Baryon-baryon bound states in the strangeness S=-2, S=-3, and S=-4 sectors are considered. In particular, the dependence of the corresponding binding energies on the quark mass (or equivalently the pion mass) is explored in the framework of chiral effective field theory, in order to connect with current lattice QCD calculations. For a bound state in the Xi-Xi 1S0 channel, predicted by our leading-order effective field theory interaction, binding energies are inferred that are roughly in line with a recent lattice QCD result at meson and baryon masses that correspond to those in the lattice simulation. With regard to the so-called H-dibaryon it is shown that the SU(3) breaking effects induced by the differences of the pertinent two-baryon thresholds (Lambda-Lambda, Xi-N, Sigma-Sigma) have a very pronounced impact on its binding energy. A bound H-dibaryon as found in two lattice calculations could be shifted above the Lambda-Lambda or even above the Xi-N threshold for physical masses of the involved baryons.
In this talk I look into three different topics, addressing first the possibility that the $Θ^+$ is a bound state of $K πN$, exploiting the results of this study to find out the contribution of two meson and one baryon components in the baryon antidecuplet and in the third place I present results on a new resonant exotic baryonic state which appears as dynamically generated by the Weinberg Tomozawa $ΔK$ interaction.
The mass formulae for the supernarrow dibaryons and the exotic baryons with small masses are consructed. With this aim their self energies are calculated in one loop approximation using the dispersion relations with two subtractions. The values of the masses obtained in this approach are in a good agreement with the experimental data. The mass formula for the baryons is also used to calculate the mass of the $Δ(1232)$ resonance.
We speculate about a heavy bottom-charm six-quark baryon. A semiclassical and a gaussian estimate reveal that the octet-octet bbb-ccc configuration can be energetically favored with respect to the singlet-singlet one. This result suggests that a confined bbb-ccc six-quark state may exist. Such objects may be produced in appreciable amount in heavy ion collisions at LHC energies.
We cautiously review the treatment of pentaquark exotic baryons in chiral soliton models. We consider two examples and argue that any consistent and self-contained description must go beyond the mean field approximation that only considers the classical soliton and the canonical quantization of its (would-be) zero modes via collective coordinates.
Exotic antidecuplet baryons are predicted to be not only surprisingly light but also very narrow. First we explain how small decay width arises in the quark soliton model. Next, we study possible mixing of exotic antidecuplet with Roper octet and discuss its phenomenological consequences.
We follow a model based on the SU(8) symmetry for the interaction of mesons with baryons. The model treats on an equal footing the pseudo-scalars and the vector mesons, as required by heavy quark symmetry. The T-matrix calculated within an unitary scheme in coupled channels has poles which are interpreted as baryonic resonances.
Recent experimental data appear to confirm the existence of the exotic Theta+ (uudd\bar{s}) baryon. Simple statistical considerations, which have generally proven rather successful, suggest that this particle should be produced in observable abundance in relativistic nuclear collisions at RHIC, where it may be identifed through the p-K0_s invariant mass spectrum. The observation would not only add new evidence for its existence, but would also provide an additional means for probing the collision system, especially with regard to strangeness.
In this work we study the possible QCD exotic states in the doubly charmed baryon sector. Within chiral effective theory, it is predicted that several excited baryons result from the $S$-wave scattering of ground-state doubly charmed baryons ($Ξ_{cc}^{++}, Ξ_{cc}^{+}, Ω_{cc}^{+}$) and light pseudoscalar mesons ($π, K, η$). The excited doubly charmed baryons can be classified by the strangeness ($S$) and isospin ($I$) quantum numbers. Two of the excited states are clearly exotic, in the sense that they cannot be explained by the conventional baryons with three quarks, since their quantum number…
The mass spectrum of the lowest lying octet baryons is calculated to next-to-next-to-leading order in heavy baryon chiral perturbation theory and partially quenched heavy baryon chiral perturbation theory. We work in the isospin limit and treat the decuplet baryons as dynamical fields. These results are necessary for extrapolating QCD and partially quenched QCD lattice simulations of the octet baryon masses.
