arXiv subjects

Ulf-G. Meißner

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

At least 55 records · Page 3Linked to original sources

arXiv2026

Vacuum energy in effective field theory of general relativity

It is shown to all orders of perturbation theory that in the effective field theory of general relativity the condition of vanishing of the vacuum energy leads to the same value of the cosmological constant, viewed as a parameter of the effective Lagrangian, as obtained by demanding the consistency of the effective field theory in Minkowski background. The resulting effective action is characterized by the cosmological constant term that vanishes exactly.

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arXiv2026

Comments on Baryon Transition Form Factors

We discuss in rather general terms the properties of space-like baryon transition form factors. In particular, we argue why these are necessarily complex-valued, what can be deduced from the respective phase motion and why dealing with real valued transition form factors in general leads to misleading results. For illustration the transition form factors for the Roper resonance as derived in the Jülich-Bonn-Washington framework are discussed.

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arXiv2026

Ab initio charge form factors and radii of light isoscalar nuclei: Role of the two-body charge density

We make \textit{ab initio} predictions of charge form factors (FFs) and radii for the isoscalar nuclei $^6$Li and $^8$Be using the Jacobi-coordinate No-Core Shell Model. The calculations employ chiral semilocal momentum-space regularized two- and three-nucleon interactions, together with consistently regularized one- and two-nucleon electromagnetic charge operators. With the short-range charge density fixed to the $^4$He charge radius, the predicted FFs and the $^6$Li radius show good agreement with available experimental data. We find that two-nucleon charge density contributions are essential for describing the FFs, particularly at intermediate and large momentum transfers. Although their influence on the charge radii is limited, these contributions remain crucial for attaining accurate predictions. The present results highlight the importance of two-nucleon charge operators in addressing the long-standing underestimation of nuclear charge radii in \textit{ab initio} calculations based on modern chiral interactions.

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arXiv2026

On the quantum numbers of the $X(1880)$

We study the properties of the $X(1880)$, the structure around the $\bar{p}p$ threshold that appears in the $3(π^+π^-)$ invariant mass spectrum in the decay process of $J/ψ\to γ3(π^+π^-)$. Nucleon-antinucleon rescattering is taken into account in our analysis, and the decay amplitude of $J/ψ\to γ3(π^+π^-)$ can be obtained by the distorted wave Born approximation. With these amplitudes, we analyze the contributions to the $X(1880)$ from different partial waves. Our analysis suggests that the $X(1880)$ should be isoscalar $0^{-+}$, and it is generated by the threshold behavior.

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arXiv2025

Properties of hyperons in nuclear matter from chiral hyperon-nucleon interactions at next-to-next-to-leading order

The $Λ$ and $Σ$ single-particle potentials in infinite nuclear matter are analyzed within a recently established chiral hyperon-nucleon ($YN$) interaction up to N$^2$LO in combination with an nucleon-nucleon interaction derived in the same scheme. The self-consistent Brueckner-Hartree-Fock method with the continuous choice of the single-particle potential is employed. It is found that the $Λ$ single-particle potential is comparable to the results achieved with the NLO $YN$ interaction from 2019. The resulting $Σ$ potential becomes more attractive compared to the previous NLO results due to the constraint from the recent $ΣN$ differential cross section data measured in the J-PARC E40 experiment. An estimate of the theoretical uncertainty of the single-particle potentials is provided in terms of the truncation error in the chiral expansion.

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arXiv2025

Universality of nucleon short-range behavior with chiral forces

Modern advanced nuclear ab initio approaches with the similarity renormalization group (SRG) softened interactions miss high-momentum information, thus rendering them less suitable for characterizing nucleon-nucleon short-range physics. We introduce a novel framework to construct SRG-independent nuclear wave functions from No-Core Shell Model calculations. Applying our method to densities obtained with semilocal momentum-space-regularized chiral NN and NNN forces, we show key universalities of short-range behavior: (1) The two-body density ratio in the np S=1 channel, relative to the deuteron (d), is remarkably insensitive to interaction details. (2) More strikingly, while the ratio of total two-body densities to the deuteron exhibits cutoff dependence, the same ratio to the $α$-particle (4-He) is almost independent of the interactions.

