Nuclear Theory·nucl-th

Monday·January 2, 2023

12 papers—6 primary·6 cross-listed

01
Properties of $^{208}$ Pb predicted from the relativistic equation of state in the full Dirac space
Hui Tong · Jing Gao · Chencan Wang · Sibo Wang
Relativistic Brueckner-Hartree-Fock (RBHF) theory in the full Dirac space allows one to determine uniquely the momentum dependence of scalar and vector components of the single-particle potentials. In order to extend this new method from nuclear matter to finite nuclei, as a first step, properties of $^{208}$ Pb are explored by using the microscopic equation of state for asymmetric nuclear matter and a liquid droplet model. The neutron and proton density distributions, the binding energies, the neutron and proton radii, and the neutron skin thickness in $^{208}$ Pb are calculated. In order to further compare the charge densities predicted from the RBHF theory in the full Dirac space with the experimental charge densities, the differential cross sections and the electric charge form factors in the elastic electron-nucleus scattering are obtained by using the phase-shift analysis method. The results from the RBHF theory are in good agreement with the experimental data. In addition, the uncertainty arising from variations of the surface term parameter $f_{0}$ in the liquid droplet model is also discussed.
nucl-thPRC(2023)·8 citations
02
Ridge regression for minimizing the couplings of hyperon resonances in the $K^{+} Λ$ photoproduction
Dimitrios Petrellis🇨🇿 · Dalibor Skoupil🇨🇿
We employed the isobar model for investigating the $K^{+} Λ$ photoproduction process. We paid special attention to the recent CLAS polarization data and enhanced the $χ^{2}$ minimization by adding a penalty term. Without changing the set of included resonances used by the model, this technique known as Ridge regression leads to reduced couplings that in previous studies acquired unreasonably large values. As a result, we have arrived at a much more robust model with hyperon couplings which are reduced to more physical values. This model serves us to extract valuable information on the background to the $K^{+} Λ$ photoproduction and particularly on the role of various hyperon resonances. The set of the nucleon resonances is the same with respect to previous fits but their role may have changed due to different couplings which they acquire in the present fit.
nucl-thPRC(2023)·9 citations
03
Charged-particle bound states in periodic boxes
Hang Yu · Sebastian König · Dean Lee
We consider the binding energy of a two-body system with a repulsive Coulomb interaction in a finite periodic volume. We define the finite-volume Coulomb potential as the usual Coulomb potential, except that the distance is defined as the shortest separation between the two bodies in the periodic volume. We investigate this problem in one and three-dimensional periodic boxes and derive the asymptotic behavior of the volume dependence for bound states with zero angular momentum in terms of Whittaker functions. We benchmark our results against numerical calculations and show how the method can be used to extract asymptotic normalization coefficients for charged-particle bound states. The results we derive here have immediate applications for calculations of atomic nuclei in finite periodic volumes for the case where the leading finite-volume correction is associated with two charged clusters.
nucl-thPRL(2023)·10 citations
04
Global angular momentum generation in heavy-ion reactions within a hadronic transport approach
Nils Sass🇩🇪 · Marco Müller🇩🇪 · Oscar Garcia-Montero🇩🇪 · Hannah Elfner🇩🇪
In 2017, the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC) has measured finite global angular momentum in heavy-ion collisions through a spin polarization measurement of $Λ$ hyperons. This measurement revealed a high angular momentum of the heavy ions and provided experimental evidence for vorticity in the quark-gluon plasma (QGP) for the first time. In order to investigate the underlying mechanisms, a dynamic description of the transfer of angular momentum is required. In this work, the microscopic non-equilibrium transport approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) is applied to study the generation of global angular momentum by the interaction of two nuclei. As SMASH provides access to the whole phase-space evolution of every particle at any given time, it allows to assess the fraction of angular momentum generated in the fireball by all participants. We confirm the previous modeling by Becattini \textit{et al} within a geometric Glauber model approach, which found that the angular momentum transfer reaches a unique maximum in mid-central collisions during time evolution. The corresponding impact parameter is around $b = 4 - 6$ fm for all beam energies from $s_{NN} = 2.41 - 200$ GeV. Even though angular momentum is not conserved locally in the transport approach a priori, we identify the contributions to the conservation violation and propose optimal setups for different energy regimes that recover conservation, based upon the test particle method and the treatment of Fermi motion. Furthermore, the system size and centrality dependence are investigated.
nucl-thhep-phPRC(2023)·15 citations
05
Relativistic approach to the nuclear breathing mode
Elena Litvinova
Microscopic theory of the nuclear response based on the relativistic meson-nucleon Lagrangian is applied to the description of the isoscalar giant monopole resonance (ISGMR) in a variety of nuclear systems. It is shown that the parameter-free inclusion of beyond-mean-field correlations of the quasiparticle-vibration coupling (qPVC) type in the leading approximation allows for a simultaneous realistic description of the ISGMR in nuclei of lead, tin, zirconium, and nickel mass regions, which is difficult on the mean-field level. The calculations employ the finite-range effective meson-nucleon interaction, which, in combination with the qPVC, has consistently demonstrated the ability to reliably describe many other nuclear structure phenomena. Systematic calculations of the isoscalar monopole response for nickel isotopes help reveal the central role of the coupling between the ISGMR and the low-energy quadrupole states in the placement of the ISGMR centroids.
