If the exotic baryon $\Theta^+(1540)$ is a correlated $udud\bar{s}$ with $J^P = {1/2}^+$, then there should exist an exotic meson, $J^P = 1^-$ $\vartheta^+ (S=+2)$ $\to K^+K^0$ $\sim 1.6$GeV with width $O(10-100)$MeV. The $\pi_1(1400;1600)$ may be broad members of {\bf 10} $\pm$ \10bar in such a picture. Vector mesons in the 1.4 - 1.7GeV mass range are also compared with this picture.

The interesting state X(1600) with $J^{PC}I^G=2^{++}2^+$ can't be a conventional $q \bar q$ meson in the quark model. Using interpolating currents with different color configurations, we investigate its possible color structure in the framework of QCD sum rules. Our analysis is unable to exclude its existence. If it really exists, our analysis indicates that X(1600) is probably a tetraquark state with two quarks in the $\mathbf{\bar 3}_c$ representation. Taken seriously, this implies some evidence of the $\mathbf{\bar 3}_c$ type diquark structure within multiquark hadrons. We propose several reactions to look for this state.

We present a model for the formation of the charmed pentaquark Theta_c in hard scattering processes such as deep inelastic scattering, e^+e^- annihilation, and high-energy p pbar collisions. The model assumes that the cross section for Theta_c formation is proportional to the rate of production of p D^{*-} (or pbar D^{*+}) pairs in close proximity both in momentum space and in coordinate space. The constant of proportionality is determined from the Theta_c cross section in deep inelastic scattering as reported by the H1 experiment. The HERWIG Monte Carlo is used to generate simulated DIS events and also to model the space-time structure of the final state. Requiring the proton and the D^* be within a 100 MeV mass window and separated by a spacelike distance of no more than 2 fm, we find that a large "coalescence enhancement factor" F_co \sim 10 is required to account for the H1 signal. The same approach is then applied in order to estimate the number and characteristics of Theta_c events produced at LEP and the Tevatron.

Roles of instanton induced interactions (III) in the masses of pentaquark baryons, Theta^+ (J=1/2 and 3/2) and Xi^{--}, and a dibaryon, H, are discussed using the MIT bag model in the negative parity case. It is shown that the two-body terms in III give a strong attraction mainly due to the increase of the number of pairs in multi-quark systems. In contrast, the three-body u-d-s interaction is repulsive. It is found that III lowers the mass of Theta^+ as much as 100 MeV from the mass predicted by the bag model without III.

We study the decay of Theta+ in a non-relativistic quark model. The wave function of Theta+ is constructed for the two cases JP = 1/2+- as products of color, spin, flavor and orbital parts respecting total antisymmetrization among the four quarks. We find that for the negative parity Theta+ the width becomes very large which is of order of several hundreds MeV, while it is about a several tens MeV for the positive parity. By assuming additionally diquark correlations, the width is reduced to be of order 10 MeV. It is also pointed out that a similar calculation for 3/2- results in strong suppression of its width.

If the X(3872) is a loosely-bound Dbar^0 D^{*0} / D^0 Dbar^{*0} molecule, its inclusive production rate can be described by the NRQCD factorization formalism that applies to inclusive quarkonium production. We argue that if the molecule has quantum numbers J^{PC} = 1^{++}, the most important terms in the factorization formula should be the same as for chi_{c1} and the ratio of the inclusive production rates for X and chi_{c1} should be roughly the same in all processes. This assumption is used to estimate the inclusive production rate of X in B meson decays, Z^0 decays, and in p pbar collisions.

The feasibility of tetraquark detection is studied. For the cc\bar{u}\bar{d} tetraquark we show that in present (SELEX, Tevatron, RHIC) and future facilities (LHCb, ALICE) the production rate is promising and we propose some detectable decay channels.

We examine cross sections for the processes $\gamma N\to NK\bar{K}$ in the framework of a phenomenological Lagrangian. We include contributions from $\Lambda$ and $\Sigma$ resonances up to spin 3/2, as well as those from an exotic $\Theta^+$. We allow the $\Theta^+$ to have spin 1/2 or 3/2, with either positive or negative parity in each case. We also allow the state to be either isovector or isoscalar. We find that the scenario that most closely matches observations at Jefferson Laboratory requires a moderately large coupling of the $\Theta^+$ to $NK^*$.

We discuss how the differential cross section near threshold for the reaction $\gamma N\to K\Theta^+$ can be an important tool to determine the parity of the $\Theta^+$ in a model-independent way. Using the CGLN amplitudes, we present a justification to our description. We extend our analysis to the photon polarization asymmetry which can play an important role in determining the $\Theta^+$ parity without ambiguity.

The recently reported Theta(1540) exotic baryon seems to be very narrow: Gamma(Theta)< 1 MeV according to some analyses. Using methods of low energy scattering theory, we develop expectations for the width of the Theta, an elastic resonance in KN scattering in a theory where the characteristic range of interactions is ~1 Fermi. If the Theta is a potential scattering resonance, generated by the forces in the KN channel, its width is hard to account for unless the KN-channel orbital angular momentum, l, is two or greater. If the Theta is a CDD pole, its coupling to the scattering channel is at least an order of magnitude less than the coupling of the Lambda(1520) unless l is two or greater. Either way, if the Theta proves to be in the KN s- or p-wave, new physics must be responsible for its narrow width.

We critically examine the possibility of determining the parity of the $\Theta^+(1540)$ from the reactions $NN\to \Theta^+Y$ ($Y$ = $\Lambda$, $\Sigma$) recently discussed in the literature. Specifically, we study the energy dependence of those observables that were suggested to be the most promising ones to unravel the parity of the $\Theta^+$, namely the spin correlation coefficient $A_{xx}$, and the spin transfer coefficient $D_{xx}$. We show that the energy dependence of $\sigma_0(1+A_{xx})$, corresponding to the spin-triplet production cross section, guarantees unambiguous information on the parity of the $\Theta^+$. Here, $\sigma_0$ denotes the unpolarized cross section. Also, the possibility to determine the parity of the $\Theta^+$ through the energy dependence of $\sigma_0D_{xx}$ is discussed.

We suggest that the recently discovered charm-strange meson D_sJ(2632), with unusual properties, could be a cyptoexotic tetraquark baryonium state cdd_bars_bar. We predict other four narrow states, as Regge recurrences of D_sJ(2632), below the possible baryon-antibaryon thresholds.

