In Memoriam: Igal Talmi (1925-2026)
A brief obituary of Igal Talmi (1925-2026) focusing on his scientific heritage. Published in Nuclear Physics News 36 (2026) 39-40.
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arXiv subjects
Avraham Gal
Publications and source records attributed to Avraham Gal.
Remarks on MAMI's recent determination of $B_{\Lambda}({_{\Lambda}^3}{\rm H})$
A recent report on ${^7{\rm Li}}(e,e'K^+)$ electroproduction runs by the A1 collaboration at the Mainz Microtron (MAMI) assigns a sharp pion-momentum line at $p_{\pi^-}\approx 113.8\pm 0.1$ MeV/c to ${_{\Lambda}^3}{\rm H}\to\pi^-+{^3{\rm He}}$ weak decay, resulting in exceptionally large ${_{\Lambda}^3}{\rm H}$ binding-energy $B_{\Lambda}({_{\Lambda}^3}{\rm H})=0.523\pm 0.013\pm 0.075$ MeV. Here I discuss an alternative interpretation of the observed sharp line in terms of ${_{\Lambda}^7}{\rm He}_{\rm g.s.}\to\pi^-+{^7{\rm Li}}(E_{\rm x}=478$ keV) weak decay and its implications for $B_{\Lambda}({_{\Lambda}^7}{\rm He})$.
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Hypernuclear constraints on $\Lambda N$ and $\Lambda NN$ interactions
Recent work on using density dependent $\Lambda$-nuclear optical potentials in calculations of $\Lambda$-hypernuclear binding energies is reviewed. It is found that all known $\Lambda$ binding energies in the mass range $16 \leq A \leq 208$ are well fitted in terms of two interaction parameters: one, attractive, for the spin-averaged $\Lambda N$ interaction and another one, repulsive, for the $\Lambda NN$ interaction. The $\Lambda N$ interaction term by itself overbinds $\Lambda$ hypernuclei, in quantitative agreement with recent findings obtained in EFT and Femtoscopy studies. The strength of the $\Lambda NN$ interaction term is compatible with values required to resolve the hyperon puzzle.
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Tribute to Tullio Bressani, Bogdan Povh and Toshimitsu Yamazaki
In this HYP2025 talk I pay tribute to Tullio Bressani (1940-2024), Bogdan Povh (1932-2024) and Toshimitsu Yamazaki (1934-2025), all of whom made lasting contributions to shaping up Strangeness Nuclear Physics. Yoshinori Akaishi's (1941-2025) record is also noted.
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Compatibility of recent ${\cal S}=-2$ emulsion events
We question the compatibility of recent ${\cal S}=-2$ hypernuclear assignments of J-PARC E07 $\Xi^-$-capture emulsion events with assignments deduced from other experiments.
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Tribute to Toshimitsu Yamazaki (1934-2025): Quest for Exotic Hadronic Matter
In this talk I pay tribute to Toshimitsu Yamazaki who died earlier this year. Yamazaki's leading contributions to Hadronic Physics, in particular to Strangeness Nuclear Physics in Japan and elsewhere, are well known. Two of the five Recurring Themes of his research, as listed in the Japan Academy site, are highlighted here: (i) Discovery of deeply bound pionic-atom states, and (ii) Search for kaonic nuclei -- Kaonic Proton Matter (KPM). I conclude by reviewing briefly my own recent work, confirming Farrar's conjecture that a deeply bound $H$ dibaryon is not ruled out by the weak-decay observation of $\Lambda\Lambda$ hypernuclei. However, the relatively long lifetime of such a deeply bound $H$ is much too short to qualify it for a Dark-Matter candidate.
