Search

Herein we report the X-ray characterization of four sildenafil solvates where the conformation of the pyrazolo[3,4-d]pyrimidine and phenyl rings depends on the solvent. It conditions the formation of an apparently innocent intramolecular H-bond that has a remarkable influence on the solid state architecture of the sildenafil solvates. DFT calculations indicate that a delicate balance between the energies of H-bonding and π–π (or lp–π) interactions are crucial. [ABSTRACT FROM AUTHOR]

The elastic I = 1 / 2 , s - and p -wave kaon-pion scattering amplitudes are calculated using a single ensemble of anisotropic lattice QCD gauge field configurations with N f = 2 + 1 flavors of dynamical Wilson-clover fermions at m π = 230 MeV . A large spatial extent of L = 3.7 fm enables a good energy resolution while partial wave mixing due to the reduced symmetries of the finite volume is treated explicitly. The p -wave amplitude is well described by a Breit–Wigner shape with parameters m K ⁎ / m π = 3.808 ( 18 ) and g K ⁎ K π BW = 5.33 ( 20 ) which are insensitive to the inclusion of d -wave mixing and variation of the s -wave parametrization. An effective range description of the near-threshold s -wave amplitude yields m π a 0 = − 0.353 ( 25 ) . [ABSTRACT FROM AUTHOR]

We present the first QCD-based calculation of hadronic matrix elements with penguin topology determining direct CP-violating asymmetries in D 0 → π − π + and D 0 → K − K + nonleptonic decays. The method is based on the QCD light-cone sum rules and does not rely on any model-inspired amplitude decomposition, instead leaning heavily on quark–hadron duality. We provide a Standard Model estimate of the direct CP-violating asymmetries in both pion and kaon modes and their difference and comment on further improvements of the presented computation. [ABSTRACT FROM AUTHOR]

We show that the interplay of chiral effective field theory and lattice QCD can be used in the evaluation of so-called disconnected diagrams, which appear in the study of the isoscalar and isovector channels of pion–pion scattering and have long been a major challenge for the lattice community. By means of partially-quenched chiral perturbation theory, we distinguish and analyze the effects from different types of contraction diagrams to the pion–pion scattering amplitude, including its scattering lengths and the energy-dependence of its imaginary part. Our results may be used to test the current degree of accuracy of lattice calculation in the handling of disconnected diagrams, as well as to set criteria for the future improvement of relevant lattice computational techniques that may play a critical role in the study of other interesting QCD matrix elements. [ABSTRACT FROM AUTHOR]

Following up on recent work by Caron-Huot et al. we consider a generalization of the old Lovelace-Shapiro model as a toy model for ππ scattering satisfying (most of) the properties expected to hold in ('t Hooft's) large- N limit of massless QCD. In particular, the model has asymptotically linear and parallel Regge trajectories at positive t, a positive leading Regge intercept α < 1, and an effective bending of the trajectories in the negative- t region producing a fixed branch point at J = 0 for t < t < 0. Fixed (physical) angle scattering can be tuned to match the power-like behavior (including logarithmic corrections) predicted by perturbative QCD: A( s, t) ∼ s log( s) F ( θ). Tree-level unitarity (i.e. positivity of residues for all values of s and J ) imposes strong constraints on the allowed region in the α- β-γ parameter space, which nicely includes a physically interesting region around α = 0 .5, β = 2 and γ = 3. The full consistency of the model would require an extension to multi-pion processes, a program we do not undertake in this paper. [ABSTRACT FROM AUTHOR]

We calculate the width of the delta resonance at leading two-loop order in baryon chiral perturbation theory. This gives a correlation between the leading pion–nucleon–delta and pion–delta couplings, which is relevant for the analysis of pion–nucleon scattering and other processes. [ABSTRACT FROM AUTHOR]

The pion branching ratio, $R_{\pi } = \frac { {\Gamma }(\pi ^{+} \rightarrow e^{+} \nu _{e} + \pi ^{+}\rightarrow e^{+} \nu _{e} \gamma )}{\Gamma (\pi ^{+} \rightarrow \mu ^{+} \nu _{\mu } + \pi ^{+} \rightarrow \mu ^{+} \nu _{\mu } \gamma )}$ , provides a sensitive test of lepton universality and constraints on many new physics scenarios. The theoretical uncertainty on the Standard Model prediction of R is 0.02 %, a factor of twenty smaller than the experimental uncertainty. The analysis of a subset of data taken by the PIENU experiment will be presented. The result, R = (1.2344 ± 0.0023( s t a t) ± 0.0019( s y s t)) ⋅ 10 [1], is consistent with the Standard Model prediction and represents a 0.1 % constraint on lepton non-universality. [ABSTRACT FROM AUTHOR]

