Nuclear Theory·nucl-th

Tuesday·May 3, 2022

15 papers—9 primary·6 cross-listed

01
Perturbative approaches in relativistic kinetic theory and the emergence of first-order hydrodynamics
Gabriel S. Rocha🇧🇷 · Gabriel S. Denicol🇧🇷 · Jorge Noronha🇺🇸
Hydrodynamics can be formulated in terms of a perturbative series in derivatives of the temperature, chemical potential, and flow velocity around an equilibrium state. Different formulations for this series have been proposed over the years, which consequently led to the development of various hydrodynamic theories. In this work, we discuss the relativistic generalizations of the perturbative expansions put forward by Chapman and Enskog, and Hilbert, using general matching conditions in kinetic theory. This allows us to describe, in a comprehensive way, how different out-of-equilibrium definitions for the hydrodynamic fields affect the development of the hydrodynamic perturbative series. We provide a perturbative method for systematically deriving the hydrodynamic formulation recently proposed by Bemfica, Disconzi, Noronha, and Kovtun (BDNK) from relativistic kinetic theory. The various transport coefficients that appear in BDNK (at first-order) are explicitly computed using a new formulation of the relaxation time approximation for the Boltzmann equation. Assuming Bjorken flow, we also determine the hydrodynamic attractors of BDNK theory and compare the overall hydrodynamic evolution obtained using this formulation with that generated by the Israel-Stewart equations of motion and also kinetic theory.
nucl-thhep-phhep-thPRD(2022)·46 citations
02
Implications of the isobar run results for chiral magnetic effect in heavy ion collisions
Dmitri E. Kharzeev🇺🇸 · Jinfeng Liao🇺🇸 · Shuzhe Shi🇺🇸
Chiral magnetic effect (CME) is a macroscopic transport phenomenon induced by quantum anomaly in the presence of chiral imbalance and an external magnetic field. Relativistic heavy ion collisions provide the unique opportunity to look for CME in a non-Abelian plasma, where the chiral imbalance is created by topological transitions similar to those occurring in the Early Universe. The isobar run at Relativistic Heavy Ion Collider was proposed as a way to separate the possible CME signal driven by magnetic field from the background. The first blind analysis results from this important experiment have been recently released by the STAR Collaboration. Under the pre-defined assumption of identical background in RuRu and ZrZr, the results are inconsistent with the presence of CME, as well as with all existing theoretical models (whether including CME or not). However the observed difference of backgrounds must be taken into account before any physical conclusion is drawn. In this paper, we show that once the observed difference in hadron multiplicity and collective flow are quantitatively taken into account, the STAR results could be consistent with a finite CME signal contribution of about $(6.8 \pm 2.6) %$ .
nucl-thhep-phnucl-exPRC(2022)·46 citations
03
Rate and ellipticity of dilepton production in a magnetized quark-gluon plasma
Xinyang Wang🇨🇳 · Igor A. Shovkovy🇺🇸
Using the Landau-level representation for the imaginary part of the photon polarization tensor, we derive an explicit expression for the dilepton production rate from a hot quark-gluon plasma in a quantizing background magnetic field. We study in detail the dependence of the production rate on the dilepton invariant mass and the transverse momentum at mid-rapidity. We also investigate the angular dependence and ellipticity of dilepton emission. By comparing the result with the zero-field Born approximation, we find that the magnetic field leads to a strong enhancement of the dilepton rate at small values of the invariant mass ( $M ≲ ∣ e B ∣$ ). In the same kinematic region, the dilepton production is characterized by a sizable ellipticity. At large values of the dilepton invariant mass ( $M ≳ ∣ e B ∣$ ), the role of the magnetic field decreases and the result approaches the isotropic zero-field Born rate. By investigating the dependence of ellipticity on the transverse momentum, we argue that the future measurements of dilepton rate in the region of small invariant masses can constrain the magnetic field produced in heavy-ion collisions.
