arXiv subjects

Ulf-G. Meißner

Publications and source records attributed to Ulf-G. Meißner.

At least 145 records · Page 8Linked to original sources

arXiv2022

Dispersion-theoretical analysis of the electromagnetic form factors of the $Λ$ hyperon

The electromagnetic form factors of the $Λ$ hyperon in the time-like region are determined precisely through a dispersion-theoretical analysis of the world data for the cross section of the annihilation process $e^+e^-\to \barΛΛ$. The spectral function is represented by a superposition of narrow and broad vector meson poles. We test different scenarios for the spectral function and obtain a good description of the world data in the time-like region. The uncertainties in the extracted form factors are estimated by means of the bootstrap sampling method. The analytical continuation of the form factors to the space-like region introduces large errors due to the lack of data. When the electric $Λ$ radius from chiral perturbation theory is taken as a constraint, the magnetic radius is predicted as $r_M = 0.681 \pm 0.002$ fm. We also extract various vector meson to baryon coupling constants.

hep-ph↗

arXiv2022

Probing nuclear observables via primordial nucleosynthesis

We study the dependence of primordial nuclear abundances on fundamental nuclear observables such as binding energies, scattering lengths, neutron lifetime, \textit{etc.} by varying these quantities. The numerical computations were performed with four publicly available codes, thus facilitating an investigation of the model-dependent (systematic) uncertainties on these dependences. Indeed deviations of the order of a few percent are found. Moreover, accounting for the temperature dependence of the sensitivity of the rates to some relevant parameters leads to a reduction of the sensitivity of the final primordial abundances, which in some cases is appreciable. These effects are considered to be relevant for studies of the dependence of the nuclear abundances on fundamental parameters such as quark masses or couplings underlying the nuclear parameters studied here.

nucl-th↗

arXiv2022

$P_{cc}^N$ states in a unitarized coupled-channel approach

Starting from an effective Lagrangian with heavy quark spin symmetry embedded, the coupled-channel dynamics of the doubly charmed systems $D^{(*)} Σ_c^{(*)}$ is investigated. The potential underlying our investigation includes $t$-channel pseudoscalar and vector meson exchanges. A series of $S$-wave bound states with isospin $I=1/2$ is found by applying the first iterated solution of the $N/D$ method: one state with binding energy $23$ MeV in the $5/2^-$ $D^*Σ_c^*$ channel, three states with binding energy $26$, $30$ and $7$ MeV (relative to the thresholds from low to high, respectively) in the $3/2^-$ $DΣ_c^*$-$D^*Σ_c$-$D^*Σ_c^*$ system and three states with binding energy $32$, $8$ and $16$ MeV in the $1/2^-$ $DΣ_c$-$D^*Σ_c$-$D^*Σ_c^*$ system. Those $P_{cc}^N$ states serve as the open-charm partners of the hidden charm pentaquarks $P_ψ^N$ observed by the LHCb Collaboration.

hep-ph↗

arXiv2022

Precision calculation of the recoil--finite-size correction for the hyperfine splitting in muonic and electronic hydrogen

We present a high-precision calculation of the recoil--finite-size correction to the hyperfine splitting (HFS) in muonic and electronic hydrogen based on nucleon electromagnetic form factors obtained from dispersion theory. This will help guide the upcoming searches of the HFS transition in muonic hydrogen, and will allow a precise determination of the polarizability and Zemach radius contributions when this transition is found.

nucl-th↗

arXiv2022

Electron Mass Singularities in Semileptonic Kaon Decays

We show that recent improvements in the $O(α)$ long-distance quantum electrodynamics (QED) corrections to the radiative inclusive $K_{e3}$ decay rate using the Sirlin representation are free from infrared divergences and collinear electron mass singularities in the limit $m_e\rightarrow0$, as predicted by the Kinoshita-Lee-Nauenberg theorem. We also verify that in massless QED with the simultaneous dimensional regularization of QED photon infrared divergences and electron mass singularities leads to the same result for the inclusive rate in the limit of four space-time dimensions. The equivalence of the two approaches results in part from an interesting interplay between a small chirality-breaking effect in the massless electron limit and the generalization of space-time algebra and phase space integrals to $d>4$ dimensions. Our finding supports the small theoretical uncertainty claimed for $K_{e3}$ radiative inclusive rates and reaffirms its utility in precision unitarity tests of the quark mixing matrix.