We report the synthesis of an insulated π-conjugated polymer containing 2,2′-bipyridine moieties as metal coordination sites. Metal coordination to the polymer enabled easy and reversible tuning of the luminescent color without changes to the main chain skeleton. The permethylated α-cyclodextrin (PM α-CD)-based insulation structure allowed the metalated polymers to demonstrate efficient emission even in the solid state, with identical spectral shapes to the dilute solutions. In addition, the coordination ability of the metal-free polymer was maintained in the solid state, resulting in reversible changes in the luminescent color in response to the metal ions. The synthesized polymer is expected to be suitable for application in recyclable luminescent sensors to distinguish different metal ions. [ABSTRACT FROM AUTHOR]

An approximate light-cone wave function for the pion effective quark-antiquark Fock sector corresponding to a small value of the renormalization group parameter is presented. The approximate wave function is motivated by the LF-holography and the quadratic confinement potential in the front form of Hamiltonian dynamics, which is in harmony with the linear confining potential in the instant form. The pion radius, decay constant and form-factor are also presented. [ABSTRACT FROM AUTHOR]

By extending the $$\Phi $$ -derivable approach in the Nambu-Jona-Lasinio model to a finite magnetic field we calculate the properties of pion, $$\sigma $$ , and $$\rho $$ mesons in a magnetic field at finite temperature not only in the quark-antiquark bound state scheme but also in the pion-pion scattering resonant state scenario. Our calculation as a result makes manifest that the masses of $$\pi ^{0}$$ and $$\sigma $$ meson can be nearly degenerate at the pseudo-critical temperature which increases with increasing magnetic field strength, and the $$\pi ^{\pm }$$ mass ascends suddenly at almost the same critical temperature. Meanwhile the $$\rho $$ mesons' masses decrease with the temperature but increase with the magnetic field strength. We also check the Gell-Mann-Oakes-Renner relation and find that the relation can be violated clearly with increasing temperature, and the effect of the magnetic field becomes pronounced around the critical temperature. With different criteria, we analyze the effect of the magnetic field on the chiral phase transition and find that the pseudo-critical temperature of the chiral phase cross, $$T_\mathrm{c}^{\chi }$$ , is always enhanced by the magnetic field. Moreover, our calculations indicate that the $$\rho $$ mesons will get melted as the chiral symmetry has not yet been restored, but the $$\sigma $$ meson does not disassociate even at very high temperature. Particularly, it is the first to show that there does not exist a vector meson condensate in the QCD vacuum in the pion-pion scattering scheme. [ABSTRACT FROM AUTHOR]

We report the results of the femtoscopic analysis of pairs of identical pions measured in p-Pb collisions at ↶sNN = 5.02 TeV. Femtoscopic radii are determined as a function of event multiplicity and pair momentum in three spatial dimensions. As in the pp collision system, the analysis is complicated by the presence of sizable background correlation structures in addition to the femtoscopic signal. The radii increase with event multiplicity and decrease with pair transverse momentum. When taken at comparable multiplicity, the radii measured in p-Pb collisions, at high multiplicity and low pair transverse momentum, are 10%-20% higher than those observed in pp collisions but below those observed in A-A collisions. The results are compared to hydrodynamic predictions at large event multiplicity as well as discussed in the context of calculations based on gluon saturation. [ABSTRACT FROM AUTHOR]

We present a dispersive representation of the D-term form factor for hard exclusive reactions, using unsubtracted t -channel dispersion relations. The t -channel unitarity relation is saturated with the contribution of two-pion intermediate states, using the two-pion distributions amplitude for the γ ⁎ γ → π π subprocess and reconstructing the π π → N N ¯ subprocess from available information on pion-nucleon partial-wave helicity amplitudes. Results for the D-term form factor as function of t as well as at t = 0 are discussed in comparison with available model predictions and phenomenological parametrizations. [ABSTRACT FROM AUTHOR]

The article looks at a study that derives standard expression of shear viscosity for nucleonic constituents of pion-baryon loops from the two-point function of nucleonic viscous stress tensors at finite temperature and density. Topics discussed include nucleon-pion-baryon interactions, inclusion of finite thermal width in the nucleon propagators, and effective Lagrangian densities of standard hadronic model.

