Nuclear Theory Publications (50)

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Nuclear Theory Publications

Large baryon density fluctuations are expected to appear in the matter produced in relativistic heavy-ion collisions if it undergoes a first-order phase transition from the quark-gluon plasma to the hadronic matter. In the case that the density fluctuations can survive final-state interactions during the hadronic evolution and persist until the kinetic freeze-out, they then provide a unique probe to the critical endpoint (CEP), at which the first-order phase transition changes to a smooth crossover, in the QCD phase diagram. In the present study, we demonstrate for the first time that information on the neutron relative density fluctuation $\Delta n= \langle (\delta n)^2\rangle/\langle n\rangle^2$ at freeze-out can be obtained from the yield ratio of light nuclei, i. Read More


There are polarized structure functions $b_{1-4}$ for the spin-1 deuteron. We calculated the leading-twist tensor structure function $b_1$ by using convolution description for the deuteron. We found large differences between our theoretical functions and HERMES experimental data on $b_1$. Read More


We propose a new approach to initialize the hydrodynamic fields such as energy density distributions and four flow velocity fields in hydrodynamic modeling of high-energy nuclear collisions at the collider energies. Instead of matching the energy-momentum tensor or putting initial conditions of quark-gluon fluids at a fixed initial time, we utilize a framework of relativistic hydrodynamic equations with source terms to describe the initial stage. Putting the energy and momentum loss rate of initial partons into the source terms, we obtain hydrodynamic initial conditions dynamically. Read More


Wave-particle duality in quantum mechanics allows for a halo bound state whose spatial extension far exceeds a range of the interaction potential. What is even more striking is that such quantum halos can be arbitrarily large on special occasions. The two examples known so far are the Efimov effect and the super Efimov effect, which predict that spatial extensions of higher excited states grow exponentially and double-exponentially, respectively. Read More


The weak magnetism correction and its uncertainty to nuclear beta-decay play a major role in determining the significance of the reactor neutrino anomaly. Here we examine the common approximation used for one-body weak magnetism in the calculation of fission antineutrino spectra, wherein matrix elements of the orbital angular momentum operator contribution to the magnetic dipole current are assumed to be proportional to those of the spin operator. Although we find this approximation invalid for a large set of nuclear structure situations, we conclude that it is valid for the relevant allowed beta-decays between fission fragments. Read More


We revisit the Glauber model to study the heavy ion reaction cross sections and elastic scattering angular distributions at low and intermediate energies. The Glauber model takes nucleon-nucleon cross sections and nuclear densities as inputs and has no free parameter and thus can predict the cross sections for unknown systems. The Glauber model works at low energies down to Coulomb barrier with very simple modifications. Read More


In this third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon $(g-2)_\mu$, including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of $\gamma^*\gamma^*\to\pi\pi$. Read More


The thermal contribution to the chiral vortical effect is believed to be tied to the axial anomaly in external gravitational fields. We use the universality of the spin-gravity interaction to extend this idea to a wider set of phenomena. We consider the Kubo formula at weak coupling for the spin current of a vector field and derive a novel anomalous effect caused by the medium rotation: chiral vortical effect for bosons. Read More


Magnetic field is unstable in a medium with time-independent chiral conductivity. Owing to the chiral anomaly, the electromagnetic field and the medium exchange helicity which results in time-evolution of the chiral conductivity. Using the fastest growing momentum and helicity state of the vector potential as an ansatz, the time-evolution of the chiral conductivity and magnetic field is solved analytically. Read More


Vector boson-tagged jet production in collisions of heavy nuclei opens new opportunities to study parton shower formation and propagation in strongly interacting matter. It has been argued to provide a golden channel that can constrain the energy loss of jets in the quark-gluon plasma created in heavy ion reactions. We present theoretical results for isolated photon-tagged and $Z^0$ boson-tagged jet production in Pb+Pb collisions with $\sqrt{s_{NN}} = 5. Read More


We analyze the quark-mass dependence of electromagnetic properties of two and three-nucleon states. To that end, we apply the pionless effective field theory to experimental data and numerical lattice calculations which simulate QCD at pion masses of 450~MeV and 806~MeV. At the physical pion mass, we postdict the magnetic moment of helium-3, $\mu_{^3He}=-2. Read More


