次世代技術の芽と新しい物理をつくる

理論核物理学

[English]

鷹野　正利　［教授・理工研］
e-mail
専門分野	原子核物理学
Homepage	www.np.phys.waseda.ac.jp
研究テーマ・研究活動
◯核物質状態方程式の研究と天体物理学への応用 ◯強い粒子間相関をもつFermi粒子系に対する変分法
●日本物理学会 ●アメリカ物理学会

原子核は核子（陽子と中性子）が核力という力で結合している系で、現在約３０００種類の原子核が実験的に知られています。それらの膨大な実験データの多くについて、まだ理論的に十分な説明がなされていません。　原子核構造研究の困難さは２つの側面を持ちます。１つは、核力の複雑さです。核力は強い短距離引力と斥力芯から成り、また核子のスピンや速度等によって変化する、非常に複雑な力です。さらに、３つの核子の間に働く３体力も重要であると考えられています。　もう１つは、多体問題的側面です。一般に多体問題を解く事は困難ですが、例えば鉛の原子核208Pbは、８２個の陽子と１２６個の中性子から成り、その構造を知るためには２０８体問題を解かなければなりません。現状で、これを厳密に解く事は不可能です。
そこで我々は、無限個の核子から成る無限に大きい仮想的な原子核（以下では核物質と呼びます）を考えます。そして、主に変分法を用いて、核物質の多体問題的研究を行う事により、核物質の観点から原子核の大局的性質を理解する事を目指します。　核物質エネルギーの理論計算により、いわゆる核物質の状態方程式(EOS)が得られます。計算された核物質EOSの信頼性を調べるために、我々は宇宙に目を向けます。

Masatoshi Takano [Professor]
e-mail
homepage	www.np.phys.waseda.ac.jp
research field	Theoretical study of Nuclear Equation of State
research keywords
Equation of state for nuclear matter Variational method Neutron stars Supernovae
link
Research Profiles (at Faculty of Science and Engineering) Research Profiles (Elsevier SciVal Experts)

Theoretical study of Nuclear Equation of State

The atomic nucleus is a quantum-mechanical system composed of nucleons (protons and neutrons) interacting through nuclear and Coulomb forces. One of the fundamental properties of the atomic nucleus is the so-called “saturation property of nuclear forces,” i.e., that the nucleon number densities inside the nuclei and the binding energies per nucleon are nearly constant for all nuclei. In order to explain this basic property of the atomic nucleus quantitatively, the Schrodinger equation for the atomic nucleus must be solved. So far, however, this has not been achieved because the nuclear Hamiltonian, especially the potential of the nuclear force, has some uncertainty. More seriously, the quantum many-body problem is especially difficult to solve.

In order to overcome the latter difficulty, we have been studying the quantum variational many-body theory for infinitely-large fermion systems. The variational method is a powerful technique to treat the quantum systems in which the particles interact through strong short-range forces, such as infinite hypothetical nuclear matter and liquid helium. In the case of liquid 3He, the spin-1/2 3He atoms interact through intermolecular forces, and the Hamiltonian bears some resemblance to that of nuclear matter. Furthermore, the experimental data to be compared with the theoretical calculations for liquid 3He are more abundant than in the case of nuclear matter. Therefore, we are studying not only nuclear matter but also liquid 3He.

Infinitely-large nuclear matter can be found as neutron stars. A neutron star is a compact object whose mass is about twice the solar mass (or somewhat less), with the radius being about 10 kilometers. Inside the star is high-density nuclear matter. Against strong self-gravity, the stiffness of the interior nuclear matter supports the neutron star. Therefore, the neutron star structure is determined by the stiffness of the interior nuclear matter, or more generally, by the equation of state (EOS) of nuclear matter. Furthermore, owing to the recent development of neutron star observations, various constraints are imposed on the nuclear EOS. We are studying the neutron star structure in connection with the nuclear EOS obtained with our variational method.

The nuclear EOS is also important for studies of core-collapse supernovae and other high-energy astrophysical phenomena such as hypernovae, black-hole formations, and neutron star mergers. In order to study these astrophysical phenomena with numerical hydrodynamic simulations, the EOS of nuclear matter covering an extremely wide range of densities, temperatures, and proton fractions is necessary. We are constructing a new nuclear EOS appropriate for these astrophysical phenomena based on the variational many-body theory.