The article looks at a study that investigate the system-size and energy dependence of the pion production in high energy collisions with the use of ultrarelativistic quantum molecular dynamics (UrQMD) transport model. Topics discussed include spectra of negatively charged pions in proton-proton interactions at Super Proton Synchrotron (SPS) energies, Mean pion multiplicity per participant nucleon and role of isospin effects.

The article discusses the research study conducted which analyses the neutron density distribution and neutron skin thickness of lead 208Pb using various nonrelativistic and relativistic mean-field models for the nuclear structure. Topics discussed include pion photoproduction data, parity-violating asymmetry parameter for elastic electron scattering, and comparison of neutron skin thickness.

The article discusses the study conducted which uses the pion form factor for space-like kinematics to extract the proton transverse charge density and its uncertainty. Topics discussed include propagation patterns of mesons, existence of a kaon-nucleon in-medium potential, and use of Jefferson National Accelerator Facility (JLab) 12 Gigaelectro volt and the Electron-Ion Collider (EIC) for the study.

The article discusses the study conducted which analyzes the experimental data on the inclusive double-differential cross section by neutrinos charged current. Topics discussed include use of multinucleon component to reproduce the data, use of two-pion-emission channel, and the excitations of low-lying giant resonances.

The article discusses the study conducted which examines the exclusive neutral-pion electroproduction π0 electroproduction with a 5.75-Gigaelectron Volt electron beam and the Jefferson Lab (CEBAF) Large Acceptance Spectrometer (CLAS) detector. Topics discussed include inclusion of vector meson rescattering processes, hadrons and their interactions, and Pseudoscalar meson electroproduction.

The LHC energies are those at which the asymptotic regime in hadron–hadron diffractive collisions (pp, πp, ππ) might be switched on. Based on results of the Dakhno–Nikonov eikonal model which is a generalization of the Good–Walker eikonal approach for a continuous set of channels, we present a picture for transformation of the constituent quark mode to the black disk one. In the black disk mode (⎷s ≥ 10 TeV), we have a growth of the logarithm squared type for total and elastic cross-sections, σtot ~ ln2 s and σel ~ ln2 s and (τ = q⊥2 σtot)-scaling for diffractive scattering and diffractive dissociation of hadrons. The diffractive dissociation cross-section grows as σD ~ ln s, σDD ~ ln s, and their relative contribution tends to zero: σD/σtot → 0, σDD/σtot → 0. Asymptotic characteristics of diffractive and total cross-sections are universal, and this results in the asymptotical equality of cross-sections for all types of hadrons (the Gribov universality). The energy scale for switching on the asymptotic mode is estimated for different processes. [ABSTRACT FROM AUTHOR]

We have evaluated the shear viscosity of pion gas with vanishing chemical potential taking into account its scattering with the low mass resonances a and p during propagation in the medium. The thermal width (or collisional rate) of pions is calculated from no and np loop diagrams using effective interactions in the real-time formulation of finite temperature field theory. A very small value of shear viscosity by entropy density ratio (?y/i), close to the quantum bound, is obtained which approximately matches the range of values of rj/s used by Niemi etal. [H. Niemi, G. S. Denicol, P. Huovinen, E. Molnár, and D. H. Rischke, Phys. Rev. Lett. 106, 212302 (2011); Phys. Rev. C 86, 014909 (2012)] to fit the elliptic flow data from the Relativistic Heavy Ion Collider. [ABSTRACT FROM AUTHOR]

