow for a dynamical generation of these states as hadronic molecules. The force includes short-range contact terms and the one-pion exchange potential, both treated fully nonperturbatively. Read More


We study experimental background reconstruction methods for the measurement of $D-\overline{D}$ correlation using a PYTHIA simulation. Like-sign and side-band background methods that are widely used in the experimental measurements of single $D$-meson production yields were deployed for the correlation background study. It is found that the like-sign method which well describes the combinatorial background of single $D^{0}$ meson yields fails to reproduce the correlated background in the $D^{0}-\overline{D^{0}}$ correlation measurement, while the side-band background method yields a good description of the background for both the single $D^0$ yields and of the correlated background of the $D^{0}-\overline{D^{0}}$ correlation measurement. Read More


We study the Polyakov loop correlator in the weak coupling expansion and show how the perturbative series re-exponentiates into singlet and adjoint contributions. We calculate the order $g^7$ correction to the Polyakov loop correlator in the short distance limit. We show how the singlet and adjoint free energies arising from the re-exponentiation formula of the Polyakov loop correlator are related to the gauge invariant singlet and octet free energies that can be defined in pNRQCD, namely we find that the two definitions agree at leading order in the multipole expansion, but differ at first order in the quark-antiquark distance. Read More


$K^-$ optical potentials relevant to calculations of $K^-$ nuclear quasi-bound states were developed within several chiral meson-baryon coupled-channel interaction models. The applied models yield quite different $K^-$ binding energies and widths. Then, the $K^-$ multinucleon interactions were incorporated by a phenomenological optical potential fitted recently to kaonic atom data. Read More


Quantum phase transitions between competing equilibrium shapes of nuclei with an odd number of nucleons are explored using a microscopic framework of nuclear energy density functionals and a particle-boson core coupling model. The boson Hamiltonian for the even-even core nucleus, as well as the spherical single-particle energies and occupation probabilities of unpaired nucleons, are completely determined by a constrained self-consistent mean-field calculation for a specific choice of the energy density functional and pairing interaction. Only the strength parameters of the particle-core coupling have to be adjusted to reproduce a few empirical low-energy spectroscopic properties of the corresponding odd-mass system. Read More


2017Apr

The second and the third order anisotropic flow, $V_{2}$ and $V_3$, are determined by the corresponding initial spatial anisotropy coefficients, $\varepsilon_{2}$ and $\varepsilon_{3}$, in the initial density distribution. On the contrary, the higher order anisotropic flow $V_n$ ($n > 3$), in addition to their dependence on the same order initial anisotropy coefficient $\varepsilon_{n}$, have a significant contribution from lower order initial anisotropy coefficients, which leads to mode-coupling effects. In this contribution, we present the investigations on linear and non-linear modes in higher order anisotropic flow ($V_{4}$, $V_{5}$ and $V_{6}$) in Pb--Pb collisions at $\sqrt{s_{\rm NN}} =$ 2. Read More


We develop a reaction model for $\eta$ photoproduction off the deuteron ($\gamma d\to\eta pn$), and study the reaction at a special kinematics, where the photon beam energy is $\sim 0.94$ GeV and the scattered proton is detected at $\sim 0^\circ$, for the purpose of determining the $\eta$-nucleon scattering length ($a_{\eta N}$) and effective range ($r_{\eta N}$). In this kinematics, the $\eta$-nucleon elastic rescattering is significantly enhanced while other background mechanisms being suppressed. Read More


Despite recent advancements in the study and understanding of the phase diagram of strongly interacting matter, the region of high baryonic densities and low temperatures has remained difficult to reach in the lab. Things are expected to change with the planned HIC experiments at FAIR in Germany and NICA in Russia, which will open a window to the high-density-low-temperature segment of the QCD phase map, providing a unique opportunity to test the validity of model calculations that have predicted the formation of spatially inhomogeneous phases with broken chiral symmetry at intermediate-to-high densities. Such a density region is also especially relevant for the physics of neutron stars, as they have cores that can have several times the nuclear saturation density. Read More


We study charmonium and bottomonium as relativistic bound states in a light-front quantized Hamiltonian formalism. The effective Hamiltonian is based on light-front holography. We use a recently proposed longitudinal confinement to complete the soft-wall holographic potential for the heavy flavors. Read More


2017Apr
Affiliations: 1Department of Physics, Lomonosov Moscow State University, 2Department of Physics, Lomonosov Moscow State University, 3Department of Physics, Lomonosov Moscow State University, 4Department of Physics, Lomonosov Moscow State University, 5Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University

The ground state multiplet structure for nuclei over the wide range of mass number $A$ was calculated in $\delta$-approximation and different mass relations for pairing energy was analysed in this work. Correlation between the calculated multiplet structure and experimental data offer a guideline in deciding between mass relations for nucleon pairing. Read More