hep-ph↗

arXiv2022

Complete theory of radiative corrections to $K_{\ell 3}$ decays and the $V_{us}$ update

We fill up the missing piece in our own re-analysis of the long-distance electromagnetic radiative corrections to semileptonic kaon decays by performing a rigorous study in the $K\rightarrowπμ^+ν_μ(γ)$ channels. With appropriate experimental and lattice inputs, we achieve a precision level of $10^{-4}$ in these channels. This is comparable to our previous analysis in the $K\rightarrowπe^+ν_e(γ)$ channels. With this new result, we present an updated global analysis to extract the Standard Model parameter $|V_{us}|$ from semileptonic kaon decays. We obtain $|V_{us}|=0.22308(55)$ and $0.22356(73)$, using the lattice average of the $K^0\rightarrowπ^-$ transition form factor at $N_f=2+1+1$ and $N_f=2+1$, respectively.

hep-ph↗

arXiv2022

Nuclear properties with semilocal momentum-space regularized chiral interactions beyond N2LO

We present a comprehensive investigation of few-nucleon systems as well as light and medium-mass nuclei up to $A=48$ using the current Low Energy Nuclear Physics International Collaboration two-nucleon interactions in combination with the third-order (N$^2$LO) three-nucleon forces. To address the systematic overbinding of nuclei starting from $A \sim 10$ found in our earlier study utilizing the N$^2$LO two- and three-nucleon forces, we take into account higher-order corrections to the two-nucleon potentials up through fifth order in chiral effective field theory. The resulting Hamiltonian can be completely determined using the $A=3$ binding energies and selected nucleon-deuteron cross sections as input. It is then shown to predict other nucleon-deuteron scattering observables and spectra of light $p$-shell nuclei, for which a detailed correlated truncation error analysis is performed, in agreement with experimental data. Moreover, the predicted ground state energies of nuclei in the oxygen isotopic chain from $^{14}$O to $^{26}$O as well as $^{40}$Ca and $^{48}$Ca show a remarkably good agreement with experimental values, given that the Hamiltonian is fixed completely from the $A \leq 3$ data, once the fourth-order (N$^3$LO) corrections to the two-nucleon interactions are taken into account. On the other hand, the charge radii are found to be underpredicted by $\sim 10\%$ for the oxygen isotopes and by almost $20\%$ for $^{40}$Ca and $^{48}$Ca.

nucl-th↗

arXiv2022

W-exchange contribution to the decays $Ξ_{cc}^{++}\toΞ_{c}^{+(\prime)}π^{+}$ using light-cone sum rules

We calculate the W-exchange contribution to the $Ξ_{cc}^{++}\toΞ_{c}^{+(\prime)}π^{+}$ decay using light-cone sum rules. The two-particle light-cone distribution amplitudes of the pion are used as non-perturbative input for the sum rules calculation, and the perturbative kernel is calculated at the leading order. We obtain the corresponding decay branching fractions by combining our W-exchange amplitudes with the factorizable amplitudes given by various theoretical methods from the literature. It is shown that with the factorizable amplitudes from heavy quark effective theory, we obtain the branching fraction ratio ${\cal B}(Ξ_{cc}^{++}\toΞ_{c}^{+\prime}π^{+})/{\cal B}(Ξ_{cc}^{++}\toΞ_{c}^{+}π^{+})= 1.42\pm 0.78$, which is consistent with the experimental value of $1.41\pm 0.17\pm 0.1$.

