The non-mesonic weak decay of $Λ$--hypernuclei is studied within a one-meson-exchange potential supplemented by a chirally motivated two-pion-exchange mechanism. The effects of final state interactions on the outgoing nucleons are also taken into account. In view of the severe discrepancies between theoretical expectations and experimental data, particular attention is payed to the asymmetry of the protons emitted by polarized hypernuclei. The one-meson-exchange model describes the non-mesonic rates and the neutron-to-proton ratio satisfactorily but predicts a too large and negative asymmetry parameter. The uncorrelated and correlated two-pion mechanisms change the rates moderately, thus maintaining the agreement with experiment. The modification in the strength and sign of some decay amplitudes becomes crucial and produces asymmetry parameters which lie well within the experimental observations.
We review the mechanism of weak decay of hypernuclei, with emphasis on the non-mesonic decay channels. Various theoretical approaches are discussed and the results are compared with the available experimental data.
We analyze the recent data on the non-mesonic decays of light Lambda-hypernuclei up to ^12_Lambda C using the phenomenological model of Block and Dalitz. Fitting the spin-isospin dependent Lambda N -> NN reaction rates to six data points, we predict the remaining data in reasonable consistency. We find that despite the short-range nature of the Lambda N -> NN interaction, the non-mesonic decay of p-shell hypernuclei seems to be strongly induced by the p-shell neutrons. Also, the recent data indicate that the Delta I = 1/2 rule, well proved at the hadronic level, may not be sacred in the nuclea…
By employing recent data on non-mesonic decay of s-shell Lambda-hypernuclei we study, within the phenomenological model of Block and Dalitz, the validity of the Delta I=1/2 rule in the Lambda N--> NN process. Due to the low experimental precision, a possible violation of this rule can be neither proved nor excluded at present with sufficient accuracy: a pure Delta I=1/2 transition amplitude is excluded at 40% confidence level.
The contribution of Pauli exchange terms to the two--nucleon induced non--mesonic weak decay of $^{12}_Λ$C hypernuclei, $ΛNN\to nNN$ ($N=n$ or $p$), is studied within a nuclear matter formalism implemented in a local density approximation. We have adopted a weak transition potential including the exchange of the complete octets of pseudoscalar and vector mesons as well as a residual strong interaction modeled on the Bonn potential. The introduction of exchange terms turns out to reduce the two--nucleon induced non--mesonic rate by 18% and, jointly with an increase in the one--nucleon induced r…
We present an evaluation of the non-mesonic decay widths for Lambda-hypernuclei (Lambda N --> NN, Lambda NN --> NNN) within the framework of the polarization propagator method. The full Lambda self-energy is evaluated microscopically in nuclear matter by using the functional approach, which supplies a theoretically well grounded approximation scheme for the classification of the relevant diagrams, according to the prescriptions of the bosonic loop expansion. We employ average Fermi momenta, suitably adapted to different mass number regions (medium-light, medium and heavy hypernuclei). Moreover…
The focus of these Lectures is on the weak decay modes of hypernuclei, with special attention to Lambda-hypernuclei. The subject involves many fields of modern theoretical and experimental physics, from nuclear structure to the fundamental constituents of matter and their interactions. The various weak decay modes of Lambda-hypernuclei are described: the mesonic mode and the non-mesonic ones. The latter are the dominant decay channels of medium--heavy hypernuclei, where, on the contrary, the mesonic decay is disfavoured by Pauli blocking effect on the outgoing nucleon. In particular, one can d…
The non--mesonic weak decay of double--$Λ$ hypernuclei is studied within a microscopic diagrammatic approach. Besides the nucleon--induced mechanism, $ΛN\to nN$, widely studied in single--$Λ$ hypernuclei, additional hyperon--induced mechanisms, $ΛΛ\to Λn$, $ΛΛ\to Σ^0 n$ and $ΛΛ\to Σ^-p$, are accessible in double--$Λ$ hypernuclei and are investigated here. As in previous works on single--$Λ$ hypernuclei, we adopt a nuclear matter formalism extended to finite nuclei via the local density approximation and a one--meson exchange weak transition potential (including the ground state pseudoscalar an…