This article contains a discussion in which we showed that observation of splitting in the energy levels of prolate nuclei, is possible. Similar effects is atomic physics is known as Zeeman effect which is well-known, but in nuclear physics such topic has not been discussed and mentioned if it is possible or is not. In this article, after introducing deformation in commutation relation in three dimensional, these relations has been used in X(3) model. Read More


A recently suggested equation of state with the induced surface tension is generalized to the case of quantum gases with mean-field interaction. The self-consistency conditions and the necessary one to obey the Third Law of thermodynamics are found. The quantum virial expansion of the Van der Waals models of such type is analyzed. Read More


We discuss new transport phenomena in the presence of both a strong magnetic field and a vortex field. Their interplay induces a charge distribution and a current along the magnetic field. We show that the associated transport coefficients can be obtained from a simple analysis of the single-particle distribution functions and also from the Kubo formula calculation. Read More


We show that the interplay of chiral effective field theory and lattice QCD can be used in the evaluation of so-called disconnected diagrams, which appear in the study of the isoscalar and isovector channel of pion-pion scattering and have long been a major challenge for the lattice community. By means of partially-quenched chiral perturbation theory, we distinguish and analyze the effects from different types of contraction diagrams to the pion-pion scattering amplitude, including its scattering lengths and the energy-dependence of its imaginary part. Our results may be used to test the current degree of accuracy of lattice calculation in the handling of disconnected diagrams, as well as to set criteria for the future improvement of relevant lattice computational techniques that may play a critical role in the study of other interesting QCD matrix elements. Read More


A nonlocal dispersive-optical-model analysis has been carried out for neutrons and protons in $^{48}$Ca. Elastic-scattering angular distributions, total and reaction cross sections, single-particle energies, the neutron and proton numbers, and the charge distribution have been fitted to extract the neutron and proton self-energies both above and below the Fermi energy. From the single-particle propagator resulting from these self-energies we have determined the charge and neutron matter distributions in $^{48}$Ca. Read More


This contribution presents a theoretical overview of hydrodynamic modelling of heavy-ion collisions, with highlights on some recent developments. In particular, the formulation of anisotropic hydrodynamics, the role of hydrodynamic fluctuations, and the non-linear coupling of flow coefficients will be discussed. Read More


Exotic nuclei, particularly those near the driplines, are at the core of one of the fundamental questions driving nuclear structure and astrophysics today: what are the limits of nuclear binding? Exotic nuclei play a critical role in both informing theoretical models as well as in our understanding of the origin of the heavy elements. Our purpose is to refine existing mass models through the training of an artificial neural network that will mitigate the large model discrepancies far away from stability. The basic paradigm of our two-pronged approach is an existing mass model that captures as much as possible of the underlying physics followed by the implementation of a Bayesian Neural Network (BNN) refinement to account for the missing physics. Read More


We have studied the effect of free space nucleon radius on the nuclear matter and slowly rotating neutron star properties within a relativistic mean field model with the inclusion of omega-rho mixing nonlinear term. We use the same density dependent radius as in our previous work. However, in the present work we utilize the parameter sets with more proper symmetric nuclear matter (SNM) predictions for a number of different nucleon radii. Read More


In high energy heavy-ion collisions the magnetic field is very strong right after the nuclei penetrate each other and a non-equilibrium system of quarks and gluons builds up. Even though quarks might not be very abundant initially, their dynamics must necessarily be influenced by the Lorentz force. Employing the 3+1d partonic cascade BAMPS we show that the circular Larmor movement of the quarks leads to a strong positive anisotropic flow of quarks at very soft transverse momenta. Read More


We construct a simple model for describing the hadron-quark crossover transition by using lattice QCD (LQCD) data in the 2+1 flavor system, and draw the phase diagram in the 2+1 and 2+1+1 flavor systems through analyses of the equation of state (EoS) and the susceptibilities. In the present hadron-quark crossover (HQC) model is successful in reproducing LQCD data on the EoS and the flavor susceptibilities.We define the hadron-quark transition temperature. Read More


The nuclear symmetry energy is defined by the second derivative of the energy per nucleon with respect to the proton-neutron asymmetry, and is sometimes approximated by the energy difference between the neutron matter and the symmetric matter. Accuracy of this approximation is assessed analytically and numerically, within the Hartree-Fock theory using effective interactions. By decomposing the nuclear-matter energy, the relative error of each term is expressed analytically; it is constant or is a single-variable function determined by the function type. Read More


