arXiv subjects

Johann Haidenbauer

Publications and source records attributed to Johann Haidenbauer.

At least 37 records · Page 2Linked to original sources

arXiv2021

Implications of an increased $Λ$-separation energy of the hypertriton

Stimulated by recent indications that the binding energy of the hypertriton could be significantly larger than so far assumed, requirements of a more strongly bound $^3_Λ{\rm H}$ state for the hyperon-nucleon interaction and consequences for the binding energies of $A=4,5$ and $7$ hypernuclei are investigated. As basis a $YN$ potential derived at next-to-leading order in chiral effective field theory is employed, Faddeev and Yakubovsky equations are solved to obtain the corresponding $3$- and $4$-body binding energies, respectively, and the Jacobi no-core shell model is used for $^5_Λ$He and $^7_Λ$Li. It is found that the spin-singlet $Λp$ interaction would have to be much more attractive which can be, however, accommodated within the bounds set by the available $Λp$ scattering data. The binding energies of the $^4_Λ{\rm He}$ hypernucleus are predicted to be closer to the empirical values than for $YN$ interactions that produce a more weakly bound $^3_Λ{\rm H}$. The quality of the description of the separation energy and excitation spectrum for $^7_Λ$Li remains essentially unchanged.

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arXiv2020

Jacobi no-core shell model for $p$-shell hypernuclei

We extend the recently developed Jacobi no-core shell model to hypernuclei. Based on the coefficients of fractional parentage for ordinary nuclei, we define a basis where the hyperon is the spectator particle. We then formulate transition coefficients to states that single out a hyperon-nucleon pair which allow us to implement a hypernuclear many-baryon Hamiltonian for $p$-shell hypernuclei. As a first application, we use the basis states and the transition coefficients to calculate the ground states of $^{4}_Λ$He, $^{4}_Λ$H, $^{5}_Λ$He, $^{6}_Λ$He, $^{6}_Λ$Li, and $^{7}_Λ$Li and, additionally, the first excited states of $^{4}_Λ$He, $^{4}_Λ$H, and $^{7}_Λ$Li. In order to obtain converged results, we employ the similarity renormalization group (SRG) to soften the nucleon-nucleon and hyperon-nucleon interactions. Although the dependence on this evolution of the Hamiltonian is significant, we show that a strong correlation of the results can be used to identify preferred SRG parameters. This allows for meaningful predictions of hypernuclear binding and excitation energies. The transition coefficients will be made publicly available as HDF5 data files.

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arXiv2020

Hyperon electromagnetic form factors in the timelike region

Electromagnetic form factors of hyperons ($Λ$, $Σ$, $Ξ$) in the timelike region, accessible in the reaction $e^+e^- \to \bar YY$, are studied. The focus is on energies close to the reaction thresholds, where the properties of these form factors are significantly influenced by the interaction in the final $\bar YY$ system. This interaction is taken into account in the calculation, utilizing $\bar YY$ potential models that have been constructed by the Jülich group for the analysis of data from the reaction $\bar pp \to \bar YY$ in the past. The enhancement of the effective form factor for energies close to the threshold, seen in experiments of $e^+e^- \to \bar ΛΛ$ and $e^+e^- \to \bar Σ^0Λ$, is reproduced. With regard to the reactions $e^+e^- \to \bar Σ^- Σ^+, \ \barΣ^0Σ^0, \ \barΣ^+Σ^-$ a delicate interplay between the three channels is observed in the results at low energies, caused by the $\barΣΣ$ interaction. Predictions for the electromagnetic form factors $G_M$ and $G_E$ in the timelike region are presented for the $Λ$, $Σ$, and $Ξ$ hyperons.