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$\Lambda NN$ input to neutron stars from hypernuclear data
This work is a sequel to our two 2023 publications [PLB 837 137669, NPA 1039 122725] where fitting 14 1$s_\Lambda$ and 1$p_\Lambda$ single-particle binding energies in hypernuclei across the periodic table led to a well-defined $\Lambda$-nucleus optical potential. The potential consists of a Pauli modified linear-density ($\Lambda N$) and a quadratic-density ($\Lambda NN$) terms. The present work reports on extending the above analysis to 21 $\Lambda$ single-particle data points input by including 1$d_\Lambda$ and 1$f_\Lambda$ states in medium-weight and heavy hypernuclei. The upgraded results for the $\Lambda N$ and $\Lambda NN$ potential depths at nuclear-matter density $\rho_0=0.17$~fm$^{-3}$, $D^{(2)}_\Lambda=-37.5\mp 0.7$~MeV and $D^{(3)}_\Lambda=+9.8\pm 1.2$~MeV together with the total depth $D_\Lambda=-27.7\pm 0.5$~MeV, agree within errors with the earlier results. The $\Lambda$ hypernuclear overbinding associated with the $\Lambda N$-induced potential depth $D^{(2)}_\Lambda$ agrees quantitatively with a recent combined analysis of low-energy $\Lambda p$ scattering data and correlation functions [PLB 850 (2024) 138550]. These results, particularly the size of the repulsive $D^{(3)}_\Lambda$, provide an essential input towards resolving the 'hyperon puzzle' in the core of neutron stars. We also show that a key property of our $\Lambda NN$-induced potential term, i.e. a need to suppress the quadratic-density $\Lambda NN$ term involving an excess neutron and a $N=Z$ core nucleon, can be tested in the forthcoming JLab E12-15-008 experiment.
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Hypernuclear constraints on the existence and lifetime of a deeply bound $H$ dibaryon
We study to what extent the unique observation of $\Lambda\Lambda$ hypernuclei by their weak decay into known $\Lambda$ hypernuclei, with lifetimes of order 10$^{-10}$ s, rules out the existence of a deeply bound doubly-strange (${\cal S}$=$-$2) $H$ dibaryon. Treating ${_{\Lambda\Lambda}^{~~6}}{\rm He}$ (the Nagara emulsion event) in a realistic $\Lambda-\Lambda-{^4}$He three-body model, we find that the ${_{\Lambda\Lambda}^{~~6}}{\rm He}\to H + {^4{\rm He}}$ strong-interaction lifetime increases beyond 10$^{-10}$ s for $m_H < m_{\Lambda}+m_n$, about 176 MeV below the $\Lambda\Lambda$ threshold, so that such a deeply bound $H$ is not in conflict with hypernuclear data. Constrained by $\Lambda$ hypernuclear $\Delta{\cal S}$=1 nonmesonic weak-interaction decay rates, we follow EFT methods to evaluate the $\Delta{\cal S}$=2 $H\to nn$ weak-decay lifetime of $H$ in the mass range $2m_n \lesssim m_H < m_{\Lambda}+m_n$. The resulting $H$ lifetime is of order 10$^5$ s, many orders of magnitude shorter than required to qualify for a dark-matter candidate.
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Deciphering $\Xi^-$ capture events in light emulsion nuclei
We recently showed that all five KEK and J-PARC uniquely assigned two-body $\Xi^-$+${^A}$Z$\to{_{\Lambda}^{A'}}$Z'+${_{\Lambda}^{A''}}$Z'' capture events in CNO light emulsion nuclei are consistent with Coulomb-assisted $1p_{\Xi^-}$ nuclear states in a $\Xi$-nuclear potential of nuclear-matter depth $V_{\Xi}\gtrsim 20$ MeV [1]. Here we argue that the recently reported $^{14}$N capture events named KINKA and IRRAWADDY are more likely $1p_{\Xi^0}$--$^{14}$C nuclear states [2] than $1s_{\Xi^-}$--$^{14}$N states, the latter assignment implying considerably smaller values of $V_{\Xi}$.
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$\Lambda NN$ content of $\Lambda$-nucleus potential
A minimally constructed $\Lambda$-nucleus density-dependent optical potential is used to calculate binding energies of observed $1s_{\Lambda}$, $1p_{\Lambda}$ states across the periodic table, leading to a repulsive $\Lambda NN$ contribution $D_{\Lambda}^{(3)}\approx 14$ MeV to the phenomenological $\Lambda$-nucleus potential depth $D_{\Lambda}\approx -30$ MeV. This value is significant in connection with the so-called 'hyperon puzzle'.
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$\Xi$-nuclear constraints from $\Xi^-$ emulsion capture events
All five KEK and J-PARC two-body $\Xi^-$+$^A$Z $\to$ $^{A'}_{\Lambda}$Z'+$^{A''}_{\Lambda}$Z'' capture events in light emulsion nuclei, including KISO and IBUKI in $^{14}$N, are consistent with Coulomb-assisted $1p_{\Xi^-}$ nuclear states. The underlying $\Xi$-nuclear potential is strongly attractive, with nuclear-matter depth $V_{\Xi}$ larger than 20 MeV. The recent $^{14}$N capture events KINKA and IRRAWADDY assigned by J-PARC E07 to $1s_{\Xi^-}$ nuclear states, and implying considerably shallower $V_{\Xi}$, have also another interpretation as $1p_{\Xi^0}$ nuclear states.