The masses of the spin-3/2 baryons are calculated to next-to-next-to-leading order in heavy baryon chiral perturbation theory and partially quenched heavy baryon chiral perturbation theory. The calculation is performed for three light flavors in the isospin limit. These results are necessary for extrapolating QCD and partially quenched QCD lattice calculations of the decuplet baryon masses.
We have analyzed the chiral expansion of the baryon masses to second order in the quark masses, including strong isospin violation. The calculations are performed in Lorentz-invariant baryon chiral perturbation theory. Chiral extrapolation functions for three-flavor unquenched lattice simulations are derived. The matching to the two-flavor case and the sigma terms are also considered.
The relevance of chiral symmetry in baryons is highlighted in three examples in the nucleon spectroscopy and structure. The first one is the importance of chiral dynamics in understanding the Roper resonance. The second one is the role of chiral symmetry in the lattice calculation of $πN σ$ term and strangeness. The third one is the role of chiral $U(1)$ anomaly in the anomalous Ward identity in evaluating the quark spin and the quark orbital angular momentum. Finally, the chiral effective theory for baryons is discussed.
We compute the spectra of exotic pentaquarks and monopole excitations of the low--lying ${1/2}^+$ and ${3/2}^+$ baryons in a chiral soliton model. Once the low--lying baryon properties are fit, the other states are predicted without any more adjustable parameters. This approach naturally leads to a scenario in which the mass spectrum of the next to lowest--lying $J^π={1/2}^+$ states is fairly well approximated by the ideal mixing pattern of the $\mathbf{8}\oplus\bar{\mathbf{10}}$ representation of flavor SU(3). We compare our results to predictions obtained in other pictures for pentaquarks an…
Recent experiments at RHIC and LHC have demonstrated that there are excellent opportunities to produce light baryonic clusters of exotic matter (strange and anti-matter) in ultra-relativistic ion collisions. Within the hybrid-transport model UrQMD we show that the coalescence mechanism can naturally explain the production of these clusters in the ALICE experiment at LHC. As a consequence of this mechanism we predict the rapidity domains where the yields of such clusters are much larger than the observed one at midrapidity. This new phenomenon can lead to unique methods for producing exotic nuc…
From the interpretation of the $Θ^+$ baryon resonance as an excitation of the ``skyrmion liquid'' with SU(3) flavor symmetry $\bar{10}$ we deduce a new series of baryons, $Θ_1^{++}$, $Θ_1^{+}$ and $Θ_1^0$, situated at the top of the 27-plet of SU(3) flavor, with hypercharge Y=2, isospin T=1 and spin $J=\frac32$. The mass of $Θ_1$ is estimated 55 MeV/c^2 higher then the mass of $Θ^+$ and its width at 80 MeV. We also discuss the other baryons from the 27-plet.
A meson-baryon interaction in the charm $+1$, strangeness $-2$ and isospin $0$ sector is built from a t-channel vector meson exchange model employing effective Lagrangians. The implementation of coupled-channel unitarization in the s-wave scattering amplitudes gives rise to two structures that have similar masses and widths to those of the $Ω_c(3050)^0$ and $Ω_c(3090)^0$ states recently observed by the LHCb collaboration. A meson-baryon molecular interpretation of these resonances would assign their spin-parity to be $J^P=1/2^-$.
The K+ nucleon elastic scattering process has been reexamined in light of recent measurements which have found a narrow exotic S=+1 resonance in their KN invariant mass distributions. We have analyzed the existing database in order to consider the effect of a narrow state on fits to K+ nucleon observables.
The role of zero mode quantum corrections to the energy of baryonic systems with exotic quantum numbers (strangeness) is discussed. A simple expression for the contribution depending on strange inertia is obtained in the $SU(3)-$collective coordinate quantization approach, and it is shown that this correction stabilizes the systems the stronger the greater their baryon number is. Furthemore, systems are considered which could be interpreted in the quark model language as containing additional $q\bar q-$pairs. It is argued that a strange skyrmion crystal should have additional binding in compar…
We calculate hyperon-nucleon and hyperon-hyperon interactions at next-to-leading order in SU(3) baryon chiral perturbation theory extending earlier work by the Bonn-Juelich group. The constructed potentials in momentum space include all one- and two-meson exchange terms generated by the SU(3) chiral Lagrangian. Effects from intermediate decuplet baryons are considered as well. These chiral baryon-baryon potentials, together with appropriate contact terms, provide a new basis for systematic studies of hyperon-nucleon scattering and light hypernuclei.