nucl-thastro-ph.SRnucl-exPRC(2023)·27 citations
06
Effect of color superconductivity on the mass of hybrid neutron stars in an effective model with pQCD asymptotics
David Blaschke🇵🇱 · Udita Shukla🇵🇱 · Oleksii Ivanytskyi🇵🇱 · Simon Liebing🇩🇪
The effective cold quark matter model by Alford, Braby, Paris and Reddy (ABPR) is used as a tool for discussing the effect of the size of the pairing gap in three-flavor (CFL) quark matter on the maximum mass of hybrid neutron stars (NSs). This equation of state (EOS) has three parameters which we suggest to determine by comparison with a nonlocal NJL model of quark matter in the nonperturbative domain. We show that due to the momentum dependence of the pairing which is induced by the nonlocality of the interaction, the effective gap parameter in the EOS model is well approximated by a constant value depending on the diquark coupling strength in the NJL model Lagrangian. For the parameter $a_{4} = 1 - 2 α_{s} / π$ a constant value below about \num{0.4} is needed to explain hybrid stars with $M_{max} ≳ 2.0 M_{⊙}$ , which would translate to an effective constant $α_{s} \sim 1$ . The matching point with a running coupling at the 1-loop $β$ function level is found to lie outside the range of chemical potentials accessible in NS interiors. A dictionary is provided for translating the free parameters of the nlNJL model to those of the ABPR model. Both models are shown to be equivalent in the nonperturbative domain but the latter one allows to quantify the transition to the asymptotic behaviour in accordance with perturbative QCD. We provide constraints on parameter sets that fulfill the $2 M_{⊙}$ mass constraint for hybrid NSs, as well as the low tidal deformability constraint from GW170817 by a softening of the EOS on the hybrid NS branch with an early onset of deconfinement at $M_{onset} < 1.4 M_{⊙}$ . We find that the effective constant pairing gap should be around 100 MeV but not exceed values of about 130 MeV because a further increase of the gap would entail a softening of the EOS and contradict the $2 M_{⊙}$ mass constraint.
nucl-thastro-ph.HEhep-phPRD(2023)·27 citations
07
Reduced basis emulation of pairing in finite systems
Virgil V. Baran · Denis R. Nichita
In recent years, reduced basis methods (RBMs) have been adapted to the many-body eigenvalue problem and they have been used, largely in nuclear physics, as fast emulators able to bypass expensive direct computations while still providing highly accurate results. This work is meant to show that the RBM is an efficient and accurate emulator for the strong correlations induced by the pairing interaction in a variety of finite systems like ultrasmall superconducting grains, interacting topological superfluids and mesoscopic hybrid superconductor-semiconductor devices, all of which require an expensive, beyond-mean-field, particle-number conserving description. These systems are modelled by the number-conserving Richardson pairing Hamiltonian and its appropriate generalizations. Their ground state is solved for exactly using the Density Matrix Renormalization Group. The reduced basis is assembled iteratively from a small number of exact ground state vectors, well-chosen from across the relevant parameter space using a fast estimate of the emulation error and a greedy local optimization algorithm. The reduced basis emulation is found to accurately describe the weak-to-strong pairing cross-over in small grains, the third-order topological phase transition of the interacting Richardson-Kitaev chain, and the complex charge stability diagram of a hybrid quantum dot - superconductor device. RBMs are thus confirmed to be cheap and accurate emulators for the widely encountered superconducting phenomena. Capable of providing orders of magnitude computational speed-up with respect to approaches based only on traditional many-body solvers, they open new possibilities in building and solving models of interacting many-body systems and in better interfacing them with experimental design and data analysis.
↳ cond-mat.supr-concond-mat.mes-hallcond-mat.str-elnucl-thPRB(2023)·11 citations
08
Connecting Euclidean to light-cone correlations: From flavor nonsinglet in forward kinematics to flavor singlet in non-forward kinematics
Fei Yao🇨🇳 · Yao Ji🇩🇪 · Jian-Hui Zhang🇨🇳
We present a unified framework for the perturbative factorization connecting Euclidean correlations to light-cone correlations. Starting from nonlocal quark and gluon bilinear correlators, we derive the relevant hard-matching kernel up to the next-to-leading-order, both for the flavor singlet and non-singlet combinations, in non-forward and forward kinematics, and in coordinate and momentum space. The results for the generalized distribution functions (GPDs), parton distribution functions (PDFs), and distribution amplitudes (DAs) are obtained by choosing appropriate kinematics. The renormalization and matching are done in a state-of-the-art scheme. We also clarify some issues raised on the perturbative matching of GPDs in the literature. Our results provide a complete manual for extracting all leading-twist GPDs, PDFs as well as DAs from lattice simulations of Euclidean correlations in a state-of-the-art strategy, either in coordinate or in momentum space factorization approach.
