Various parametrizations of sigma(gamma p) are tried out on the small-x fixed target and HERA data. A two-Pomeron type parametrization is found to give the best reproduction of the data. The data indicate that the value of lambda(eff) for parametrizations of the form sigma(gamma p)~l^lambda(eff) approaches a constant value at high Q^2. The extrapolated values of sigma(gamma p) to very long coherence lengths are found to cross in some parametrizations for l>10^7 fm, indicating the possibility that sigma(gamma p) becomes Q^2 independent at large values of the coherence length l.
A parametrisation of the real photon structure function F_2^gamma in the low Q^2, low x region is formulated. It includes both the VMD and the QCD components, the latter suitably extrapolated to the low Q^2 region and based on arbitrary parton distributions in the photon. The parametrisation used together with the GRV and GRS' parton densities describes reasonably well the existing high energy data on F_2^gamma, sigma(gamma,gamma) and the low Q^2 data on sigma(gamma^*, gamma). Predictions for sigma(gamma,gamma) and for sigma(gamma^* ,gamma) for energies which may become accessible in future li…
The process gamma* gamma -> sigma is investigated in the framework of the SU(2)xSU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of gamma* in the Euclidean kinematic domain. The asymptotic behaviour of this form factor resembles the asymptotic behaviour of the gamma* gamma -> pi form factor.
The gamma + D -> Lambda + Theta+ and gamma + D -> Sigma + Theta+ reactions can be used to determine the width of Theta+ almost model-independently. We calculate the differential cross sections of the gamma +D -> Lambda + Theta+, gamma + D -> Sigma + Theta+ and relevant background reactions in the photon energy range 1.2 < E_γ < 2.6 GeV. We determine the most favorable kinematic conditions and observables for the experimental studies of Theta+ in the considered processes. We argue that a comparison of the gamma + D -> Lambda + Theta+ and gamma + D -> Sigma + Theta+ cross sections should unambig…
We reanalyse the gamma-gamma scattering data and conclude that in the mass region below 1 GeV the cross section for gamma-gamma to pi^0-pi^0 can be largely explained by the one pion exchange process with pi-pi rescattering. The radiative width of the sigma is estimated and a model dependent separation into contributions from direct gamma-gamma decay and decay through rescattering is obtained. We confront these findings with QCD spectral sum rule (QSSR) predictions and conclude that the sigma can have a large gluonium component in its wave function.
The coupling constant g_{rho sigma gamma} is determined from light cone QCD sum rules. A comparison of our result with the ones existing in literature is presented.
The lightest QCD resonance, the sigma, has been recently fixed in the pi-pi scattering amplitude. The nature of this state remains nowadays one of the most intriguing and difficult issues in particle physics. Its coupling to photons is crucial to discriminate its structure. We propose a new method that fixes this coupling using only available precise experimental data on the proton electromagnetic polarizabilities together with analyticity and unitarity. Taking into account the uncertainties in the analysis and in the parameter values, our result is Gamma_{pole}(sigma -> gamma gamma) = (1.2 +-…
We show that therecently observed pion invariant mass distribution of the phi ->pi0 pi0 gamma decay can be satisfactorily described by the chiral U(3) X U(3) Linear Sigma Model.
We propose a new method that fixes the coupling to two photons of the recently found lightest QCD resonance, the sigma. This coupling provides crucial information for discriminating the yet unknown nature of this special state. Our method uses available data on the nucleon polarizabilities together with analyticity and unitarity. Taking into account all the uncertainties, our result is Gamma_{pole}= 1.2 +- 0.4 keV.
We calculate the branching ratio of omega --> pi^+ pi^- gamma decay in a phenomenological framework in which the contributions of VMD, chiral loops, sigma-meson intermediate state amplitudes and the effects of omega-rho mixing are considered. We conclude that the sigma-meson intermediate state amplitude and omega-rho mixing make substantial contribution to the branching ratio.