The recently observed new member of the charm-strange family D_s(2632) which has a surprisingly narrow width is challenging our theory. D_s(2317) and D_s(2457) which were observed earlier have similar behaviors and receive various theoretical explanations. Some authors use the heavy hadron chiral effective theory to evaluate heavy-light quark systems and obtain a reasonable evaluation on the masses of D_s(2317) and D_s(2457). An alternative picture is to interpret them as four-quark or molecular states. In this work, we are following the later and propose a unitive description for all the three new members D_s(2632), D_s(2317) and D_s(2457) and at least, so far our picture is consistent with the data.

We present results for the selfenergy of the $\Theta^+$ pentaquark in nuclei associated with two sources: the $KN$ decay of the $\Theta^+$ and the two meson baryon decay channels of the $\Theta^+$ partners in an antidecuplet of baryons. The first source is shown to produce a small potential, unable to bind the $\Theta^+$ in nuclei, while the second source gives rise to a large attractive potential. At the same time we show that the width of the $\Theta^+$ in nuclei is small, such that, in light and medium nuclei, many bound $\Theta^+$ states would appear with a separation between levels appreciably larger than the width of the states, thus creating an ideal scenario for pentaquark spectroscopy in nuclei.

After explaining necessity of exotic hadrons, we discuss mechanisms which could determine production of the exotic Theta-baryon. A possible important role of resonances (producing the Theta in real or virtual decays) is emphasized for various processes. Several experimental directions for studies of such resonances, and the Theta itself, are suggested. We briefly discuss also recent negative results on the Theta-baryon.

An existing single resonance model with S11, P11 and P13 Breit-Wiegner resonances in the s-channel has been re-applied to the old pi N -> K Lambda data. It has been shown that the standard set of resonant parameters fails to reproduce the shape of the differential cross section. The resonance parameter determination has been repeated retaining the most recent knowledge about the nucleon resonances. The extracted set of parameters has confirmed the need for the strong contribution of a P11(1710) resonance. The need for any significant contribution of the P13 resonance has been eliminated. To reproduce the total cross section at the same time with the linear dependence of the differential cross sections with the cos(theta) in the energy range 1650 MeV < W < 1800 MeV the P11 resonance can not but be quite narrow. It emerges as a good candidate for the non-strange counter partner of the established pentaquark anti-decuplet.

The unusual properties of the X(3872) have led to speculation that it is a weakly bound state of mesons, chiefly $D^0\bar D^{0*}$. Tests of this hypothesis are investigated and it is proposed that measuring the $3\pi J/\psi$, $\gamma J/\psi$, $\gamma \psi'$, $\bar K K^*$, and $\pi\rho$ decay modes of the $X$ will serve as a definitive diagnostic of the molecule hypothesis.

Properties of a hypothetical baryonium with the quark content ($uds\ov{u}\ov{d}\ov{s}$) are discussed. The MIT bag model predicts its mass to be unexpectedly low, approximately 1210 MeV. Possible hadronic decay modes of this state are analyzed. Ultrarelativistic heavy-ion collisions provide favorable conditions for the formation of such particles from the baryon-free quark-gluon plasma. We estimate multiplicities of such exotic baryonia on the basis of a simple thermal model.

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, we study the strong decays of light and heavy parity-even pentaquark states using the light-front quark model in conjunction with the spectator approximation. The narrowness of the Theta width is ascribed to the p-wave configuration of the diquark pair. Taking the Theta width as a benchmark, we estimate the rates of the strong decays Xi_{3/2}-- to Xi- pi-, Sigma- K-, Sigma_{5c}0 to D_s- p, D_{s0}*- p and Xi_{5c}0 to D_s- Sigma+, D_{s0}^{*-} Sigma+ with Sigma_{5c} Xi_{5c} being antisextet charmed pentaquarks and D_{s0}* a scalar strange charmed meson. The ratio of Gamma(P_c to Baryon D_{s0}*)/Gamma(P_c to Baryon D_s) is very useful for verifying the parity of the antisextet charmed pentaquark P_c. It is expected to be of order unity for an even parity P_c and much less than one for an odd parity pentaquark.

H1 Collaboration recently observed the charmed pentaquark. In this short note, we point out that the dominant production mechanism for pentaquark consisting of a heavy quark is heavy quark fragmentation. We obtain a crude estimate on the fragmentation probability for charm quark into Theta_c^0, based on the known fragmentation probabilities of charm quark into mesons and baryons: f(c-bar --> Theta_c^0) =~ (2-7) x 10^{-3}. Similarly, we also obtain the fragmentation probability for bottom quark into Theta_b^+: f(b-bar --> Theta_b^+) =~ (5-20) x 10^{-3}. We also estimate the prospect of observing Theta_c^0 and Theta_b^+ at HERA, LEP, and Tevatron.

We study the Theta+(1540) discovered at SPring-8. We apply Quark Model techniques, that explain with success the repulsive hard core of nucleon-nucleon and kaon-nucleon exotic scattering, and the short range attraction present in pion-nucleon and pion-pion non-exotic scattering. We find a K-N repulsion which excludes the Theta+ as a K-N s-wave pentaquark. We explore the Theta+ as a crypto-heptaquark, equivalent to a K-pi-N borromean boundstate, with positive parity and total isospin I=0. The attraction is provided by the pion-nucleon and pion-kaon interactions. The other candidates to pentaquarks Xi--(1860), observed at NA49, and D*-p(3100), observed at H1, are also studied as linear molecular heptaquarks.

We investigate the production of the newly found pentaquark exotic baryon $\Xi_5$ in the $\bar{K}N\to K\Xi_5$ and $\bar{K}N\to K^{*}\Xi_5$ reactions at the tree level. We consider the both positive- and negative-parities of the $\Xi_5$. The reactions are dominated by the $s$- and $u$-channel processes, and it is observed that the resulting cross sections are very much dependent 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 would be useful for the further study of the pentaquark baryons.

We explore the connection between pentaquarks and dibaryons composed of three diquarks in the framework of the diquark model. With the available experimental data on H dibaryon, we estimate the Pauli blocking and annihilation effects and constrain the $P=-$ pentaquark $SU(3)_F$ singlet mass. Using the $\Theta^+$ pentaquark mass, we estimate $P=-$ dibaryon mass.

We investigate the impact of the \Theta^+(1540) resonance on differential and integrated cross sections for the reaction K^+d{\to}K^0pp, where experimental information is available at kaon momenta below 640 MeV/c. The calculation utilizes the J\"ulich KN model and extensions of it that include contributions from a \Theta^+(1540) state with different widths. The evaluation of the reaction K^+d{\to}K^0pp takes into account effects due to the Fermi motion of the nucleons within the deuteron and the final three-body kinematics. We conclude that the available data constrain the width of the \Theta^+(1540) to be less than 1 MeV.