hep-ph↗

arXiv2022

Lattice Monte Carlo Simulations with Two Impurity Worldlines

We develop the impurity lattice Monte Carlo formalism, for the case of two distinguishable impurities in a bath of polarized fermions. The majority particles are treated as explicit degrees of freedom, while the impurities are described by worldlines. The latter serve as localized auxiliary fields, which affect the majority particles. We apply the method to non-relativistic three-dimensional systems of two impurities and a number of majority particles where both the impurity-impurity interaction and the impurity-majority interaction have zero range. We consider the case of an attractive impurity-majority interaction, and we study the formation and disintegration of bound states as a function of the impurity-impurity interaction strength. We also discuss the potential applications of this formalism to other quantum many-body systems.

nucl-th↗

arXiv2022

Towards a theory of hadron resonances

In this review, we present the current state of the art of our understanding of the spectrum of excited strongly interacting particles and discuss methods that allow for a systematic and model-independent calculation of the hadron spectrum. These are lattice QCD and effective field theories. Synergies between both approaches can be exploited allowing for deeper understanding of the hadron spectrum. Results based on effective field theories and hadron-hadron scattering in lattice QCD or combinations thereof are presented and discussed. We also show that the often used Breit-Wigner parameterization is at odds with chiral symmetry and should not be used in case of strongly coupled channels.

hep-ph↗

arXiv2022

Perturbative quantum Monte Carlo method for nuclear physics

While first order perturbation theory is routinely used in quantum Monte Carlo (QMC) calculations, higher-order terms present significant numerical challenges. We present a new approach for computing perturbative corrections in projection QMC calculations. We demonstrate the method by computing nuclear ground state energies up to second order for a realistic chiral interaction. We calculate the binding energies of several light nuclei up to $^{16}$O by expanding the Hamiltonian around the Wigner SU(4) limit and find good agreement with data. In contrast to the natural ordering of the perturbative series, we find remarkably large second order energy corrections. This occurs because the perturbing interactions break the symmetries of the unperturbed Hamiltonian. Our method is free from the sign problem and can be applied to QMC calculations for many-body systems in nuclear physics, condensed matter physics, ultracold atoms, and quantum chemistry.

nucl-th↗

arXiv2022

Magnetic dipole moments as a strong signature for $α$-clustering in even-even self-conjugate nuclei

We investigate the magnetic dipole moments in even-even self-conjugate nuclei from ${}^{12}\mathrm{C}$ to ${}^{44}\mathrm{Ti}$. For the latter, the measured gyromagnetic factors of excited states turn out to assume the same value of $g \approx + 0.5$ within statistical errors. This peculiar feature can be interpreted on the basis of collective excitations of $α$-clusters. Analogously, the behaviour of the same observable is studied for all isotopes obtained by adding one or two neutrons to the considered self-conjugate nuclei. It is found that for the $N = Z + 1$ isotopes the $α$-cluster structure hardly contributes to the observed negative g- factor value, corroborating molecular $α$-cluster models. The addition of a further neutron, however, restores the original $α$-cluster g-factors, except for the semi-magic isotopes, in which the deviations from $g \approx + 0.5$ can be associated with the relevant shell closures. Secondly, we analyze the same observable in the framework of a macroscopic $α$-cluster model on a finite lattice of side length $L$. We focus on the discretization effects induced in the magnetic dipole moments of the $2_1^+$ and the $3_1^-$ states of ${}^{12}\mathrm{C}$ at different values of the lattice spacing $a$.

nucl-th↗

arXiv2022

Localization of Electronic States in Hybrid Nano-Ribbons in the Non-Perturbative Regime

We investigate the localization of low-energy single quasi-particle states in the 7/9-hybrid nanoribbon system in the presence of strong interactions and within a finite volume. We consider two scenarios, the first being the Hubbard model at half-filling and perform quantum Monte Carlo simulations for a range $U$ that includes the strongly correlated regime. In the second case we add a nearest-neighbor superconducting pairing $Δ$ and take the symmetric line limit, where $Δ$ is equal in magnitude to the hopping parameter $t$. In this limit the quasi-particle spectrum and wavefunctions can be directly solved for general onsite interaction $U$. In both cases we extract the site-dependent quasi-particle wavefunction densities and demonstrate that localization persists in these non-perturbative regimes under particular scenarios.