A variety of strong and electroweak interaction properties of the pion and the light scalar sigma meson are computed in a relativistic quark model. Under the assumption that the resulting coupling of these mesons to the constituent quarks is identical, the sigma meson mass is determined as M_sigma=385.4 MeV. We discuss in detail the gauging of the non-local meson-quark interaction and calculate the electromagnetic form factor of the pion and the form factors of the pi(0) -> gamma gamma and sigma -> gamma gamma processes. We obtain explicit expressions for the relevant form factors and evaluate…
We present an analysis on the exclusive rare radiative decay modes Sigma_b->Sigma gamma and Xi_b->Xi gamma. The transition form factors which parameterize these processes are calculated using QCD light-cone sum rules. The decay widths we predict are Gamma(Sigma_b->Sigma gamma)=(7.21\pm0.04)\times10^{-18}GeV} and Gamma(Xi_b->Xi gamma)=(1.34\pm0.07)\times10^{-16}GeV. The Branching ratio of Xi_b->Xi gamma is predicted to be Br(Ξ_b->Xi gamma)=(3.03\pm0.10)\times10^{-4}.
The parametrisation of the photon structure function in the low Q^2 region is formulated. It includes the VMD contribution and the QCD improved parton model component suitably extrapolated to the low Q^2 region. The parametrisation describes reasonably well existing experimental data on sigma_{γγ} for real photons and the low Q^2 data on sigma_{γ^* γ}. Predictions for sigma_{γγ} and for sigma_{γ^* γ} for energies which may be accesssible in future linear colliders are also given.
We calculate the P0 to gamma gamma, V0 to P0 gamma and V0to V'0 gamma gamma decays in the framework of a U(3)xU(3) linear sigma model which includes constituent quarks. For the first two decays this approach improves results based on the anomalous Wess-Zumino term, with contributions due to SU(3) symmetry breaking and vector mixing. The phi to (omega,rho) gamma gamma decays are dominated by resonant eta' exchange . Our calculation for the later decays improves and update similar calculations in the -closely related- framework of vector meson dominance. We obtain BR(phi to rho gamma gamma)=2.5x…
We analyse the angular distributions of the Sigma^0 --> Lambda^0 + gamma decay rate in the laboratory and in the rest frame of the Sigma^0 - hyperon in the dependence on baryon polarizations. We calculate the dynamical polarization vector of the Lambda^0 - hyperon. Within the Effective quark model with chiral U(3) x U(3) symmetry (PRC 59, 451 (1999)) we calculate the transition magnetic moment mu_(Sigma^0 Lambda^0). The theoretical value mu_(Sigma^0 Lambda^0) = - 1.62, measured in nuclear magnetons, agrees well with the experimental data |mu^(\exp)_(Sigma^0 Lambda^0)| = (1.61 +/-0.08) and the …
We study the theoretical predictions for the total inelastic $γγ$ cross-sections, with an emphasis on the eikonalised minijet model (EMM). In the context of the EMM, we discuss a new ansatz for the overlap function involving the photons. We discuss the dependence of the EMM predictions on various input parameters as well as predictions for \siggg from a simple extension of the Regge Pomeron Exchange model. We then compare both with the recent LEP data.
Using an eikonal analysis, we examine the validity of the factorization theorem for nucleon-nucleon, gamma p and gamma gamma collisions. As an example, using the additive quark model and meson vector dominance, we directly show that for all energies and values of the eikonal, that the factorization theorem sigma_{nn}/sigma_{gamma p} = sigma_{gamma p}/sigma_{gamma gamma} holds. We can also compute the survival probability of large rapidity gaps in high energy pbar p and pp collisions. We show that the survival probabilities are identical (at the same energy) for gamma p and gamma gamma collisio…
The empirical scaling law, wherein the total photoabsorption cross section depends on the single variable eta=(Q^2+m_0^2)/Lambda^2(W^2), provides empirical evidence for saturation in the sense of sigma_{gamma* p}(W^2,Q^2)/sigma_{gamma p}(W^2) --> 1 for W^2 --> infinity at fixed Q^2. The total photoabsorption cross section is related to elastic diffraction in terms of a sum rule. The excess of diffractive production over the elastic component is due to inelastic diffraction that contains the production of hadronic states of higher spins. Motivated by the diffractive mass spectrum, the generaliz…
We extract the pole positions, hadronic and gamma-gamma widths of sigma and f_0(980, from pi-pi and gamma-gamma scattering data using an improved analytic K-matrix model. Our results favour a large gluon component for the sigma and a \bar ss or/and gluon component for the f_0(980) but neither a large four-quark nor a molecule component. Gluonium sigma_B production from J/psi, phi radiative and D_s semi-leptonic decays are also discussed.