We analyse the width of the $\theta(\frac12^+)$ pentaquark assuming that it is a bound state of two extended spin-zero $ud$-diquarks and the $\bar s$ antiquark (the Jaffe-Wilczek scenario). The width obtained when the size parameters of the pentaquark wave function are taken to be close to the parameters of the nucleon is found to be $\simeq 150$ MeV, i.e. it has a normal value for a $P$-wave hadron decay with the corresponding energy release.However, we found a strong dynamical suppression of the decay width if the pentaquark has an asymmetric "peanut" structure with the strange antiquark in the center and the two diquarks rotating around. In this case a decay width of $\simeq$ 1 MeV is a natural possibility.

The contradiction between evidence for and against the existence of the Theta+ pentaquark might be resolved if it only appears as a result of a particular production mechanism which is present in some experiments and absent in others. We examine the implications of Theta+ production via decay of a cryptoexotic N* resonance with a mass of about 2.4 MeV corresponding to a peak in the experimental data for the invariant mass of the (Theta+,K-) system. Further experimental checks are suggested.

Interpreting the recently discovered narrow exotic baryons as pentaquark states, we discuss, along an old argument of ours, the isospin mixing occurring within the two doublets of $Q = -1$ and Q=0 states lying inside the $S=-2$ ($\Xi$-cascade) sector. We argue that, at least within the Jaffe-Wilczek assignment, presently available data already indicate that mixing should occur at an observable level in both charge sectors, with mixing angles that can be predicted in terms of ratios of observable mass splittings.

If the recently-discovered charmonium state X(3870) is a loosely-bound S-wave molecule of the charm mesons \bar D^0 D^{*0} or \bar D^{*0} D^0, it can be produced in B meson decay by the coalescence of charm mesons. If this coalescence mechanism dominates, the ratio of the differential rate for B^+ \to \bar D^0 D^{*0} K^+ near the \bar D^0 D^{*0} threshold and the rate for B^+ \to X K^+ is a function of the \bar D^0 D^{*0} invariant mass and hadron masses only. The identification of the X(3870) as a \bar D^0 D^{*0}/\bar D^{*0} D^0 molecule can be confirmed by observing an enhancement in the \bar D^0 D^{*0} invariant mass distribution near the threshold. An estimate of the branching fraction for B^+ \to X K^+ is consistent with observations if X has quantum numbers J^{PC} = 1^{++} and if J/\psi \pi^+ \pi^- is one of its major decay modes.

We investigate the photoproduction of $K^*$ vector meson for the study of the $\Lambda(1405)$ resonance. The invariant mass distribution of $\pi\Sigma$ shows a different shape from the nominal one, peaking at 1420 MeV. This is considered as a consequence of the double pole structure of $\Lambda(1405)$, predicted in the chiral unitary model. Combined with other reactions, such as $\pi^- p \to K^0 \pi\Sigma$, experimental confirmation of this fact will reveal a novel structure of the $\Lambda(1405)$ state.

We analyze the magnetic moment of the exotic pentaquarks of the flavor antidecuplet in the constituent quark model for the case in which the ground state is in an orbital L(p)=0(+) or a L(p)=1(-) state. We derive sum rules for the magnetic moments. The magnetic moment of the Theta(1540) is found to be 0.38, 0.09 and 1.05 mu_N for J(p)=1/2(-), 1/2(+) and 3/2(+), respectively, which is compared with the results obtained in other approaches.

Additional broader I=0 states in the KN channel near $\Theta^+$(1540) are expected in many models, making the absence of any signature in the K$^+$-deuteron scattering data even more puzzling. In an ideal "three-body" picture the $\Theta$ is viewed as two compact ud(1)ud(2) $\bar{3}$ color diquarks and an $\bar{s}$ quark. A "QCD-type" inequality involving $m(\Theta^+), m(\Lambda)$, the mass of the $\Lambda(1/2^-) $ L=1 excitation and that of a new I=0 tetraquark vector meson then follows. The inequality suggests a very light new vector meson, and is violated. We note that "associated production" of the pentaquark with another quadriquark or anti-pentaquark may be favored. This along with some estimates of the actual production cross sections suggest that the $\Theta$ can be found in BaBar or Belle e$^+$-e$^-$ colliders.

If the recently-discovered charmonium state X(3870) is a loosely-bound molecule of the charm mesons D^0 and \bar D^{*0} or \bar D^0 and D^{*0}, it can be produced in e^+ e^- annihilation at the \Upsilon(4S) resonance by the coalescence of charm mesons produced in the decays of B^+ and B^- mesons. Remarkably, in the case of 2-body decays of the B mesons, the leading contribution to the coalescence probability depends only on hadron masses and on the width and branching fractions of the B meson. As the binding energy E_b of the molecule goes to zero, the coalescence probability scales as E_b^{1/2} log(E_b). Unfortunately, the coalescence probability is also suppressed by two powers of the ratio of the width to the mass of the B meson, and is therefore many orders of magnitude too small to be observed in current experiments at the B factories.

We study $np\to \Lambda\Theta^{+}$ and $np\to \Sigma^{0}\Theta^{+}$ processes for both of the positive and negative parities of the $\Theta^{+}$. Employing the effective chiral Lagrangians for the $KNY$ and $K^*NY$ interactions, we calculate differential cross sections as well as total cross sections for the $np\to \Sigma^0 \Theta^+$ and $np\to \Lambda\Theta^+$ reactions. The total cross sections for the positive-parity $\Theta^+$ turn out to be approximately ten times larger than those for the negative parity $\Theta^+$ in the range of the CM energy $\sqrt{s}_{\rm th}\le \sqrt{s}\le 3.5 {\rm GeV}$. The results are rather sensitive to the mechanism of $K$ exchanges in the $t$ -- channel.

We investigate medium modifications of the pentaquark $\Theta^+$ in dense matter, taking into account different parities of the $\Theta^+$ baryon. We obtain the density-dependent shifts of mass and decay width of the $\Theta^+$ to one-loop order. We find that the reduced nucleon mass plays a crucial role in the change of the decay width. The results turn out to depend on the parity of the $\Theta^+$. In the case of the positive parity, the results indicate that once the $\Theta^+$ is produced in heavy ion collisions, it may survive until the freeze-out unless there is rescattering.