In this present work, the scattering state solutions of the Spinless Salpeter equation with the Varshni potential model were investigated. The approximate scattering phase shift, normalization constant, bound state energy, wave number and wave function in the asymptotic region were obtained. The behaviour of the phase shift with the two-body mass index {\eta} were discussed and presented. Read More


The first collisions of lead nuclei, delivered by the CERN Large Hadron Collider (LHC) at the end of 2010, at a centre-of-mass energy per nucleon pair $\sqrt{s_{NN}}$ = 2.76 TeV, marked the beginning of a new era in ultra-relativistic heavy-ion physics. Following the Run 1 period, LHC also successfully delivered PbPb collisions at the collision energy $\sqrt{s_{NN}}$ = 5. Read More


The first collisions of lead nuclei, delivered by the CERN Large Hadron Collider (LHC) at the end of 2010, at a centre-of-mass energy per nucleon pair $\sqrt{s_{NN}}$ = 2.76 TeV, marked the beginning of a new era in ultra-relativistic heavy-ion physics. The study of the properties of the produced hot and dense strongly-interacting matter at these unprecedented energies is currently experimentally pursued by all four big LHC experiments, ALICE, ATLAS, CMS, and LHCb. Read More


We derive formulas for the efficiency correction of cumulants with many efficiency bins. The derivation of the formulas is simpler than the previously suggested method, but the numerical cost is drastically reduced from the naive method. From analytical and numerical analyses in simple toy models, we show that the use of the averaged efficiency in the efficiency correction can lead to wrong corrected values, which have larger deviation for higher order cumulants. Read More


In this talk the role of spin and polarization is discussed in experimental search for new excited baryon states and in the study of the internal quark-gluon structure of the proton and neutron. Also the perspective of spin physics at the 12 GeV CEBAF electron accelerator is discussed and what we hope to learn about fundamental properties of hadrons such as their multi-dimensional structure through the momentum and spatial imaging, and about the forces on the quarks in the proton and how quark confinement may be realized through the spatial distribution of such forces. Read More


We analyse the worldline holographic framework for fermions. Worldline holography is based on the observation that in the worldline approach to quantum field theory, sources of a quantum field theory over Mink$_4$ naturally form a field theory over AdS$_5$ to all orders in the elementary fields and in the sources. Schwinger's proper time of the worldline formalism automatically appears with the physical four spacetime dimensions in an AdS$_5$ geometry. Read More


The explosion mechanism of core-collapse supernovae is a long-standing problem in stellar astrophysics. We briefly outline the main contenders for a solution and review recent efforts to model core-collapse supernova explosions by means of multi-dimensional simulations. We discuss several suggestions for solving the problem of missing or delayed neutrino-driven explosions in three-dimensional supernova models, including -- among others -- variations in the microphysics and large seed perturbations in convective burning shells. Read More


We study the real-time evolution of an electron influenced by intense electromagnetic fields using the time-dependent basis light-front quantization (tBLFQ) framework. We focus on demonstrating the non-perturbative feature of the tBLFQ approach through a realistic application of the strong coupling QED problem, in which the electromagnetic fields are generated by an ultra-relativistic nucleus. We calculate transitions of an electron influenced by such electromagnetic fields and we show agreement with light-front perturbation theory when the atomic number of the nucleus is small. Read More


Photoproduction of the $\Lambda^*(1520)$ resonance of spin-parity ${3\over2}^-$ off the proton target is investigated within the Regge framework where the $t$-channel reggeization is applied for the $K(494)+K^*(892)+K_2^*(1430)$ exchanges in the Born amplitude. The present model is based on the two basic ingredients; the one is the minimal gauge prescription for the convergence of the reaction and the other is the role of the $K_2^*$ crucial to agree with high energy data. The cross sections for the total, differential and photon polarization asymmetry are reproduced to compare with existing data. Read More