We study heavy baryons with exotic flavor quantum numbers formed by a heavy meson and a nucleon (DbarN and BN) with positive parity. One pion exchange interaction, providing a tensor force, dominates as a long range force to bind the DbarN and BN ystems. In the heavy quark mass limit, pseudoscalar meson and vector meson are degenerate and the binding mechanism by the tensor force analogous to that in the nuclear systems becomes important. As a result, we obtain the DbarN and BN resonant states in the J^P=1/2^+, 3/2^+ and 5/2^+ channels with I=0.
Evidences and hints, both from the theoretical and experimental side, of exotic baryon resonances with B=S, have been with us for the last thirty years. The poor status of the general acceptance of these Z* resonances is partly due to the prejudice against penta-quark baryons and partly due to the opinion that a proof of the existence of exotic states must be rigorous. This can refer to the quality and amount of data gathered, and also to the analytical methods applied in the study of these resonances. It seems then mandatory that all possibilities and aspects be exploited. We do that by analy…
It is suggested that the narrow width of the recently observed resonance $Θ^{+}(1540)$ with strangeness $S=+1$ could be a result of the super-radiance mechanism of the redistribution of the widths of overlapping resonances due to their coupling through common decay channels.
A searche for supernarrow dibaryons (SND) and exotic baryons with small masses is reviewed. As a result of the study of the reaction pd->p+pX_1, three narrow peaks at M_{pX_1}=1904, 1926, and 1942 MeV have been observed. The analysis of the angular distributions of the protons from the decay of the pX_1 states showed that the peaks found can be explained as a manifestation of the isovector SNDs, the decay of which into two nucleons is forbidden by the Pauli exclusion principle. The observation of the peaks in the missing mass M_{X_1} spectra at 966, 986, and 1003 MeV is an additional indicatio…
It is argued that an appearance of the near parity doublets in the upper part of the light baryon spectrum is an evidence for the chiral symmetry restoration in the regime where a typical momentum of quarks is around the chiral symmetry restoration scale. At high enough baryon excitation energy the nontrivial gap solution, which signals the chiral symmetry breaking regime, disappears and the chiral symmetry should be restored. Thus one observes a phase transition in the upper part of the light baryon spectrum. The average kinetic energy of the constituent quarks in this region is just around t…
I report on recent progress in the description of baryon-baryon systems within chiral effective field theory. In particular, I discuss results for the strangeness S=-3 to -4 baryon-baryon systems, obtained to leading order.
Using the lowest order chiral Lagrangian we study s-wave interactions of the baryon decuplet with the octet of pseudoscalar mesons. We find two bound states in the flavour SU(3) limit corresponding to the octet and decuplet representations. These are found to split into eight different trajectories in the complex plane when the SU(3) symmetry is broken gradually. Finally, we are able to provide a reasonable description for a good number of 4-star 3/2- resonances listed by the Particle Data Group. In particular, the Xi(1820), the Lambda(1520) and the Sigma(1670) states are well reproduced. We p…
We study the exotic hadrons in s-wave scattering of the Nambu-Goldstone boson with a target hadron based on chiral dynamics. Utilizing the low energy theorem of chiral symmetry, we show that the s-wave interaction is not strong enough to generate bound states in exotic channels in flavor SU(3) symmetric limit, although the interaction is responsible for generating some nonexotic hadron resonances dynamically. We discuss the renormalization condition adopted in this analysis.
The full QCD chiral symmetry algebra has predictive consequences at low energies. I discuss the ground-state chiral multiplet involving the light baryons and emphasize the special role of the Roper resonance.