General formulae for the spin-spin correlation parameters $C_{i,j}$ and spin-transfer coefficients $K_i^j$ are derived for the reaction $N N\to Y \Theta^+$ at the threshold for an arbitrary spin of the pentaquark $\Theta^+$. It is shown that a measurement of the sign of $C_{y,y}$ or an observation of the non-zero polarization transfer from the nucleon to the hyperon $Y$ allow one to determine the P-parity of the $\Theta^+$ unambiguously and independently on the spin of the $\Theta^+$. Measurement of these spin observables in the both $pp$- and $pn$- channels of this reaction determines also the isospin of the $\Theta^+$.

We investigate the decay modes of pentaquark baryons for both the anti-decuplet and the octet states, which were recently claimed by Close and Dudek to be potentially narrow due to a hidden ``selection rule''. We introduce a tensor method for the pentaquark states, which respects the ``selection rule'', and then present the possible decay modes for both the unmixed and ideally mixed antidecuplet and octet pentaquark states. The exclusive decay modes can be used to experimentally search for the pentaquark states. We also discuss how ideal mixing between the pentaquark octet and antidecuplet states follows naturally from the ``selection rule'', which effectively is the OZI rule in the pentaquark decays.

A model recently introduced by Jaffe and Wilczek based on the quarks being dynamically bound into diquarks has been used to predict that the recently observed exotic baryons (pentaquarks) fall into a nearly ideally mixed combination of an octer and anti-decuplet representations of SU(3) flavor. The model predicts two states with nucleon quantum numbers which have tentatively been identified with the N*(1440) and the N*(1710). This paper examines the viability of this model by focusing on the decay width of the nucleon members of the multiplet. An inequality relating the partial widths of these nucleon states in the N+nucleon channel to the width of the theta+ is derived for this model under the assuming ideal mixing and that the only significant exact SU(3) symmetry violations are the result of ideal mixing, threshold effects and the masses of pseudo-Goldstone bosons. This inequality is badly violated if the states in the multiplet are the N*(1440) and the N*(1710) and if the recent bounds extracted for the theta+ width are reliable. Thus, the model appears to require a scenario with the existence of at least one presently unknown resonance with nucleon quantum numbers.

Within the chiral soliton model the SU(3) breaking collective hamiltonian introduces representation mixing in the baryonic wave functions. We calculate ${\cal{O}}(m_s)$ effects of this mixing on the decay widths of decuplet and antidecuplet baryons. We find importance of the 27-plet admixture in the $\Theta^+$ and $\Xi_{\bar{10}}$ decays. The role of the $1/N_c$ nonleading terms in ${\cal{O}}(m_s)$ transition matrix elements is discussed.

We derive an upper bound on the mass difference between the $\Xi^*$ and $\Theta^+$ pentaquarks which are the manifestly exotic members of the $SU(3)_f$ antidecuplet. The derivation is based on simple assumptions about $SU(3)_f$ symmetry breaking and uses the standard quantum mechanical variational method. The resulting rather robust bound is more than 20 MeV below the experimentally reported $\Xi^*-\Theta^+$ mass difference, emphasizing the need for confirmation of the experimental mass values and placing strong constraints on quark models of the pentaquark structure.

Spin structure of the reaction ${\vec p}{\vec n}\to {\vec \Lambda^0} {\vec \Theta}$ is analysed at the threshold in a model independent way under assumption that the $\Theta^+$ is an isosinglet. We found that the sign of the spin-spin correlation parameter $C_{x,x}$ being measured in a double-spin experiment, determines the P-parity of the $\Theta^+$ unambiguously. Furthermore we show that the polarization coefficients $K_x^x,K_y^y$ and $K_z^z$ which describe the polarization transfer from polarized beam or target to the final $\Lambda^0$ and $\Theta^+$ are nonzero for a positive parity of the $\Theta^+$ and equal zero for a negative parity. It allows one to determine the P-parity of the $\Theta^+$ in a single-spin measurement, since the polarization of the $\Lambda^0$ can be measured via its decay $\Lambda^0\to \pi^-+ p$.

We evaluate the leading order amplitude for the deep exclusive electroproduction of an exotic hybrid meson in the Bjorken regime. We show that, contrary to naive expectation, this amplitude factorizes at the twist 2 level and thus scales like usual meson electroproduction when the virtual photon and the hybrid meson are longitidinally polarized. Exotic hybrid mesons may thus be studied in electroproduction experiments at JLAB, HERA (HERMES) or CERN (COMPASS).

Assuming that the recently observed $\Theta^+$ and $\Xi^{--}$ are members of an anti-decuplet of SU(3), decays to ground state baryons and mesons are calculated using an effective Lagrangian which incorporates chiral and SU(3) symmetry. We consider the possible quantum number assignments $J^\Pi ={1/2}^\pm,{3/2}^\pm$ and calculate ratios of partial widths. The branching ratios of exotic cascades can be used to discriminate between even and odd parity pentaquarks.

I study the $Ds(2317)$ and $Ds(2457)$ discovered at BABAR, CLEO and BELLE, and find that they belong to a class of strange $S=-1$ multiquarks, which is equivalent to the class of kaonic molecules bound by hard core attraction. In this class of hadrons a kaon is trapped by a s-wave meson or baryon. To describe this class of multiquarks the Resonating Group Method is applied to a standard quark model with chiral symmetry breaking, and the hard core kaon-meson(baryon) interactions are extracted. A criterion is derived to classify the attractive channels. The mesons f0(980), Bs0+, Bs1+ and also the baryons with the quantum numbers of Lambda, Sigma_c, Sigma_b, Omega_cc, Omega_cb, Omega_bb belong to the new hadronic class of the Ds(2317) and Ds(2457).

Following Rosner [hep-ph/0312269], we consider B-decay production channels for the exotic I=0 and $I=3/2$ pentaquarks that have been recently reported. We also discuss new search channels for isovector pentaquarks, such as the $\Theta^{*++} (\bar s duuu)$, that are generically present in chiral soliton models but were not observed in recent experiments. Futhermore, we argue that weak decays of charmed baryons, such as the $\Lambda_c^+$ and $\Xi_c^0$, provide another clean way of detecting exotic baryons made of light quarks only. We also discuss discovery channels for charmed pentaquarks, such as the isosinglet $\Theta_c^0 (\bar c udud)$, in weak decays of bottom mesons and baryons. Finally, we discuss prospects for inclusive production of pentaquarks in $e^+ e^-$ collisions, with associated production of particles carrying the opposite baryon number.

Recent evidence for pentaquark baryons in the channels $\Xi^-\pi^-$, $\Xi^-\pi^+$ and their anti-particles claimed by the NA49 collaboration is critically confronted with the vast amount of existing data on $\Xi$ spectroscopy which was accumulated over the past decades. It is shown that the claim is at least partially inconsistent with these data. In addition two further exotic channels of the pentaquark type available in the NA49 data are investigated. It is argued that this study leads to internal inconsistency with the purported signals.