We present a thermodynamically consistent method by which equations of state based on nonrelativistic potential models can be modified so that they respect causality at high densities, both at zero and finite temperature (entropy). We illustrate the application of the method using the high density phase parametrization of the well known APR model in its pure neutron matter configuration as an example. We also show that, for models with only contact interactions, the adiabatic speed of sound is independent of the temperature in the limit of very large temperature. Read More


During the accretion phase of a core-collapse supernovae, large amplitude turbulence is generated by the combination of the standing accretion shock instability and convection driven by neutrino heating. The turbulence directly affects the dynamics of the explosion, but there is also the possibility of an additional, indirect, feedback mechanism due to the effect turbulence can have upon neutrino flavor evolution and thus the neutrino heating. In this paper we consider the effect of turbulence during the accretion phase upon neutrino evolution, both numerically and analytically. Read More


The transverse momentum ($p_{\rm T}$) spectra in proton-proton collisions at $\sqrt{s}$ = 7 TeV, measured by the ALICE experiment at the LHC are analyzed with a thermodynamically consistent Tsallis distribution. The information about the freeze-out surface in terms of freeze-out volume, temperature and the non-extenisivity parameter, $q$, for $K^{0}_{S}$, $\Lambda+\bar{\Lambda}$, $\Xi^{-}+\bar{\Xi}^{+}$ and $\Omega^{-}+\bar{\Omega}^{+}$ are extracted by fitting the $p_{\rm T}$ spectra with Tsallis distribution function. The freeze-out parameters of these particles are studied as a function of charged particle multiplicity density ($dN_{ch}/d\eta$). Read More


Based on the experimental data released recently by the CLAS Collaboration, the $f_{1}(1285)$ photoproduction off a proton target is investigated in an effective Lagrangian approach. In our model, $s$-channel, $u$-channel, and $t$-channel Born terms are included to calculate the differential cross sections, which are compared with recent CLAS experiment. An interpolating Reggeized treatment is applied to the $t$ channel, and it is found that the $t$-channel contribution is dominant in the $f_1(1285)$ photoproduction and the $u$-channel contribution is responsible to the enhancement at backward angles. Read More


Matrix elements between shifted correlated Gaussians of various potentials with several form-factors are calculated analytically. Analytic matrix elements are of importance for the correlated Gaussian method in quantum few-body physics. Read More


Nuclear cluster physics implicitly assumes a distinction between groups of degrees-of-freedom, that is the (frozen) intrinsic and (explicitly treated) relative cluster motion. We formulate a realistic and practical method to describe the coupled motion of these two sets of degrees-of-freedom. We derive a coupled set of differential equations for the system using the phenomenologically adjusted effective in-medium Skyrme type of nucleon-nucleon interaction. Read More


We investigate the region of the nuclear chart around $A \simeq 70$ from a three-body perspective, where we compute reaction rates for the radiative capture of two protons. One key quantity is here the photon dissociation cross section for the inverse process where two protons are liberated from the borromean nucleus by photon bombardment. We find a number of peaks at low photon energy in this cross section where each peak is located at the energy corresponding to population of a three-body resonance. Read More


We systematically study the large-$q_T$ (or small-$b$) matching of transverse momentum dependent (TMD) distributions to the twist-2 integrated parton distributions. Performing operator product expansion for a generic TMD operator at the next-to-leading order (NLO) we found the complete set of TMD distributions that match twist-2. These are unpolarized, helicity, transversity, pretzelosity and linearly polarized gluon distributions. Read More


The universal behavior of a three-boson system close to the unitary limit is encoded in a simple dependence of many observables in terms of few parameters. For example the product of the three-body parameter $\kappa_*$ and the two-body scattering length $a$, $\kappa_* a$ depends on the angle $\xi$ defined by $E_3/E_2=\tan^2\xi$. A similar dependence is observed in the ratio $a_{AD}/a$ with $a_{AD}$ the boson-dimer scattering length. Read More


[Background] The neutrino-nucleus ($\nu A$) cross section is a major source of systematic uncertainty in neutrino-oscillation studies. A precise $\nu A$ scattering model, in which multinucleon effects are incorporated, is pivotal for an accurate interpretation of the data. [Purpose] In $\nu A$ interactions, meson-exchange currents (MECs) can induce two-nucleon ($2N$) knockout from the target nucleus, resulting in a two-particle two-hole (2p2h) final state. Read More


Two variational quartet models previously employed in a treatment of pairing forces are extended to the case of a general two-body interaction. One model approximates the nuclear states as a condensate of identical quartets with angular momentum $J=0$ and isospin $T=0$ while the other let these quartets to be all different from each other. With these models we investigate the role of alpha-like quartet correlations both in the ground state and in the lowest $J=0$, $T=0$ excited states of even-even $N=Z$ nuclei in the $sd$-shell. Read More


We include a resummation of large transverse momentum logarithms in the next-to-leading order (NLO) Balitsky-Kovchegov equation. The resummed evolution equation is shown to be stable, the evolution speed being significantly reduced by NLO corrections. The contributions from NLO terms that are not enhanced by large logarithms are found to be numerically important close to phenomenologically relevant initial conditions. Read More


We analyse the renormalization of the of two-nucleon interaction with multiple subtractions in peripheral waves considering two chiral forces at N3LO. Phase shifts at low energies are then computed with several subtraction points below \mu = 10 / fm. We show that for most peripheral waves the phase shifts have nearly no dependence on the renormalization scale. Read More


An analytic toy model is proposed for the nuclear elastic amplitude of high energy scattering of protons. The diffraction cone and the dip/bump structure of the differential cross section are qualitatively reproduced and their interrelation is revealed with the help of two energy dependent parameters only. The analytic estimates give some insight into the role of the parameters, impose definite requirements on the accuracy of experimental measurements at present energies and lead to the suggestions about the asymptotic behavior. Read More


We study the QCD phase diagram using a non-local SU(3) NJL model with vector interactions among quarks. We analyze several thermodynamic quantities such as entropy and specific heat, and study the influence of vector interactions on the thermodynamic properties of quark matter. Upon imposing electric charge neutrality and baryon number conservation on the field equations, we compute models for the equation of state of the inner cores of proto-neutron stars providing a non-local treatment of quark matter for astrophysics. Read More


In order for a Sullivan-like process to provide reliable access to a meson target as $t$ becomes spacelike, the pole associated with that meson should remain the dominant feature of the quark-antiquark scattering matrix and the wave function describing the related correlation must evolve slowly and smoothly. Using continuum methods for the strong-interaction bound-state problem, we explore and delineate the circumstances under which these conditions are satisfied: for the pion, this requires $-t \lesssim 0.6\,$GeV$^2$, whereas $-t\lesssim 0. Read More


New high-precision total and differential cross sections for $\eta$ and $\eta'$ photoproduction on the proton obtained by the A2 Collaboration at the Mainz Microtron are presented. The data for $\eta$ photoproduction demonstrate a cusp at the energy W$\sim$1.9~GeV. Read More


The time-dependent generator coordinate method with the gaussian overlap approximation (TDGCM+GOA) formalism is applied to describe the fission of $^{252}$Cf. We perform analysis of fission from the initial states laying in the energetic range from the ground state to the state located 4 MeV above the fission barrier. The fission fragment mass distributions, obtained for different parity, energy of levels and types of mixed states, are calculated and compared with experimental data. Read More


The production mechanisms of open strangeness ($K^*$) and open charm ($D^*$) vector mesons in $\pi^- p$ scattering, namely, $\pi^- +p \to K^{*0} + \Lambda$ and $\pi^- + p \to D^{*-} + \Lambda_c^+$, are investigated within the modified quark-gluon string model. In order to identify the major reaction mechanisms, we consider the subsequent decays of the produced vector mesons into two pseudoscalar mesons, i.e. Read More


For the last decades, multiple international facilities have developed Radioactive-Ion Beams (RIB) to measure reaction processes including exotic nuclei. These measurements coupled with an accurate theoretical model of the reaction enable us to infer information about the structure of these nuclei. The partial-wave expansion provides a precise description of two-body collisions but has a large computational cost. Read More