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arXiv2025

Sunset integrals with up to three mass scales in chiral perturbation theory: a comparative study of the Mellin-Barnes representation technique

Sunset integrals are among the simplest of two-loop integrals that appear in perturbative quantum field theories and possess up to four distinct mass scales. By means of integration by parts identities, they can be written in terms of four distinct master integrals. In this article, we discuss the independent configurations of on-shell and off-shell sunset master integrals with one, two and three mass scales that arise in chiral perturbation theory. We derive Mellin-Barnes integral representations of these integrals and analytically solve them using various methods to obtain exact results in the form of single and double convergent series of the hypergeometric type, for the values of the mass parameters that allow us to do so. We then discuss how to analytically continue the results to other regions of the parameters and conclude by discussing a few applications in chiral perturbation theory.

hep-ph↗

arXiv2025

Ab Initio Calculations of the Carbon and Oxygen Isotopes: Energies, Correlations, and Superfluid Pairing

We perform \textit{ab initio} nuclear lattice calculations of the neutron-rich carbon and oxygen isotopes using high-fidelity chiral interactions. We find good agreement with the observed binding energies and compute correlations associated with each two-nucleon interaction channel. For the isospin $T=1$ channels, we show that the dependence on $T_z$ provides a measure of the correlations among the extra neutrons in the neutron-rich nuclei. For the spin-singlet S-wave channel, we observe that any paired neutron interacts with the nuclear core as well as its neutron pair partner, while any unpaired neutron interacts primarily with only the nuclear core. For the other partial waves, the correlations among the extra neutrons grow more slowly and smoothly with the number of neutrons. These general patterns are observed in both the carbon and oxygen isotopes and may be universal features that appear in many neutron-rich nuclei.

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arXiv2025

Nature of the $P_c$ states from compositeness criteria

Based on a coupled-channel approach, we investigate the structures of four $P_c$ states through compositeness criteria. Toward a more precise description of the states, we have obtained refined fit results of the LHCb data on the $J/ψp$ invariant mass distribution of the $Λ_b^0\to J/ψp K^-$ decay. Allowing for the fact that each of the four $P_c$ states couples strongly to a nearby $S$-wave channel, three criteria on the compositeness/elementariness are adopted in this study: the pole-counting rule, the spectral density function, and the Gamow wave function. Compositeness information is extracted from the scattering amplitudes and the pole parameters (pole positions and residues), without any preconceived assumptions on the nature of the $P_c$ states, and without any dependence on the model parametrization. Consistently within the framework of all the three methods, it has been found that the $P_c(4312)\,1/2^-$ is mainly composed by $\bar{D}Σ_c$, $P_c(4380)\,3/2^-$ by $\bar{D}Σ_c^*$, while the $P_c(4440)\,1/2^-$ and $P_c(4457)\,3/2^-$ states both turn out as composite states of $\bar{D}^*Σ_c$. The upper limits of the values of their elementariness are estimated to be rather small. This paper provides an additional confirmation of the molecular interpretation for the $P_c$ states in the literature.

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arXiv2025

Ab initio study of the radii of oxygen isotopes

We present an {\em ab initio} study of the charge and matter radii of oxygen isotopes from $^{16}$O to $^{20}$O using nuclear lattice effective field theory (NLEFT) with high-fidelity N$^3$LO chiral interactions. To efficiently address the Monte Carlo sign problem encountered in nuclear radius calculations, we introduce the {\em partial pinhole algorithm}, significantly reducing statistical uncertainties and extending the reach to more neutron-rich and proton-rich isotopes. Our computed charge radii for $^{16}$O, $^{17}$O, and $^{18}$O closely match experimental data, and we predict a charge radius of $2.810(32)$ fm for $^{20}$O. The calculated matter radii show excellent agreement with values extracted from low-energy proton and electron elastic scattering data, but are inconsistent with those derived from interaction cross sections and charge-changing cross section measurements. These discrepancies highlight model-dependent ambiguities in the experimental extraction methods of matter radii and underscore the value of precise theoretical benchmarks from NLEFT calculations.

