A lattice study of the pentaquark states

We present a study of the pentaquark system in quenched lattice QCD using diquark-diquark and kaon-nucleon local and smeared interpolating fields. We examine the volume dependence of the spectral weights of local correlators on lattices of size $16^3\times 32$, $24^3\times32$ and $32^3\times 64$ at $\beta=6.0$. We find that a reliable evaluation of the volume dependence of the spectral weights requires accurate determination of the correlators at large time separations. Our main result from the spectral weight analysis in the pentaquark system is that within our variational basis and statistics we can not exclude a pentaquark resonance. However our data also do not allow a clear identification of a pentaquark state since only the spectral weights of the lowest state can be determined to sufficient accuracy to test for volume dependence. In the negative parity channel the mass extracted for this state is very close to the KN threshold whereas in the positive parity channel is about 60% above.Comment: Manuscript expanded, discussion of two-pion system included, a comment regarding Ref.13 was corrected, version to appear in Phys. Rev. D, 19 figure

A Brief Introduction to Chiral Perturbation Theory

A brief introduction to the subject of chiral perturbation theory ($\chi$pt) is presented, including a discussion of effective field theory and applications of $\chi$pt in the arena of purely mesonic interactions as well as in the $\pi N$ sector.Comment: 15 pages, talk given at TAPS detector workshop, Rez, Czech Republic, Sept. 1999, to be published in Czech. J. Phy

Positive parity pentaquark towers in large Nc QCD

We construct the complete set of positive parity pentaquarks, which correspond in the quark model to {\bar s} q^{Nc+1} states with one unit of orbital angular momentum L=1. In the large Nc limit they fall into the K=1/2 and K=3/2 irreps (towers) of the contracted SU(4)c symmetry. We derive predictions for the mass spectrum and the axial couplings of these states at leading order in 1/Nc. The strong decay width of the lowest-lying positive parity exotic state is of order O(1/Nc), such that this state is narrow in the large Nc limit. Replacing the antiquark with a heavy antiquark {\bar Q} q^{Nc+1}, the two towers become degenerate, split only by O(1/mQ) hyperfine interactions. We obtain predictions for the strong decay widths of heavy pentaquarks to ordinary baryons and heavy H(*)_{\bar Q} mesons at leading order in 1/Nc and 1/mQ.Comment: 21 pages, 2 figures, 5 table

A possible explanation why the Theta+ is seen in some experiments and not in others

To understand the whole set of positive and null data on the Theta+(1530)-production, we suggest the hypothesis that multiquark hadrons are mainly generated from many-quark states, which emerge either as short-term hadron fluctuations, or as hadron remnants in hard processes. This approach allows us to describe both non-observation of the Theta+ in current null experiments and peculiar features of its production in positive experiments. Further, we are able to propose new experiments that might be decisive for the problem of the Theta+ existence. Distributions of the Theta+ in such experiments can give important information both on higher Fock components of conventional hadrons and about structure and hadronization properties of hadron remnants produced in hard processes. We also explain that description of multiquark hadrons may require a modified form of the constituent quark model, with quark masses and couplings being intermediate between their values for the familiar constituent quarks and the current ones.Comment: 18 pages. Some changes in the text; experimental suggestions collected in a special subsection, references added and refreshe

Pion Generalized Dipole Polarizabilities by Virtual Compton Scattering πe→πeγ\pi e \to \pi e\gamma

We present a calculation of the cross section and the event generator of the reaction $\pi e\to \pi e \gamma$. This reaction is sensitive to the pion generalized dipole polarizabilities, namely, the longitudinal electric $\alpha_L(q^2)$, the transverse electric $\alpha_T(q^2)$, and the magnetic $\beta(q^2)$ which, in the real-photon limit, reduce to the ordinary electric and magnetic polarizabilities $\bar{\alpha}$ and $\bar{\beta}$, respectively. The calculation of the cross section is done in the framework of chiral perturbation theory at ${\cal O}(p^4)$. A pion VCS event generator has been written which is ready for implementation in GEANT simulation codes or for independent use.Comment: 33 pages, Revtex, 15 figure