We present experimental results on inclusive spectra and mean multiplicities of negatively charged pions produced in inelastic p+p interactions at incident projectile momenta of 20, 31, 40, 80 and 158 GeV/ c ( $$\sqrt{s} = $$ 6.3, 7.7, 8.8, 12.3 and 17.3 GeV, respectively). The measurements were performed using the large acceptance NA61/SHINE hadron spectrometer at the CERN super proton synchrotron. Two-dimensional spectra are determined in terms of rapidity and transverse momentum. Their properties such as the width of rapidity distributions and the inverse slope parameter of transverse mass spectra are extracted and their collision energy dependences are presented. The results on inelastic p+p interactions are compared with the corresponding data on central Pb+Pb collisions measured by the NA49 experiment at the CERN SPS. The results presented in this paper are part of the NA61/SHINE ion program devoted to the study of the properties of the onset of deconfinement and search for the critical point of strongly interacting matter. They are required for interpretation of results on nucleus-nucleus and proton-nucleus collisions. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the phase structure of strongly interacting matter at non-vanishing isospin before the onset of pion condensation in the framework of the unquenched Polyakov–Quark-Meson model with quark flavors. We show results for the order parameters and all relevant thermodynamic quantities. In particular, we obtain a moderate change of the pressure with isospin at vanishing baryon chemical potential, whereas the chiral condensate decreases more appreciably. We compare the effective model to recent lattice data for the decrease of the pseudo-critical temperature with the isospin chemical potential. We also demonstrate the major role played by the value of the pion mass in the curvature of the transition line, and the need for lattice results with a physical pion mass. Limitations of the model at nonzero chemical potential are also discussed. [Copyright &y& Elsevier]

Differential cross sections for elastic pion scattering on a number of nuclei at energies between 130 and 290 MeV are calculated. For this purpose, use is made of a microscopic optical pion-nucleus potential that was obtained on the basis of the Glauber theory of high-energy scattering and which is determined by the density distribution of pointlike target nucleons and by the pion-nucleon scattering amplitude. The calculation of the cross sections in question is based on solving the respective relativistic wave equation. Three parameters of the pion-nucleon amplitude are fitted in performing a comparison with experimental data. These are the total cross section for pion-nucleon scattering, the ratio of the real to the imaginary part of the forward pion-nucleon scattering amplitude, and the slope parameter. The resulting values of these parameters are then compared with their counterparts for scattering on free nucleons. The character of nuclear-matter-induced changes in these parameters is studied. [ABSTRACT FROM AUTHOR]

Using one- and two-body density matrices, we calculate the spatial and momentum distributions, two-particle Hanbury-Brown-Twiss (HBT) correlation functions, and the chaotic parameter λ in HBT interferometry for the systems of boson gas within the harmonic oscillator potentials with anisotropic frequencies in transverse and longitudinal directions. The HBT chaotic parameter, which can be obtained by measuring the correlation functions at zero relative momentum of the particle pair, is related to the degree of Bose-Einstein condensation and thus the system environment. We investigate the effects of system temperature, particle number and the average momentum of the particle pair on the chaotic parameter. The value of λ decreases with the condensed fraction, f0. It is one for f0 = 0 and zero for f0 = 1. For a certain f0 between 0 and 1, we find that λ increases with the average momentum of the particle pair and decreases with the particle number of system. The results of λ are sensitive to the ratio, ν = ωz/ωρ, of the frequencies in longitudinal and transverse directions. They are smaller for larger ν when ωρ is fixed. In the heavy-ion collisions at the Large Hadron Collider (LHC) energy the large identical pion multiplicity may possibly lead to a considerable Bose-Einstein condensation. Its effect on the chaotic parameter in two-pion interferometry is worth considering in earnest. [ABSTRACT FROM AUTHOR]

The D03 dibaryon is generated dynamically as a resonance pole in a πNΔ' three body model, where Δ' is a stable Δ baryon. Using separable interactions dominated by the Δ(1232) isobar for pN and by the D12(2150) isobar for NΔ', with D12(2150) the NΔ dibaryon deduced in and constrained by ¹D2 pp scattering, the model reduces to an effective two body problem for ΔΔ' which is solved. The mass and width of D03 are found close to those of the I(JP)=0(3+) resonance peak observed by WASA-at-COSY in pion-production pn collisions at 2.37 GeV. [ABSTRACT FROM AUTHOR]

A novel method is employed to compute the pion electromagnetic form factor, Fπ(Q2), on the entire domain of spacelike momentum transfer using the Dyson-Schwinger equation (DSE) framework in QCD. The DSE architecture unifies this prediction with that of the pion's valence-quark parton distribution amplitude (PDA). Using this PDA, the leading-order, leading-twist perturbative QCD result for Q2 Fπ(Q2) underestimates the full computation by just 15% on Q2 ≳ 8 GeV2, in stark contrast to the result obtained using the asymptotic PDA. The analysis shows that hard contributions to the pion form factor dominate for Q2 ≳ 8 GeV2, but, even so, the magnitude of Q2Fπ(Q2) reflects the scale of dynamical chiral symmetry breaking, a pivotal emergent phenomenon in the standard model. [ABSTRACT FROM AUTHOR]

