We investigate photoproduction of $ϕ$-mesons off protons within a coupled-channel effective-Lagrangian method which is based on the K-matrix approach. Since the threshold energy of the $KΛ(1520)$ channel is close to that of $ϕN$, the contribution of this channel to $ϕ$-photoproduction near the threshold energy region may give rise to some unexpected structures. In the transition amplitude $KΛ(1520) \to ϕN$, the kinematics allows an intermediate kaon to be on-shell. This happens in the energy region where a peak structure has been observed in $ϕ$-photoproduction. In our calculations the on-shell kaon effect indeed reproduces a peak structure, however, with a magnitude that is far too small to explain the observed effect. As a following step we introduce a nucleon resonance in our model. The coupling of the resonance to the $KΛ(1520)$ and $ϕN$ channels is not suppressed by the OZI rule if the resonance contains a dominant hidden strangeness component. We find that the resonance can reproduce a peak structure of the correct magnitude at the right energy. We also investigate the effects of coupled channels and the resonance on the angular distribution and the spin density matrices for $ϕ$ photoproduction.
We show that the differential cross section d_sigma/d_t of gamma p --> ϕp reaction at the threshold is finite and its value is crucial to the mechanism of the phi meson photoproduction and for the models of phi-N interaction.
We investigate Lambda(1520,3/2^-,D_03) photoproduction via the gamma N -> K Lambda^* reaction process. Using effective Lagrangians, we compute the total and differential cross sections as well as the dependence on the momentum transfer for the photoproduction at the tree-level. We employ two different form factors: The four-dimensional gauge-invariant type and the three dimensional one depending on the external momenta. We find that the total cross sections for the proton target are well reproduced as compared with the experimental data. It turns out that the total cross sections for the neutr…
P-wave amplitudes for elastic K+ K- photoproduction on hydrogen near the phi(1020) resonance have been derived in an analytical form and a partial wave decomposition of the amplitudes has been performed. We discuss the high energy limit of the resulting amplitudes and compare two types of pomeron coupling to nucleons.
We investigate the possibility that the process of phi photoproduction may have a significant hard perturbative QCD component. This suggestion is based on a study of the energy dependence of the forward phi photoproduction cross section followed by a calculation where we show that a coherent sum of the pQCD and conventional soft Pomeron contributions provides an excellent reproduction of the experimental data. Our results suggest that the transition from the predominantly soft photoproduction of light rho and omega vector mesons to the predominantly hard photoproduction of heavy J/psi and upsi…
We investigate the photoproduction of Lambda(1520,3/2^-) via the gamma N -> K Lambda^* reaction using the Born approximation and the Rariata-Schwinger vector-spinor field for the spin 3/2 particle. We reproduce the experimental data of the total cross section and the angular dependence for the proton target qualitatively well and estimate them for the neutron target. For the neutron target, we find much smaller total cross section than that of the proton and the significant K^*-exchange contribution.
We suggest to measure the triple polarization correlations in the exclusive associative charm particle photoproduction, vector gamma + vector p --> vector Lambda_c^{++} bar{D^0} with linearly polarized photons, as a method to determine the P-parity of the charmed D-meson. The dependence of these correlations on the parity P(N Lambda_c D) can be predicted in model independent way. The t-dependence of the differential cross section for vector meson photoproduction, gamma + p --> Lambda_c^{++} bar{D^{*0}}, in a model based on D-exchange, is also sensitive to P(N Lambda_c D).
We calculate the leading-order perturbative contribution to $γp \to M_{V} p$, with $M_V$ being a $Φ$ or $J/Ψ$ meson, in the kinematic region of large energy and scattering angle.
We investigate the photoproduction of Lambda(1405,1/2^-) = Lambda* off the proton target using the effective Lagrangian in the Born approximation. We observed that, depending on the choice of the K* N Lambda* coupling strength, the total cross section becomes 0.1 <~ sigma_Lambda* <~ 0.2 mu b near the threshold and starts to decrease beyond E_gamma ~ 1.6 GeV, and the angular dependence shows a mild enhancement in the forward direction. It turns out that the energy dependence of the total cross section is similar to that shown in the recent LEPS experiment. This suggests that the production mech…
The polarization observables in phi photoproduction are suggested for probing the nucleon strangeness. Based on models for phi photoproduction, some double polarization observables are shown to be very sensitive to the strangeness content of the proton because of the different spin structures of the amplitudes associated with different mechanisms.
