arXiv subjects

W. Weise

Publications and source records attributed to W. Weise.

At least 19 recordsLinked to original sources

arXiv2017

Scattering of decuplet baryons in chiral effective field theory

A formalism for treating the scattering of decuplet baryons in chiral effective field theory is developed. The minimal Lagrangian and potentials in leading-order SU(3) chiral effective field theory for the interactions of octet baryons ($B$) and decuplet baryons ($D$) for the transitions $BB\to BB$, $BB\leftrightarrow DB$, $DB\to DB$, $BB\leftrightarrow DD$, $DB\leftrightarrow DD$, and $DD\to DD$ are provided. As an application of the formalism we compare with results from lattice QCD simulations for $ΩΩ$ and $NΩ$ scattering. Implications of our results pertinent to the quest for dibaryons are discussed.

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arXiv2017

Lambda-nuclear interactions and hyperon puzzle in neutron stars

Brueckner theory is used to investigate the in-medium properties of a $Λ$-hyperon in nuclear and neutron matter, based on hyperon-nucleon interactions derived within SU(3) chiral effective field theory (EFT). It is shown that the resulting $Λ$ single-particle potential $U_Λ(p_Λ=0,ρ)$ becomes strongly repulsive for densities $ρ$ of two-to-three times that of normal nuclear matter. Adding a density-dependent effective $ΛN$-interaction constructed from chiral $ΛNN$ three-body forces increases the repulsion further. Consequences of these findings for neutron stars are discussed. It is argued that for hyperon-nuclear interactions with properties such as those deduced from the SU(3) EFT potentials, the onset for hyperon formation in the core of neutron stars is expected to be shifted to extremely high baryon density, thus potentially resolving the so-called hyperon puzzle.

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arXiv2016

Hyperons in nuclear matter from SU(3) chiral effective field theory

Brueckner theory is used to investigate the properties of hyperons in nuclear matter. The hyperon-nucleon interaction is taken from chiral effective field theory at next-to-leading order with SU(3) symmetric low-energy constants. Furthermore, the underlying nucleon-nucleon interaction is also derived within chiral effective field theory. We present the single-particle potentials of Lambda and Sigma hyperons in symmetric and asymmetric nuclear matter computed with the continuous choice for intermediate spectra. The results are in good agreement with the empirical information. In particular, our calculation gives a repulsive Sigma-nuclear potential and a weak Lambda-nuclear spin-orbit force.

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arXiv2014

Scattering lengths of Nambu-Goldstone bosons off $D$ mesons and dynamically generated heavy-light mesons

Recent lattice QCD simulations of the scattering lengths of Nambu-Goldstone bosons off the $D$ mesons are studied using unitary chiral perturbation theory. We show that the Lattice QCD data are better described in the covariant formulation than in the heavy-meson formulation. The $D^*_{s0}(2317)$ can be dynamically generated from the coupled-channels $DK$ interaction without \textit{a priori} assumption of its existence. A new renormalization scheme is proposed which manifestly satisfies chiral power counting rules and has well-defined behavior in the infinite heavy-quark mass limit. Using this scheme we predict the heavy-quark spin and flavor symmetry counterparts of the $D^*_{s0}(2317)$.

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arXiv2013

Nuclear chiral dynamics and thermodynamics

This presentation reviews an approach to nuclear many-body systems based on the spontaneously broken chiral symmetry of low-energy QCD. In the low-energy limit, for energies and momenta small compared to a characteristic symmetry breaking scale of order 1 GeV, QCD is realized as an effective field theory of Goldstone bosons (pions) coupled to heavy fermionic sources (nucleons). Nuclear forces at long and intermediate distance scales result from a systematic hierarchy of one- and two-pion exchange processes in combination with Pauli blocking effects in the nuclear medium. Short distance dynamics, not resolved at the wavelengths corresponding to typical nuclear Fermi momenta, are introduced as contact interactions between nucleons. Apart from a set of low-energy constants associated with these contact terms, the parameters of this theory are entirely determined by pion properties and low-energy pion-nucleon scattering observables. This framework (in-medium chiral perturbation theory) can provide a realistic description of both isospin-symmetric nuclear matter and neutron matter. The importance of three-body forces is emphasized, and the role of explicit Delta(1232)-isobar degrees of freedom is investigated in detail. Nuclear chiral thermodynamics is developed and a calculation of the nuclear phase diagram is performed. This includes a successful description of the first-order phase transition from a nuclear Fermi liquid to an interacting Fermi gas and the coexistence of these phases below a critical temperature T_c. Density functional methods for finite nuclei based on this approach are also discussed. Effective interactions, their density dependence and connections to Landau Fermi liquid theory are outlined. Finally, the density and temperature dependence of the chiral (quark) condensate is investigated.

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arXiv2013

Hyperon-nucleon interaction at next-to-leading order in chiral effective field theory

Results for the Lambda N and Sigma N interactions obtained at next-to-leading order in chiral effective field theory are reported. At the order considered there are contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the hyperon-nucleon interaction while the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons (pi, K, eta) is taken into account. An excellent description of the hyperon-nucleon system can be achieved at next-to-leading order. It is on the same level of quality as the one obtained by the most advanced phenomenological hyperon-nucleon interaction models.

