118658178
Quasiparticle interaction in nuclear matter with chiral three-nucleon forces☆
We derive the effective interaction between two quasiparticles in symmetric nuclear matter resulting from the leading-order chiral three-nucleon force. We restrict our study to the L=0,1 Landau parameters of the central quasiparticle interaction computed to first order. We find that the three-nucleon force provides substantial repulsion in the isotropic spin- and isospin-independent component F0 of the interaction. This repulsion acts to stabilize nuclear matter against isoscalar density oscillations, a feature which is absent in calculations employing low-momentum two-nucleon interactions only. We find a rather large uncertainty for the nuclear compression modulus K due to a sensitive dependence on the low-energy constant c3. The effective nucleon mass M⁎ on the Fermi surface, as well as the nuclear symmetry energy β, receive only small corrections from the leading-order chiral three-body force. Both the anomalous orbital g-factor δgl and the Landau–Migdal parameter gNN′ (characterizing the spin–isospin response of nuclear matter) decrease with the addition of three-nucleon correlations. In fact, δgl remains significantly smaller than its value extracted from experimental data, whereas gNN′ still compares well with empirical values. The inclusion of the three-nucleon force results in relatively small p-wave (L=1) components of the central quasiparticle interaction, thus suggesting an effective interaction of short range.
119273892
Understanding Dilepton Production in Heavy Ion Collisions by Vector Mesons of Different Varieties
A simple schematic model anchored on the notion of hadronic freedom inferred from hidden local symmetry in the vector manifestation, the infinite tower of vector mesons in holographic QCD and "stickiness" of $\pi\pi$ interactions inferred from dispersion relations is used to describe the dileptons produced in relativistic heavy ion collisions at PHENIX/RHIC. It is shown that due to the near "blindness" of dileptons to Brown-Rho scaling, those dileptons with invariant mass less than $m_\rho=770$ MeV come mostly from pion-composites that we interpret as "transient $\rho$'s."
103944970
Nuclear thermodynamics from chiral low-momentum interactions
We investigate the thermodynamic equation of state of isospin-symmetric nuclear matter with microscopic nuclear forces derived within the framework of chiral effective field theory. Two- and three-body nuclear interactions constructed at low-resolution scales form the basis for a perturbative calculation of the finite-temperature equation of state. The nuclear force models and many-body methods are benchmarked against bulk properties of isospin-symmetric nuclear matter at zero temperature, which are found to be well reproduced when chiral nuclear interactions constructed at the lowest resolution scales are employed. The calculations are then extended to finite temperatures, where we focus on the liquid-gas phase transition and the associated critical point. The Maxwell construction is applied to construct the physical equation of state, and the value of the critical temperature is determined to be ${T}_{c}=17.2$\char21{}19.1 MeV, in good agreement with the value extracted from multifragmentation reactions of heavy ions.
119297098
Chiral Fermi liquid approach to neutron matter
We present a microscopic calculation of the complete quasiparticle interaction, including central as well as noncentral components, in neutron matter from high-precision two- and three-body forces derived within the framework of chiral effective field theory. The contributions from two-nucleon forces are computed in many-body perturbation theory to first and second order (without any simplifying approximations). In addition we include the leading-order one-loop diagrams from the N2LO chiral three-nucleon force, which contribute to all Fermi liquid parameters except those associated with the center-of-mass tensor interaction. The relative-momentum dependence of the quasiparticle interaction is expanded in Legendre polynomials up to L=2. Second-order Pauli blocking and medium polarization effects act coherently in specific channels, namely for the Landau parameters f_1, h_0 and g_0, which results in a dramatic increase in the quasiparticle effective mass as well as a decrease in both the effective tensor force and the neutron matter spin susceptibility. For densities greater than about half nuclear matter saturation density \rho_0, the contributions to the Fermi liquid parameters from the leading-order chiral three-nucleon force scale in all cases approximately linearly with the nucleon density. The largest effect of the three-nucleon force is to generate a strongly repulsive effective interaction in the isotropic spin-independent channel. We show that the leading-order chiral three-nucleon force leads to an increase in the spin susceptibility of neutron matter, but we observe no evidence for a ferromagnetic spin instability in the vicinity of the saturation density \rho_0. This work sets the foundation for future studies of neutron matter response to weak and electromagnetic probes with applications to neutron star structure and evolution.
13937403
Hans Bethe: The Nuclear Many Body Problem
We discuss the work of Hans Bethe and others in formulating a theoretical foundation for the nuclear shell model. Written for a general audience, this article describes the evolution from Brueckner's reaction matrix theory to the Moszkowski-Scott separation method and ultimately to the Reference Spectrum method of Bethe, Brandow, and Petschek. We also discuss connections with the recently developed low momentum nucleon-nucleon interactions.
17480164
A Hidden Local Field Theory Description of Dileptons in Relativistic Heavy Ion Collisions
Using the notion of “hadronic freedom” inferred from the vector manifestation of hidden local symmetry we argue that, contrary to the commonly held belief, the dileptons measured in relativistic heavy-ion collisions do not carry useful information directly relevant to the spontaneous breaking of chiral symmetry and hence to the mechanism for mass generation of light-quark hadrons. The dileptons emitted from those vector mesons whose masses are shifted by the vacuum change in temperature and/or density are strongly suppressed in the hadronic free region between the chiral restoration point and the “flash point” at which the vector mesons recover ∼ > 90% of their free-space on-shell masses and the full strong coupling strength. The spectral function deduced from the dilepton measurements reflects predominantly those vector mesons decaying at the “flash temperature” Tflash ∼ 120 MeV. Thus, � ≈ + � � ∗
56294645
Three-body forces and shell structure in calcium isotopes
Understanding and predicting the formation of shell structure from nuclear forces is a central challenge for nuclear physics. While the magic numbers N = 2, 8, 20 are generally well understood, N = 28 is the first standard magic number that is not reproduced in microscopic theories with two-nucleon forces. In this paper, we show that three-nucleon forces give rise to repulsive interactions between two valence neutrons that are key to explain 48Ca as a magic nucleus, with a high 2+ excitation energy and a concentrated magnetic dipole transition strength. The repulsive three-nucleon mechanism improves the agreement with experimental binding energies. Communicated by Professor Jacek Dobaczewski