nucl-thhep-phPRD(2022)·34 citations
04
Isotopic Production Cross Sections in Proton- $^{12}$ C Interactions for Energies from 10 MeV/N to 100 GeV/N
Francis A. Cucinotta🇺🇸 · Sungmin Pak🇺🇸
Proton interactions with $^{12}$ C nuclei are a frequent nuclear interaction leading to secondary radiation in tissues for space radiation and cancer therapy with protons or $^{12}$ C beams. The fragmentation of $^{12}$ C by protons produces a large number of heavy ion (A>4) target or projectile fragments often with high ionization density. Here we develop an analytical model of energy dependent proton- $^{12}$ C cross sections for isotopic nuclei production. Using experimental data and a 2nd order optical model an accurate formula for the p- $^{12}$ C absorption cross section from <10 MeV/n to >10 GeV/N is obtained. The energy dependence of the elemental and isotopic cross sections is modeled as multiplicities scaled to absorption cross section with average isotopic fractions estimated from experimental data. We show that this approach results in an accurate analytic formula model over the full energy range in Hadron therapy and space radiation protection studies.
nucl-thNucl.Instrum.Meth.B(2023)·1 citation
05
Rotating Hybrid Stars with Color-Flavor-Locked Quark Matter
Debashree Sen🇮🇳 · Gargi Chaudhuri🇮🇳
In the present work we have achieved phase transition from $β$ stable hadronic matter to color-flavor locked (CFL) quark matter with Maxwell construction. The hybrid equation of state (EoS), obtained for different values of bag pressure $B$ and gap parameter $Δ$ , have been used to compute the speed of sound in hybrid star (HS) matter. The structural properties of the HSs in both static and rotating conditions have been calculated in the light of various constraints from different astrophysical and empirical perspectives. The effects of $B$ and $Δ$ on the EoS and structural properties have been investigated. At a certain density, shortly after phase transition, the HSs become unstable. In static conditions, the mass-radius solutions satisfy the constraints from GW190425, NICER experiment for PSR J0030+0451 and PSR J0740+6620 and from massive pulsars like PSR J0348+0432 and PSR J0740+6620. In rapidly rotating conditions at Kepler frequency, the constraints on maximum mass from the secondary component of GW190814 and that on rotational frequency from fast pulsars like PSR B1937+21 and PSR J1748-2446ad are all satisfied. In slowly rotating conditions, the universality relations in terms of normalized moment of inertia also hold quite well for most of our HS configurations.
nucl-thJ.Phys.G(2022)·9 citations
06
Investigating Possible Existence of Hyper-Heavy Nuclei in Neutron Star Environment
M. Veselsky · V. Petousis · Ch. C. Moustakidis · G. A. Souliotis · A. Bonasera
The synthesis of hyper-heavy elements is investigated under conditions simulating neutron star environment. The Constrained Molecular Dynamics (CoMD) approach is used to simulate low energy collisions of extremely n-rich nuclei. A new type of the fusion barrier due to a "neutron wind" is observed when the effect of neutron star environment (screening of Coulomb interaction) is introduced implicitly. When introducing also a background of surrounding nuclei, the nuclear fusion becomes possible down to temperatures of 10 $^{8}$ K and synthesis of extremely heavy and n-rich nuclei appears feasible. A possible existence of hyper-heavy nuclei in a neutron star environment could provide a mechanism of extra coherent neutrino scattering or an additional mechanism, resulting in X-ray burst or a gravitational wave signal and, thus, becoming another crucial process adding new information to the suggested models on neutron star evolution.