A general study of pentaquarks built with four quarks in a L=1 state and an antiquark in S-wave shows that several of such states are forbidden by a selection rule, which holds in the limit of flavour symmetry, to decay into a baryon and a meson final state. We identify the most promising \bar{10} multiplet for the classification of the Theta^+ and Xi^{--} particles recently discovered with the prediction of a narrow width for both of them.

We compute cross sections of $\Theta^+$ production near threshold for a polarized proton reaction, $\vec p \vec p \to \Sigma^+ \Theta^+$ which was recently proposed to determine unambiguously the parity of $\Theta^+$. Within theoretical uncertainties cross sections for the allowed spin configuration are estimated; it is of order of one microbarn for the positive parity $\Theta^+$ and about 1/10 microbarn for the negative parity $\Theta^+$ in the threshold energy region where the s-wave component dominates.

The narrow width of the exotic narrow baryon resonance $\Theta^+$ might be explained by mixing between the two nearly degenerate states that arise in models with two diquarks and an antiquark. The only open $\Theta^+$ decay channel is $KN$. When two states both coupled to a single dominant decay mode are mixed by the loop diagram via this decay mode, diagonalization of the loop diagram decouples one mass eigenstate from this decay mode as in some treatments of the $\rho-\pi$ decay from the mixed singlet-octet $\omega-\phi$ system, the $K^* -\pi$ decay of the strange axial vector mesons and the $NK$ couplings of some baryons. This mechanism can explain the narrow width and weak coupling of $\Theta^+ \to KN$ while allowing a relatively large production cross section from $K^*$ exchange. Interesting tests are suggested in $K^-p$ reactions where backward kaon production must go by exotic baryon exchange.

We discuss model independent methods to measure the $P$-parity of the $\Theta^+$-pentaquark, in the simplest processes of photoproduction, $\gamma+N\to \Theta^++\bar{K}$, using definite relations between T-even polarization observables, which depend on the $P$-parity of the $\Theta^+$ baryon (with respect to the $pK$ system). One method, which holds for any photon energy and any $K$ meson production angle, is based on the relation between the $\Sigma_B$ asymmetry (induced by a linearly polarized photon beam, with unpolarized target) and the $D_{nn}$ component of the depolarization tensor (for unpolarized photon beam). Another method, which applies in collinear kinematics (or in threshold conditions), is related to the sign of the $D_{nn}$ component, with linearly polarized photon beam.

The production of strange pentaquark states (Theta baryons) in hadronic interactions within a Gribov-Regge approach is explored. In this approach the Theta^+(1540) is produced by disintegration of remnants formed by the exchange of pomerons between the two protons. We predict the rapidity and transverse momentum distributions as well as the 4\pi multiplicity of the Theta^+ for sqrt{s} = 17 GeV (SPS) and 200 GeV (RHIC). In both cases more than 10^{-3} Theta^+ per pp event should be observed by the present experiments.

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 experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons.

We construct a chiral lagrangian for pentaquark baryons assuming that the recently found Theta^+ (1540) state belongs to an antidecuplet of SU(3) flavor symmetry with J^P = (1/2)^(+-). We derive the Gell-Mann-Okubo formulae for the antidecuplet baryon masses, and a possible mixing between the antidecuplet and the pentaquark octet. Then we calculate the cross sections for pi^- p -> K^- Theta^+ and gamma n -> K^- Theta^+ using our chiral lagrangian. The resulting amplitudes respect the underlying chiral symmetry of QCD correctly. We also describe how to include the light vector mesons in the chiral lagrangian.

If the $J^P$ of $\Theta_5^+$ and $\Xi_5^{--}$ pentaquarks is really found to be ${1\over 2}^+$ by future experiments, they will be accompanied by $J^P={3\over 2}^+$ partners in some models. It is reasonable to expect that these $J^P={3\over 2}^+$ states will also be discovered in the near future with the current intensive experimental and theoretical efforts. We estimate $J^P={3/2}^+$ pentaquark magnetic moments using different models.

The cross sections for production of pentaquark $\Xi^+_5$ from the reaction $\gamma p\to K^0K^0\Xi^+_5$ and $\Xi^{--}_5$ from the reaction $\gamma n\to K^+K^+\Xi^{--}_5$ are evaluated in a hadronic model that includes their couplings to both $\Sigma\bar K$ and $\Sigma\bar K^*$. With these coupling constants determined from the empirical $\pi NN(1710)$ and $\rho NN(1710)$ coupling constants by assuming that $\Xi^+_5$, $\Xi^{--}_5$, and N(1710) belong to the same antidecuplet of spin 1/2 and positive parity, and using form factors at strong interaction vertices similar to those for pentaquark $\Theta^+$ production in photonucleon reactions, we obtain a cross section of about 0.03-0.6 nb for the reaction $\gamma p\to K^0K^0\Xi^+_5$ and about 0.1-0.6 nb for the reaction $\gamma n\to K^+K^+\Xi^{--}_5$ at photon energy $E_\gamma=4.5$ GeV, depending on the value of the coupling constant $g_{K^*\Sigma\Xi_5}$.

The potential of decays of mesons containing heavy quarks [including $B$ mesons and the $\Upsilon(1S)$] for producing final states of matter with unusual quark configurations, such as $q q \bar q \bar q$ or $q q q q \bar q$, is investigated. The usefulness of antineutron detection in such searches is stressed.

Theoretical considerations prompted by discovery of the exotic Theta(uudds*) baryon led us to propose a dynamical picture emphasizing the role of diquark correlations, which are also useful in elucidating other aspects of low-energy QCD. A notable prediction of this picture is the existence of new exotic and non-exotic S=-2 ``cascade'' baryons with specific, characteristic properties. We argue here that recent observations by the NA49 collaboration are broadly consistent with our predictions, and propose further tests.

Based on the hadronic model with an improved version of gauge prescription including form factors, we investigate the possibility of determining the parity state of $\Theta^+$ baryon using photon induced processes, $\gamma n\to K^- \Theta^+$, $\gamma p\to \bar{K}^0 \Theta^+$. The total and differential cross sections are simulated in two versions of pseudovector(PV) and pseudoscalar(PS) coupling schemes for $KN\Theta$ interaction and the results are reported both on the positive and negative parity states of $\Theta^+$ baryon. It is found that in both schemes the total cross sections from the neutron are larger than those from the proton. In particular, not only the cross sections of the positive parity $\Theta^+$ production but also those of the negative parity $\Theta^+$ production are found to be comparable to the cross section observed in the SAPHIR experiment. Our analysis suggests that the observation of angular distribution rather than just the total cross section in the photoproduction processes may be a useful tool to distinguish the parity of $\Theta^+$ baryon.

Triggered by a recent paper by Thomas, Hicks and Hosaka, we investigate which observables can be used to determine the parity of the $\Theta^+$ from the reaction $\vec p\vec p \to \Sigma^+\Theta^+$ near its production threshold. In particular, we show that the sign of the spin correlation coefficient $A_{xx}$ for small excess energies yields the negative of the parity of the $\Theta^+$. The argument relies solely on the Pauli principle and parity conservation and is therefore model--independent.

If the exotic baryon $\Theta(1540)$ is $udud\bar{s}$ with $J^P = {1/2}^+$, we predict that there is a $\Theta^*(1540-1680)$ with $J^P = {3/2}^+$. The width $\Gamma(\Theta^* \to KN)$ is at least a factor of three larger than $\Gamma(\Theta)$. The possibilities of $\Theta^* \to KN\pi$ or $\Theta \gamma$ via $M1$ and $E2$ multipoles are discussed.

It is proposed that the newly discovered X(3872) is a $J^{PC} = 1^{++}$ $D^0\bar D^{0*}$ hadronic resonance stabilized by admixtures of $\omega J/\psi$ and $\rho J/\psi$. A specific model of the state is constructed and tests of its internal structure are suggested via the predicted decay modes $D^0\bar D^0\pi^0$, $D^0\bar D^0\gamma$, $\pi^+\pi^- J/\psi$, and $\pi^+\pi^-\pi^0 J/\psi$.

It is demonstrated that measurements of photon asymmetry in the $\gamma n \to K^- K^+ n$ reaction, can most likely determine the parity of the newly discovered $\Theta^+$ pentaquark. We predict that if the parity of $\Theta^+$ is positive, the photon asymmetry is significantly positive; if the parity is negative, the photon asymmetry is significantly negative. If the background contribution is large, the photon asymmetry may become very small in magnitude, thereby making it difficult to distinguish between the positive and negative parity results. However, even in this case, a combined analysis of the $(K^+ n)$ invariant mass distribution and photon asymmetry should allow a determination of the parity of $\Theta^+$.

We study $\Theta^+(1540)$ productions in kaon-nucleon ($KN$) and nucleon-nucleon ($NN$) interactions by assuming that the $\Theta^+$ is an isosinglet with $J^P = \frac12^+$. Possible $t$-channel diagrams with $K^*$ exchange are considered in both reactions as well as $K$ exchange in $NN$ reaction. The cross section for $np \to \Lambda^0 \Theta^+$, which has not been considered in previous calculations, is found to be about a factor of 5 larger than that for $np \to \Sigma^0 \Theta^+$ due to the large coupling of $KN\Lambda$ interaction. The cross sections are obtained by setting $g_{KN\Theta}^{}=1$ and varying the ratio of $g_{K^*N\Theta}^{}/g_{KN\Theta}^{}$ so that future experimental data can be used to estimate these couplings. We also find that the isospin relations hold for these reactions.

We study, within the statistical hadronization model, the influence of narrow strangeness carrying baryon resonances (pentaquarks) on the understanding of particle production in relativistic heavy ion collisions. There is a great variation of expected yields as function of heavy ion collision energy due to rapidly evolving chemical conditions at particle chemical freeze-out. At relatively low collision energies, these new states lead to improvement of statistical hadronization fits.

It is suggested that the narrow width of the recently observed resonance $\Theta^{+}(1540)$ 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.

We investigate the photoproduction of the $\Theta^+(1540)$ on a nucleon ($\gamma n \to K^- \Theta^+$, $\gamma p \to \bar{K}^0 \Theta^+$) and the pion-induced $\Theta^+$ production reaction on the proton ($\pi^- p \to K^- \Theta^+$). The total cross sections near threshold are estimated by using hadronic models with effective interaction Lagrangians and form factors that preserve gauge-invariance of the electromagnetic current. The photoproduction cross sections are found to be a few hundred nb, with the cross section on the proton being larger than that on the neutron. The pion-induced production cross section is found to be around a few hundred $\mu$b but sensitive to the $K^* N \Theta$ coupling whose value is not yet known. We also study the production cross section assuming that the $\Theta^+$ has negative parity. The cross sections are then found to be much suppressed compared to the case where $\Theta^+$ has positive parity. Hence, the interpretation of the $\Theta^+$ as an odd-parity pentaquark state seems to be disfavored from the estimates of cross section for the photon-proton reaction from the SAPHIR experiment.

We argue that a width of less than MeV of the new Theta resonance is inconsistent with the observed ratio of resonance and background events in the various photon initiated experiments if the latter can be described by K, K*, etc., exchange. An evaluation of the Feynman diagrams which were believed to be relevant is presented and supports the general claim in the one case where a cross section has been given by the experimental group. More detailed arguments based on the flux tube model explaining the narrow widths and the apparent conflict with the production rates are presented. We predict narrow Tetra-quarks at mass ~ O(1-1.2 GeV) which the analysis of LEAR may have missed.

The ${q}\bar{q}$ spectrum is studied within a chiral constituent quark model. It provides with a good fit of the available experimental data from light (vector and pseudoscalar) to heavy mesons including some recent results on charmonium. The $0^{++}$ light mesons and the new $D$ states measured at different factories cannot be described as $q\bar q$ pairs and a tetraquark structure is suggested.

We reconsider the relationship between the bound state and the SU(3) rigid rotator approaches to strangeness in the Skyrme model. For non-exotic S=-1 baryons the bound state approach matches for small m_K onto the rigid rotator approach, and the bound state mode turns into the rotator zero-mode. However, for small m_K, we find no S=+1 kaon bound states or resonances in the spectrum, confirming previous work. This suggests that, at least for large N and small m_K, the exotic state may be an artifact of the rigid rotator approach to the Skyrme model. An S=+1 near-threshold state comes into existence for only sufficiently large SU(3) breaking. If such a state exists, then it has the expected quantum numbers of Theta+: I=0, J=1/2 and positive parity. Other exotic states with I=1, J=3/2, and I=1, J=1/2 appear as its SU(2) rotator excitations. As a test of our methods, we also identify a D-wave S=-1 near-threshold resonance that, upon SU(2) collective coordinate quantization, reproduces the observed states Lambda(1520), Sigma(1670) and Sigma(1775) with good accuracy.

The impact of a (I=0, J^P=1/2^+) Z^+(1540) resonance with a width of 5 MeV or more on the K+N (I=0) elastic cross section and on the P01 phase shift is examined within the KN meson-exchange model of the Juelich group. It is shown that the rather strong enhancement of the cross section caused by the presence of a Z^+ with the above properties is not compatible with the existing empirical information on KN scattering. Only a much narrower Z^+ state could be reconciled with the existing data -- or, alternatively, the Z^+ state must lie at an energy much closer to the KN threshold.

By assigning the narrow scalar resonance (which has been recently observed at the B-factories) to one of iso-triplet four-quark mesons containing a charm quark, two body decays of the four-quark mesons are studied. It is predicted that some of them can be observed as narrow resonances.

The new narrow resonance which has been observed at the B factories is assigned to the I_z=0 component of iso-triplet charmed four-quark mesons, and as its consequence, existence of additional narrow resonances in different channels is predicted.

Extending the hadronic Lagrangians that we recently introduced for studying pentaquark $\Theta^+$ baryon production from meson-proton, proton-proton, and photon-proton reactions near threshold to include the anomalous interaction between $\gamma$ and $K^*K$, we evaluate the cross section for $\Theta^+$ production from photon-neutron reactions, in which the $\Theta^+$ was first detected in the SPring-8 experiment in Japan and the CLAS experiment at Thomas Jefferson National Laboratory. With empirical coupling constants and form factors, and assuming that the decay width of $\Theta^+$ is 20 MeV, the predicted cross section is found to have a peak value of about 280 nb, which is substantially larger than that for $\Theta^+$ production from photon-proton reactions.

We study photoproduction reactions for Theta^+, which was recently observed as a candidate of an exotic five quark state uudd(bar s). We employ effective lagrangian interactions in the linear and non-linear formalism of chiral symmetry and investigate two cases of spin and parity of Theta^+, J^P = 1/2^+ and 1/2^-. We calculate cross sections and discuss possibilities to discriminate one from the other.

We argue that the lightest isospin 1/2 partners of the Z^+(1530) s(bar)uudd penta-quark predicted by Diakonov, Petrov and Polyakov are not the N(1710) mixed anti-decuplet states, but the pure non-strange u(bar)(ud)(ud) and d(bar)(ud)(ud) penta-quark states which may lie as low as 1200 MeV. The expected low width of a few MeV of such a putative state may explain why it was missed in phase shift analyzes of pion-nucleon scattering.

Using hadronic Lagrangians that include the interaction of pentaquark $\Theta^+$ baryon with $K$ and $N$, we evaluate the cross sections for its production from meson-proton, proton-proton, and photon-proton reactions near threshold. With empirical coupling constants and form factors, the predicted cross sections are about 1.5 mb in kaon-proton reactions, 0.1 mb in rho-nucleon reactions, 0.05 mb in pion-nucleon reactions, 20 $\mu$b in proton-proton reactions, and 40 nb in photon-proton reactions.

We consider 3 types of processes pertinent to the phenomenology of an H di-baryon: conversion of two $\Lambda$'s in a doubly-strange hypernucleus to an H, decay of the H to two baryons, and -- if the H is light enough -- conversion of two nucleons in a nucleus to an H. We compute the spatial wavefunction overlap using the Isgur-Karl and Bethe-Goldstone wavefunctions, and treat the weak interactions phenomenologically. The observation of $\Lambda$ decays from doubly-strange hypernuclei puts a constraint on the H wavefunction which is plausibly satisfied. In this case the H is very long-lived as we calculate. An absolutely stable H is not excluded at present. SuperK can provide valuable limits.

We study the very recently discovered Theta+ (1540) at SPring-8, at ITEP and at CLAS-Thomas Jefferson Lab. We apply the same RGM techniques that already explained with success the repulsive hard core of nucleon-nucleon, kaon-nucleon exotic scattering, and the attractive hard core present in pion-nucleon and pion-pion non-exotic scattering. We find that the K-N repulsion excludes the Theta+ as a K-N s-wave pentaquark. We explore the Theta+ as heptaquark, equivalent to a N+pi+K borromean boundstate, with positive parity and total isospin I=0. We find that the kaon-nucleon repulsion is cancelled by the attraction existing both in the pion-nucleon and pion-kaon channels. Although we are not yet able to bind the total three body system, we find that the Theta+ may still be a heptaquark state.

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.

We point out that existing $K^+d$ scattering data available in the PDG (Particle Data Group compilation) suggest some fluctuations in those momentum bins where the (Fermi motion broadened) $\Theta^+$[1543] resonance recently indicated in many gamma nuclear reactions and predicted six years ago by Diakonv Petrov and Polyakov might have shown up. The I=0, $J^P={1/2}^+$ P-wave channel should have a universal peak cross section of $\sim 37$ mb at resonance. The smallness of the effect seen in $K^+d$ with the $\delta \sigma $ fluctuations being less than 4 mb imply an indirect bound $\Gamma_{\Theta^+} < 6$ MeV, far stronger than the direct gamma-d measurements. This renders the theoretical interpretation of the new state very difficult.

The recent discovery of a narrow resonance in the decay $J/\psi \to \gamma p \bar{p}$ is described as a zero baryon number, ``deuteron-like singlet ${}^1S_0 $'' state. The difference in binding energy of the deuteron (-2.225 MeV) and of the new state (-17.5 MeV) can be accounted for in a simple potential model with a $\lambda \cdot \lambda$ confining interaction.

We discuss the mechanisms that lead to $\Lambda(1405)$ production in the $\pi^-p\to K^0\pi\Sigma$ reaction. The problem has gained renewed interest after different works converge to the conclusion that there are two resonances around the region of 1400 MeV, rather than one, and that they couple differently to the $\pi\Sigma$ and $\bar{K}N$ channels. We look at the dynamics of that reaction and find two mechanisms which eventually filter each one of the resonances, leading to very different shapes of the $\pi\Sigma$ invariant mass distributions. The combination of the two mechanisms leads to a shape of this distribution compatible with the experimental measurements.

It is shown that the exotic non-qqq hadrons of pentaquark $qqqq\bar{q}$ states can be clearly distinguished from the conventional qqq-baryon resonances or their hybrids if the flavor of $\bar{q}$ is different from any of the other four quarks. We suggest the physical process $p(e,e'K^-)Z(uuud\bar{s})$, which can be investigated at the Thomas Jefferson National Accelerator Facility (JLab), as an ideal process to search for the existence or non-existence of the exotic hadron of minimal pentaquark state $Z(uuud\bar{s})$. (The search for the existence of $Z(uudd\bar{s})$ is also discussed in the paper. We added this sentence after the original published form of this paper.)