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arXiv2025

Multi-strangeness matter from ab initio calculations

Hypernuclei and hypernuclear matter connect nuclear structure in the strangeness sector with the astrophysics of neutron stars, where hyperons are expected to emerge at high densities and affect key astrophysical observables. We present the first {\em ab initio} calculations that simultaneously describe single- and double-$Λ$ hypernuclei from the light to medium-mass range, the equation of state for $β$-stable hypernuclear matter, and neutron star properties. Despite the formidable complexity of quantum Monte Carlo~(QMC) simulations with multiple baryonic degrees of freedom, by combining nuclear lattice effective field theory with a newly developed auxiliary-field QMC algorithm we achieve the first sign-problem free {\em ab initio} QMC simulations of hypernuclear systems containing an arbitrary number of neutrons, protons, and $Λ$ hyperons, including all relevant two- and three-body interactions. This eliminates reliance on the symmetry-energy approximation, long used to interpolate between symmetric nuclear matter and pure neutron matter. Our unified calculations reproduce hyperon separation energies, yield a neutron star maximum mass consistent with observations, predict tidal deformabilities compatible with gravitational-wave measurements, and give a trace anomaly in line with Bayesian constraints. By bridging the physics of finite hypernuclei and infinite hypernuclear matter within a single {\em ab initio} framework, this work establishes a direct microscopic link between hypernuclear structure, dense matter composition, and the astrophysical properties of neutron stars.

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arXiv2025

Lattice calculation of the Sn isotopes near the proton dripline

We present the first $\textit{ab initio}$ lattice calculations of the proton-rich tin isotopes $^{99}$Sn to $^{102}$Sn using nuclear lattice effective field theory with high-fidelity two- and three-nucleon forces. For a given set of three-nucleon couplings, we reproduce binding energies with $\sim 1\%$ accuracy for the even-even systems, and obtain energy splitting and two-nucleon separation energies in agreement with experiment. Our results confirm the $N=50$ shell closure and reveal that the binding energy of $^{99}$Sn lies below values extrapolated from heavier isotopes.

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arXiv2025

Ab initio description of hypernuclei

Hypernuclei are bound states of neutrons, protons and one or two hyperons, thus extending the nuclear landscape to a third dimension. They also encode information about the baryon-baryon and three-baryon interactions. Here, we review recent work on chiral effective field theory for two- and three-baryon interactions and their application in nuclei based on ab initio methods. These include the Faddeev-Yakubovsky equations, the no-core-shell-model (NCSM) and nuclear lattice effective field theory (NLEFT). Besides of providing an overview of the formalisms explicit results for the separation energies of light $Λ$ hypernuclei are provided. Two-body and three-body forces are included consistently, in line with the underlying power counting. Calculations of $Λ$ hypernuclei within the NCSM, performed up to A=7 so far, suggest that agreement with the experimental binding energies can be achieved once appropriate three-body forces are taken into account. Similar conclusions are drawn from the study based on NLEFT, where even hypernuclei up to A=16 can be computed. Additionally, applications of ab initio approaches in calculations of $ΛΛ$ and $Ξ$ hypernuclei are discussed and possible candidates for the lightest systems that could be bound are identified, namely $^{\ \ 5}_{ΛΛ}{\rm He}$ and $^4_Ξ{\rm H}$.

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arXiv2025

Coupled-channel contributions to the GDH sum rule from the Jülich-Bonn approach

We study the Gerasimov-Drell-Hearn (GDH) sum rule within a dynamical coupled-channel approach, the Jülich-Bonn model for light baryon resonances based on fits to an extensive data base of pion and photon induced data. Recently published photoproduction data for different observables with $πN$ and $ηN$ final states are analyzed simultaneously with older data for the reactions $πN\to πN$, $ηN$, $KΛ$, $KΣ$ and $γp\toπN$, $ηN$, $KΛ$, $KΣ$. The impact of the new data on the resonance spectrum is investigated and the contribution of the individual channels to the GDH integral is determined.

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arXiv2025

Precision calculations of $B\to K^*$ form factors from SCET sum rules beyond leading-power contributions