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arXiv2013

Microscopic optical potential from chiral nuclear forces

The energy- and density-dependent single-particle potential for nucleons is constructed in a medium of infinite isospin-symmetric nuclear matter starting from realistic nuclear interactions derived within the framework of chiral effective field theory. The leading-order terms from both two- and three-nucleon forces give rise to real, energy-independent contributions to the nucleon self-energy. The Hartree-Fock contribution from the two-nucleon force is attractive and strongly momentum dependent, in contrast to the contribution from the three-nucleon force which provides a nearly constant repulsive mean field that grows approximately linearly with the nuclear density. Together, the leading-order perturbative contributions yield an attractive single-particle potential that is however too weak compared to phenomenology. Second-order contributions from two- and three-body forces then provide the additional attraction required to reach the phenomenological depth. The imaginary part of the optical potential, which is positive (negative) for momenta below (above) the Fermi momentum, arises at second-order and is nearly inversion-symmetric about the Fermi surface when two-nucleon interactions alone are present. The imaginary part is strongly absorptive and requires the inclusion of an effective mass correction as well as self-consistent single-particle energies to attain qualitative agreement with phenomenology.

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arXiv2012

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 ρ_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 ρ_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.

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arXiv2012

SU(3) breaking corrections to the $D$, $D^$, $B$, and $B^$ decay constants

We report on a first next-to-next-to-leading order calculation of the decay constants of the $D$ ($D^*$) and $B$ ($B^*$) mesons using a covariant formulation of chiral perturbation theory. It is shown that, using the state-of-the-art lattice QCD results on $f_{D_s}/f_D$ as input, one can predict quantitatively the ratios of $f_{D_s^*}/f_{D^*}$, $f_{B_s}/f_B$, and $f_{B^*_s}/f_{B^*}$ taking into account heavy-quark spin-flavor symmetry breaking effects on the relevant low-energy constants. The predicted relations between these ratios, $f_{D^*_s}/f_{D^*} f_{D_s}/f_D$, and their light-quark mass dependence should be testable in future lattice QCD simulations, providing a stringent test of our understanding of heavy quark spin-flavor symmetry, chiral symmetry and their breaking patterns.

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arXiv2011

Chiral nuclear dynamics with three-body forces

We review recent progress in implementing high-precision chiral two- and three-body forces in nuclear many-body systems beyond light nuclei. We begin with applications to finite nuclei, which we study through the nuclear shell model and self-consistent mean field theory. We then turn our attention to infinite nuclear matter treated within the framework of Landau's theory of normal Fermi liquids.

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arXiv2011

Spin structure of the nucleon: QCD evolution, lattice results and models

The question how the spin of the nucleon is distributed among its quark and gluon constituents is still a subject of intense investigations. Lattice QCD has progressed to provide information about spin fractions and orbital angular momentum contributions for up- and down-quarks in the proton, at a typical scale μ^2~4 GeV^2. On the other hand, chiral quark models have traditionally been used for orientation at low momentum scales. In the comparison of such model calculations with experiment or lattice QCD, fixing the model scale and the treatment of scale evolution are essential. In this paper, we present a refined model calculation and a QCD evolution of lattice results up to next-to-next-to-leading order. We compare this approach with the Myhrer-Thomas scenario for resolving the proton spin puzzle.

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arXiv2011

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 F_0 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 due to a sensitive dependence on the low-energy constant c_3. The effective nucleon mass on the Fermi surface, as well as the nuclear symmetry energy, receive only small corrections from the leading-order chiral three-body force. Both the anomalous orbital g-factor and the Landau-Migdal parameter g'_{NN} (characterizing the spin-isospin response of nuclear matter) decrease with the addition of three-nucleon correlations. In fact, the anomalous orbital g-factor remains significantly smaller than its value extracted from experimental data, whereas g'_{NN} 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.

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arXiv2011

Finite-volume effects on octet-baryon masses in covariant baryon chiral perturbation theory

We study finite-volume effects on the masses of the ground-state octet baryons using covariant baryon chiral perturbation theory (ChPT) up to next-to-leading order by analyzing the latest $n_f=2+1$ lattice Quantum ChromoDynamics (LQCD) results from the NPLQCD collaboration. Contributions of virtual decuplet baryons are taken into account using the "consistent" coupling scheme. We compare our results with those obtained from heavy baryon ChPT and show that, although both approaches can describe well the lattice data, the underlying physics is different: In HBChPT, virtual decuplet baryons play a more important role than they do in covariant ChPT. This is because the virtual octet baryon contributions to finite-volume corrections are larger in covariant ChPT than in HBChPT, while the contributions of intermediate decuplet baryons are smaller, because of relativistic effects. We observe that for the octet baryon masses, at fixed $m_πL$ ($\gg1$) finite-volume corrections decrease as $m_π$ approaches its physical value, provided that the strange quark mass is at or close to its physical value, as in most LQCD setups.