We have constructed the leading order strangeness S=-1,-2 baryon-baryon potential in a chiral effective field theory approach. The chiral potential consists of one-pseudoscalar-meson exchanges and non-derivative four-baryon contact terms. The potential, derived using SU(3) symmetry constraints, contains six independent low-energy coefficients. We have solved a regularized Lippmann-Schwinger equation and achieved a good description of the available scattering data. Furthermore a correctly bound hypertriton has been obtained.
We derive the leading order strangeness S=-2 baryon-baryon interactions in chiral effective field theory. The potential consists of contact terms without derivatives and of one-pseudoscalar-meson exchanges. The contact terms and the couplings of the pseudoscalar mesons to the baryons are related via SU(3) flavor symmetry to the S=-1 hyperon-nucleon channels. We show that the chiral effective field theory predictions with natural values for the low-energy constants agree with the experimental information in the S=-2 sector.
In the past, the axion-nucleon coupling has been calculated in the framework of SU(2) heavy baryon chiral perturbation theory up to third order in the chiral power counting. Here, we extend these earlier studies to the case of heavy baryon chiral perturbation theory with SU(3) flavor symmetry and derive the axion coupling to the full SU(3) baryon octet, showing that the axion also significantly couples to hyperons. As studies on dense nuclear matter suggest the possible existence of hyperons in stellar objects such as neutron stars, our results should have phenomenological implications related…
We investigate the production of the newly found pentaquark exotic baryon Xi_5 in the bar{K} N -> K Xi_5 and the bar{K} N -> K* Xi_5 reactions at the tree level. We consider both positive- and negative parities of the Xi_5. The reactions are dominated by the s- and u-channel processes, and the resulting cross sections depend very much on the parity of Xi_5 and on the type of form factor. We have seen that the cross sections for the positive-parity Xi_5 are generally about a hundred times larger than those of the negative-parity one. This large difference in the cross sections will be useful fo…
We evaluate a hadronic molecule formed by a heavy meson and a nucleon respecting heavy quark symmetry. The tensor force of pion exchange potential plays a dominate role to produce an strong attraction in this system. Solving coupled channel Schrödinger equations for PN and P* N, we find many bound and resonant states with isospin I=0 while there are few resonances in I=1 state. The rich structures with I=0 indicate that the spectrum of heavy baryons near the threshold is influenced by the contributions from such hadron composite structures.
We construct the most general chiral effective Lagrangian for baryon-baryon contact interactions in flavor SU(3) up to order q^2 using a covariant power counting. A subset of these contact terms contributes to the baryon-baryon potential in chiral effective field theory. The Lorentz invariant effective Lagrangian is constructed to fulfill the invariance under charge conjugation, parity transformation, Hermitian conjugation and the local chiral symmetry group SU(3)_L x SU(3)_R. Goldstone bosons and external fields are included as well, thus providing additional four-baryon contact vertices invo…
Given the existing empirical information about the exotic Theta+ baryon, we analyze possible properties of its SU(3)F-partners, paying special attention to the nonstrange member of the antidecuplet N*. The modified piN partial-wave analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases, the N* should be rather narrow and highly inelastic. Our results suggest several directions for experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons. Recent experimental evidence from the GRAAL and STAR Collaboration…
We explore a possibility to generate exotic hadrons dynamically in the scattering of hadrons. The s-wave scattering amplitude of an arbitrary hadron with the Nambu-Goldstone boson is constructed so as to satisfy the unitarity condition and the chiral low energy theorem. We find that the chiral interaction for the exotic channels is in most cases repulsive, and that the strength of the possible attractive interaction is uniquely determined. We show that the attractive interaction in exotic channels is not strong enough to generate a bound state, while the interaction in nonexotic channel genera…
Predictions for a light collective $Θ^+$ baryon state (with strangeness +1) based on the collective quantization of chiral soliton models are shown to be inconsistent with large $N_c$ QCD. The lightest strangeness +1 state to emerge from the analysis has an excitation energy which at large $N_c$ scales as $N_c^0$ while collective quantization is legitimate only for excitations which go to zero as $N_c \to \infty$. This inconsistency strongly suggests that predictions for $Θ^+$ properties based on collective quantization of chiral solitons are not valid.