Using a recent calculation of transition magnetic moments in the 1/N_c expansion and a calculation showing the suppression of E2/M1 by powers of N_c, we compute the widths for the radiative decays Sigma^* --> Sigma gamma, Sigma^* --> Lambda gamma, and Xi^* --> Xi gamma.
While data for the proton structure function demand the presence of a hard-pomeron contribution even at quite small Q^2, previous fits to the pp and p\bar p total cross sections have found that in these there is little or no room for such a contribution. We re-analyse the data and show that itmay indeed be present and that, further, it probably obeys Regge factorisation: sigma^{gamma p}(s,Q_1^2)sigma^{gamma p}(s,Q_2^2)= sigma^{pp}(s)sigma^{gamma gamma}(s,Q_1^2,Q_2^2) for all values of Q_1^2 and Q_2^2.
We work out the Linear Sigma Model (LSM) predictions for the 2 gamma decay rates of the a_0(980),f_0(980) mesons under the assumption that they are respectively the I=1 and I=0 members of the bar q q scalar nonet. Agreement with experimental data is achieved provided we include the contribution of a κmeson with mass approx. 900 MeV, and a scalar mixing angle (sigma -f_0 mixing in the {|NS>,|S>} basis) varphi_s approx. -14^\circ, as predicted by the model.
The ALLM parameterization of sigma_{tot}(gamma* p) has been updated by using all published F_2 data to determine its parameters. The fit yields a chi^2/ndf of 0.97 for the 1356 data points. The updated ALLM parameterization, ALLM97, gives a good description of all the available data in the whole x and Q^2 range studied so far (3\times10^{-6} < x < 0.85, 0 \le Q^2 < 5000 GeV^2).
We present the estimates of the order $O(α^{4}_{s})$ QCD corrections to $R(s)$, $R_τ$ and to the deep-inelastic scattering sum rules, namely to the non-polarized and polarized Bjorken sum rules and to the Gross-Llewellyn Smith sum rule. The estimates are obtained in the $\overline{MS}$-scheme using the principle of minimal sensitivity and the effective charges approach.
In this talk, we report the theoretical studies of baryon resonances for the gamma p ---> K*0 Sigma+ and gamma p ---> K*+ Sigma0 reaction processes by making use of the effective Lagrangian method in the tree-level Born approximation. The numerical results for the total and differential cross sections are shown with the presently available data. It turns out that the contributions from the N* and Delta* resonances are almost negligible near the threshold energy. On the other hand, the effects of the K exchange in the t channel and Delta(1232) in the s channel are considerably larger than other…
In an attempt to explain the latest experimental result about the branching ratio of $ω\to π^0π^0γ$ decay we reexamine the decay mechanism of this decay in a phenomenological framework in which the contributions of VMD, chiral loops, $σ$-meson intermediate state amplitudes and the effects of $ω-ρ$ mixing are considered. We conclude that in order to obtain the experimental value of the branching ratio $B(ω\to π^0π^0γ)$ $σ$-meson amplitude which makes a substantial contribution should be included into the reaction mechanism and the effects of $ω-ρ$ mixing should be taken into account. We also es…
To establish the Higgs mechanism experimentally, one has to determine the Higgs self-interaction potential responsible for the electroweak symmetry breaking. This requires a measurement of the trilinear and quadrilinear self-couplings of the Higgs particle, as predicted by the Standard Model (SM). We propose to measure the trilinear Higgs self-coupling in gamma-gamma collisions just above the kinematic threshold E_thr = 2M_H, where M_H is the Higgs mass. Our calculation reveals that the sensitivity of the cross-section sigma(gamma gamma -> HH) to the Higgs self-coupling is maximal near the 2M_…
We estimate the I=0 scalar meson sigma/f_0(600) parameters from pi-pi and gamma-gamma scattering data below 700 MeV using an improved analytic K-matrix model. A fit of the hadronic data gives a complex pole mass M_sigma= 422-i290 MeV, while simultaneous best fits of the gamma-gamma to pi+pi-, pi0pi0 data give a direct width of (0.13+-0.05)keV, a rescattering component of (2.7+-0.4)keV and a total (direct+rescattering) width of (3.9+-0.6)keV. "Running" these results to the physical real axis, the small "direct" gamma-gamma and the large hadronic widths at the "on-shell" mass are compatible with…