The reactions gamma p -> K+ Lambda and gamma p -> K* Lambda are analyzed within perturbative QCD, allowing for diquarks as quasi-elementary constituents of baryons. The diquark-model parameters and the quark-diquark distribution amplitudes of proton and Lambda are taken from previous investigations of electromagnetic baryon form factors and Compton-scattering off protons. Unpolarized differential cross sections and polarization observables are computed for different choices of the K and K* distribution amplitudes. The asymptotic form of the K distribution amplitude (proportional to x1 x2) is f…
The complex scalar quantum field theory with a lambda (phi^*phi)^2 interaction is considered in the Feshbach-Villars formulation. It is shown that exact few-particle eigenstates of the QFT Hamiltonian can be obtained. The resulting relativistic few-body equations correspond to Klein-Gordon particles interacting via delta-function, or ``contact'', potentials. Momentum-space solutions of the two-body equation yield a `trivial' unity S-matrix.
A simple model for the photoproduction of kaons off protons with a lambda hyperon in the final state is presented. In a quark model, the interaction is modelled by the pair-creation of the (anti-) strange quarks in the final state which recombine with the three quarks of the proton to form the lambda and kaon. The calculated scattering cross sections for photon energies up to $E_γ= 1.9 \; \mbox{GeV}$ are compared to experiment. The pair-creation process is found to have a significant contribution to the total cross section.
We show that the shear viscosity of lambda phi^4 theory is sensitive at next-to-leading order to soft physics, which gives rise to subleading corrections suppressed by only a half power of the coupling, eta = [3033.54 + 1548.3 m_{th}/T] N T^3]/[ (N+2)/3 lambda^2], with m^2_th=(N+2)/72 lambda T^2. The series appears to converge about as well (or badly) as the series for the pressure.
Exclusive diffractive photoproduction of heavy vector mesons (V=phi, J/psi and Upsilon) at HERA is studied in a model employing a dipole Pomeron exchange (P) with an inelastic gamma-P-V vertex. The model is fitted to the data on dsigma/dt, B and elastic sigma for Q^2=0 and beyond the threshold region. The elastic cross sections for both phi and J/psi photoproduction show a moderate increase within the HERA energy region. The flattening of the slope B(s) (little or no shrinkage) for J/psi is not correlated with the slope of the Pomeron trajectory. Estimates for Upsilon photoproduction at HERA a…
The contributions of direct knockout processes, in addition to the diffractive production and one-pion-exchange processes associated with the phi-rho-pi and phi-gamma-pi couplings, to the polarization observables of the phi photoproduction from proton are calculated. We make use of Pomeron-photon analogy and a relativistic harmonic oscillator quark model. We find that some of the double polarization observables are very sensitive to a possible (s s-bar) admixture in the proton. It arises from the difference in the spin structures of the three different amplitudes. This suggests that such measu…
We study the photoproduction of $K^*(892)$ vector meson from both the charged and neutral reactions, $γp \to K^{*+} Λ$ and $γn \to K^{*0} Λ$. The production mechanisms that we consider include $t$-channel $K^*$, $K$, $κ$ exchanges, s-channel nucleon diagram, and $u$-channel $Λ$, $Σ$, $Σ^*$ diagrams. These could constitute important backgrounds for future investigation of ``missing'' resonances that can be searched for especially in these reactions. The $t$-channel $K$ meson exchange is found to dominate both reactions. The total and differential cross sections are presented together with some …
In this report, we present our recent studies on the Lambda(1405,1/2-)=Lambda* photoproduction via the gamma p -> K+ pi Sigma scattering process, employing a coupled-channel formalism, i.e., the chiral unitary model, which respects chiral dynamics in terms of the Weinberg-Tomozawa meson baryon interaction. In addition to the dynamically generated s-wave resonance, Lambda*, we include the p-wave resonance contribution from Sigma(1385,3/2+). We observe that the p-wave contribution provides considerable effects on the pi-Sigma invariant-mass spectrum. It also turns out that, within the present le…
We explore the analytical properties of the traceless stress tensor 2-point function at zero momentum and small frequency (relevant for shear viscosity and hydrodynamic response) in hot, weakly coupled lambda phi^4 theory. We show that, rather than one or a small number of poles, the correlator has a cut along the negative imaginary frequency axis. We briefly discuss this result's relevance for constructing 2'nd order hydrodynamic models of hot relativistic field theories.
We study the vector meson density matrix and the associated polarization asymmetries in $ϕ$ photoproduction near threshold. In order to study the OZI violating processes, we consider the direct $ϕNN$ coupling as well as the knockout processes arising from the non-vanishing $s\bar{s}$ sea quarks in the nucleon. The polarization asymmetries in $ϕ$ meson decays are found to be very useful to constrain the $ϕNN$ coupling constant. The hidden strangeness of the nucleon can also be studied by these asymmetries, but mostly at large $|t|$ region.
We study the domain of validity of a Schwinger-Dyson (SD) approach to non-equilibrium dynamics when there is broken symmetry. We perform exact numerical simulations of the one- and two-point functions of lambda phi^4 field theory in 1+1 dimensions in the classical domain for initial conditions where < phi(x) > not equal to 0. We compare these results to two self-consistent truncations of the SD equations which ignore three-point vertex function corrections. The first approximation, which sets the three-point function to one (the bare vertex approximation (BVA)) gives an excellent description f…
Photoproduction of the Theta+ pentaquark on the proton is analyzed by using an isobar and a Regge models. The difference in the calculated total cross section is found to be more than two orders of magnitude for a hadronic form factor cut-off Lambda > 1 GeV. Comparable results would be obtained for 0.6 < Lambda < 0.8 GeV. We also calculate contribution of the Theta+ photoproduction to the GDH integral. By comparing with the current phenomenological calculation, it is found that the GDH sum rule favors the result obtained from Regge approach and isobar model with small Lambda.
We study the reaction mechanism for the photoproduction of the Lambda(1520), based on an effective Lagrangian approach. We investigate each contribution of the s-, u-, t-channel processes and contact term, separately. One of the most characteristic features of this reaction is the contact-term dominance which governs the photoproduction from the proton, when the K*-exchange contribution is possibly not too large. We suggest several different ways of the polarizations and arrangement of the beam and target to make to understand the role of each contribution separately in future experiments.
We study, within phenomenological Lagrangian approach, the possibility that the near-threshold peak found in the phi-photoproduction cross section is caused by a resonance. We show that, by employing a J^P=3/2^- resonance with a mass of 2.08 +/- 0.05 GeV and a width of 0.570 +/- 0.169 GeV, the LEPS data which include new data on nine spin-density matrix elements can indeed be described reasonably well. We also find that the ratio of helicity amplitudes A_1/2/A_3/2 calculated from the resulting coupling constants differs in sign from that of D13(2080). The resonance is further found to be able …
The polarization observables in phi meson photoproduction is studied to probe the strangeness content of the nucleon. In addition to the dominant diffractive production and the one-pion-exchange process, we take into account the direct knockout mechanism that arises from the possible hidden strangeness content of the nucleon. We find that some double polarization observables are very sensitive to the strangeness content of the proton because of the different spin structures of the amplitudes associated with different mechanisms. This suggests that such measurements could be very useful in prob…
We study whether the nonmonotonic behavior found in the differential cross section of the phi-meson photoproduction near threshold can be described by a resonance. The resonant contribution is evaluated by using an effective Lagrangian approach. We find that, with the assumption of a J^P=3/2^- resonance with mass of 2.10 \pm 0.03 GeV and width of 0.465 \pm 0.141 GeV, LEPS data can indeed be well described. The ratio of the helicity amplitudes A_1/2/A_3/2 calculated from the resulting coupling constants differs in sign from that of the known D13(2080). We further find that the addition of this …
We study the reaction mechanism of K*Lambda(1116) photoproduction off the proton target near threshold considering the contributions from nucleon-resonances. Employing the effective Lagrangian method at the tree-level Born approximation, we investigate the role of the D13(2080) and the D15(2200). We found that the D13 plays a crucial role to reproduce the experimental data well in the forward scattering region at low energy. We also present theoretical predictions on the single photon-beam asymmetry as well as the energy and angular dependence for the cross sections of this reaction.
