Instanton-induced flavour mixing in mesons

The U_L(N_f)×U_R(N_f) chiral symmetric version of the Nambu-Jona-Lasinio model is extended by the 't Hooft determinant and bosonized for an arbitrary number of flavours N_f. The resulting effective meson lagrangian is explicitly calculated to leading order in the derivatives for three flavours. The 't Hooft determinant induces flavour mixing of the mesons with diagonal flavour content (π⁰, η, η′, and their scalar chiral partners δ⁰, S, ϵ) and pushes up the physical η′-mass. The η-η′ mixing angle is found to be −31°.     

η → 3π decay and πη scattering in chiral SU(2) × SU(2) symmetry

The problem of η → 3π decay in chiral SU(2) × SU(2) symmetry is investigated. We argue that the well-known difficulties of the conventional pole model originate from underestimating the role of the η-meson pole graph. This model is shown to be suitable for describing η → 3π decay if the strong ηηππ vertex in the η-pole graph is determined by an SU(2) × SU(2)-invariant interaction. The π^o ? η transition constant g_πη is evaluated from U-spin invariance with the help of a current-mixing model: | g_πη | ≈ 0.05. It turns out that the experimental data on both the decay widths and the energy spectrum can be satisfied by fitting the value of the ηηππ coupling constant as a parameter. As a result, predictions for the s- and p-wave πη scattering lengths are obtained: |a_πη⁰| ≈ 0.2m_π^?1, |a_πη¹| ≈ 0.1m_π^?3.     

A perturbative QCD estimate of the η1-Mass

Using perturbative QCD expansions for the two-point correlation function of the U_A(1) current in a properly constructed dispersion sum rule, and using a previously obtained estimate for the strange quark mass, we obtain a realistic upper bound on the η₁-mass.     

The second EMC effect,semileptonic baryon decays and the chiral bag

TheU(1) anomaly gives a massiveη ₀ in the chiralSU(3) limit. We show in this limit how a chiral bag model givesboth theF andD amplitudes consistent with all baryon semileptonic decays,and the integral over the spin structure function measured by the EMC collaboration.     

Thermal diffusivity and 3D-XY critical behavior of ferroelectric semiconductors (PbxSn1−x)2P2Se6

An ac photopyroelectric calorimeter has been used to study the thermal diffusivity of the ferroelectric semiconductors family (Pb_xSn_1−x)₂P₂Se₆ (x=0–1) from 30 K to room temperature. Phase transitions have been found for x=0, 0.05, 0.2, 0.47 but not for x=1 in the full temperature range. A continuous phase transition has been found for x=0, 0.05, 0.2 and 0.47 which corresponds to the paraelectric commensurate to incommensurate phase. It has been possible to study the critical behavior of this transition for x=0, 0.05 and the critical parameters obtained have been α=−0.019, A⁺/A⁻=1.00 and α=−0.026, A⁺/A⁻=1.03, respectively, having fitted at the same time both the low and high temperature branches of the transition as rigorous critical theory indicates; these results agree with the theoretical prediction from renormalization group theory that this kind of transition complies with the 3D-XY universality class (α_theor=−0.014, A⁺/A⁻=1.06), which has been experimentally confirmed only in a few materials. A first order incommensurate to ferroelectric phase transition has been characterized in x=0, 0.05 at lower temperature.     

Instantons: Dynamical mass generation,chiral Ward identities and the topological charge correlation function

When dynamical mass generation resulting from the breakdown of chiral symmetry is taken into account, instanton dynamics treated within the dilute gas approximation may satisfy the constraints on the quark condensates and the topological charge correlation function derived by Crewther from an analysis of the chiral Ward identities assuming the absence of a physical axial U(1) Goldstone boson. From a consideration of the contribution of the η′ to the topological charge correlation function, a relationship is derived in which m_η′²f_η′² is proportional to the vacuum energy density.     