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arXiv2020

Predictions for charmed nuclei based on $Y_c N$ forces inferred from lattice QCD simulations

Charmed nuclei are investigated utilizing $Λ_c N$ and $Σ_c N$ interactions that have been extrapolated from lattice QCD simulations at unphysical masses of $m_π= 410$--$570$ MeV to the physical point using chiral effective field theory as guideline. Calculations of the energies of $Λ_c$ single-particle bound states for various charmed nuclei from $^{\ 5}_{Λ_c}$Li to $^{209}_{Λ_c}$Bi are performed using a perturbative many-body approach. This approach allows one to determine the finite nuclei $Λ_c$ self-energy from which the energies of the different bound states can be obtained. Though the $Λ_c N$ interaction inferred from the lattice results is only moderately attractive, it supports the existence of charmed nuclei. Already the lightest nucleus considered is found to be bound. The spin-orbit splitting of the p- and d-wave states turns out to be small, as in the case of single $Λ$ hypernuclei. Additional calculations based on the Faddeev-Yakubovsky equations suggest that also $A=4$ systems involving a $Λ_c$ baryon are likely to be bound, but exclude a bound $^{\, 3}_{Λ_c}$He state.

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arXiv2020

Hyperon-nuclear interactions from SU(3) chiral effective field theory

The interaction between hyperons and nucleons has a wide range of applications in strangeness nuclear physics and is a topic of continuing great interest. These interactions are not only important for hyperon-nucleon scattering but also essential as basic input to studies of hyperon-nuclear few- and many-body systems including hypernuclei and neutron star matter. We review the systematic derivation and construction of such baryonic forces from the symmetries of quantum chromodynamics within non-relativistic SU(3) chiral effective field theory. Several applications of the resulting potentials are presented for topics of current interest in strangeness nuclear physics.

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arXiv2019

Neutron-antineutron oscillations in the deuteron studied with $NN$ and $\bar NN$ interactions based on chiral effective field theory

Neutron-antineutron ($n-\bar n$) oscillations in the deuteron are considered. Specifically, the deuteron lifetime is calculated in terms of the free-space $n-\bar n$ oscillation time $τ_{n-\bar n}$ based on $NN$ and $\bar NN$ interactions derived within chiral effective field theory (EFT). This results in $(2.6\pm 0.1) \times 10^{22}\,τ^2_{n-\bar n}$ s, which is close to the value obtained by Dover and collaborators more than three decades ago, but disagrees with recent EFT calculations that were performed within the perturbative scheme proposed by Kaplan, Savage, and Wise. Possible reasons for the difference are discussed.

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arXiv2019

Structure of single-$Λ$ hypernuclei with chiral hyperon-nucleon potentials

The structure of single-$Λ$ hypernuclei is studied using the chiral hyperon-nucleon potentials derived at leading order (LO) and next-to-leading order (NLO) by the Jülich--Bonn--Munich group. Results for the separation energies of $Λ$ single-particle states for various hypernuclei from $^5_Λ$He to $^{209}_{\,\,\,\,\,Λ}$Pb are presented for the LO interaction and the 2013 (NLO13) and 2019 (NLO19) versions of the NLO potentials. It is found that the results based on the LO potential show a clear tendency for overbinding while those for the NLO13 interaction underbind most of the considered hypernuclei. A qualitatively good agreement with the data is obtained for the NLO19 interaction over a fairly large range of mass number values when considering the uncertainty due to the regulator dependence. A small spin-orbit splitting of the $p$-, $d$-, $f$-, and $g$-wave states is predicted by all interactions, in line with the rather small values observed in pertinent experiments.

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arXiv2018

$J/ψ\to γη'π^+π^-$ and the structure observed around the $\bar pp$ threshold

We analyze the origin of the structure observed in the reaction $J/ψ\to γη'π^+π^-$ for $η'π^+π^-$ invariant masses close to the antiproton-proton ($\bar pp$) threshold, commonly associated with the $X(1835)$ resonance. Specifically, we explore the effect of a possible contribution from the two-step process $J/ψ\to γ\bar NN \to γη'π^+π^-$. The calculation is performed in distorted-wave Born approximation which allows an appropriate inclusion of the $\bar NN$ interaction in the transition amplitude. The $\bar NN$ amplitude itself is generated from a corresponding potential recently derived within chiral effective field theory. We are able to reproduce the measured spectra for the reactions $J/ψ\to γ\bar pp$ and $J/ψ\to γη'π^+π^-$ for invariant masses around the $\bar pp$ threshold. The structure seen in the $η'π^+π^-$ spectrum emerges as a threshold effect due to the opening of the $\bar pp$ channel.

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arXiv2017

Search for time-reversal-invariance violation in double polarized antiproton-deuteron scattering

Apart from the $pd$ reaction also the scattering of antiprotons with transversal polarization $p_y^p$ on deuterons with tensor polarization $P_{xz}$ provides a null-test signal for time-reversal-invariance violating but parity conserving effects. Assuming that the time-reversal-invariance violating $\bar NN$ interaction contains the same operator structure as the $NN$ interaction, we discuss the energy dependence of the null-test signal in $\bar pd$ scattering on the basis of a calculation within the spin-dependent Glauber theory at beam energies of 50-300 MeV.

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arXiv2017

Re-examining the $X(4630)$ resonance in the reaction $e^+e^-\rightarrow Λ^+_c\barΛ^-_c$

The reaction $e^+e^-\rightarrow Λ^+_c\barΛ^-_c$ is investigated at energies close to the threshold with emphasis on the role played by the $X(4630)$ resonance. The interaction in the final $Λ^+_c \barΛ^-_c$ system, constructed within chiral effective field theory and supplemented by a pole diagram that represents a bare $X(4630)$ resonance, is taken into account rigorously. The pole parameters of the $X(4630)$ are extracted and found to be compatible with the ones of the $X(4660)$ resonance that have been established in the reaction $e^+e^- \to π^+π^-ψ(2S)$. The actual result for the $X(4630)$ is $M = (4652.5\pm 3.4)$ MeV and $Γ= (62.6\pm 5.6)$ MeV. Predictions for the $Λ^+_c$ electromagnetic form factors in the timelike region are presented.

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arXiv2017

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

Results for the antinucleon-nucleon ($\bar NN$) interaction obtained at next-to-next-to-next-to-leading order in chiral effective field theory (EFT) are reported. A new local regularization scheme is used for the pion-exchange contributions that has been recently suggested and applied in a pertinent study of the $NN$ force within chiral EFT. Furthermore, an alternative strategy for estimating the uncertainty is utilized that no longer depends on a variation of the cutoffs. The low-energy constants associated with the arising contact terms are fixed by a fit to the phase shifts and inelasticities provided by a phase-shift analysis of $\bar pp$ scattering data. An excellent description of the $\bar NN$ amplitudes is achieved at the highest order considered. Moreover, because of the quantitative reproduction of partial waves up to $J=3$, there is also a nice agreement on the level of $\bar pp$ observables. Specifically, total and integrated elastic and charge-exchange cross sections agree well with the results from the partial-wave analysis up to laboratory energies of $300$ MeV, while differential cross sections and analyzing powers are described quantitatively up to $200$-$250$ MeV. The low-energy structure of the $\bar NN$ amplitudes is also considered and compared to data from antiprotonic hydrogen.

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arXiv2016

Density-dependent effective baryon-baryon interaction from chiral three-baryon forces

A density-dependent effective potential for the baryon-baryon interaction in the presence of the (hyper)nuclear medium is constructed, based on the leading (irreducible) three-baryon forces derived within SU(3) chiral effective field theory. We evaluate the contributions from three classes: contact terms, one-pion exchange and two-pion exchange. In the strangeness-zero sector we recover the known result for the in-medium nucleon-nucleon interaction. Explicit expressions for the Lambda-nucleon in-medium potential in (asymmetric) nuclear matter are presented. Our results are suitable for implementation into calculations of (hyper)nuclear matter. In order to estimate the low-energy constants of the leading three-baryon forces we introduce the decuplet baryons as explicit degrees of freedom and construct the relevant terms in the minimal non-relativistic Lagrangian. With these, the constants are estimated through decuplet saturation. Utilizing this approximation we provide numerical results for the effect of the three-body force in symmetric nuclear matter and pure neutron matter on the Lambda-nucleon interaction. A moderate repulsion that increases with density is found in comparison to the free Lambda-nucleon interaction.

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arXiv2016

Foundations of Strangeness Nuclear Physics derived from chiral Effective Field Theory

Dense compact objects like neutron stars or black holes have always been one of Gerry Brown's favorite research topics. This is closely related to the effects of strangeness in nuclear physics. Here, we review the chiral Effective Field Theory approach to interactions involving nucleons and hyperons, the possible existence of strange dibaryons, the fate of hyperons in nuclear matter and the present status of three-body forces involving hyperons and nucleons.

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arXiv2016

Leading three-baryon forces from SU(3) chiral effective field theory

Leading three-baryon forces are derived within SU(3) chiral effective field theory. Three classes of irreducible diagrams contribute: three-baryon contact terms, one-meson exchange and two-meson exchange diagrams. We provide the minimal non-relativistic terms of the chiral Lagrangian, that contribute to these diagrams. SU(3) relations are given for the strangeness S=0 and -1 sectors. In the strangeness-zero sector we recover the well-known three-nucleon forces from chiral effective field theory. Explicit expressions for the lambda-nucleon-nucleon chiral potential in isospin space are presented.

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arXiv2015

Origin of the structures observed in $e^+e^-$ annihilation into multipion states around the $\bar pp$ threshold

We analyze the origin of the structures observed in the reactions $e^+e^-\to 3(π^+π^-)$, $2(π^+π^-π^0)$, $ωπ^+π^-π^0$, and $e^+e^-\to 2(π^+π^-)π^0$ around the antiproton-proton ($\bar pp$) threshold. We calculate the contribution of the two-step process $e^+e^-\to \bar NN \to$ multipions to the total reaction amplitude. The amplitude for $e^+e^-\to \bar NN$ is constrained from near-threshold data on the $e^+e^-\to \bar pp$ cross section and the one for $\bar NN \to$ multipions can be likewise fixed from available experimental information, for all those $5 π$ and $6π$ states. The resulting amplitude for $e^+e^-\to$ multipions turns out to be large enough to play a role for the considered $e^+e^-$ annihilation channels and, in three of the four reactions, even allows us to reproduce the data quantitatively near the $\bar NN$ threshold. The structures seen in the experiments emerges then as a threshold effect due to the opening of the $\bar NN$ channel.

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arXiv2013

Antinucleon-nucleon interaction in chiral effective field theory

Results of an exploratory study of the antinucleon-nucleon interaction within chiral effective field theory are reported. The antinucleon-nucleon potential is derived up to next-to-next-to-leading order, based on a modified Weinberg power counting, in close analogy to pertinent studies of the nucleon-nucleon interaction. The low-energy constants associated with the arising contact interactions are fixed by a fit to phase shifts and inelasticities provided by a recently published phase-shift analysis of antiproton-proton scattering data. The overall quality of the achieved description of the antinucleon-nucleon amplitudes is comparable to the one found in case of the nucleon-nucleon interaction at the same order. For most S-waves and several P-waves good agreement with the antinucleon-nucleon phase shifts and inelasticities is obtained up to laboratory energies of around 200 MeV.

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arXiv2010

Chiral perturbation theory calculation for pn -> dpipi at threshold

We investigate the reaction pn -> dpipi in the framework of Chiral Perturbation Theory. For the first time a complete calculation of the leading order contributions is presented. We identify various diagrams that are of equal importance as compared to those recognized in earlier works. The diagrams at leading order behave as expected by the power counting. Also for the first time the nucleon-nucleon interaction in the initial, intermediate and final state is included consistently and found to be very important. This study provides a theoretical basis for a controlled evaluation of the non-resonant contributions in two-pion production reactions in nucleon-nucleon collisions.

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arXiv2010

Reconciling the X(4630) with the Y(4660)

The Belle Collaboration observed an enhancement called X(4630) in the Lambda_c^+ Lambda_c^- mass distribution using initial state radiation. We demonstrate that the enhancement could be consistent with the psi'f_0(980) molecular picture of the Y(4660) taking into account the Lambda_c^+ Lambda_c^- final state interaction. To test the hypothesis that the X(4630) and Y(4660) are the same molecular state, we give predictions for its spin partner, the eta_c'f_0(980) molecule. High statistic measurements of the B decays into the K Lambda_c^+ Lambda_c^- and K eta_c' pi^+ pi^- are strongly recommended.

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