A method is explained through which a pointwise accurate approximation to the pion's valence-quark distribution amplitude (PDA) may be obtained from a limited number of moments. In connection with the single nontrivial moment accessible in contemporary simulations of lattice-regularized QCD, the method yields a PDA that is a broad concave function whose pointwise form agrees with that predicted by Dyson-Schwinger equation analyses of the pion. Under leading-order evolution, the PDA remains broad to energy scales in excess of 100 GeV, a feature which signals persistence of the influence of dynamical chiral symmetry breaking. Consequently, the asymptotic distribution φπasy(x) is a poor approximation to the pion's PDA at all such scales that are either currently accessible or foreseeable in experiments on pion elastic and transition form factors. Thus, related expectations based on φπasy(x) should be revised. [ABSTRACT FROM AUTHOR]

The multichannel S- and P-wave amplitudes for the ππ scattering, constructed requiring analyticity and unitarity of the S-matrix and using the uniformization procedure, are elaborated using the dispersion relations with imposed crossing symmetry condition. The amplitudes are modified in the low-energy region to improve their consistency with experimental data and the dispersion relations. Agreement with data is achieved for both amplitudes from the threshold up to 1.8 GeV and with dispersion relations up to 1.1 GeV. Consequences of the applied modifications, e.g. changes of the S-wave lowest-pole positions, are presented. [ABSTRACT FROM AUTHOR]

We study DD̅ * (D*D̅ ) scattering in the framework of unitarized heavy meson chiral perturbation theory with pion exchange and a contact interaction. 3S1-3D1 mixing effects are taken into account. A loosely bound state X(3872), with the pole position being Mpole=(3871.70-i0.39)  MeV, is found. The result is not sensitive to the strength of the contact interaction. Our calculation provides a theoretical confirmation of the existence of the 1++ state X(3872). The light quark mass dependence of the pole position indicates it has a predominately DD̅ * (D*D̅ ) molecular nature. When the π mass is larger than 142 MeV, the pole disappears, which makes impossible the lattice simulation of this state at large quark mass. [ABSTRACT FROM AUTHOR]

The study of the neutral current elastic scattering of neutrinos on protons at lower energies can be used as a compelling probe to improve our knowledge of the strangeness of the proton. We consider a neutrino beam generated from pion decay at rest, as provided by a cyclotron or a spallation neutron source and a 1 kton scintillating detector with a potential similar to the Borexino detector. Despite several backgrounds from solar and radioactive sources, it is possible to estimate two optimal energy windows for the analysis, one between 0.65 and 1.1 MeV and another between 1.73 and 2.2 MeV. The expected number of neutral current events in these two regions, for an exposure of 1 yr, is enough to obtain an error on the strange axial charge 10 times smaller than available at present. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the feasibility of studying in-medium properties of the ω meson in photoproduction experiments via the decay . We use the GiBUU transport model to compare different methods of obtaining in-medium information, such as the invariant mass spectrum, transparency ratio, excitation function and momentum spectrum. We show that the final-state interaction of the pion poses a major obstacle for the interpretation of the invariant mass spectrum. The other three observables turn out to be fairly independent of final-state interactions and thus, taken together, can give access to the ωʼs in-medium properties. [Copyright &y& Elsevier]

We re-examine one-pion exchange as a possible binding mechanism in the X (3872) charmonium-like state and argue it to be not sufficiently binding for this purpose. We conclude therefore that other short-range dynamics are responsible for the X formation. [ABSTRACT FROM AUTHOR]

An analysis of $${B^\pm \to \pi^\pm \pi^\mp \pi^\pm}$$ decay data in a quasi two-body B → π [ π π] QCD factorization framework is performed. The short distance amplitudes are calculated including next-to-leading order in α vertex and penguin corrections. The long distance amplitudes due to the [ π π] final state interactions are described by the pion non-strange scalar and vector form factors for the [ π π] S-wave state and [ π π] P-wave state, respectively and by a relativistic Breit-Wigner formula for the[ π π] D-wave state. We achieve a good fit of the data with only three parameters for the S wave, one for the P wave and one for the D wave. Our model gives a unified unitary description of the three scalar resonances, f(600), f(980) and f(1400) in terms of the pion scalar form factor. We predict for the B to f(1270) transition form factor, $${F^{Bf_2}(m_\pi^2)=0.098\pm0.007}$$ . [ABSTRACT FROM AUTHOR]

Abstract: We extend the usual chiral perturbation theory framework (χPT) to allow the inclusion of a light dynamical isosinglet scalar. Using lattice QCD results, and a few phenomenological inputs, we explore the parameter space of the effective theory. We discuss the S-wave pion–pion scattering lengths, extract the average value of the two light quark masses and evaluate the impact of the dynamical singlet field in the low-energy constants , and of χPT. We also show how to extract the mass and width of the sigma resonance from chiral extrapolations of lattice QCD data. [Copyright &y& Elsevier]

Abstract: We study the correlation among impact parameter, multiplicity and longitudinal rapidity of neutral and charged pions, protons and neutrons produced in the interactions of charged pions with xenon nuclei at momenta of 2.34, 3.5, 9 and 30GeV/c. The correlation is investigated using a JAM modeling code. [Copyright &y& Elsevier]

Comparisons of predictions from two simple event generators followed by a rescattering model are made with pion interferometry data from the STAR experiment. The systematics with impact parameter, pair momentum and azimuthal angle are presented and a general agreement with all main trends in the data is demonstrated; however, the experimentally observed approach of the three radius values toward a common value at the highest pair momenta is not found for the model values. In addition, an analysis of source times as derived from the interferometry analysis is presented and a quantitative estimate of the model freeze-out duration times is presented. [ABSTRACT FROM AUTHOR]

The search for genuine two-particle dynamical correlations among the pions produced in 16O-AgBr interactions at 60 AGeV and 32S-AgBr interactions at 200 AGeV (super proton synchrotron data) has been carried out by the method of normalized factorial cumulant moments in pseudo-rapidity (η), azimuthal angle (ϕ) and two-dimensional anisotropic (η-ϕ) phase space. The analysis reveals the presence of genuine two-particle dynamical correlations among the pions in 16O-AgBr and 32S-AgBr interactions in both one and two dimensions. Stronger correlation has been observed in higher dimensional space. Correlations between the pions are found to decrease with the increase of projectile mass and energy. Experimental results have been compared with the FRITIOF data sample in the pseudo-rapidity space. In azimuthal angle space, events simulated by generating random numbers (Monte Carlo Simulation) have been used for the purpose of comparison. The FRITIOF data and the data of the simulated interactions have failed to reproduce the experimental results. The experimental results have also been compared with the event sample generated by the UrQMD model in both pseudo-rapidity and azimuthal angle space. Like the FRITIOF model, the UrQMD model is also unable to replicate the experimental results. The variation of normalized cumulant moment (K2) against the number of bin M has been fitted with a function K2 = aMb in both one and two dimensions. No fitting of this kind has been possible in the case of the FRITIOF data, UrQMD data and the MC simulated data. [ABSTRACT FROM AUTHOR]

We study the three-pion decays of the lightest isoscalar vector mesons, ω and ɸ, in a dispersive framework that allows for a consistent description of final-state interactions between all three pions. Our results are solely dependent on the phenomenological input for the pion-pion P-wave scattering phase shift. We predict the Dalitz plot distributions for both decays and compare our findings to recent measurements of the ɸ→3π Dalitz plot by the KLOE and CMD-2 collaborations. Dalitz plot parameters for future precision measurements of ω→3π are predicted. We also calculate the ππ P-wave inelasticity contribution from ωπ intermediate states. [ABSTRACT FROM AUTHOR]