One of the main open problems in the physics of Lambda-hypernuclei is the lack of a sound theoretical interpretation of the large experimental values for the ratio Gn/Gp=G(Lambda n -> nn)/G(Lambda p -> np). To approach the problem, we have incorporated a one-meson-exchange model for the Lambda N -> nN transition in finite nuclei in an intranuclear cascade code for the calculation of single and double-coincidence nucleon distributions corresponding to the non-mesonic weak decay of 5_Lambda-He and 12_Lambda-C. Due to the elimination of interferences, two-nucleon coincidences are expected to give…
Theoretical descriptions of the non-mesonic weak decay of Lambda-hypernuclei are unable to reproduce the experimental values of the ratio Gn/Gp=G(Lambda n -> nn)/G(Lambda p -> np). In this contribution we discuss a new approach to this problem. We have incorporated a one-meson-exchange model for the Lambda N -> nN transition in finite nuclei in an intranuclear cascade code for the calculation of double-coincidence nucleon distributions corresponding to the non-mesonic decay of 5_Lambda-He and 12_Lambda-C. The two-nucleon induced decay mechanism, Lambda np -> nnp, has been taken into account wi…
The main open problem in the physics of Lambda-hypernuclei is the lack of a sound theoretical interpretation of the large experimental values for the ratio G_n/G_p. To approach the problem, we have incorporated a Lambda N-> nN one-meson-exchange model in an intranuclear cascade code for a finite nucleus calculation of the nucleon-nucleon (angular and energy) coincidence distributions in the non-mesonic weak decay of 5_Lambda-He and 12_Lambda-C hypernuclei. The two-nucleon induced decay mechanism, Lambda np-> nnp, has been taken into account by means of the polarization propagator formalism in …
The non--mesonic weak decay of polarized $Λ$-hypernuclei is studied with a microscopic diagrammatic formalism in which one- and two-nucleon induced decay mechanisms, $\vecΛ N \to NN$ and $\vecΛ NN \to NNN$, are considered together with (and on the same ground of) nucleon final state interactions. We adopt a nuclear matter formalism extended to finite nuclei via the local density approximation. Our approach adopts different one-meson-exchange weak transition potentials, while the strong interaction effects are accounted for by a Bonn nucleon-nucleon interaction. We also consider the two-pion-ex…
We review recent developments concerning the weak decay of Lambda hypernuclei. New studies covering the mesonic decay channel as well as recent models for the non-mesonic one are discussed and compared with experimental data. The puzzle of the neutron- to proton-induced decay ratio, Gamma_n/Gamma_p, is addressed in connection to the two-nucleon induced decay channel and proposals for more efficient experimental analyses of this ratio are made.
The physics of the weak decay of hypernuclei is briefly reviewed from a theoretical point of view. Special regard is devoted to the recent progress concerning the determination of the non--mesonic decay widths and the asymmetry parameters. While convincing evidence has been achieved for a solution of the long-standing puzzle on the ratio Gamma_n/Gamma_p, the discrepancies between theory and experiment on the decay asymmetries clearly highlight the exigence of dedicating further efforts in exploring new aspects of the dynamics underlying the non-mesonic weak decay.
The non-mesonic weak decay of polarized Lambda-hypernuclei is studied for the first time by taking into account, with a Monte Carlo intranuclear cascade code, the nucleon final state interactions. A one-meson-exchange model is employed to describe the Lambda N-> n N processes in a finite nucleus framework. The relationship between the intrinsic Lambda asymmetry parameter a_Λand the asymmetry a^M_Λaccessible in experiments is discussed. A strong dependence of a^M_Λon nucleon final state interactions and detection threshold is obtained. Our results for a^M_Λare consistent with ^{11}_ΛB and ^{12}…
The $Λ$-$Λ$ effective interaction, in the channel $L=S=0$, in the nuclear medium is fitted to the available binding energies, $B_{ΛΛ}$, of double $Λ$ hypernuclei: $^{6}_{ΛΛ}$He, $^{10}_{ΛΛ}$Be and $^{13}_{ΛΛ}$B. The mesonic decay of these hypernuclei is also investigated. Finally, this effective interaction is used to predict the binding energies and mesonic decays widths of heavier double $Λ$ hypernuclei.