We apply the $δ$-expansion perturbation scheme to the $λϕ_{4}$ self-interacting scalar field theory in 3+1 D at finite temperature. In the $δ$-expansion the interaction term is written as $λ(ϕ^{2})^{1 + δ}$ and $δ$ is considered as the perturbation parameter. We compute, in this perturbation approach, the renormalized mass at finite temperature from which we get the critical temperature. The results are compared with the usual loop-expansion at finite temperature.
If spacetime contains large compact extra dimensions, the fundamental mass scale of nature, $Lambda$, may be close to the weak scale, allowing gravitational physics to significantly modify electroweak symmetry breaking. Operators of the form $(1/Lambda^2) |phi^* D phi|^2$ and $(1/Lambda^2) phi^* W B phi$, where $W$ and $B$ are the SU(2) and U(1) field strengths and $phi$ is the Higgs field, remove the precision electroweak bound on the Higgs boson mass for values of $Lambda$ in a wide range: $4 TeV < Lambda < 11 TeV$. Within this framework, there is no preference between a light Higgs boson, a…
We have analyzed the K+K- photoproduction on hydrogen in the effective mass region around the mass of the phi(1020) meson. The interference of the S-wave contribution with the P-wave has been studied. Both scalar resonances f0(980) and a0(980) have been taken into account. We have obtained a good description of the available experimental data, in particular the mass distributions and the moments of the kaon angular distribution. Our calculations give values of the integrated S-wave total photoproduction cross section between 4 and 7 nb for the K+K- effective mass range around the phi(1020) mas…
We develop a model that describes the gamma p -> K^+ pi Sigma reaction in the Lambda(1405) region. The model consists of gauge invariant photo-production mechanisms, and the chiral unitary model that gives the rescattering amplitudes where Lambda(1405) is contained. The model also contains phenomenological parameters, associated with short-range dynamics, to be used in fitting data. We successfully fit recent CLAS data for the pi-Sigma invariant mass distributions (line-shape) in the gamma p -> K^+ pi Sigma reaction for all the charge states. We find that the higher mass pole for Lambda(1405) …
We study whether the nonmonotonic behavior found in the differential cross section of the phi-meson photoproduction near threshold can be described by a resonance. Namely, we add a resonance to a model consisting of Pomeron and (pi,eta) exchange by fiat and see if, with a suitable assignment of spin and parity, mass and width, as well as the coupling constants, one would be able to obtain a good description to all the data reported by the LEPS collaboration in the low-energy region. The resonant contribution is evaluated by using an effective Lagrangian approach. We find that, with the assumpt…
We present a strategy to extract the position of the two $Λ(1405)$ poles from experimental photoproduction data measured recently at different energies in the $γp \to K^+ π^0 Σ^0 $ reaction at Jefferson Lab. By means of a chiral dynamics motivated potential but with free parameters, we solve the Bethe Salpeter equation in the coupled channels $\bar K N$ and $πΣ$ in isospin I=0 and parameterize the amplitude for the photonuclear reaction in terms of a linear combination of the $πΣ\to πΣ$ and $\bar K N \to πΣ$ scattering amplitudes in I=0, with a different linear combination for each energy. Goo…
Recent cross section data for the reaction gamma + p \to K^+ + Lambda are examined for evidence of scaling in both the low-t Regge domain and in the high \sqrt{s} and -t domain where constituent counting may apply. It is shown that the reaction does scale in both regimes. At large center of mass angles, s^{-7} scaling appears to hold at essentially all -t, but with angle-dependent oscillations. The scaled data show particularly strong evidence for s-channel resonances for -t below 2 GeV^2 and for W below about 2.3 GeV. The dominant contributions are consistent with an N^* S_{11} resonance at 1…
Recent CLAS data for the pi Sigma invariant mass distributions (line-shapes) in the gamma p -> K^+ pi Sigma reaction are theoretically investigated. The line-shapes have peaks associated with the Lambda(1405) excitation. Our model consists of gauge invariant photo-production mechanisms, and the chiral unitary model that gives the rescattering amplitudes where Lambda(1405) is contained. It is found that, while the pi Sigma line-shape data in the Lambda(1405) region are successfully reproduced by our model for all the charge states, the production mechanism is not so simple that we need to intro…