The polarization of direct photons produced in an ultrarelativistic heavy-ion collision reflects the momentum anisotropy of the quark-gluon plasma created in the collision. This paper presents a general framework, based on the photon spectral functions in the plasma, for analyzing the angular distribution and thus the polarization of dileptons in terms of the plasma momentum anisotropies. The rates of dilepton production depend, in general, on four independent spectral functions, corresponding to two transverse polarizations, one longitudinal polarization, and -- in plasmas in which the momentum anisotropy is not invariant under parity in the local rest frame of the matter -- a new spectral function, $\rho_n$, related to the anisotropy direction in the collision. Read More


Considering the mass constraint from the resent pulsar observations, we study the properties of neutron stars including hyperons and quarks explicitly. Using the chiral quark-meson coupling model with relativistic Hartree-Fock approximation, the equation of state (EoS) for hadronic matter is calculated by taking into account the strange ($\sigma^{\ast}$ and $\phi$) mesons as well as the light non-strange ($\sigma$, $\omega$, $\vec{\rho}$, and $\vec{\pi}$) mesons in SU(3) flavor symmetry. On the other hand, the EoS for quark matter is constructed with the simple MIT bag or the flavor-SU(3) Nambu-Jona-Lasinio model, and we investigate the effect of the hadron-quark coexistence on the neutron-star properties, imposing smooth crossover or Gibbs criterion for chemical equilibrium. Read More


The modification of hard jets in the Quark Gluon Plasma (QGP) is studied using the MATTER event generator. Based on the higher twist formalism of energy loss, the MATTER event generator simulates the evolution of highly virtual partons through a medium. These partons sampled from an underlying PYTHIA kernel undergo splitting through a combination of vacuum and medium induced emission. Read More


Using the experimental data from the ALICE program on the centrality dependence of the transverse momentum ($p_T$) spectra in Pb+Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV, we show that the double-Tsallis distribution and the generalized Fokker-Plank (FP) solution can not describe the spectra of pions, kaons and protons from central to peripheral collisions in the entire $p_T$ region, simultaneously. Hence, a new two-component distribution, which is a hydrodynamic extension of the generalized FP solution accounting for the collective motion effect in heavy-ion collisions, is proposed in order to reproduce all the particle spectra. Read More


We present a systematic analysis of transverse momentum $(p_{T})$ spectra of the strange hadrons in different multiplicity events produced in pp collision at $\sqrt{s}$ = 7 TeV, pPb collision at $\sqrt{s_{NN}}$ = 5.02 TeV and PbPb collision at $\sqrt{s_{NN}}$ = 2.76 TeV. Read More


We study the production and evolution of charm and bottom quarks in hot partonic medium produced in heavy ion collisions. The heavy quarks loose energy in the medium which is reflected in the transverse momentum spectra of heavy mesons. The collisional energy loss of heavy quarks has been calculated using QCD calculations. Read More


The main focus of this article is to obtain various transport coefficients for a hot QCD medium that is produced while colliding two heavy nuclei ultra-relativistically. As the hot QCD medium follows dissipative hydrodynamics while undergoing space-time evolution, the knowledge of the transport coefficients such as thermal conductivity, electrical conductivity, shear and bulk viscosities are essential to understand the underlying physics there. The approach adopted here is semi-classical transport theory. Read More


We study the non-radial oscillation modes of strange quark stars with a homogeneous core and a crust made of strangelets. Using a 2-component equation of state (core+crust) for strange quark stars that can produce stars as heavy as 2 solar masses, we identify the high-frequency l=2 spheroidal (f, p) in Newtonian gravity, using the Cowling approximation. The results are compared to the case of homogeneous compact stars such as polytropic neutron stars, as well as bare strange stars. Read More


In this work, we study the effects of different magnetic field configurations in neutron stars described by a many-body forces formalism (MBF model). The MBF model is a relativistic mean field formalism that takes into account many-body forces by means of a meson field dependence of the nuclear interaction coupling constants. We choose the best parametrization of the model that reproduces nuclear matter properties at saturation and also describes massive neutron stars. Read More


In this work, we study the effects of strong magnetic field configurations on the population of neutron stars. The stellar matter is described within a relativistic mean field formalism which considers many-body force contributions in the scalar couplings. We choose the parametrization of the model that reproduces nuclear matter properties at saturation and also describes massive hyperon stars. Read More