We discuss the possibility that the recently reported resonance in the $D_s \pi^0$ spectrum can be described in terms of residual $D\pi$ interactions.

We discuss the implications of a possible quasinuclear DK bound state at 2.32 GeV. Evidence for such a state was recently reported in D_s^+pi^o by the BaBar Collaboration. We first note that a conventional quark model c-sbar assignment is implausible, and then consider other options involving multiquark systems. An I=0 c sbar n nbar baryonium assignment is one possibility. We instead favor a DK meson molecule assignment, which can account for the mass and quantum numbers of this state. The higher-mass scalar c-sbar state expected at 2.48 GeV is predicted to have a very large DK coupling, which would encourage formation of an I=0 DK molecule. Isospin mixing is expected in hadron molecules, and a dominantly I=0 DK state with some I=1 admixture could explain both the narrow total width of the 2.32 GeV state as well as the observed decay to D_s^+ pi^o. Additional measurements that can be used to test this and related scenarios are discussed.

We calculate the suppression in the rate at which two baryons in a nucleus (viz., nucleons or $\Lambda$'s) convert to an H dibaryon, using an Isgur-Karl wavefunction for quarks in the baryons and H, and a Bethe-Goldstone wavefunction for the baryons in the nucleus. If $r_H \lsi 1/3~ r_N$, we find $\tau_{A_{\Lambda\Lambda}\to A'_H}\gsi \tau_\Lambda$ and the observation of $\Lambda$ decays from double-$\Lambda$ hypernuclei does not exclude the existence of the H. If $m_H < 2 m_p$, nuclei are unstable but have very long lifetimes. For reasonable values of $r_H$ and the nuclear wavefunction, the lifetime can be long enough to evade anticipated SuperK limits $\tau_{A_{NN}\to A'_H}\gsi {\rm few} 10^{29}$ yr, or short enough to be observed. An analysis of SuperK data to look for this possibility should be undertaken.

Strongly attractive color forces in the flavor singlet channel may lead to a stable H dibaryon. Here we show that an H or other compact, flavor singlet hadron is unlikely to bind to nuclei, so that bounds on exotic isotopes do not exclude their stability. Remarkably, a stable H appears to evade other experimental constraints as well, when account is taken of its expected compact spatial wavefunction.

We show that it is necessary to go beyond a single hadron (beyond the quark-antiquark or three-quark systems) in order to distinguish the colour structure of the effective quark-quark interaction and the relevance of 3-body forces. We critically discuss the proposed models which suggest the dimeson bb\bar{u}\bar{d} to be bound by ~ 100 MeV and the cc\bar{u}\bar{d} dimeson to be unbound. Only experiment can judge. We estimate the probability of producing bb-\bar{u}\bar{d} at LHC by double gluon-gluon fusion and search for a characteristic decay.

The existence of a shallow or virtual tetraquark state, $cc\bar{u}\bar{d}$, is discussed. Using the putative masses for the doubly charmed baryons ($ccu/ccd$) from SELEX, the mass of the $cc\bar{u}\bar{d}$ state is estimated to be about $3.9 GeV$, only slightly above the $DD^*$ threshold. The experimental signatures for various $cc\bar{u}\bar{d}$ masses are also discussed.

A novel mechanism of H^0 and strangelet production in hadronic interactions within the Gribov-Regge approach is presented. In contrast to traditional distillation approaches, here the production of multiple (strange) quark bags does not require large baryon densities or a QGP. The production cross section increases with center of mass energy. Rapidity and transverse momentum distributions of the H^0 are predicted for pp collisions at E_lab = 160 AGeV (SPS) and \sqrt s = 200 AGeV (RHIC). The predicted total H^0 multiplicities are of order of the Omega-baryon yield and can be accessed by the NA49 and the STAR experiments.

The quark-delocalization, color-screening model, extended by inclusion of a one-pion-exchange (OPE) tail, is applied to the study of the deuteron and the d* dibaryon. The results show that the properties of the deuteron (an extended object) are well reproduced, greatly improving the agreement with experimental data as compared to our previous study (without OPE). At the same time, the mass and decay width of the d* (a compact object) are, as expected, not altered significantly.

The formation of dibaryons with strangeness are discussed for the interior of neutron stars and for central relativistic heavy-ion collisions. We derive limits for the properties of H-dibaryons from pulsar data. Signals for the formation of possible bound states with hyperons at BNL's Relativistic Heavy-Ion Collider (RHIC) are investigated by studying their weak decay patterns and production rates.

An analysis of experimental data, obtained at the Linear Accelerator of INR, is carried out with the aim of searching for supernarrow dibaryons in the reactions pd->p+X and pd->p+pX_1. Dibaryons with masses 1904\pm 2, 1926\pm 2, and 1942\pm 2 MeV have been observed in M_{X} missing mass spectra. In M_{X_1} missing mass spectra, the peaks have been found at M_{X_1}=966\pm 2, 986\pm 2, and 1003\pm 2 MeV. These values of M_{X_1} coincide with the ones obtained by a simulation of a decay of the dibaryons into \gamma+pn. The analysis of the data obtained leads to the conclusion that the observed dibaryons are supernarrow dibaryons, the decay of which into two nucleons is forbidden by the Pauli exclusion principle. A possible interpretation of exited nucleon states with small masses is suggested.

The unpolarized cross section for the electroproduction of the isoscalar $J^\pi = 3^+$ di-delta dibaryon $d^*$ is calculated for deuteron target using a simple picture of elastic electron-baryon scattering from the $\Delta \Delta (^7D_1)$ and the $NN (^3S_1)$ components of the deuteron. The calculated differential cross section at the electron lab energy of 1 GeV has the value of about 0.24 (0.05) nb/sr at the lab angle of 10$^\circ$ (30$^\circ$) for the Bonn B potential when the dibaryon mass is taken to be 2.1 GeV. The cross section decreases rapidly with increasing dibaryon mass. A large calculated width of 40 MeV for $d^*(\Delta\Delta ^7S_3)$ combined with a small experimental upper bound of 0.08 MeV for the $d^*$ decay width appears to have excluded any low-mass $d^*$ model containing a significant admixture of the $\Delta\Delta (^7S_3)$ configuration.

$d^*$ dibaryon study is a critical test of hadron interaction models. The electro production cross sections of $ed\to ed^*$ have been calculated based on the meson exchange current model and the cross section around 30 degree of 1 GeV electron in the laboratory frame is about 10 nb. The implication of this result for the $d^*$ dibaryon search has been discussed.

We review ideas and speculations concerning possible bound states or resonances coupled to the nucleon-antinucleon channel.