We use lattice simulations to examine the detailed dynamics of inflaton fragmentation during and after preheating in $λϕ^4$ chaotic inflation. The dynamics are qualitatively similar to preheating after $m^2 ϕ^2$ inflation, involving the exponential growth and subsequent expansion and collision of bubble-like inhomogeneities of the inflaton and other scalar fields. During this stage fluctuations of the fields become strongly non-Gaussian. In the quartic theory, the conformal nature of the theory allows us to extend our simulations to much greater times than is possible for the quadratic model. …
Diffractive photoproduction of rho, phi and J/psi was studied in the BFKL approach to hard colour singlet exchange. Differential cross sections, the energy dependence and spin density matrix elements were calculated and compared to data from HERA. The overall description of data is reasonably good, except of the single flip amplitude which has the wrong sign. Importance of chiral odd components of the photon is stressed.
The time evolution of O(N) symmetric lambda Phi^4 scalar field theory is studied in the large N limit. In this limit the <Phi> mean field and two-point correlation function <Phi Phi> evolve together as a self-consistent closed Hamiltonian system, characterized by a Gaussian density matrix. The static part of the effective Hamiltonian defines the True Effective Potential U_eff for configurations far from thermal equilibrium. Numerically solving the time evolution equations for energy densities corresponding to a quench in the unstable spinodal region, we find results quite different from what m…
We investigate the reaction gamma+p -> V+p, with V denoting a Phi or a J/Psi meson, within the scope of perturbative QCD, treating the proton as a quark-diquark system. Our predictions extrapolate the existing forward differential cross-section data into the few-GeV momentum-transfer region. In case of the J/Psi reasonable results are only obtained by properly taking into account its mass in the perturbative calculation of the hard-scattering amplitude.
Photoproduction of neutral-kaon pairs is studied from the perspective of CP and CPT studies. Interference of the P and S waves, with the former due to diffractive phi production and the latter to f_0/a_0 production, is shown to enhance the CPT reach. Results are presented of Monte Carlo studies based on rates expected in future experiments.
We analyze the electromagnetic production of K^+Lambda and K^0Lambda near their production thresholds by using isobar models. In the K^+Lambda channel we show that the model can nicely describe the available experimental data. In the K^0Lambda channel we demonstrate that the K^0 charge form factor has sizable effects on the longitudinal cross section. By extending the model up to W = 1730 MeV, we are able to observe the existence of the narrow P_{11} (J^p = 1/2^+) resonance in the kaon photoproduction process. It is found that the most convincing mass (width) of this resonance is 1650 MeV (5 M…
We discuss the physics of the 3+1 dimensional lambda Phi^4 quantum field theory in terms of the statistical mechanics of a gas of particles (`atoms') that interact via a -1/r^3-plus-hard-core potential. The hard-core potential, delta^(3)(r), arises from the bare vertex diagram, while the attractive, long-range -1/r^3 potential is due to exchange of a particle pair via the t,u-channel "fish" diagram. (Higher-order diagrams preserve this form of the interparticle potential.) For sufficiently small atom mass, the lowest-energy state is not the `empty' state with no atoms, but a state with a non-z…
Does massless (lambda Phi^4)_4 theory exhibit spontaneous symmetry breaking (SSB)? The raw 1-loop result implies that it does, but the "RG-improved" result implies the opposite. I argue that the appropriate "low-energy effective theory" is a nonlocal field theory involving an attractive, long-range interaction Phi^2(x) Phi^2(y)/z^4, where z=|x-y|. RG improvement then requires running couplings for both this interaction and the original pointlike interaction. A crude calculation in this framework yields SSB even after "RG improvement" and closely agrees with the raw 1-loop result.
Recent lattice data for the effective potential of lambda Phi^4 theory fits the massless one-loop formula with amazing precision. Any corrections are at least 100 times smaller than is reasonable, perturbatively. This is strong evidence for the "exactness conjecture" of Consoli and Stevenson.
We investigate the Lambda(1520) photoproduction via the reaction process, gamma N -> K Lambda(1520). We employ the Born approximation and the Rarita Schwinger formalism is used for Lambda(1520). We reproduce the total cross sections and the various angular distributions qualitatively well for the proton target and estimate them for the neutron one. We find that the contact term contributes much more to the process than the other kinematical channels. Taking into account this fact, we reanalyze the K^*--exchange dominance hypothesis suggested by the previous experiments.
We investigate the inclusive photoproduction of J/Psi mesons at HERA within the framework of the kt-factorization QCD approach. Our consideration is based on the color singlet model supplemented with the relevant off-shell matrix elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS collaborations. Special attention is put on the J/Psi polarization parameters lambda and nu which are sensitive to the p…
We study the photoproduction of the ^12{_Lambda}B hypernucleus within a fully covariant effective Lagrangian based model, employing Lambda bound state spinors derived from the latest quark-meson coupling model. The kaon production vertex is described via creation, propagation and decay of N*(1650), N*(1710), and N*(1720) intermediate baryonic resonant states in the initial collision of the photon with a target proton in the incident channel. The parameters of the resonance vertices are fixed by describing the total and differential cross section data on the elementary gamma (p, K+) Lambda reac…
We study the contribution of the Drell mechanism driven by K^+ and K^- exchange to the reaction gamma N -> KKbar N. Our calculation implements the full KN and KbarN reaction amplitudes in the form of partial wave amplitudes taken from a meson-exchange model (KN) and a partial wave analysis (KbarN), respectively. Comparing our results to data of the LAMP2 collaboration we observe that the Drell mechanism alone cannot describe the large Lambda(1520) photoproduction rate observed experimentally. We argue that the discrepancy could be due to significant contributions from K*-meson exchange with su…
We investigate OZI rule violation in omega and phi-meson photoproduction off nucleons. Data on the total cross sections indicate a large phi/omega ratio of about 0.8 at the maximal available photon energy that is in good agreement with expectations from QCD. On the other hand, data at large four momentum transfer exhibit a ratio of about 0.07, showing that the perturbative QCD regime is not approached at |t| > 2 GeV^2 and photon energies E_γ< 4 GeV. The anomanously large phi/omega ratio at low energies, that is close to the reaction threshold, remains to be explained within nonperturbative QCD…
New SAPHIR p(gamma,K+)Lambda total cross section data show a resonance structure at a total c.m. energy around 1900 MeV. We investigate this feature with an isobar model and find that the structure can be well explained by including a new D_{13} resonance at 1895 MeV. Such a state has been predicted by a relativistic quark model at 1960 MeV with significant gamma-N and K-Lambda branching ratios. We demonstrate how the measurement of the photon asymmetry can be used to further study this resonance. In addition, verification of the predicted large decay widths into the eta-N and eta'-N channels …
We have studied the partial wave interference effects to obtain a new information about the contribution of the S-wave to the cross section of the K+K- photoproduction on hydrogen. The K+K- photoproduction channel for the effective masses around 1 GeV is dominated by the phi(1020) resonance with only a small fraction of events coming from decays of scalar resonances f0(980) and a0(980). However, a careful analysis of angular distributions of the outgoing kaons shows that the S-wave adds an asymmetry to the angular distribution of kaons. A fairly precise estimation of the K+K- photoproduction c…
We discuss various aspects of the O(N)-model in the vacuum and at finite temperature within the Phi-derivable expansion scheme to order lambda^2. In continuation to an earlier work, we look for a physical parametrization in the N=4 case that allows to accommodate the lightest mesons. Using zero-momentum curvature masses to approximate the physical masses, we find that, in the parameter range where a relatively large sigma mass is obtained, the scale of the Landau pole is lower compared to that obtained in the two-loop truncation. This jeopardizes the insensitivity of the observables to the ult…
The real meaning of `triviality' of (lambda Phi^4)_4 theory is outlined. Assuming `triviality' leads to an effective potential that is just the classical potential plus the zero-point energy of the free-field fluctuations. This V_{eff} gives spontaneous symmetry breaking. Its proper renormalization has the consequence that all scattering amplitudes vanish, self-consistently validating the original assumption. Nevertheless, the theory is physically distinguishable from a free field theory; it has a symmetry-restoring phase transition at a finite critical temperature.