A chiral effective theory of quarks and diquarks is formulated and applied to exotic tetraquarks and pentaquarks. The effective theory is similar to the chiral quark effective theory with the addition of diquark degrees of freedom and couplings to quarks. Chiral symmetry through generalized Goldberger-Treiman relations, fixes the mass splitting between the even and odd parity diquarks to be about 600 MeV. We provide an estimate of the parameters of the effective theory from both the random instanton model and known data on the low lying scalar nonet. We assess the static properties of the exot…
We investigate the magnetic moments of the baryon antidecuplet within the framework of the chiral quark-soliton model in the chiral limit in a ``\emph{model-independent}'' approach. Sum rules for the magnetic moments are derived. The magnetic moment of $Θ^{+}$ is found to be about $0.2\sim 0.3 μ_{N}$.
It is shown that in the large $N_c$ limit the light baryon spectrum exhibits the chiral restoration phase transition at high enough excitation energy. Such a phase transition is evidenced by the systematical parity doublets observed in the upper part of $N$ and $Δ$ spectra.
We compute the octet baryon charge radii to O(1/Heavy^3) in heavy baryon chiral perturbation theory. We examine the effect of including the decuplet of spin-3/2 baryons explicitly. We find that it does no t improve the level of agreement between the HBchiPT and experimental values for the Sigma^- charge radius.
We revisit the formation of pion-mediated heavy-light exotic molecules with both charm and bottom and their chiral partners under the general strictures of both heavy-quark and chiral symmetry. The chiral exotic partners with good parity formed using the $(0^+, 1^+)$ multiplet are about twice more bound than their primary exotic partners formed using the $(0^-,1^-)$ multiplet. The chiral couplings across the multiplets $(0^\pm, 1^\pm)$ cause the chiral exotic partners to unbind, and the primary exotic molecules to be about twice more bound, for $J\leq 1$. Our multi-channel coupling results sho…
Interactions of two baryons are considered in large $N_C$ chiral perturbation theory and compared to the interactions derived from the Skyrme model. Special attention is given to a torus-like configuration known to be present in the Skyrme model.
We illustrate the exotic SU(3) baryon sub-multiplets in the SU(4) baryon multiplets predicted from the flavor SU(4) collective-coordinate quantization, and investigate the exotic states with charm number $C=\pm1$ up to leading order of $1/N_c$ under chiral $SU(3)_L\times SU(3)_R$ symmetry and the heavy quark limit from bound state approach. We find that there exist the $\bar{15}$-plets and 24-plets with C=1 and the $\bar{6}$-plets, 15-plets and $15^{\prime}$-plets with $C=-1$ bounded in this approach, qualitatively consistent with predictions from the flavor SU(4) collective-coordinate quantiz…
We report on the recent studies of leading order baryon-baryon interactions in covariant baryon chiral perturbation theory. In the strangeness $S=0$ sector, one can achieve a rather good description of the Nijmegen $np$ phase shifts with angular momenta $J\leq 1$, particularly the $^1S_0$ and $^3P_0$ partial waves, comparable with the next-to-leading order (NLO) heavy baryon approach. In the strangeness $S=-1$ hyperon-nucleon sector, the best fit of the 36 scattering data is similar to the sophisticated phenomenological models and the NLO heavy baryon approach.
Results from an ongoing study of baryon-baryon systems with strangeness S=-1 and -2 within chiral effective field theory are reported. The investigations are based on the scheme proposed by Weinberg which has been applied rather successfully to the nucleon-nucleon interaction in the past. Results for the hyperon-nucleon and hyperon-hyperon interactions obtained to leading order are reviewed. Specifically, the issue of extrapolating the binding energy of the H-dibaryon, extracted from recent lattice QCD simulations, to the physical point is addressed. Furthermore, first results for the hyperon-…
Given presently known empirical information about the exotic Theta+ baryon, we analyze possible properties of its SU(3)F partners, paying special attention to the nonstrange member of the antidecuplet N*. The modified PWA analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases the N* should be highly inelastic. The theoretical analysis, based on the soliton picture and assumption of Gamma(Theta+) < 5 MeV, shows that most probably Gamma(N*) < 30 MeV. Similar analysis for Xi3/2 predicts its width to be not more than about 10 MeV. Our results suggest several directions for ex…
It is shown that the principal pattern in baryon spectroscopy, which is associated with the flavor-spin dependent hyperfine interaction, is due to the spontaneous breaking of chiral symmetry in QCD and persists in the chiral limit. All corrections, which are associated with a finite quark (Goldstone boson) mass are suppressed by the factor $(μ/Λ_χ$)^2 and higher.