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Recent progress on few-body hypernuclei
Few-body $\Lambda$ hypernuclei provide valuable information towards understanding strange matter. Recent experimental progress by the STAR Collaboration at the RHIC facility and by the ALICE Collaboration at the LHC has been matched by theoretical progress reviewed here: (i) lifetimes of the hypertriton $_{\Lambda}^3$H, $_{\Lambda}^3$n if particle-stable, $_{\Lambda}^4$H and $_{\Lambda}^4$He and their charge symmetry breaking, and (ii) the onset of $\Lambda\Lambda$ hypernuclear binding.
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Extracting $\sigma_{\pi N}$ from pionic atoms
We discuss a recent extraction of the $\pi N$ $\sigma$ term $\sigma_{\pi N}$ from a large-scale fit of pionic-atom strong-interaction data across the periodic table. The value thus derived, $\sigma_{\pi N}^{\rm FG}=57\pm 7$ MeV, is directly connected via the Gell-Mann--Oakes--Renner expression to the medium-renormalized $\pi N$ isovector scattering amplitude near threshold. It compares well with the value derived recently by the Bern-Bonn-J\"{u}lich group, $\sigma_{\pi N}^{\rm RS}=58\pm 5$ MeV, using the Roy-Steiner equations to control the extrapolation of the vanishingly small near threshold $\pi N$ isoscalar scattering amplitude to zero pion mass.
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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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The d*(2380) and its family of pion assisted dibaryons
The status of $N\Delta$ and $\Delta\Delta$ dibaryons introduced by Dyson and Xuong in 1964 is briefly reviewed with focus on the d*(2380), tentatively assigned as a $\Delta\Delta$ dibaryon resonance. It is argued that the apparently small value of width, $\Gamma_{d^\ast}$$\approx$70 MeV, favors hadronic structure for the d*(2380) dibaryon rather than a six-quark structure.
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Recent progress on hypernuclei
Some of last year's progress made in hypernuclear physics is reviewed as follows: (i) resolving the $_{\Lambda}^5$He overbinding problem in single-$\Lambda$ hypernuclei [1]; (ii) arguing that the onset of binding double-$\Lambda$ hypernuclei is most likely at $A$=5, with the neutral systems $_{\Lambda\Lambda}^{\,\,3}$n and $_{\Lambda\Lambda}^{\,\,4}$n unbound by a large margin [2]; and (iii) revising the calculated value of the loosely bound $_{\Lambda}^3$H lifetime to a level of $\sim$20% shorter than the free $\Lambda$ lifetime [3], given recent claims from relativistic heavy ion experiments that $\tau(_{\Lambda}^3$H) is shorter than $\tau_{\Lambda}$ by as much as $\approx$(30$\pm$8)%. Also discussed briefly in this context is the lifetime expected for the questionable $_{\Lambda}^3$n hypernucleus.
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B$_\Lambda$($^5_\Lambda$He) from short range effective field theory
We present an effective field theory (EFT) at leading order to describe light single-$\Lambda$ hypernuclei. Owing to the weak $\Lambda$ binding and to the $\Lambda N$ short interaction range, meson exchange forces are approximated by contact interactions within a pionless EFT where the only degrees of freedom are baryons. At leading order, the $\Lambda$-nuclear interaction contains two 2-body (singlet and triplet) and three 3-body interaction terms, a total of 5 terms associated with 5 coupling strengths or low energy constants (LECs). We adopt the 2-body LECs from hyperon-nucleon scattering data and interaction models that constrain the $\Lambda N$ scattering lengths, while the 3-body LECs are adjusted using both 3-body and 4-body hypernuclear binding energies. To calculate the binding energies for A-body systems with A$>$2, we expand the wavefunctions using a correlated Gaussian basis. The stochastic variational method is employed to select the non-linear parameters. The resulting \nopieft~is then applied to calculate the $\Lambda$ separation energy in $_\Lambda^5$He, where the adjusted 3-body interactions largely resolve the known overbinding problem of $_\Lambda^5$He.
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A diquark model for the d*(2380) dibaryon resonance?
Diquark models have been applied with varying degree of success to tetraquark and pentaquark states involving both light and heavy quark degrees of freedom. We discuss the applicability of such models to light quark dibaryons, viewed as three-diquark objects. Highlighting the case of the d*(2380) dibaryon resonance, we demonstrate the inapplicability of diquark models in the light quark sector.
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