Recent calculations in one-loop and Gaussian appro- ximation, using the so-called autonomous renormalization scheme, indicate a comparatively massive, narrow Higgs excitation at about 2 TeV. Here I show that this result qualitatively persists in the framework of a post-Gaussian variational approximation for the pure O(N)-symmetric phi**4-theory for N>1. The method is based on nonlinear transformations of path-integral variables, and the optimization amounts to a Schwinger-Dyson-type summation of diagrams. In the case of O(4), for example, I find M_Higgs = 2.3 TeV, compared to 1.9 TeV and 2.1 T…
Considered is the N=1 SQCD-like theory with SU(N_c) colors and 0<N_F<2N_c flavors of light quarks Q_i,\bar Q_j and with the additional N^2_F colorless flavored fields Phi_{ij} with the large mass parameter μ_{Phi}>>Lambda. The mass spectra of this Phi-theory (and its dual variant, the dPhi-theory) are calculated at different values of μ_{Phi}/Lambda >>1 within the dynamical scenario which implies the (quasi)spontaneous breaking of chiral symmetry. It is shown that, under appropriate conditions, the seemingly heavy and dynamically irrelevant fields Phi 'return back' and there appear two additio…
New kaon photoproduction data on a proton, gamma + p --> K+ + Lambda, are analyzed using a multipole approach. The background terms are given in terms of gauge invariant, crossing symmetric, Born diagrams with hadronic form factors, while the resonances are parameterized using Breit-Wigner forms. Preliminary results suggest a number of new resonances, as predicted by many quark model studies. A comparison between the extracted multipoles and those obtained from KAON-MAID is presented.
The strong evidence for the `triviality' of (lambda Phi^4)_4 theory is not incompatible with spontaneous symmetry breaking. Indeed, for a `trivial' theory the effective potential should be given exactly by the classical potential plus the free-field zero-point energy of the shifted field; i.e., by the one-loop effective potential. When this is renormalized in a simple, but nonperturbative way, one finds, self-consistently, that the shifted field does become non-interacting in the continuum limit. For a classically scale-invariant (CSI) lambda Phi^4 theory one finds m_h^2 = 8 pi^2 v^2, predicti…
We argue that massless (lambda Phi^4)_4 is "trivial" without being entirely trivial. It has a non-trivial effective potential which leads to spontaneous symmetry breaking, but the particle excitations above the broken vacuum are non-interacting. The key to this picture is the realization that the constant background field (the mode with zero 4-momentum) renormalizes differently from the fluctuation field (the finite-momentum modes). This picture reconciles rigorous results and lattice calculations with one-loop and Gaussian-approximation analyses. Because of "triviality", these latter two meth…
We present a non-perturbative study of the lambda phi**4 model on a non-commutative plane. The lattice regularised form can be mapped onto a Hermitian matrix model, which enables Monte Carlo simulations. Numerical data reveal the phase diagram; at large lambda it contains a "striped phase", which is absent in the commutative case. We explore the question whether or not this phenomenon persists in a Double Scaling Limit (DSL), which extrapolates simultaneously to the continuum and to infinite volume, at a fixed non-commutativity parameter. To this end, we introduce a dimensional lattice spacing…
The new experimental data of kaon photoproduction on the nucleon, gamma p -> K+ Lambda, have been analyzed by means of a multipoles model. Different from the previous models, in this analysis the resonance decay widths are constrained to the values given by the Particle Data Group (PDG). The result indicates that constraining these parameters to the PDG values could dramatically change the conclusion of the important resonances in this reaction found in the previous studies.