In this contribution we discuss an evaluation of double-nucleon coincidence spectra for the non-mesonic weak decay of Lambda-hypernuclei. The results have been obtained by combining a one-meson-exchange model for the Lambda N -> nN transition in finite nuclei with a Monte Carlo code accounting for the nucleon final state interactions. A weak-decay-model independent analysis of KEK coincidence data allows us to extract Gn/Gp values around 0.3-0.4 for 5_Lambda-He and 12_Lambda-C, thus representing an important progress towards the solution of the Gn/Gp puzzle. Preliminary results for the angular…
Contributions of the direct quark mechanism are studied in the nonmesonic weak decays of light hypernuclei. The $ΛN \to NN$ transition is described by the one pion exchange mechanism and the direct quark mechanism, induced by the four-quark vertices in the effective weak Hamiltonian. By employing a realistic wave function of the $Λ$ inside the hypernuclei, nonmesonic decay rates of $^4_Λ$H, $^4_Λ$He, and $^5_Λ$He are calculated. The results show that the direct quark mechanism is significantly large and gives a large $ΔI =3/2$ contribution in the J=0 channel. The relative phase between the one…
$Λ^+_c$ hypernuclei are expected to have binding energies and other properties similar to those of strange hypernuclei in view of the similarity between the quark structures of the strange and charmed hyperons, namely $Λ(uds)$ and $Λ^+_c (udc)$. One striking difference however occurs in their mesonic decays, as there is almost no Pauli blocking in the nucleonic decay of a charm hypernucleus because the final-state nucleons leave the nucleus at high energies. The nuclear medium nevertheless affects the mesonic decays of charm hypernucleus because the nuclear mean fields modify the masses of the…
Previous studies of proton and neutron spectra from Non-Mesonic Weak Decay of eight Lambda-Hypernuclei (A = 5-16) have been revisited. New values of the ratio of the two-nucleon and the one-proton induced decay widths, Gamma_2N/Gamma_p, are obtained from single proton spectra, Gamma_2N/Gamma_p = 0.50 +/- 0.24, and from neutron and proton coincidence spectra, Gamma_2N/Gamma_p = 0.36 +/- 0.14stat +0.05sys -0.04sys , in full agreement with previously published ones. With these values, a method is developed to extract the one-proton induced decay width in units of the free Lambda decay width, Gamm…
We evaluate pionic decay widths of Lambda hypernuclei using a shell model for, both the nuclear bound and the continuum nucleon wave functions in the final state, and distorted waves for the outgoing pion. An excellent agreement with the recent KEK measurement of $π^-$-decay widths of $^{12}_Λ$C and $^{28}_Λ$Si is found. Besides, results for $^{56}_Λ$Fe are consistent with the existing upper bound.
We have made a new evaluation of the Lambda decay width in nuclear matter within the Propagator Method. Through the Local Density Approximation it is possible to obtain results in finite nuclei. We have also studied the dependence of the widths on the N-N and Lambda-N short range correlations. Using reasonable values for the parameters that control these correlations, as well as realistic nuclear densities and Lambda wave functions, we reproduce, for the first time, the experimental non-mesonic widths in a wide range of mass numbers (from medium to heavy hypernuclei).
The Lambda decay rates in nuclei has been calculated in ref. 1 using the Propagator Method in Local Density Approximation. We have studied the dependence of the widths (including the one for the two-body induced process Lambda NN -> NNN) on the N-N and Lambda-N short range correlations. Using a reasonable parametrization of these correlations, as well as realistic nuclear densities and Lambda wave functions, we reproduce, for the first time, the experimental non-mesonic widths from medium to heavy hypernuclei.
In this review we discuss the present status of strange nuclear physics, with special attention to the weak decay of Lambda hypernuclei. The models proposed for the evaluation of the Lambda decay widths are summarized and their results are compared with the data. Despite the recent intensive investigations, the main open problem remains a sound theoretical interpretation of the large experimental values of the ratio G_n/G_p. Although recent works offer a step forward in the solution of the puzzle, further efforts must be invested in order to understand the detailed dynamics of the non-mesonic …
We study the non-mesonic weak decay of the doubly-strange hypernucleus $^{ΛΛ}_6$He within a model which considers the exchange of pseudoscalar and vector mesons. Special attention is paid into quantifying the strong interaction effects, focussing on the interaction among the two Λ hyperons which induces novel weak transitions, whereby ΛΛ, ΞN and ΣΣ states decay into a hyperon-nucleon pair. The initial strangeness -2 wave function is obtained from the solution of a G-matrix equation with the input of realistic strong baryon-baryon potentials, while the final hyperon-nucleon wave functions are d…
Properties of $Λ,~Ξ^0$ hypernuclei and neutron stars are investigated in quark mean field model with pion and gluon corrections. Firstly, $u, ~d$, and $s$ quarks are confined by relativistic harmonic oscillator potentials to generate the baryons, like nucleon, $Λ, ~Σ$, and $Ξ$ hyperons. The effects of pion-quark coupling and one-gluon exchange are considered perturbatively. Then, the baryons interact with each other through exchanging $σ, ~ω,$ and $ρ$ mesons between quarks in hypernuclei and nuclear matter. The strengths of confinement potentials for $u, ~d,$ and $s$ quarks are determined by t…
We fit the $^1 S_0 ΛΛ$ interaction in the nuclear medium to the masses of the experimentally known double-$Λ$ hypernuclei: $^{\phantom{6}6}_{ΛΛ}$He, $^{10}_{ΛΛ}$Be and $^{13}_{ΛΛ}$B. We derive this effective interaction from OBE Jülich $ΛΛ$-type potentials and using both Hartree-Fock and variational approaches. We find that the inclusion of $ΛΛ$ correlations in the variational scheme leads to significant differences and a better understanding of the dynamical features of the system. We investigate the sensitivity of the binding energies and the mesonic decay widths of the above double-$Λ$ hype…
The weak decays of hyperons and hypernuclei are studied from the chiral symmetry viewpoint. The soft pion relations are useful in understanding the isospin properties of the weak hyperon decays. Recent development on the short-range part of the $\Lam N\to NN$ weak transitions shows fairly good account of the weak decays of hypernuclei, though it fails to explain the $n/p$ ratio. The $\pip$ decays of light hypernuclei are studied in the soft pion approach. They are related to the $\DI=3/2$ amplitudes of the nonmesonic decay.
Low energy $π^+$ emission in hypernuclear weak decays is studied in the soft pion limit. It is found that the $π^+$ decay amplitude is dominated by the $ΔI=3/2$ part of nonmesonic weak decays according to the soft pion theorem. The ratios, $R(π^+/soft π^-) $, for light hypernuclei are estimated in the direct quark mechanism, which predicts violation of the $ΔI=1/2$ rule, and found to be about 1/3 for $^4_ΛHe$.
We take an approach to the Lambda non-mesonic weak decay in nuclei based on the exchange of mesons. The one pion and one kaon exchange are considered, together with the exchange of two pions, either correlated, leading to an important scalar-isoscalar exchange (sigma-like exchange), or uncorrelated (box diagrams). Extra effects of omega exchange in the scalar-isoscalar channel are also considered. Constraints of chiral dynamics are used to generate these exchanges. A drastic reduction of the OPE results for the Gamma_n/Gamma_p ratio is obtained and the new results are compatible with all prese…
A consistent microscopic diagrammatic approach is applied for the first time to the calculation of the nucleon emission spectra in the non-mesonic weak decay of Lambda-hypernuclei. We adopt a nuclear matter formalism extended to finite nuclei via the local density approximation, a one--meson exchange weak transition potential and a Bonn nucleon-nucleon strong potential. Ground state correlations and final state interactions, at second order in the nucleon--nucleon interaction, are introduced on the same footing for all the isospin channels of one- and two-nucleon induced decays. Single and dou…
The general character of 4-quark (mesonic) and strange 6-quark (baryonic) quark systems is very briefly reviewed a la Jaffe, i.e. in the MIT bag, and so far still possibly viable candidates are indicated. Concentration is on S=-2 systems. Traditionally, one employs the (K^-,K^+) reaction on a relatively light target and hopes to retain two units of strangeness on a single final state fragment. Alternatively, heavy ion reactions can be used to produce Lambda-hyperons copiously and one seeks to observe coalescence of two of these particles into the lightest S=-2 nucleus, the H-dibaryon. The comp…
Recent progress has been experienced in the field of hypernuclear weak decay, especially concerning the ratio of the neutron- to proton-induced Lambda non-mesonic decay rates, G_n/G_p. Theoretical analyses of nucleon coincidence data have been performed in a finite nucleus framework. They led to the extraction of G_n/G_p values in agreement with pure theoretical estimates, thus providing an evidence for the solution of a longstanding puzzle. Here we present an alternative approach to the problem, based on a nuclear matter formalism extended to finite nuclei via the local density approximation.…
The nonmesonic weak decay of $Λ$ hypernuclei is studied using nuclear matter. We have developed a formalism which gives a microscopic interpretation of the process of emission of particles originated in this decay. More specifically, our scheme provides a unified treatment of $Γ(ΛN \to NN$) and $N_{N}$ ($N_{NN}$), the $Λ$ non-mesonic weak decay widths and the number of emitted particles (pair of particles) of kind $N$ ($NN$), respectively. We have also evaluated for the first time the quantum interference terms between the $n$- and $p$-induced weak decay amplitudes. Explicit expressions for $N…
Single and double coincidence nucleon spectra in the $Λ$-hypernuclei weak decay are evaluated and discussed using a microscopic formalism. Nuclear matter is employed together with the local density approximation which allows us to analyze the $^{12}_ΛC$ hypernucleus non-mesonic weak decay. Final state interactions (FSI) are included via the first order (in the nuclear residual interaction) terms to the RPA, where the strong residual interaction is modelled by a Bonn potential. At this level of approximation, these FSI are pure quantum interference terms between the primary decay $(ΛN \to NN)$ …
A detailed comparison is made between the spin-orbit interactions in $Λ$ hypernuclei and ordinary nuclei. We argue that there are three major contributions to the spin-orbit interaction: 1) a short-range component involving scalar and vector mean fields; 2) a ''wrong-sign'' spin-orbit term generated by the pion exchange tensor force in second order; and 3) a three-body term induced by two-pion exchange with excitation of virtual $Δ(1232)$-isobars (a la Fujita-Miyazawa). For nucleons in nuclei the long-range pieces related to the pion-exchange dynamics tend to cancel, leaving room dominantly fo…
The ratio N_{nn}/N_{np} between the number of neutron-neutron and neutron--proton pairs emitted in the non--mesonic weak decay of Λ-hypernuclei is calculated within a nuclear matter formalism extended to ^{12}_{Lambda}C via the local density approximation. The single--nucleon emission spectra, N_p and N_n, are also evaluated. Our formalism takes care of both ground state correlations (gsc) and final state interactions (FSI). The evaluation of N_{nn}/N_{np} which, unlike Gamma_n/Gamma_p = Gamma(Lambda n -> nn)/Gamma(Lambda p -> np), is an actual observable quantity in non--mesonic decay is perf…
The momentum distributions of pions and $ρ$-mesons in the nucleon are extracted from experiment. Perspectives of the quark microscopic theory of mesonic cloud are outlined.
Generalized mesonic Super-Čerenkov Radiations (SČR) are investigated. The energy behavior of the pionic refractive index in the low energy pionic SCR-sector is presented. We estimated that the true coherent SCR-pion emission is possible mainly in the SCRS-energy bands 190-315 MeV for all pions; 910-960 MeV only for positive pions, and 80-1000 GeV for all pions, in certain nuclear reactions. We predicted that SČR-pionic band will be enlarged for the pion energies higher than 80 GeV. The strong correlations between angle of SCR-pion emission and (meson and projectile)-energies are evidentiated. …
We use the self-consistent mean-field theory to discuss the ground state and decay properties of $Λ$ hypernuclei. We first discuss the deformation of $Λ$ hypernuclei using the relativistic mean-field (RMF) approach. We show that, although most of hypernuclei have a similar deformation parameter to the core nucleus, the shape of $^{28}$Si is drastically altered, from oblately deformed to spherical, if a $Λ$ particle is added to this nucleus. We then discuss the pionic weak decay of neutron-rich $Λ$ hypernuclei using the Skyrme Hartree-Fock + BCS method. We show that, for a given isotope chain, …
The non-mesonic weak decay of $Λ$-hypernuclei is studied within a microscopic diagrammatic approach which includes, for the first time, the effect or the $Δ$-baryon resonance. We adopt a nuclear matter formalism extended to finite nuclei via the local density approximation, a one-meson exchange weak transition potential, a Bonn nucleon-nucleon strong potential and a $ΔN\to NN$ strong potential based on the Landau-Migdal theory. Ground state correlations and final state interactions (FSI), at second order in the baryon-baryon strong interaction, are introduced on the same footing for all the is…
The contribution of ground state correlations (GSC) to the non--mesonic weak decay of $^{12}_Λ$C and other medium to heavy hypernuclei is studied within a nuclear matter formalism implemented in a local density approximation. We adopt a weak transition potential including the exchange of the complete octets of pseudoscalar and vector mesons as well as a residual strong interaction modeled on the Bonn potential. Leading GSC contributions, at first order in the residual strong interaction, are introduced on the same footing for all isospin channels of one-- and two--nucleon induced decays. Toget…
We consider the $ΛN\to NN$ weak transition, responsible for a large fraction of the non-mesonic weak decay of hypernuclei. We follow on the previously derived effective field theory and compute the next-to-leading one-loop corrections. Explicit expressions for all diagrams are provided, which result in contributions to all relevant partial waves.
Two different approaches have been employed for the evaluation of the decay widths of Lambda-hypernuclei (ranging from $^5_Λ$He to $^{208}_Λ$Pb) with the polarization propagator method. In ref.[1], the two-nucleon stimulated non-mesonic decay, $ΛNN\to NNN$, has been parameterized phenomenologically by means of data on the pion-nucleus optical potential. The other approach [2] consisted in a fully microscopic description of the non-mesonic decays through the first order approximation of the so-called bosonic-loop-expansion. Both calculations reproduce, with approximately the same accuracy, the …
We analyze the contributions of hadronic final-state interactions to the strong phases generated in the B -> Kpipi weak decays. To this end, we develop an alternative approach to the commonly employed isobar model based upon scalar and vector form factors for pion-pion and pion-kaon interactions.
Pion-nucleon elastic scattering in the dominant $P_{33}$ channel is examined in the model in which the interaction is of the form $π+ N\leftrightarrow N, Δ(1232)$. New expressions are found for the elastic pion-nucleon scattering amplitude which differ from existing formula both in the kinematics and in the treatment of the renormalization of the nucleon mass and coupling constant. Fitting the model to the phase shifts in the $P_{33}$ channel does not uniquely fix the parameters of the model. The cutoff for the pion-nucleon form factor is found to lie in the range $β= 750\pm350$ MeV/c. The mas…
We present a nonrelativistic transition potential for the weak strangeness-changing reaction $ΛN \to NN$. The potential is based on a one meson exchange model (OME), where, in addition to the long-ranged pion, the exchange of the pseudoscalar $K, η$, as well as the vector $ρ, ω, K^*$ mesons is considered. Results obtained for different hypernuclear decay observables are compared to the available experimental data.
