Low-density neutron matter is characterized by fascinating emergent quantum phenomena, such as the formation of Cooper pairs and the onset of superfluidity. We model this density regime by capitalizing on the expressivity of the hidden-nucleon neural-network quantum states combined with variational Monte Carlo and stochastic reconfiguration techniques. Our approach is competitive with the auxiliary-field diffusion Monte Carlo method at a fraction of the computational cost. Using a leading-order pionless effective field theory Hamiltonian, we compute the energy per particle of infinite neutron matter and compare it with those obtained from highly realistic interactions. In addition, a comparison between the spin-singlet and triplet two-body distribution functions indicates the emergence pairing in the $^1S_0$ channel.
The internal structure of neutron stars and the physical properties of nuclei depend on the equation of state (EOS) of neutron matter. Dilute neutron matter is a quantum system of spin-1/2 Fermi particles interacting via s-wave scattering. Although a nuclear system and an ultracold atomic system have length scales and energy scales that differ by several orders of magnitude, both systems follow a common universal EOS considering their non-dimensional universal interaction parameters. In this study, we determine the EOS of neutron matter in the dilute region, where the influence of the s-wave s…
Dynamics of dilute nuclear matter with light clusters and in-medium effects
Istituto Nazionale di Fisica Nucleare (INFN), Sezione di Catania（意大利国家核物理研究所（INFN）卡塔尼亚分部）；INFN, Laboratori Nazionali del Sud（意大利国家核物理研究所（INFN）南方实验室）；Dipartimento di Fisica e Astronomia（物理与天文学系）
We explore the thermodynamic properties of homogeneous cold (zero-temperature) nuclear matter including nucleons and $α$-particle condensation at low densities by using a generalized nonlinear relativistic mean-field (gNL-RMF) model. In the gNL-RMF model, the $α$-particle is included as explicit degree of freedom and treated as point-like particle with its interaction described by meson exchanges and the in-medium effects on the $α$ binding energy is described by density- and temperature-dependent energy shift with the parameters obtained by fitting the experimental Mott density. We find that …
Conventional and Unconventional Pairing and Condensates in Dilute Nuclear Matter
这篇文章将调查最近的进展，在稀核物质在小和中等的同位旋不对称的理解不同的配对现象，与超新星信封和原中子星的潜在相关性的结果。应用{ \it ab initio}多体技术已经揭示了一系列丰富的温度-密度相图，以同位旋不对称性为索引，其中包括常规和非常规的超流相。在低密度下，存在均匀的平移不变BCS相、违反平移不变性的均匀LOFF相和非均匀的平移不变相分离BCS相。从BCS到BEC阶段的过渡的特点是在演化方面，从弱到强耦合，对间隙，凝聚波函数，准粒子占有数和光谱。此外，在低到中等密度的中子物质配对的示意性正式分析，建立了常规和非常规配对解决方案的出现条件，并包括双中子形成的可能性。
Joint Institute for Nuclear Research（俄罗斯联合核研究所）；National Center of Physics and Mathematics（国家物理数学中心）；Matej Bel University（马特伊·贝尔大学）；National Research Nuclear University (MEPhI)（国立研究核子大学（莫斯科工程物理学院））
We present a comprehensive analysis of hot and dilute isospin-asymmetric nuclear matter employing the temperature-dependent effective-relativistic mean-field theory (E-RMF). The E-RMF is applied to study the effect of $δ$ and $ω-ρ$ meson cross-coupling on the thermal properties of asymmetric nuclear matter using two recently developed IOPB-I and G3 parameter sets. These sets are known to reproduce the nuclear matter properties in agreement with various experimental and observational constraints. We consider the nuclear matter to be homogeneous and study the equation of state (EoS) for densitie…
We study the composition of nuclear matter at sub-saturation densities, non-zero temperatures, and isospin asymmetry, under the conditions characteristic of binary neutron star mergers, stellar collapse, and low-energy heavy-ion collisions. The composition includes light clusters with mass number $A\le 4$, a heavy nucleus ($\isotope[56]{Fe}$), the $Δ$-resonances, the isotriplet of pions, as well as the $Λ$ hyperon. The nucleonic mean-fields are computed from a zero-range density functional, whereas the pion-nucleon interactions are treated to leading order in chiral perturbation theory. We sho…
We discuss high-order calculations in perturbative effective field theory for fermions at low energy scales. The Fermi-momentum or $k_{\rm F} a_s$ expansion for the ground-state energy of the dilute Fermi gas is calculated to fourth order, both in cutoff regularization and in dimensional regularization. For the case of spin one-half fermions we find from a Bayesian analysis that the expansion is well-converged at this order for ${| k_{\rm F} a_s | \lesssim 0.5}$. Further, we show that Pad{é}-Borel resummations can improve the convergence for ${| k_{\rm F} a_s | \lesssim 1}$. Our results provid…
The phase diagram of isospin-asymmetrical nuclear matter may feature a number of unconventional phases, which include the translationally and rotationally symmetric, but isospin-asymmetrical BCS condensate, the current-carrying Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase, and the heterogeneous phase-separated phase. Because the Cooper pairs of the condensate carry a single unit of charge, these phases are charged superconductors and respond to electromagnetic gauge fields by either forming domains (type-I superconductivity) or quantum vortices (type-II superconductivity). We evaluate the Gin…
Recent proposals have suggested that a previously unknown decay mode of the neutron into a dark matter particle could solve the long lasting measurement problem of the neutron decay width. We show that, if the dark particle in neutron decay is the major component of the dark matter in the universe, this proposal is in disagreement with modern astro-physical data concerning neutron star masses.