We study CP violation and the contribution of the strong pion-pion interactions in the three-body B± → π ± π … π ± decays within a quasi two-body QCD factorization approach. The short distance interaction amplitude is calculated in the next-to-leading order in the strong coupling constant with vertex and penguin corrections. The meson-meson final state interactions are described by pion non-strange scalar and vector form factors for the S and P waves and by a relativistic Breit-Wigner formula for the D wave. The pion scalar form factor is calculated from a unitary relativistic coupled-channel model including ππ, KK̄ and effective (2π)(2π) interactions. The pion vector form factor results from a Belle Collaboration analysis of Τ̅ → pi; ̅π0VΤ data. The recent B± → π ± π … π ± BABAR Collaboration data are fitted with our model using only three parameters for the S wave, one for the P wave and one for the D wave. We find not only a sizable contribution of the S wave just above the π π threshold but also under the ρ(770) peak a significant interference, mainly between the S and P waves. For the B to f2(1270) transition form factor, we predict FBf2 (m Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. ) = 0:098 ± 0:007. Our model yields a unified unitary description of the contribution of the three scalar resonances f0(600), f0(980) and f0(1400) in terms of the pion non-strange scalar form factor. [ABSTRACT FROM AUTHOR]

In high-energy heavy ion collisions a hot and dense medium is formed, where the UA(1) or chiral symmetry may temporarily be restored. As a consequence, the mass of the η′(958) mesons may be reduced to its quark model value, and the abundance of η′ mesons at low pT may be enhanced by more than a factor of 10. The intercept parameter λ* of the charged pion Bose Einstein correlations provides a sensitive observable of the possibly enhanced η′ abundance. We have analyzed λ*(mT) data from √sNN=200 GeV central Au+Au reactions measured at the BNL Relativistic Heavy Ion Collider (RHIC), using extensive Monte Carlo simulations based on six popular models for hadronic multiplicities. Based on the combined STAR and PHENIX data set, and on various systematic investigations of resonance multiplicities and model parameters, we conclude that in √sNN=200 GeV central Au+Au reactions the mass of the η′ meson is reduced by Δmη′*>200 MeV, at the 99.9% confidence level in the considered model class. Such a significant η′ mass modification may indicate the restoration of the UA(1) symmetry in a hot and dense hadronic matter and the return of the ninth "prodigal" Goldstone boson. A similar analysis of NA44 S+Pb data at top CERN Super Proton Synchroton (SPS) energies showed no significant in-medium η′ mass modification. [ABSTRACT FROM AUTHOR]

In this work we consider the renormalization of the chiral two-pion exchange potential with explicit Δ excitations for nucleon-nucleon scattering at next-to-leading (NLO) and next-to-next-to-leading order (N²LO). Because of the singular nature of the chiral potentials, correlations between different partial waves are generated. In particular, we show that two-body scattering by a short distance power like singular attractive interaction can be renormalized in all partial waves with a single counterterm, provided the singularities are identical. A parallel statement holds in the presence of tensor interactions when the eigenpotentials in the coupled channel problem also coincide. Although this construction reduces the total number of counterterms to 11 in the case of nucleon-nucleon scattering with chiral two-pion exchange interactions with Δ degrees of freedom, the differences in the scattering phases as compared to the case with the uncorrelated partial-wave renormalization become smaller as the angular momentum is increased in the elastic scattering region. [ABSTRACT FROM AUTHOR]

We calculate the two-photon exchange amplitude for elastic electron-pion scattering in the dispersion-relation-inspired approach, including both elastic and inelastic contributions. The latter was modeled as a sum of ρ- and b1(1235)-meson contributions. We find that at Q2≲2 GeV2 the elastic contribution is dominant, similarly to the electron-proton scattering case. At higher Q2 the inelastic contribution is not negligible, but still smaller than the elastic one. We also explain the observed rapid amplitude growth at backward angles. [ABSTRACT FROM AUTHOR]

The saturation properties of the nuclear matter taking pion correlations into account are studied. We construct a Bogoliubov transformation for the pion pair operators and calculate the energy associated with the pion pairs. The pion dispersion relation is investigated. The correlation energy due to one-pion exchange in nuclear matter and neutron matter at random phase approximation using the generator coordinate method is also studied. The techniques of the charged pion correlations are discussed in the neutron matter calculations. We observe that there is no sign of the pion condensation in this model. [ABSTRACT FROM AUTHOR]