Radiative decays and transition form factors of strange mesons in the relativistic constituent quark model

Motivated by the recent lattice QCD results indicating that the topological charge contribution to the flavor singlet axial vector current can be traded off by the constituent quark masses, we investigate the radiative decays of pseudoscalar (π,K, η, η′), vector (ρ,K*, ω, ?) and axial vector (A ₁) mesons using a simple relativistic constituent quark model. For both simplicity and relativity, we take advantage of the distinguished features in the light-cone quantization method: (1) the Fock-state expansion of meson wavefunctions are not contaminated by the vacuum fluctuation, (2) the assignment of meson quantum numbers are given by the Melosh transformation. Except the well-known constituent quark masses of (u,d,s) quarks and the spin-averaged meson masses, the only parameter in the model is the gaussian parameter β which determines the broadness (or sharpness) of radial wavefunction. The computed decay widths and the transition form factors of ρ, ω → π(η)γ*,K* →Kγ* andA ₁ → πγ* at 0≤Q ²≤5 GeV² and π⁰(η) → γ*γ at 0≤Q ²≤3 GeV² are in a remarkably good agreement with the experimental data and the result forA ₁ ⁺ → π₊ γ* transition is quite consistent with the experiments of pion scattering on a nucleus using Primakoff effect. This model is potentially useful in the cocktail analyses of the dilepton productions in proton-proton, proton-nucleus and nucleus-nucleus collisions at SPS energies and a little above.     

Phase transition and ferroelastic property studied by using the Cs nuclear magnetic resonance in a CsHSO4 single crystal

The ¹³³Cs spin-lattice relaxation time in a CsHSO₄ single crystal was measured in the temperature range from 300 to 450 K. The changes in the ¹³³Cs spin-lattice relaxation rate near T_c1 (=333 K) and T_c2 (=415 K) correspond to phase transitions in the crystal. The small change in the spin-lattice relaxation time across the phase transition from II to III is due to the fact that during the phase transition, the crystal lattice does not change very much; thus, this transition is a second-order phase transition. The abrupt change of T₁ around T_c2 (II-I phase transition) is due to a structural phase transition from the monoclinic to the tetragonal phase; this transition is a first-order transition. The temperature dependences of the relaxation rates in phases I, II, and III are indicative of a single-phonon process and can be represented by T₁⁻¹=A+BT. In addition, from the stress-strain hysteresis loop and the ¹³³Cs nuclear magnetic resonance, we know that the CsHSO₄ crystal has ferroelastic characteristics in phases II and III.     

Quark masses and their hierarchies

Electroweak symmetry breaking is attributed to dynamical generation of quark masses. Quarksq (and leptonsl) are assumed to be produced by hypercolor confinement of preons at an intermediate scaleΛ _hc. Hierarchies observed in theq mass spectra can be explained by a BCS mechanism if the color interaction is enough asymptotically free and if residual ones emerging by the confinement are medium strong. The former assumption claims thatN≦4, whereN is the family number ofq andl. Dynamical equations to determineq masses and mixings are given, but they require knowledge on the physics atΛ _hc. A phenomenological approach is also made on the basis of anSU(7)×SU(7) chiral preon model withN=4. The mass ratiom _t/mb is related to (m _c/m _s)^ηB withη _B?1.1 andm _t'/mb' to (m _u/m _d)^ηA withη _A?1.4. In this scheme the fourth down quark is the heaviest (～ 110 GeV) and contributes dominantly toF ², whereF is the Fermi scale.     

Theoretical investigation of antiferroelectric (SmCA) subphases by hydrodynamical approach

We provide a hydrodynamical approach utilizing time dependent Landau-Ginzburg model (L-G) and the Cahn-Hilliard model (C-H) to investigate antiferroelectric liquid crystals (AFLCs) exhibiting different chiral phases between paraelectric smectic A (SmA^?) phase and antiferroelectric smectic C_A^? phase (SmC_A^?). Introducing conserved and non-conserved order parameters in C-H and L-G models, we have predicted the appearance of a chiral smectic C (SmC^?) phase and a ferrielectric SmC_FI1^? phase (three layers SmC_A^?) in an antiferroelectric phase sequence. The three layers periodicity for SmC_FI1^? phase is studied in detail with a non-uniform layer interactions among smectic layers with strong experimental support. Finally, we provide some theoretical basis for the non-uniformity of our proposed layer interactions.     

Systematics of charge distribution studies in low-energy fission of actinides

Charge distribution studies were carried out in the thermal neutron-induced fission of ²²⁹Th, ²⁴¹Pu and ²⁴⁵Cm as well as in the spontaneous fission of ²⁵²Cf. The width parameter (σ_z/σ_A), the most probable charge/mass (Z_p/A_p) and the charge polarization (ΔZ) as a function of fragment mass were deduced. The slope of charge polarization as a function of fragment mass [δ(ΔZ)/δA′], average charge dispersion parameter (〈σ_z〉) and proton odd-even effect (δ_p) were also obtained for these fissioning systems. These data along with the literature data for even-Z fissioning systems such as ²³³Th¹, ²³³U¹, ²³⁴U¹, ²³⁶U¹, ²³⁹U¹, ²³⁹Pu¹, ²⁴⁰Pu¹ and ²⁵⁰Cf¹ are discussed in terms of nuclear-structure effects and dynamics of descent from saddle point to the point of neck formation and from the formation of the neck to the scission point.     

Raman scattering in sodium nitrite crystals near the phase transition

Optical Raman spectra of a ferroelectric sodium nitrite crystal have been detected in a wide spectrum range at various temperatures, including the region of the ferroelectric phase transition. A manifestation of a transverse soft polar mode of the A ₁(z) type responsible for the ferroelectric phase transition has been discovered in the spectrum at room temperature. This mode has been found to become overdamped even far from the ferroelectric phase transition temperature. This mode also appears as a central peak under heating. It has been found that the pseudoscalar mode of the A ₂ type has the highest intensity in the Raman spectrum of sodium nitrite. The frequency corresponding to the maximum intensity of this mode in the Raman spectrum varies from 130 cm^–1 at 123 K to 106 cm^–1 at T = 513 K. A fair agreement of the experimental data for the A ₁(z) mode with the Lyddane–Sachs–Teller relation has been established. The polariton curves for the A ₁(z) polar mode and the dispersion curves for axinons has been plotted.     

The decaysK S 0 →γγ andK L 0 →γγ in the chiral approach

We calculate theK _S ^Emphasis>0 →γγ decay within the approach of non-linear realization of chiralS U(3)×S U(3). The branching ratio with respect to theπ ⁺ π ^- channel turns out to be 3.5×10^?6 and therefore similar to the result gotten previously by dispersion relation techniques in a non-chiral model. We also discuss theK _L ⁰ →γγ decay by taking into account new results onη ₁-η ₈ mixing from recent measurements of the η→γγ decay.     

Hard pions and axial meson exchange current effects in negative muon capture in deuterium

The contribution of the axial meson exchange current effects to the doublet transition rate in the reaction μ^? +d → 2n+ ν_μ is calculated by using the minimal, chiral and approximately gauge invariant Lagrangian model for the A₁ρπ system. The contribution from the ρ-π weak decay process current usually considered is found to be nearly cancelled by that from the A₁ pole graph which is prescribed by the underlying invariance principles. Correct treatment of the N¹ propagator in the N¹ excitation current of the pion range leads to ≈ 30 % suppression of the N¹ effect.     

A Wilson-Yukawa Model with undoubled chiral fermions in 2D

We consider the fermion mass spectrum in the strong coupling vortex phase (VXS) of a lattice fermion-scalar model with a global U(1)_L × U(1)_R, in two dimensions, in the context of a recently proposed two-cutoff lattice formulation. The fermion doublers are made massive by a strong Wilson-Yukawa coupling, but in contrast with the standard formulation of these type of models, in which the light fermion spectrum was found to be vector-like, we find massless fermions with chiral quantum numbers at finite lattice spacing. When the global symmetry is gauged, this model is expected to give rise to a lattice chiral gauge theory.     

Dynamical resolution of theU (1) problem in QCD

The nonperturbative and perturbative aspects of theU(1) problem are discussed and linked to the dynamical breakdown of chiral symmetry in QCD. Then aU(1) gap equation is obtained and is approximately saturated with two-gluon intermediate states corresponding to theU(1) anomaly and consistent with η?η′ mixing.     

Aspects of UA (1) breaking in the Nambu and Jona-Lasinio model

The six-quark instanton induced ’t Hooft interaction, which breaks the unwanted U_A (1) symmetry of QCD, is a source of perturbative corrections to the leading order result formed by the four-quark forces with the U_L (3) × U_R (3) chiral symmetry. A detailed quantitative calculation is carried out to bosonize the model by the functional integral method. We concentrate our efforts on finding ways to integrate out the auxiliary bosonic variables. The functional integral over these variables cannot be evaluated exactly. We show that the modified stationary phase approach leads to a resummation within the perturbative series and calculate the integral in the “two-loop” approximation. The result is a correction to the effective mesonic Lagrangian which may be important for the low-energy spectrum and dynamics of the scalar and pseudoscalar nonets.     

SU(2) ⊗ U(1) gauge theories of the generalized σ model for π0, η, η' → γγ decays

By embedding the chiral current-mixing gauge theories in the SU(2)_L ? SU(2)_R generalized σ model, it is shown that the correct sign and magnitude for π⁰ → γγ decay, as well as the SU(3) relation of π⁰, η, η' → γγ decays can be obtained within the framework of SU(2) ? U(1) gauge theories of weak and electromagnetic interactions.