nucl-thastro-ph.HEnucl-exPRC(2022)·3 citations
07
Quantum computing of the $^{6}$ Li nucleus via ordered unitary coupled clusters
Oriel Kiss🇨🇭 · Michele Grossi🇨🇭 · Pavel Lougovski🇺🇸 · Federico Sanchez🇨🇭 · Sofia Vallecorsa🇨🇭 · Thomas Papenbrock🇺🇸
The variational quantum eigensolver (VQE) is an algorithm to compute ground and excited state energy of quantum many-body systems. A key component of the algorithm and an active research area is the construction of a parametrized trial wavefunction -- a so called variational ansatz. The wavefunction parametrization should be expressive enough, i.e. represent the true eigenstate of a quantum system for some choice of parameter values. On the other hand, it should be trainable, i.e. the number of parameters should not grow exponentially with the size of the system. Here, we apply VQE to the problem of finding ground and excited state energies of the odd-odd nucleus $^{6}$ Li. We study the effects of ordering fermionic excitation operators in the unitary coupled clusters ansatz on the VQE algorithm convergence by using only operators preserving the $J_{z}$ quantum number. The accuracy is improved by two order of magnitude in the case of descending order. We first compute optimal ansatz parameter values using a classical state-vector simulator with arbitrary measurement accuracy and then use those values to evaluate energy eigenstates of $^{6}$ Li on a superconducting quantum chip from IBM. We post-process the results by using error mitigation techniques and are able to reproduce the exact energy with an error of 3.8% and 0.1% for the ground state and for the first excited state of $^{6}$ Li, respectively.
nucl-thPRC(2022)·92 citations
08
Theoretical study of the $γ d \to π^{0} η d$ reaction
A. Martinez Torres🇧🇷 · K. P. Khemchandani🇧🇷 · E. Oset🇪🇸
We have done a theoretical study of the $γ d \to π^{0} η d$ reaction starting with a realistic model for the $γ N \to π^{0} η N$ reaction that reproduces cross sections and polarization observables at low energies and involves the $γ N \to Δ (1700) \to η Δ (1232) \to η π^{0} N$ process. For the coherent reaction in the deuteron we considered the impulse approximation together with the rescattering of the pions and the $η$ on a different nucleon than the one where they are produced. We found this second mechanism very important since it helps share between two nucleons the otherwise large momentum transfer of the reaction. Other contributions to the $γ d \to π^{0} η d$ reaction, involving the $γ N \to π^{\pm} π^{0} N^{'}$ process, followed by the rescattering of the $π^{\pm}$ with another nucleon to give $η$ and a nucleon, have also been included. We find a natural explanation, tied to the dynamics of our model, for the shift of the $η - d$ mass distribution to lower invariant masses, and of the $π^{0} - d$ mass distribution to larger invariant masses, compared to a phase space calculation. We also study theoretical uncertainties related to the large momenta of the deuteron wave function involved in the process as well as to the couplings present in the model. Striking differences are found with the experimental angular distribution and further theoretical investigations might be necessary.
nucl-thhep-phnucl-exPRC(2023)·10 citations
09
Pre-hydrodynamic evolution and its impact on quark-gluon plasma signatures
Dananjaya Liyanage🇺🇸 · Derek Everett🇺🇸 · Chandrodoy Chattopadhyay🇺🇸 · Ulrich Heinz🇺🇸
State-of-the-art hydrodynamic models of heavy-ion collisions have considerable theoretical model uncertainties in the description of the very early pre-hydrodynamic stage. We add a new computational module, K $_{T}$ Iso, that describes the pre-hydrodynamic evolution kinetically, based on the relativistic Boltzmann equation with collisions treated in the Isotropization Time Approximation. As a novelty, K $_{T}$ Iso allows for the inclusion and evolution of initial-state momentum anisotropies. To maintain computational efficiency K $_{T}$ Iso assumes strict longitudinal boost invariance and allows collisions to isotropize only the transverse momenta. We use it to explore the sensitivity of hadronic observables measured in relativistic heavy-ion collisions to initial-state momentum anisotropies and microscopic scattering during the pre-hydrodynamic stage.
nucl-thphysics.comp-phPRC(2022)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE