arXiv subjects

Jiří Mareš

Publications and source records attributed to Jiří Mareš.

12 recordsLinked to original sources

arXiv2021

Multi-fermion systems with contact theories

We address the question of minimal requirements for the existence of quantum bound states. In particular, we demonstrate that a few-body system with zero-range momentum-independent two-body interactions is unstable against decay into clusters, if mixed-symmetry of its wave function is enforced. We claim that any theory in which the two-body scattering length is much larger than any other scale involved exhibits such instability. We exemplify this with the inability of the leading-order pionless effective field theory to describe stable states of $A>4$ nuclei. A finite interaction range is identified as a sufficient condition for a bound mixed-symmetry system. The minimal value of this range depends on the proximity of a system to unitarity, on the number of constituents, and on the particular realization of discrete scale invariance of the three-body spectrum.

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arXiv2020

From $\bar{K}N$ Interactions to $\bar{K}$-Nuclear Quasi-Bound States

We review the current status of our study of $K^-$-nuclear interactions and $K^-$-nuclear quasi-bound states. The adopted $K^-$-nuclear optical potential consists of two parts -- the single-nucleon one constructed microscopically from chirally motivated $\bar{K}N$ amplitudes, and a phenomenological multi-nucleon one constrained in fits to kaonic atoms data. The inclusion of multi-nucleon absorption in our calculations of $K^{-}$ quasi-bound states in many-body systems leads to huge widths, considerably exceeding the binding energies. If this feature is confirmed the observation of such states is unlikely. Finally, a development of a new microscopical model for in-medium $K^-NN$ absorption is discussed as well.

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arXiv2019

Calculation of NMR Shielding in Paramagnetic Molecules: Roadmap and Magnetic Couplings

We present a simple derivation of the nuclear shielding in paramagnetic molecules, extendable to strong spin-orbit coupling cases of relevance to lanthanides and actinides, as well as encompassing contributions from excited multiplets. While our general formulation does not need electron paramagnetic resonance parameters, using them a simple and practical expression is obtained for the special case of the zero-field-split ground-state manifold, including magnetic (Zeeman and hyperfine) couplings between the sublevels. The latter method is implemented computationally and applied in the context of first-principles calculations on example Ni(II) and Co(II) complexes.

physics.chem-ph↗

arXiv2018

$Λ^{\ast}(1405)$-matter: stable or unstable?

A recent suggestion [PLB 774 (2017) 522] that purely-$Λ^{\ast}(1405)$ nuclei provide the absolute minimum energy in charge-neutral baryon matter for baryon-number $A\gtrsim 8$, is tested within RMF calculations. A broad range of $Λ^{\ast}$ interaction strengths, commensurate with $(\bar K \bar K NN)_{I=0}$ binding energy assumed to be of order 100 MeV, is scanned. It is found that the binding energy per $Λ^{\ast}$, $B/A$, saturates for $A\gtrsim 120$ with values of $B/A$ considerably below 100 MeV, implying that $Λ^{\ast}(1405)$ matter is highly unstable against strong decay to $Λ$ and $Σ$ hyperon aggregates. The central density of $Λ^{\ast}$ matter is found to saturate as well, at roughly twice nuclear matter density. Moreover, it is shown that the underlying very strong $\bar K N$ potentials, fitted for isospin $I=0$ to the mass and width values of $Λ^{\ast}(1405)$, fail to reproduce values of single-nucleon absorption fractions deduced across the periodic table from $K^-$ capture-at-rest bubble chamber experiments.

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arXiv2018

Antiproton-nucleus quasi-bound states within the 2009 version of the Paris $\bar{N}N$ potential

We studied the ${\bar p}$ interactions with the nuclear medium within the 2009 version of the Paris ${\bar N}N$ potential model. We constructed the $\bar{p}$--nucleus optical potential using the Paris $S$- and $P$-wave ${\bar p}N$ scattering amplitudes and treated their strong energy and density dependence self-consistently. We considered a phenomenological $P$-wave term as well. We calculated $\bar{p}$ binding energies and widths of the $\bar{p}$ bound in various nuclei. The $P$-wave potential has very small effect on the calculated ${\bar p}$ binding energies, however, it reduces the corresponding widths noticeably. Moreover, the $S$-wave potential based on the Paris amplitudes supplemented by a phenomenological $P$-wave term yields the ${\bar p}$ binding energies and widths in very good agreement with those obtained within the RMF model consistent with ${\bar p}$-atom data.

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arXiv2017

Onset of $η$ nuclear binding

Recent studies of $η$ nuclear quasibound states by the Jerusalem-Prague Collaboration are reviewed, focusing on stochastic variational method self consistent calculations of $η$ few-nucleon systems. These calculations suggest that a minimum value Re$\,a_{ηN} \approx 1$ fm (0.7 fm) is needed to bind $η\,^3$He ($η\,^4$He).

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arXiv2017

Studies of mesic atoms and nuclei

$K^-$ mesons offer a unique setting where mesic atoms have been studied both experimentally and theoretically, thereby placing constraints on the possible existence and properties of meson-nuclear quasibound states. Here we review progress in this field made recently by the Jerusalem--Prague Collaboration using near-threshold $K^-N$ scattering amplitudes generated in several meson--baryon coupled channels models inspired by a chiral EFT approach. Our own procedure of handling subthreshold kinematics self consistently is used to transform these free-space energy dependent amplitudes to in-medium density dependent amplitudes from which $K^-$ optical potentials are derived. To fit the world data of kaonic atoms, these single-nucleon optical potentials are augmented by multi-nucleon terms. It is found that only two of the studied models reproduce also the single-nucleon absorption fractions available from old bubble chamber experiments. These two models are then checked for possible $K^-$ nuclear quasibound states, despite realizing that $K^-$ optical potentials are not constrained by kaonic atom data at densities exceeding half nuclear-matter density. We find that when such states exist, their widths are invariably above 100 MeV, forbiddingly large to allow observation. Multi-nucleon absorption is found to be substantial in this respect. This suggests that observable strongly bound $K^-$ mesons are limited to the very light systems, such as $K^-pp$.

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arXiv2017

Interaction of antiprotons with nuclei

We report on self-consistent calculations of $\bar{p}$ quasi-bound states in selected nuclei performed within the relativistic mean-field (RMF) model employing $\bar{p}$ coupling constants tuned to reproduce $\bar{p}$-atom data. We confirmed considerable polarization of the nuclear core induced by the antiproton. The $\bar{p}$ annihilation was treated dynamically, taking into account the reduced phase space in the nuclear medium as well as the compressed nuclear density. The energy available for the annihilation products was evaluated self-consistently, considering additional energy shift due to particle momenta in the ${\bar p}$-nucleus system. Next, we constructed the $\bar{p}$-nucleus optical potential using scattering amplitudes related to the latest version of the Paris $\bar{N}N$ potential. We explored energy dependence of the potential and the implications for $\bar{p}$-nucleus quasi-bound states.

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arXiv2017

Antibaryon interactions with the nuclear medium

This contribution deals with our recent study of antibaryon interactions with the nuclear medium within the relativistic mean-field approach using antibaryon coupling constants consistent with available experimental data. We performed calculations of $\bar{B}$ ($\bar{B}=\bar{p}, \barΛ, \barΣ, \barΞ$) bound states in selected nuclei. Due to the lack of information on the in-medium antihyperon annihilation near threshold only the $\bar{p}$ absorption was considered. It was described by the imaginary part of a phenomenological optical potential fitted to $\bar{p}$-atom data. The annihilation was treated dynamically, taking into account explicitly the reduced phase space for annihilation products in the nuclear medium, as well as the compressed nuclear density due to the antiproton. The energy available for the annihilation products was evaluated self-consistently, considering additional energy shift due to particle momenta in the ${\bar p}$-nucleus system. Corresponding $\bar{p}$ widths were significantly reduced, however, they still remain sizable. Next, the $\bar{p}$-nucleus interaction was constructed using the latest version of the Paris $\bar{N}N$ potential. Related scattering amplitudes were used to define the complex $\bar{p}$ optical potential in the nuclear medium. The resulting $\bar{p}$ $1s$ binding energies are about 10% smaller and widths about 20% larger than those obtained with the phenomenological approach.

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arXiv2017

Calculations of antiproton-nucleus quasi-bound states using the Paris $\bar{N}N$ potential

An optical potential constructed using the ${\bar p}N$ scattering amplitudes derived from the 2009 version of the Paris ${\bar N}N$ potential is applied in calculations of ${\bar p}$ quasi-bound states in selected nuclei across the periodic table. A proper self-consistent procedure for treating energy dependence of the amplitudes in a nucleus appears crucial for evaluating ${\bar p}$ binding energies and widths. Particular attention is paid to the role of $P$-wave amplitudes. While the $P$-wave potential nearly does not affect calculated ${\bar p}$ binding energies, it reduces considerably the corresponding widths. The Paris $S$-wave potential supplemented by a phenomenological $P$-wave term yields in dynamical calculations ${\bar p}$ binding energies $B_{\bar p}\approx 200$ MeV and widths $Γ_{\bar p}\sim~200 - 230$ MeV, which is very close to the values obtained within the RMF model consistent with ${\bar p}$-atom data.

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arXiv2014

In-medium antikaon interactions and bound states

Correct treatment of subthreshold Kbar-N dynamics is mandatory in kaonic-atom and Kbar-nuclear bound-state calculations, as demonstrated by using in-medium chirally-based models of Kbar-N interactions. Recent studies of kaonic-atom data reveal appreciable multi-nucleon contributions. Kbar-nuclear widths larger than 50 MeV are anticipated.

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arXiv2014

In-medium antikaon and eta-meson interactions and bound states

The role played by subthreshold meson-baryon dynamics is demonstrated in kaonic-atom, Kbar-nuclear and eta-nuclear bound-state calculations within in-medium models of Kbar-N and eta-N interactions. New analyses of kaonic atom data reveal appreciable multi-nucleon contributions. Calculations of eta-nuclear bound states show, in particular, that the eta-N scattering length is not a useful indicator of whether or not eta mesons bind in nuclei nor of the widths anticipated for such states.

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