The quenching of the experimental spectroscopic factor for proton emission from the short-lived $d_{3/2}$ isomeric state in $^{151m}$Lu was a long-standing problem. In the present work, proton emission from this isomer has been reinvestigated in an experiment at the Accelerator Laboratory of the University of Jyv\"{a}skyl\"{a}. The proton-decay energy and half-life of this isomer were measured to be 1295(5) keV and 15. Read More


Theoretical uncertainties in the predictions of inner fission barrier heights in superheavy elements have been investigated in a systematic way for a set of state-of-the-art covariant energy density functionals which represent major classes of the functionals used in covariant density functional theory. They differ in basic model assumptions and fitting protocols. Both systematic and statistical uncertainties have been quantified where the former turn out to be larger. Read More


The distribution of flow harmonics in heavy ion experiment can be characterized by standardized cumulants. We first use the Elliptic-Power distribution together with the hydrodynamic linear response to study the two dimensional standardized cumulants of elliptic and triangular flow ($v_2$ and $v_3$) distribution. Using this, the $2q$-particle correlation functions $c_3\{2\}$, $c_3\{4\}$ and $c_3\{6\}$, are related to the second, forth and sixth standardized cumulants of the $v_3$ distribution, respectively. Read More


Recent $N_f=2+1$ lattice data for meson-meson scattering in $p$-wave and isospin $I=1$ are analyzed using a unitarized model inspired by Chiral Perturbation Theory in the inverse-amplitude formulation for two and three flavors. Chiral extrapolations are performed that postdict phase shifts extracted from experiment quite well. In addition, the low-energy constants are compared to the ones from a recent analysis of $N_f=2$ lattice QCD simulations to check for the consistency of the hadronic model used here. Read More


The semi-inclusive deep inelastic electron scattering off transversely polarized $^3$He, i.e. the process, $e + \vec{^3 {\rm He}} \to e' + h+X$, with $h$ a detected fast hadron, is studied beyond the plane wave impulse approximation. Read More


We discuss a scenario in which the $P_c(4450)^{+}$ heavy pentaquark is a $\Sigma_c \bar{D}^*$-$\Lambda_{c}(2595) \bar{D}$ molecule. The $\Lambda_{c1} \bar{D} \to \Sigma_c \bar{D}^*$ transition is mediated by the exchange of a pion almost on the mass shell that generates a long-range $1/r^2$ potential. This is analogous to the effective force that is responsible for the Efimov spectrum in three-boson systems interacting through short-range forces. Read More


We review recent progress in studies of nuclear final-state interactions in deep inelastic scattering (DIS) off the lightest nuclei tagged by a recoil nucleon. These processes hold a lot of potential for resolving the outstanding issues related to the dynamics of hadronization in QCD. Within the minimal Fock component framework, valid at large Bjorken $x$, the main features of the theoretical approach based on the virtual nucleon approximation are elaborated. Read More


The fully self-consistent Hartree-Fock (HF) plus random phase approximation (RPA) based on Skyrme-type interaction is used to study the existence problem of proton semi-bubble structure in the $2_1^+$ state of $^{34}$Si. The experimental excitation energy and the B(E2) strength of the $2_1^+$ state in $^{34}$Si can be reproduced quite well. The tensor effect is also studied. Read More


We complement studies of the neutral pion transition form factor pi^0 --> gamma^(*) gamma^(*) with calculations for the electromagnetic decay widths of the processes pi^0 --> e^+ e^-, pi^0 --> e^+ e^- gamma and pi^0 --> e^+ e^- e^+ e^-. Their common feature is that the singly- or doubly-virtual transition form factor serves as a vital input that is tested in the non-perturbative low-momentum region of QCD. We determine this form factor from a well-established and symmetry-preserving truncation of the Dyson-Schwinger equations. Read More


We present results for the QCD Equation of State at non-zero chemical potentials corresponding to the conserved charges in QCD using Taylor expansion upto sixth order in the baryon number, electric charge and strangeness chemical potentials. The latter two are constrained by the strangeness neutrality and a fixed electric charge to baryon number ratio. In our calculations, we use the Highly Improved Staggered Quarks (HISQ) discretization scheme at physical quark masses and at different values of the lattice spacings to control lattice cut-off effects. Read More


We study the effect of the chiral symmetry restoration (CSR) on heavy-ion collisions observables in the energy range $\sqrt{s_{NN}}$ = 3-20 GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach. The PHSD includes the deconfinement phase transition as well as essential aspects of CSR in the dense and hot hadronic medium, which are incorporated in the Schwinger mechanism for particle production. Our systematic studies show that chiral symmetry restoration plays a crucial role in the description of heavy-ion collisions at $\sqrt{s_{NN}}$ = 3-20 GeV, realizing an increase of the hadronic particle production in the strangeness sector with respect to the non-strange one. Read More