Chiral Anomaly and Eta-Eta' Mixing

We determine the $\eta-\eta'$ mixing angle via a procedure relatively independent of theoretical assumptions by simultaneously fitting $\eta- eta'$ reactions involving the anomaly--$\eta,\eta'\to\gamma\gamma, \pi^+\pi^-\gamma$. We extract reasonably precise renormalized values of the octet and singlet pseudoscalar decay constants $F_8,F_0$ as well as the mixing angle $\theta$.Comment: 12 page standard Latex file, three figures, added comment

Chiral Anomaly and γ3π\gamma 3\pi

Measurement of the $\gamma 3\pi$ process has revealed a possible conflict with what should be a solid prediction generated by the chiral anomaly. We show that inclusion of appropirate energy-momentum dependence in the matrix element reduces the discrepancy.Comment: 8 page standard Latex fil

Photoproduction of neutral pion pairs in the Coulomb field of the nucleus

The total cross section for Coulomb photoproduction of neutral pion pairs in the reaction gamma A --> pi0 pi0 A is estimated within the effective chiral lagrangian approach. The amplitude of gamma gamma* --> pi0 pi0 with one off-shell photon is calculated at O(p^6) in the momentum expansion; in addition, nuclear absorption is taken into account. Besides its experimental feasibility, the results of the calculation demonstrate that the reaction gamma A --> pi0 pi0 A is a powerful source of information on the process gamma gamma --> pi0 pi0 close to threshold.Comment: 18 pages, 6 figures, uses epsf, ioplppt.sty, iopl12.sty (included); Added a discussion of main background from double pion photoproduction on nucleon gamma N --> 2pi0 N via baryon resonance exchange mechanis

Photon-Photon Scattering, Pion Polarizability and Chiral Symmetry

Recent attempts to detect the pion polarizability via analysis of $\gamma\gamma\rightarrow\pi\pi$ measurements are examined. The connection between calculations based on dispersion relations and on chiral perturbation theory is established by matching the low energy chiral amplitude with that given by a full dispersive treatment. Using the values for the polarizability required by chiral symmetry, predicted and experimental cross sections are shown to be in agreement.Comment: 21 pages(+10 figures available on request), LATEX, UMHEP-38

Atrial remodelling comparison after maze-3 and cryo-maze procedures in combined cardiac interventions: a retrospective study

Background. The maze procedure aims to eliminate atrial fibrillation (AF), restore sinus rhythm (SR) and atrial contractility. However, conflicting evidence exists regarding the extent of atrial remodelling in various techniques, which directed the focus of our study.Objectives. An atrial remodelling comparison after a cut-and-sew maze-3 surgery and its biatrial cryo-maze modification using 2D echocardiography.Methods. The study is a retrospective uncontrolled interrupted two-cohort time-series trial, with patients selected by pseudorandomisation according to a normal sinus rhythm-maintaining AF surgery method. A total of 217 maze-3 and 113 cryo-maze combined cardiac interventions have been performed within 2012–2021. The interventions included valve repair, coronary artery bypass grafting and their combination. Due to differences in long-term follow-up, the cohorts were pseudorandomised to select by 50 restored vs. maintained sinus rhythm patients using a nearest-neighbour classifier coupled with logistic regression. Mean follow-up period was 6 (1–17) months. The patients had paroxysmal, persistent and longstanding persistent AF. Echocardiography values prior to and long-term post-surgery were further analysed to determine the atrial remodelling dynamics. Results. A statistically significant atrial volume reduction is evident in a long-term within-cohort comparison. Meanwhile, a statistically more pronounced remodelling is observed between cohorts after maze-3 procedure. The cohort 1 vs. 2 estimates are: mean left atrial volume 120/125 mL3 (p = 0.011), left atrial size in apical view 52/53 mm (p = 0.023), right atrial size in apical view 58/62 mm (p = 0.004), right atrial size in parasternal short axis view 43/45 mm (p = 0.004), right atrial area in apical 4-chamber view 25/28 cm2 (p = 0.007). Maintained atrial pacing patients had positive systolic atrial function recovery rates (E/A ratio increased to average 1.5) in the long-term in both comparison cohorts.Conclusion. Remodelling is biatrial after all the maze procedures compared. A more pronounced atrial volume reduction occurs after maze-3 surgery. The presence of sinus rhythm is facilitated by cardiac conduction leading to mechanical and electrical remodelling of the atria