Nuclear Theory·nucl-th
11 papers—3 primary·8 cross-listed
A brief overview of the recent developments concerning theoretical description of event-by-event fluctuations in heavy-ion collisions is presented, with an emphasis on the role of exact conservation laws and calculations based on relativistic hydrodynamics.
Li-Yong Zhang · Jian-Jun He · Motohiko Kusakabe · Zhen-Yu He · Toshitaka Kajino
A new thermonuclear O(,)O rate is derived based on a complete calculation of the direct-capture (DC) and resonant-capture contributions, for a temperature region up to 2 GK of astrophysical interest. We have firstly calculated the DC and subthreshold contributions in the energy region up to 1 MeV, and estimated the associated uncertainties by a Monte-Carlo approach. It shows that the present rate is remarkably larger than that adopted in the JINA REACLIB in the temperature region of 0.01 2 GK, by up to a factor of 80. The astrophysical impacts of our rate have been examined in both -process and -process models. In our main -process model which simulates flash-driven convective mixing in metal deficient asymptotic giant branch stars, both O and F abundances in interpulse phases are enhanced dramatically by factors of -- due to the new larger O(,)O rate. It shows, however, that this reaction hardly affects the weak -process in massive stars since the O abundance never becomes significantly large in the massive stars. For the -process nucleosynthesis, we have studied impacts of our rate in both the collapsar and neutron burst models, and found that the effect can be neglected, although an interesting "loophole" effect is found owing to the enhanced new rate, which significantly changes the final nuclear abundances if fission recycling is not involved in the model, however, these significant differences are almost completely washed out if the fission recycling is considered.
A formula to calculate the quantum fluctuations of energy in small subsystems of a hot and relativistic gas is derived. We find an increase in fluctuations for subsystems of small sizes, but we agrees with the energy fluctuations in the canonical ensemble if the size is large enough. Not only one can use our expression to find the limit of the concepts of energy density or fluid element in connection to relativistic heavy-ion collisions, but also in other areas of physics where one studies matter with high temperature and velocity.
Yu Fu🇨🇳 · Jacopo Ghiglieri🇫🇷 · Shahin Iqbal🇵🇰 · Aleksi Kurkela🇳🇴
We provide the first next-to-leading-order (NLO) weak-coupling description of the thermalization process of far-from-equilibrium systems in non-abelian gauge theory. We study isotropic systems starting from either over- or under-occupied initial conditions and follow their time evolution towards thermal equilibrium by numerically solving the QCD effective kinetic theory at NLO accuracy. We find that the NLO corrections remain well under control for a wide range of couplings and that the overall effect of NLO corrections is to reduce the time needed to reach thermal equilibrium in the systems considered.
Swagato Mukherjee🇺🇸 · Fabian Rennecke🇺🇸 · Vladimir V. Skokov🇺🇸
For theories plagued with a sign problem at finite density, a Taylor expansion in the chemical potential is frequently used for lattice gauge theory based computations of the equation of state. Recently, in arXiv:2106.03165, a new resummation scheme was proposed for such an expansion that resums contributions of correlation functions of conserved currents to all orders in the chemical potential. Here, we study the efficacy of this resummation scheme using a solvable low energy model, namely the mean-field quark-meson model. After adapting the scheme for a mean-field analysis, we confront the results of this scheme with the direct solution of the model at finite density as well as compare with results from Taylor expansions. We study to what extent the two methods capture the analytical properties of the equation of state in the complex chemical potential plane. As expected, the Taylor expansion breaks down as soon as the baryon chemical potential reaches the radius of convergence defined by the Yang-Lee edge singularity. Encouragingly, the resummation not only captures the location of the Yang-Lee edge singularity accurately, but is also able to describe the equation of state for larger chemical potentials beyond the location of the edge singularity for a wide range of temperatures.