We estimate the valence quark contributions for the gamma* Y -> Lambda* (Y=Lambda, Sigma0) electromagnetic transition form factors. We focus particularly on the case Lambda*=Lambda(1670) as an analog reaction with gamma* N -> N(1535). The results are compared with those obtained from chiral unitary model, where the Lambda* resonance is dynamically generated and thus the electromagnetic structure comes directly from the meson cloud excitation of the baryon ground states. The form factors for the case Y=Sigma0 in particular, depend crucially on the two real phase (sign) combination, a phase betw…
An important role of the scalar isoscalar sigma-meson in the low-energy physics is discussed. The behavior of the sigma-meson in the hot and dense medium is studied. It is shown that in the vicinity of critical values of temperature(T) and chemical potential(m) the sigma-meson can become a sharp resonance. This effect can lead to a strong enhancement of the processes pi pi -> gamma gamma and pi pi-> pi pi near the two-pion threshold. Experimental observation of this phenomenon can be interpreted as a signal of approaching the domain where the chiral symmetry restoration and phase transition of…
New data on the anomalous magnetic moment a_mu of the muon together with the b->s gamma decay rate are considered within the supergravity inspired constrained minimal supersymmetric model. We perform a global statistical chi^2 analysis of these data and show that the allowed region of parameter space is bounded from below by the Higgs limit, which depends on the trilinear coupling and from above by the anomalous magnetic moment a_mu. The newest b->s gamma data deviate 1.7 sigma from recent SM calculations and prefer a similar parameter region as the 2.6 sigma deviation from a_mu.
Using an improved "analytic K-matrix model", we reconsider the extraction of the sigma/f_0(600) and f_0(980) gamma-gamma widths from gamma-gamma to pi-pi scatterings data of Crystal Ball and Belle. Our main results are summarized in Tables 3 and 4. The averaged sigma "direct width" to gamma-gamma is 0.16(3) keV which confirms a previous result of [1] and which does neither favour a large four-quark (diquark-antidiquark) nor a molecule nor a pure \bar qq component. The "direct width" of the f_0(980) of 0.28(2) keV is much larger than the four-quark expectation but can be compatible with a \bar …
The strong coupling constants g_{K LAMBDA N} and g_{K SIGMA N} for the structure (sigma_{mu,nu} gamma_5) are calculated within light cone QCD sum rules. A comparison of our results on these couplings with predictions from traditional QCD sum rules is presented.
The complementarity between Chiral Perturbation Theory and the Linear Sigma Model in the scalar channel is exploited to study $π^0π^0$ production in $ρ$ and $ω$ radiative decays, where the effects of a low mass scalar resonance $σ(500)$ should manifest. The recently reported data on $ρ\toπ^0π^0γ$ seem to require the contribution of a low mass and moderately narrow $σ(500)$. The properties of this controversial state could be fixed by improving the accuracy of these measurements. Data on $ω\toπ^0π^0γ$ can also be accommodated in our framework, but are much less sensitive to the $σ(500)$ propert…
The reaction gamma p --> K0 Sigma+ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross section and the polarization of the Sigma+ as a function of the kaon production angle in the centre-of-mass system, cos(Theta_K^{c.m.}), and the photon energy. The cross section is lower and varies less with photon energy and kaon production angle than that of gamma p --> K+ Sigma0. The Sigma+ is polarized predominantly at cos(Theta_K^{c.m.}) \approx 0. The data presented h…
We calculate the CP-violating polarization asymmetry of tt-bar, delta =[ sigma(ee-bar --> t(-)t-bar(-))-sigma(ee-bar --> t(+)t-bar(+)) ]/ sigma(ee-bar --> tt-bar), for the most general tt-bar gamma/Z couplings without dropping any non-standard contribution. We find that one term which is usually neglected increases with s and will eventually become non-negligible at very high energy.
Kaon photoproductions on the proton gamma p --> K+Sigma0 and gamma p --> K0Sigma+ have been simultaneously analyzed by using isobar models and new SAPHIR data. The result shows that isobar models such as KAON MAID require more resonances in order to explain the data.
In their 1997 paper, CDF measured sigma_effective, the normalization factor that relates the cross section for double parton scattering to the product of the inclusive cross sections of the two individual scatters, in a model in which they are assumed to be independent. In his 2007 paper, Treleani pointed out that CDF used a non-standard definition, in which the double parton scattering cross section corresponds to exactly two scatters, rather than the more conventional one in which it is the inclusive two-scatter cross section. He also estimated the correction from one definition to the other…
We study the effect of the sigma(600) and a_1(1260) resonances in the rho^0 -> pi^+ pi^- gamma decay, within the meson dominance model. Major effects are driven by the mass and width parameters of the sigma(600), and the usually neglected contribution of the a_1(1260), although small by itself, may become sizable through its interference with pion bremsstrahlung, and the proper relative sign can favor the central value of the experimental branching ratio. We present a procedure, using the gauge invariant structure of the resonant amplitudes, to kinematically enhance the resonant effects in the…
We calculate the "pi Sigma Lambda" and "pi Sigma Sigma" coupling constants in light cone QCD sum rules for the structure "sigma_{alpha beta} gamma_5 p^alpha q^beta". A comparison of our results on these coupling constants with prediction of the SU(3) symmetry is presented.
We replace ordinary chiral SU(3)_L * SU(3)_R perturbation theory CHPT_3 by a new theory CHPT_sigma based on a low-energy expansion about an infrared fixed point alpha_IR for 3-flavor QCD. At alpha_IR, the quark condensate <bar{q}q>_vac =\= 0 induces nine Nambu-Goldstone bosons: pi, K, eta and a 0++ QCD dilaton sigma. Physically, sigma appears as the f_0(500) resonance, a pole at a complex mass with real part < m_K. The ΔI = 1/2 rule for nonleptonic K-decays is then a consequence of CHPT_sigma, with a K_S-sigma coupling fixed by data for K_S^0 --> gamma gamma and gamma gamma --> pi pi. We estim…
Fermilab E781 plans measurements of gamma-Sigma and $γ$-pion interactions using a 600 GeV beam of Sigmas and pions, and a virtual photon target. Pion polarizabilities and radiative transitions will be measured in this experiment. The former can test a precise prediction of chiral symmetry; the latter for a_1(1260) ----> pi + gamma is important for understanding the polarizability. The experiment also measures polarizabilities and radiative transitions for Sigma hyperons. The polarizabilities can test predictions of baryon chiral perturbation theory. The radiative transitions to the Sigma*(1385…
Preliminary results of the analysis of the reaction p(gamma,K0)Sigma+ are presented. We show the first measurement of the differential cross section and much improved data for the total cross section than previous data. The data are compared with model predictions from different isobar and quark models that give a good description of p(gamma,K+)Lambda and p(gamma,K+)Sigma0 data in the same energy range. Results of ChPT describe the data adequately at threshold while isobar models that include hadronic form factors reproduce the data at intermediate energies.
We study nonleptonic Lambda_b -> Lambda_c pi, Sigma_c pi and Sigma_c^* pi decays in the limit m_b, m_c, E_pi >> Lambda_{QCD} using the soft-collinear effective theory. Here Sigma_c = Sigma_c(2455) and Sigma_c^* = Sigma_c(2520). At leading order the Lambda_b -> Sigma_c^{(*)} pi rates vanish, while the Lambda_b -> Lambda_c pi rate is related to Lambda_b -> Lambda_c\ell\barν, and is expected to be larger than Gamma(B -> D^{(*)} pi). The dominant contributions to the Lambda_b -> Sigma_c^{(*)} pi rates are suppressed by Lambda_{QCD}^2/E_pi^2. We predict Gamma(Lambda_b -> Sigma_c^* pi) / Gamma(Lambd…
A Monte Carlo generator has been constructed to simulate the reaction e+ e- --> gamma + 2 pions and gamma + 4 pions, where the photon is assumed to be observed in the detector. Predictions are presented for cms energies of 1GeV, 3GeV and 10GeV, corresponding to the energies of DAPHNE, BEBC and of B-meson factories. The event rates are sufficiently high to allow for a precise measurement of R(Q^2) in the region of Q between approximately 1GeV and 2.5GeV. Estimates for the kinematic breaking of isospin relations between different channels as a consequence of the mass difference between charged a…
Properties and temperature behavior of pi and sigma bound states are studied in the framework of the nonlocal model with a separable interaction kernel based on the quark Dyson-Schwinger and the meson Bethe-Salpeter equations. M_pi(T), f_pi(T), M_sigma(T) and Gamma_{sigma -> pi pi}(T) are considered above and below the deconfinement and chiral restoration transitions.
The coherence factor and average strong phase difference of D0 and D0bar decay amplitudes to the same final state play an important role in the precision determination of the CKM parameter gamma using B- -> DK- and related decay modes. So far, this important input from the charm sector could only be obtained from measurements based on quantum-correlated DDbar pairs produced at the charm threshold. We propose to constrain these parameters using charm mixing, using the large charm samples available at the B factories and LHCb. We demonstrate for the example of D0->Kpipipi that a substantial impr…
We analyse data on pi pi and gamma gamma scattering below 700 MeV within an improved analytic K-matrix model. This model is based on an effective theory with couplings between resonances, hadrons and photons. The two-photon decay of a resonance can proceed through intermediate transition into charged hadrons (here: pi^+ pi^-) and their subsequent annihilation or through a ``direct'' transition into photons. Our analysis confirms the rather large total radiative width of the sigma/f_0(600) resonance which we find as (3.9 \pm 0.6) keV but suggests its dominance by the pi pi rescattering process.…
We explore the consequences for diffractive production, gamma* p --> X p, in deep inelastic scattering at low values of x\sim Q^2/W^2 <<1 that follow from our recent representation of the total photoabsorption cross section, sigma_{gamma* p}, in the generalized vector dominance/ color dipole picture(GVD/CDP) that is based on the generic structure of the two-gluon-exchange from QCD. Sum rules are derived that relate the transverse and the longitudinal (virtual) photoabsorption cross section to diffractive forward production of q q-bar states that carry photon quantum numbers ("elastic diffracti…
A consistent description of $σ(500)$ meson effects in $ρ^0\toπ^0π^0γ$ and $π^+π^-γ$ decays is proposed in terms of reasonably simple amplitudes which reproduce the expected chiral-loop behaviour for large $m_σ$ values. For the neutral case, in addition to the well known $ω$ exchange, there is an important contribution from the $σ(500)$ meson that is in agreement with recent experimental data. For the charged case, where the dominant contribution comes from bremsstrahlung, the effects of the $σ(500)$ meson are relevant only at high values of the photon energy and compatible with present data. A…
Using 43 months of public gamma-ray data from the Fermi Large Area Telescope, we find in regions close to the Galactic center at energies of 130 GeV a 4.6 sigma excess that is not inconsistent with a gamma-ray line from dark matter annihilation. When taking into account the look-elsewhere effect, the significance of the observed signature is 3.2 sigma. If interpreted in terms of dark matter particles annihilating into a photon pair, the observations imply a partial annihilation cross-section of about 10^-27 cm^3s^-1 and a dark matter mass around 130 GeV. We review aspects of the statistical an…