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arXiv2011

Nuclear energy density functional from chiral two- and three-nucleon interactions

An improved density-matrix expansion is used to calculate the nuclear energy density functional from chiral two- and three-nucleon interactions. The two-body interaction comprises long-range one- and two-pion exchange contributions and a set of contact terms contributing up to fourth power in momenta. In addition we employ the leading order chiral three-nucleon interaction with its parameters $c_E, c_D$ and $c_{1,3,4}$ fixed in calculations of nuclear few-body systems. With this input the nuclear energy density functional is derived to first order in the two- and three-nucleon interaction. We find that the strength functions $F_\nabla(ρ)$ and $F_{so}(ρ)$ of the surface and spin-orbit terms compare in the relevant density range reasonably with results of phenomenological Skyrme forces. However, an improved description requires (at least) the treatment of the two-body interaction to second order. This observation is in line with the deficiencies in the nuclear matter equation of state $\bar E(ρ)$ that remain in the Hartree-Fock approximation with low-momentum two- and three-nucleon interactions.

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arXiv2011

Second-order quasiparticle interaction in nuclear matter with chiral two-nucleon interactions

We employ Landau's theory of normal Fermi liquids to study the quasiparticle interaction in nuclear matter in the vicinity of saturation density. Realistic low-momentum nucleon-nucleon interactions evolved from the Idaho N3LO chiral two-body potential are used as input potentials. We derive for the first time exact results for the central part of the quasiparticle interaction computed to second order in perturbation theory, from which we extract the L=0 and L=1 Landau parameters as well as some relevant bulk equilibrium properties of nuclear matter. The accuracy of the intricate numerical calculations is tested with analytical results derived for scalar-isoscalar boson exchange and (modified) pion exchange at second order. The explicit dependence of the Fermi liquid parameters on the low-momentum cutoff scale is studied, which provides important insight into the scale variation of phase-shift equivalent two-body potentials. This leads naturally to explore the role that three-nucleon forces must play in the effective interaction between two quasiparticles.

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arXiv2011

Thermodynamics of the in-medium chiral condensate

The temperature dependence of the chiral condensate in isospin-symmetric nuclear matter at varying baryon densities is investigated starting from a realistic free energy density of the correlated nuclear many-body system. The framework is thermal in-medium chiral effective field theory which permits a systematic calculation of the quark mass dependence of the free energy density. One- and two-pion exchange processes, virtual $Δ(1232)$-isobar excitations and Pauli blocking corrections are treated up to and including three-loop order. It is found that nuclear matter remains in the Nambu-Goldstone phase with spontaneously broken chiral symmetry at least in the range of temperatures $T\lesssim 100\,$MeV and baryon densities up to about twice the density of normal nuclear matter.

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arXiv2010

Light quark mass dependence of the $D$ and $D_s$ decay constants

We study the light quark mass dependence of the $D$ and $D_s$ meson decay constants, $f_D$ and $f_{D_s}$, using a covariant formulation of chiral perturbation theory ($χ$PT) at next-to-next-to-leading order (NNLO). Using the HPQCD lattice results for the $D$($D_s$) decay constants as a benchmark we show that covariant $χ$PT can describe the HPQCD results better than heavy meson $χ$PT (HM$χ$PT) at both NLO and NNLO. Within the same framework, taking into account sub-leading ($1/m_Q$, with $m_Q$ the heavy quark mass) corrections to the values of the low-energy constants and employing the lattice QCD results for $g_{BB^*π}$, we estimate the ratio of $f_{B_s}/f_B$ to be $1.22^{+0.05}_{-0.04}$, which agrees well with the HPQCD result $1.226(26)$.

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arXiv2010

Density-dependent nuclear interactions and the beta decay of 14C: chiral three-nucleon forces and Brown-Rho scaling

We study the role of density-dependent low-momentum nucleon-nucleon interactions in describing the anomalously long beta decay lifetime of 14C. We approach this problem both from the perspective of chiral effective field theory, in which genuine three-body forces generate an effective density-dependent two-body interaction, as well as from the perspective of Brown-Rho scaling, in which the masses and form factor cutoffs in one-boson-exchange interactions are modified in a dense nuclear medium due to the partial restoration of chiral symmetry. The beta decay transition of 14C to the ground state of 14N is calculated within the shell model using a model space consisting of two 0p-shell holes within a closed 16O core. The effective 0p-shell interaction is calculated up to second order in perturbation theory with single-particle energies extracted from experiment. We find that both three-nucleon forces and Brown-Rho scaling medium modifications give qualitatively similar results not only for the ground state to ground state Gamow-Teller transition but also for Gamow-Teller transitions from excited states of 14C to the ground state of 14N. In this way, it is observed that at a low-momentum scale of V_(low-k) = 2.1 fm-1, medium-modifications of the nuclear force play an essential role in increasing the lifetime of 14C from a few minutes to an archaeologically long one of 5730 years.

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