Huaiyu Duan (UNM)🇺🇸 · Joshua D. Martin (LANL)🇺🇸 · Sivaprasad Omanakuttan (UNM)🇺🇸
Flavor oscillations can occur on very short spatial and temporal scales in the dense neutrino media in a core-collapse supernova (CCSN) or binary neutron star merger (BNSM) event. Although the dispersion relations (DRs) of the fast neutrino oscillations can be obtained by linearizing the equations of motion (EoM) before the emergence of any significant flavor conversion, one largely depends on numerical calculations to understand this interesting phenomenon in the nonlinear regime. In this work we demonstrate that there exist nontrivial solutions to the flavor EoM that govern the fast oscillations in one-dimensional axisymmetric neutrino gases. These solutions represent a coherent flavor isospin wave similar to the magnetic spin wave in a lattice of magnetic dipoles. We also compute the DRs of such waves in some example cases which are closely related to the DRs of the fast neutrino oscillations obtained in the linear regime. This result sheds new light on the long-term behavior of fast neutrino oscillations which can have various implications for the CCSN and BNSM events.
Jingyi Zhou🇺🇸 · Vladimir Khachatryan🇺🇸 · Haiyan Gao🇺🇸 · Simon Gorbaty🇺🇸 · Douglas W. Higinbotham🇺🇸
Systematic differences exist between values of the proton's electric form factors in the low- region extracted by different experimental and theoretical groups, though they are all making use of basically the same electron-proton scattering data. To try understand the source of these differences, we make use of the analytically well-behaved rational (N=1, M=1) function, a predictive function that can be reasonably used for extrapolations at . First, we test how well this deceptively simple two-parameter function describes the extremely complex and state-of-the-art dispersively improved chiral effective field theory calculations. Second, we carry out a complete re-analysis of the 34 sets of eletron-proton elastic scattering cross-section data of the Mainz A1 Collaboration with its unconstrained 31 normalization parameters up to . We find that subtle shifts in the normalization parameters can result in relatively large changes in the extracted physical qualities. In conclusion, we show that by simply using a well-behaved analytic function, the apparent discrepancy between recent form-factor extractions can be resolved.
F. Gulminelli🇫🇷 · A. F. Fantina🇫🇷
Neutron stars are unique laboratories to probe matter in extreme conditions, not accessible in terrestrial laboratories. Here, we discuss the modelling of the neutron-star equation of state, particularly in connection with recent constraints coming from both nuclear physics (experiments and ab-initio calculations) and astrophysical observations.
Fabian Rennecke🇩🇪 · Robert D. Pisarski🇺🇸
Dense QCD matter can exhibit spatially modulated regimes. They can be characterized by particles with a moat spectrum, where the minimum of the energy is over a sphere at nonzero momentum. Such a moat regime can either be a precursor for the formation inhomogeneous condensates, or signal a quantum pion liquid. We introduce the quantum pion liquid and discuss the underlying physics of the moat regime based on studies in low-energy models and preliminary results in QCD. Heavy-ion collisions at small beam energies have the potential to reveal the rich phase structure of QCD at low temperature and nonzero density. We show how moat regimes can be discovered through such collisions. Particle production is enhanced at the bottom of the moat, resulting in a peak at nonzero momentum, instead of zero, in the particle spectrum. Particle number correlations can even increase by several orders of magnitude at nonzero momentum in the moat regime.
Yan Li🇨🇳 · Feng-Kun Guo🇨🇳 · Jin-Yi Pang🇨🇳 · Jia-Jun Wu🇨🇳
We generalize the time-honored Weinberg's compositeness relations by including the range corrections through considering a general form factor. In Weinberg's derivation, he considered the effective range expansion up to and made two additional approximations: neglecting the non-pole term in the Low equation; approximating the form factor by a constant. We lift the second approximation, and work out an analytic expression for the form factor. For a positive effective range, the form factor is of a single-pole form. An integral representation of the compositeness is obtained and is expected to have a smaller uncertainty than that derived from Weinberg's relations. We also establish an exact relation between the wave function of a bound state and the phase of the scattering amplitude neglecting the non-pole term. The deuteron is analyzed as an example, and the formalism can be applied to other cases where range corrections are important.
Elena M. Kantor · Mikhail E. Gusakov
We analyze the effect of magnetic field in superconducting neutron-star cores on the chemical heating of millisecond pulsars (MSPs). We argue that the magnetic field destroys proton superconductivity in some volume fraction of the stellar core, thus allowing for unsuppressed non-equilibrium reactions of particle mutual transformations there. The reactions transform the chemical energy, accumulated by a neutron star core during the low-mass X-ray binary stage, into heat. This heating may keep an NS warm at the MSP stage (with the surface temperature ) for more than a billion of years after ceasing of accretion, without appealing to the rotochemical heating mechanism.
first authorsco-authorsvia INSPIRE