We construct light-cone sum rules (LCSR) for the $B\to K^*$ form factors in the large recoil region using vacuum-to-$B$-meson correlation functions, and systematically calculate subleading-power corrections to these form factors at tree level, including next-to-leading power contributions from the hard-collinear propagator, the subleading effective current $\bar{q}Γ[i\slashed{D}_{\perp}/(2m_b)]h_v$, and twist-five/six four-particle higher-twist effects. By incorporating the available leading-power results at $\mathcal{O}(α_s)$ and the corrections to higher-twist $B$-meson light-cone distribution amplitudes from our previous work, we improve the precision of theoretical predictions for $B\to K^*$ form factors and find that the subleading-power contributions amount to 30\% of the corresponding leading-power results. Employing the Bourrely-Caprini-Lellouch (BCL) parametrization, we determine the numerical results for $B\to K^*$ form factors across the full kinematic range through a combined fit of LCSR predictions in the large recoil region and lattice QCD results in the small recoil region. Using the newly obtained $B\to K^*$ form factors, we compute the branching fractions for the rare decays $B \to K^* ν_\ell\barν_\ell$ in the Standard Model, obtaining $\mathcal{BR}(\bar{B}^0 \to \bar{K}^{*0} ν_\ell\barν_\ell)=8.09(96)\times 10^{-6}$ and $\mathcal{BR}(\bar{B}^+ \to \bar{K}^{*+} ν_\ell\barν_\ell)=9.95(1.05)\times 10^{-6}$. Additionally, we predict that the longitudinal $K^*$ polarization fraction is $F_L=0.44(4)$.

hep-ph↗

arXiv2025

Universal parameters of the $Λ(1380)$, the $Λ(1405)$ and their isospin partners from a combined analysis of Lattice QCD and experimental results

We perform a global analysis of lattice and experimental data on negative-strangeness meson-baryon scattering using a large set of variations of the theoretical framework based on the Chiral Unitary Approach. For the former, the Lüscher formalism is utilized taking into account all pertinent coupled-channel effects. Through this, systematic uncertainties related to data scarcity, potential ambiguities, and possible framework dependence are quantified for the first time. The implementation of information criteria and other statistical tools is discussed. As a final result we provide pole positions for isoscalar resonances at the physical and lattice points including statistical and systematic uncertainties. Predictions for the isovector states are also provided showing large uncertainties.

hep-ph↗

arXiv2025

Resonance parameters of the vector charmoniumlike state $G(3900)$

Motivated by the updated analysis of the $G(3900)$ by the BESIII collaboration, we perform a global analysis of the cross sections of the $e^+e^-\to D\bar{D}$, $e^+e^-\to D\bar{D}^*+c.c.$, $e^+e^-\to D^*\bar{D}^*$ processes, especially focusing on the properties of the $G(3900)$. As the energy region of interest is limited by the next opening threshold, i.e. the $D_1\bar{D}$ threshold, we focus on the energy region $[3.7,4.25]~\mathrm{GeV}$, where three charmonia $ψ(1D)$, $ψ(3S)$ and $ψ(2D)$ explicitly contribute to the cross sections. By constructing the $P$-wave contact interaction between the $(D,D^*)$ doublet and its antiparticle in the heavy quark limit, we extract the physical scattering amplitude by solving the Lippmann-Schwinger equation. No matter whether three or two charmonium states are included in our framework, we always find a dynamically generated state corresponding to the $G(3900)$, which suggests it to be a $P$-wave dynamically generated state. We also predict several dynamically generated states in the corresponding $1^{-+}$ channel. These states can be further searched for in the electron-positron annihilation process involving the emission of a single photon.

hep-ph↗

arXiv2025

Ab initio lattice study of neutron-alpha scattering with chiral forces at N3LO

We present the first ab initio lattice calculation of neutron-alpha ($n$-$α$) scattering using nuclear lattice effective field theory (NLEFT) with chiral interactions at next-to-next-to-next-to-leading order (N3LO). Building on the high-fidelity chiral Hamiltonian introduced in Ref. [1], we compute scattering phase shifts in the $S$- and $P$-wave channels using the Lüscher finite-volume method. Our results demonstrate excellent agreement with empirical $R$-matrix phase shifts in the $^2S_{1/2}$ and $^2P_{3/2}$ channels, while revealing persistent discrepancies in the $^2P_{1/2}$ channel for neutron energies above 5 MeV. To systematically investigate these discrepancies, we construct and analyze a simplified neutron-alpha toy model, demonstrating that these discrepancies are not due to the use of the Lüscher finite-volume method. Additionally, we revisit our three-nucleon (3N) force fitting procedure, explicitly incorporating neutron-alpha scattering data through comprehensive Markov Chain Monte Carlo (MCMC) sampling. This analysis confirms the stability of nuclear binding-energy predictions and highlights the need for further refinements in the lattice N3LO three-nucleon forces to fully describe neutron-alpha scattering in the challenging ${}^2P_{1/2}$ channel.

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