I review the present status of three flavor baryon chiral perturbation theory in the heavy fermion formalism. It is argued that precise calculations have to include all terms quadratic in the quark masses. As examples, I consider the chiral expansion of the octet baryon masses, the baryon magnetic moments and kaon photoproduction off nucleons.
We have systematically investigated the magnetic moments and magnetic form factors of the decuplet baryons to the next-to-next-leading order in the framework of the heavy baryon chiral perturbation theory. Our calculation includes the contributions from both the intermediate decuplet and octet baryon states in the loops. We also calculate the charge and magnetic dipole form factors of the decuplet baryons. Our results may be useful to the chiral extrapolation of the lattice simulations of the decuplet electromagnetic properties.
We study s-wave scattering of a hadron and a Nambu-Goldstone boson induced by the model-independent low energy interaction in the flavor SU(3) symmetric limit. Establishing the general structure of the low energy interaction based on group theoretical arguments, we find that the interaction in the exotic channels are in most cases repulsive, and that for possible attractive channels the interaction strengths are weak and uniquely given independent of channel. Solving the scattering problem with this interaction, we show that the attraction in the exotic channels is not strong enough to generat…
We review recent progress in the understanding of low-energy baryon structure by means of chiral perturbation theory. In particular, we discuss the application of this formalism to the description of various properties such as the baryon-octet magnetic moments, the electromagnetic structure of decuplet resonances and the hyperon vector coupling $f_1(0)$. Moreover, we present the results on the chiral extrapolation of recent lattice QCD results on the lowest-lying baryon masses and we predict the corresponding baryonic sigma-terms.
We discuss the masses of the ground state baryon octet and the nucleon sigma terms in the framework of manifestly Lorentz-invariant baryon chiral perturbation theory. In order to obtain a consistent power counting for renormalized diagrams the extended on-mass-shell renormalization scheme is applied.
The thermal properties of cold dense nuclear matter are investigated with chiral perturbation theory. The evolution curves for the baryon number density, baryon number susceptibility, pressure and the equation of state are obtained. The chiral condensate is calculated and our result shows that when the baryon chemical potential goes beyond $1150 \mathrm{MeV}$, the absolute value of the quark condensate decreases rapidly, which indicates a tendency of chiral restoration.
We report on some recent developments in our understanding of the light-quark mass dependence and the SU(3) flavor symmetry breaking corrections to the magnetic moments of the ground-state baryons in a covariant formulation of baryon chiral perturbation theory, the so-called EOMS formulation. We show that this covariant ChPT exhibits some promising features compared to its heavy-baryon and infrared counterparts.
It is demonstrated that using a suitable renormalization condition one obtains a consistent power counting in manifestly Lorentz-invariant baryon chiral perturbation theory including vector mesons as explicit degrees of freedom.
The QCD sum-rule method has been widely used in studying various baryon properties. For a given problem, there are usually more than one sum rules and they do not work equally well. In this paper, we point out that chirality plays an important role in determining the reliability of a baryon sum rule. The contributions of positive- and negative-parity excited baryon states partially cancel each other in the chiral-odd sum rules, but add up in the chiral-even sum rules. As such, the chiral-odd sum rules are generally more reliable than the chiral-even sum rules. This allows one to identify the m…
The stability of strange matter depends on the implicit assumption that baryon number is conserved. We examine the relevant effective operators which allow strangelets to decay by violating the conservation of baryon number. From the experimental lower limit of 10$^{25}$ years on the stability of nuclei, we find a lower limit of the order 10$^6$ years on the stability of strangelets against such exotic decays.