Owing to the Kubo relation, the shear viscosities of pionic and nucleonic components have been evaluated from their corresponding retarded correlators of viscous stress tensor in the static limit, which become non-divergent only for the non-zero thermal widths of the constituent particles. In the real-time thermal field theory, the pion and nucleon thermal widths have respectively been obtained from the pion self-energy for different meson, baryon loops and the nucleon self-energy for different pion-baryon loops. We have found a non-monotonic momentum distributions of pion and nucleon thermal …
We present a study of the nonmesonic weak decay (NMWD) of charmed hypernuclei using a relativistic formalism. We work within the framework of the independent particle shell model and employ a ($π$,$K$) one-meson-exchange model for the decay dynamics. We implement a fully relativistic treatment of nuclear recoil. Numerical results are obtained for the one-neutron-induced transition NMWD rates of the $_{Λ^{+}_{c}}^{12}$N. The effect of nuclear recoil is sizable and goes in the direction to decrease the nuclear decay rate. We found that the NMWD decay rate of $_{Λ^{+}_{c}}^{12}$N is of the same o…
The dynamical content of rho-N-N and rho-N-Delta vertex functions is studied with a mesonic model. A set of coupled integral equations satisfied by these vertex functions were solved self-consistently. These soulutions indicate that the dominant mesonic content arises from di-pion dynamics. With the experimentally determined pion-baryon-baryon coupling constants and ranges as input, the model predicts a g_{ρNN} that agrees with the meson-exchange-potential results. On the other hand, it predicts a smaller f_{ρNΔ} and much softer form factors. Implications of the findings on the use of phenomen…
We compute for the first time the decay width of lambda-hypernuclei in a relativistic mean-field approximation to the Walecka model. Due to the small mass difference between the lambda-hyperon and its decay products---a nucleon and a pion---the mesonic component of the decay is strongly Pauli blocked in the nuclear medium. Thus, the in-medium decay becomes dominated by the non-mesonic, or two-body, component of the decay. For this mode, the lambda-hyperon decays into a nucleon and a spacelike nuclear excitation. In this work we concentrate exclusively on the pion-like modes. By relying on the …
Electromagnetic current-current correlators in pionic and nucleonic medium have been evaluated in the static limit to obtain electrical conductivities for pion and nucleon components respectively, where former decreases and latter one increases with the variation of temperature $T$ and baryon chemical potential $μ_N$. Therefore, total electrical conductivity of pion and nucleon system exhibits a valley structure in the $T$-$μ_N$ plane. To get non-divergent and finite values of correlators, finite thermal widths of medium constituents, pion and nucleon have been considered, where these thermal …
The finite temperature phase transition of strongly interacting matter is studied within a nonlocal chiral quark model of the NJL type coupled to a Polyakov loop. In contrast to previous investigations which were restricted to the mean-field approximation, mesonic correlations are included by evaluating the quark-antiquark ring sum. For physical pion masses, we find that the pions dominate the pressure below the phase transition, whereas above T_c the pressure is well described by the mean-field approximation result. For large pion masses, as realized in lattice simulations, the meson effects …
The contribution of mesonic exchange currents to nuclear Compton scattering is investigated within the framework of a Fermi gas model of nuclear matter in the non-relativistic limit. The additional interaction between the nucleons is accounted for by including two- and three-body diagrams. As a test of this model, the enhancement constant $κ$ is calculated. The full correlators for the central and tensor part of the nucleon-nucleon interaction due to pion exchange are obtained and the energy dependence of the amplitude is investigated. The contribution of the $Δ$-excitation to the mesonic part…
The quark mean-field (QMF) model is applied to study the single $Λ^+_c$ hypernuclei. The charm baryon, $Λ^+_c$, is constructed by three constituent quarks, $u, ~d$, and $c$, confined by central harmonic oscillator potentials. The confinement potential strength of charm quark is determined by fitting the experimental masses of charm baryons, $Λ^+_c,~Σ^+_c$, and $Ξ^{++}_{cc}$. The effects of pions and gluons are also considered to describe the baryons at the quark level. The baryons in $Λ^+_c$ hypernuclei interact with each other through exchanging the $σ,~ω$, and $ρ$ mesons between the quarks c…
A recently introduced relativistic nuclear energy density functional, constrained by features of low-energy QCD, is extended to describe the structure of hypernuclei. The density-dependent mean field and the spin-orbit potential of a $Λ$-hyperon in a nucleus, are consistently calculated using the SU(3) extension of in-medium chiral perturbation theory. The leading long-range $ΛN$ interaction arises from kaon-exchange and $2π$-exchange with a $Σ$-hyperon in the intermediate state. Scalar and vector mean fields, originating from in-medium changes of the quark condensates, produce a sizeable {\em…