Abstract: We calculate in chiral perturbation theory the double-pion photoproduction processes and at low energies. At leading order these reactions are governed by the chiral pion-pion interaction. The next-to-leading order corrections arise from pion-loop diagrams and chiral-invariant counterterms involving the low-energy constants , , and . The pertinent production amplitudes and depending on five kinematical variables are given in closed analytical form. We find that the total cross section for neutral pion-pair production gets enhanced in the region by a factor by the next-to-leading order corrections. In contrast to this behavior the total cross section for charged pion-pair production remains almost unchanged in the region in comparison to its tree-level result. Although the dynamics of the pion-pair production reactions is much richer, this observed pattern can be understood from the different influence of the chiral corrections on the pion-pion final state interaction ( versus ). We present also results for the complete set of two-pion invariant mass spectra. The predictions of chiral perturbation theory for the processes can be tested by the COMPASS experiment which uses Primakoff scattering of high-energy pions in the Coulomb field of a heavy nucleus to extract cross sections for reactions with various final states. [Copyright &y& Elsevier]

We calculate the one-photon loop radiative corrections to the neutral pion-pair photoproduction process $\pi^-\gamma \ensuremath \rightarrow\pi^-\pi^0\pi^0$ . At leading order this reaction is governed by the chiral pion-pion interaction. Since the chiral $ \pi^{+}_{}$ $ \pi^{-}_{}$ $ \rightarrow$ $ \pi^{0}_{}$ $ \pi^{0}_{}$ contact vertex depends only on the final-state invariant mass it factors out of all photon loop diagrams. We give analytical expressions for the multiplicative correction factor $\ensuremath R\sim \alpha/2\pi$ arising from eight classes of contributing one-photon loop diagrams. An electromagnetic counterterm has to be included in order to cancel the ultraviolet divergences generated by the photon loops. Infrared finiteness of the virtual radiative corrections is achieved (in the standard way) by including soft photon radiation below an energy cut-off $ \lambda$ . The radiative corrections to the total cross-section vary between +2% and -2% for center-of-mass energies from threshold up to $\ensuremath 7m_{\pi}$ . We study also the radiative corrections to the $\ensuremath \pi^0\pi^0$ mass spectrum. [ABSTRACT FROM AUTHOR]

The unitarization of the amplitude for the decay process K → ππ and allowance for the rescattering of final-state pions in the decay process K → πππ make it possible to evaluate, by using the parameters extracted from data on K → 2π decays, the K → πππ decay width. The result agrees with the experimental width value at a level of a few percent. Allowance for corrections for higher order terms of the momentum expansion of the amplitude for the decay process K → πππ leads to the slope-parameter value of g = 0.2182, which agrees with its experimental counterpart, g = 0.2154 ± 0.0035. [ABSTRACT FROM AUTHOR]

Recent BaBar data on the pion transition form factor, whose Q-dependence is much steeper then predicted by asymptotic Quantum Chromodynamics (QCD), have caused a renewed interest in its theoretical description. We present here a formalism based on a model-independent description for low photon virtuality and a high photon virtuality description based on QCD, which match at a scale Q. The high photon virtuality description incorporates a flat pion distribution amplitude, $ \phi$( x) = 1 , at the matching scale Q and QCD evolution from Q to Q > Q . The flat pion distribution is connected, through soft pion theorems and chiral symmetry, to the pion valence parton distribution at the same low scale Q. The procedure leads to a good description of the data, and by incorporating additional twist-three effects, to an excellent description of the data. [ABSTRACT FROM AUTHOR]

We explore the interplay between the few-body aspects of few-pion states and the many-body aspects of their quark structure. We show for a schematic quasispin model similar to the Nambu–Jona-Lasinio model how one can derive rather accurately the pion–pion scattering length from the excitation spectrum in a box. [ABSTRACT FROM AUTHOR]

Abstract: We evaluate the contribution of pion–pion rescattering to the and reactions. We compare our results with the close-to-threshold experimental data. The pion–pion rescattering contribution is found there to be negligible. The predictions for future experiments with PANDA detector at High Energy Storage Ring (HESR) in GSI Darmstadt are presented. It is discussed how to cut off the dominant Roper resonance and double-Δ excitation mechanisms leading to the channel in final state. Differential distributions in momentum transfers, transverse momentum, effective two-pions mass, relative azimuthal angle between pions, and pion rapidities are presented. [Copyright &y& Elsevier]

Abstract: We re-investigate the impact of isospin violation for extracting the s-wave ππ scattering phase shift difference from decays. Compared to our previous analysis in 2003, more precise experimental data and improved knowledge of low-energy constants are used. In addition, we employ a more robust data-driven method to obtain the phase shift difference . [Copyright &y& Elsevier]