cond-mat.str-el↗

arXiv2022

Resonances in heavy meson - heavy baryon coupled-channel interactions

The interactions of $\bar{D}^{(*)} Λ_c - \bar{D}^{(*)}Σ_c^{(*)}$ are studied within the framework of a dynamical coupled-channel approach. A series of bound states and resonances with different spin and parity are dynamically generated in the hidden charm sector. Four $S$-wave bound states are found in the mass range of 4.3 to 4.5 GeV, close to the pentaquark states observed by LHCb. Two of the states have a spin parity of $J^P= 1/2^-$ and the other two have $J^P=3/2^-$. In addition, several resonances with different spin and parity in higher partial waves are predicted.

hep-ph↗

arXiv2022

Three-body renormalization group limit cycles based on unsupervised feature learning

Both the three-body system and the inverse square potential carry a special significance in the study of renormalization group limit cycles. In this work, we pursue an exploratory approach and address the question which two-body interactions lead to limit cycles in the three-body system at low energies, without imposing any restrictions upon the scattering length. For this, we train a boosted ensemble of variational autoencoders, that not only provide a severe dimensionality reduction, but also allow to generate further synthetic potentials, which is an important prerequisite in order to efficiently search for limit cycles in low-dimensional latent space. We do so by applying an elitist genetic algorithm to a population of synthetic potentials that minimizes a specially defined limit-cycle-loss. The resulting fittest individuals suggest that the inverse square potential is the only two-body potential that minimizes this limit cycle loss independent of the hyperangle.

nucl-th↗

arXiv2022

Hadronic molecules

A large number of experimental discoveries especially in the heavy quarkonium sector that did not at all fit to the expectations of the until then very successful quark model led to a renaissance of hadron spectroscopy. Among various explanations of the internal structure of these excitations, hadronic molecules, being analogues of light nuclei, play a unique role since for those predictions can be made with controlled uncertainty. We review experimental evidences of various candidates of hadronic molecules, and methods of identifying such structures. Nonrelativistic effective field theories are the suitable framework for studying hadronic molecules, and are discussed in both the continuum and finite volumes. Also pertinent lattice QCD results are presented. Further, we discuss the production mechanisms and decays of hadronic molecules, and comment on the reliability of certain assertions often made in the literature.

hep-ph↗

arXiv2022

Electric dipole moments of baryons with bottom quarks

Triggered by experimental prospects to measure electromagnetic dipole moments of baryons containing a bottom quark, we calculate the CP-odd electric dipole moments (EDMs) of spin-1/2 single-bottom baryons. We consider CP-violating dimension-six operators in the Standard Model Effective Field Theory that involve bottom quarks, and apply heavy-baryon chiral perturbation theory to compute the EDMs of several baryons. We discuss the expected size of the EDMs for beyond-the-Standard Model physics appearing at the TeV scale.

hep-ph↗

arXiv2022

Substructure of Multiquark Hadrons (Snowmass 2021 White Paper)

In recent years there has been a rapidly growing body of experimental evidence for existence of exotic, multiquark hadrons, i.e. mesons which contain additional quarks, beyond the usual quark-antiquark pair and baryons which consist of more than three quarks. In all cases with robust evidence they contain at least one heavy quark Q=c or b, the majority including two heavy quarks. Two key theoretical questions have been triggered by these discoveries: (a) how are quarks organized inside these multiquark states -- as compact objects with all quarks within one confinement volume, interacting via color forces, perhaps with an important role played by diquarks, or as deuteron-like hadronic molecules, bound by light-meson exchange? (b) what other multiquark states should we expect? The two questions are tightly intertwined. Each of the interpretations provides a natural explanation of parts of the data, but neither explains all of the data. It is quite possible that both kinds of structures appear in Nature. It may also be the case that certain states are superpositions of the compact and molecular configurations. This Whitepaper brings together contributions from many leading practitioners in the field, representing a wide spectrum of theoretical interpretations. We discuss the importance of future experimental and phenomenological work, which will lead to better understandingof multiquark phenomena in QCD.

hep-ph↗