We discuss the observability of the lightest neutral Higgs boson in the constrained MSSM (CMSSM), with universal soft supersymmetry-breaking parameters, at hadron colliders such as the Tevatron and the LHC. We take account of the constraints on parameter space provided by LEP, the measured rate of b to s gamma decay, the cosmological relic density Omega h^2, and the recent measurement of g_mu - 2. We normalize products of the expected CMSSM Higgs production cross sections and decay branching ratios (sigma B)_CMSSM relative to those expected for a Standard Model Higgs boson of the same mass. In…
A distinct signature for dark matter in the form of weakly interacting massive particles (WIMPs) would be the detection of a monochromatic spectral line in the gamma-ray sky. The Fermi-LAT collaboration has searched for such a line in the energy range from 5 to 300 GeV in five sky regions around the Galactic centre. No globally significant line is detected, and 95% CL upper limits on monochromatic-line strengths are presented. The smallest search region reveals a line-like structure at 133 GeV with a local significance of 2.9 sigma after 4.4 years of data, which translates to less than 1 sigma…
We formulate the general form of omega-Z-gamma vertex in the framework based on the hidden local symmetry (HLS), which arises from the gauge invariant terms for intrinsic parity-odd (IP-odd) part of the effective action. Those terms are given as the homogeneous part of the general solution (having free parameters) to the Wess-Zumino (WZ) anomaly equation and hence are not determined by the anomaly, in sharp contrast to the Harvey-Hill-Hill (HHH) action where the relevant vertex is claimed to be uniquely determined by the anomaly. We show that, even in the framework that HHH was based on, the o…
We extract the K+K- couplings of the isoscalar scalar mesons sigma/f_0(600) and f_0(980) from pi pi to pi pi / K K scatterings and found: |g_{sigma K+K-}|/ |g_{sigma pi+pi-}|= 0.8 and |g_{f_0 K+K-}|/ |g_{f_0 pi+pi-}|= 1.7. These results, together with the tiny "direct" gamma gamma width of the sigma and its large hadronic width, are a strong indication for the gluonium/glueball nature of the sigma-meson, as predicted by QCD spectral sum rules (QSSR) + some low-energy theorems (LET), while some other assignements (pi pi molecule, tetraquark state and ordinary qq meson) do not satisfy simultaneo…
We examine the radiative decays of the Lambda (1405) to octet baryons, Lambda + gamma and Sigma + gamma. In the limit of SU(3) symmetry the decay rates for these two modes are related, and we compute the leading correction to the relation in chiral perturbation theory. Such measurements will allow the sign of the strong coupling $g_{Λ^*}$ to be determined. The SU(3) violating radiative decay to the baryon decuplet Sigma* + gamma dominated by one-loop graphs is also discussed. Experiments planned for the Jefferson Laboratory should be able to measure some, if not all, of the processes considere…
We formulated the $Lambda(1405)$ (abbreviated as $Lambda^*$) $rightarrow (Sigmapi)^0$ invariant-mass spectra produced in the $K^- + p rightarrow Sigma^+ (1660) + pi^-$, followed by $Sigma^+ (1660) rightarrow Lambda(1405) + pi^+ rightarrow Sigmapi + pi^+$, processes at $p(K^-) = 4.2$ GeV/$c$, in which both the incident channel for a quasi-bound $K^-p$ state and its decay process to $(Sigma pi)^0$ were taken into account realistically. We calculated $M(Sigma pi)$ spectral shapes using mixed transition matrices, $T_{21} = T_{ Sigmapi leftarrow K^-p}$ and $T_{22} = T_{ Sigma pi leftarrow Sigma pi}…
The nucleon resonances are investigated within a dynamical coupled-channels model of pi N and gamma N reactions up to the invariant mass W = 2 GeV. The meson-baryon (MB) channels included in the calculations are MB = pi N, eta N, K Lambda, K Sigma, and pi pi N that has pi Delta, rho N, and sigma N resonant components. The meson-baryon amplitudes T_{M'B',MB}(W) are calculated from solving a set of coupled-channels integral equations defined by an interaction Hamiltonian consisting of (a) meson-exchange interactions v_{M'B',MB} derived from phenomenological Lagrangian, and (b) vertex interaction…
We report observation of a narrow peak structure at ~1.54 GeV with a Gaussian width sigma=6 MeV in the missing of K_s in the reaction gamma+p = pK_sK_L. The observed structure may be due to the interference between a strange (or anti-strange) baryon resonance in the pK_L system and the phi(K_sK_L) photoproduction leading to the same final state. The statistical significance of the observed excess of events estimated as the log likelihood ratio of the resonant signal+background hypothesis and the phi-production based background only hypothesis corresponds to 5.3 sigma.