↳ hep-phhep-latnucl-thJHEP(2023)·38 citations
09
Resurgence for the non-conformal Bjorken flow with Fermi-Dirac and Bose-Einstein statistics
Syo Kamata🇵🇱
We consider resurgence for the nonconformal Bjorken flow with Fermi-Dirac and Bose-Einstein statistics on the extended relaxation-time approximation. We firstly consider full formal transseries expanded around the equilibrium and then construct the resurgent relation by looking to the structure of Borel transformed ODEs. We form a conjecture of the resurgent relation based on the considerations that Stokes constants constituting of the resurgent relation originate only from singularities of dissipative variables on the Borel plane and that the other variables such as temperature and chemical potential become Borel nonsummable through nonlinear terms with the dissipative variables. We numerically check the conjecture for fundamental variables by explicitly evaluating values of the dominant Stokes constant depending on initial conditions and a particle mass. We also make comments on some issues related to transseries structure and resurgence such as the case of broken $U (1)$ symmetry, the massless case, generalized relaxation-time, and attractor solution.
↳ hep-thmath-phmath.MPnucl-thPRD(2024)·7 citations
10
Spin-1 quarkonia in a rotating frame and their spin contents
HyungJoo Kim🇰🇷 · Sungtae Cho🇰🇷 · Su Houng Lee🇰🇷
We propose a new way of studying the spin content of a hadron by looking at its response in a rotating frame. By collecting all responses of quarks and gluons in a rotating frame, we describe the spin-rotation coupling of spin-1 quarkonia and thereby reveal their spin contents in a relativistic formalism. We demonstrate that both the perturbative and non-perturbative contributions in the operator product expansion follow a universal formula that identifies the spin-rotation coupling with unit strength. This allows us to recognize the total spin-1 of the vector and axial vector quarkonia in terms of the total angular momentum of quarks and gluons. Specifically, we find the spin contents of $J / ψ$ , $χ_{c 1}$ , $Υ (1 S)$ , and $χ_{b 1}$ are slightly different from the naive quark model picture. For example, the $J / ψ$ is traditionally considered as an S-wave particle, but we find quarks do not carry all of the total spin.
↳ hep-phhep-exnucl-exnucl-thPLB(2023)·6 citations
11
On the correlation functions in stable first-order relativistic hydrodynamics
Navid Abbasi🇨🇳 · Ali Davody🇺🇸 · Sara Tahery🇨🇳
First-order relativistic conformal hydrodynamics in a general (hydrodynamic) frame is characterized by a shear viscosity coefficient and two UV-regulator parameters. Within a certain range of these parameters, the equilibrium is stable and propagation is causal. In this work we study the correlation functions of fluctuations in this theory. We first compute hydrodynamic correlation functions in the linear response regime. Then we use the linear response results to explore the analytical structure of response functions beyond the linear response. A method is developed to numerically calculate the branch cut structure from the well-known Landau equations. We apply our method to the shear channel and find the branch cuts of a certain response function, without computing the response function itself. We then solve the Landau equations analytically and find the threshold singularities of the same response function. Using these results, we achieve the leading singularity in momentum space, by which, we find the long-time tail of the correlation function. The results turn out to be in complete agreement with the loop calculations in effective field theory.
↳ hep-thhep-phnucl-thPRD(2024)·15 citations
12
Pseudogap effects in the strongly correlated regime of the two-dimensional Fermi gas
S. Ramachandran · S. Jensen · Y. Alhassid
The two-species Fermi gas with attractive short-range interactions in two spatial dimensions provides a paradigmatic system for the understanding of strongly correlated Fermi superfluids in two dimensions. It is known to exhibit a BEC-BCS crossover as a function of $ln (k_{F} a)$ , where $a$ is the scattering length, and to undergo a Berezinskii-Kosterlitz-Thouless superfluid transition below a critical temperature $T_{c}$ . However, the extent of a pseudogap regime in the strongly correlated regime of $ln (k_{F} a) \sim 1$ , in which pairing correlations persist above $T_{c}$ , remains largely unexplored with controlled theoretical methods. Here we use finite-temperature auxiliary-field quantum Monte Carlo (AFMC) methods on discrete lattices in the canonical ensemble formalism to calculate thermodynamical observables in the strongly correlated regime. We extrapolate to continuous time and the continuum limit to eliminate systematic errors and present results for particle numbers ranging from $N = 42$ to $N = 162$ . We estimate $T_{c}$ by a finite-size scaling analysis, and observe clear pseudogap signatures above $T_{c}$ and below a temperature $T^{*}$ in both the spin susceptibility and free-energy gap. We also present results for the contact, a fundamental thermodynamic property of quantum many-body systems with short-range interactions.
↳ cond-mat.quant-gascond-mat.supr-conhep-latnucl-thPRL(2024)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE