Vertex Correction at Finite Temperature and Decoupling Transition in (2+1) Dimensional Chiral Gross-Neveu Model

With the aid of imaginary time temperature field theory and fermion mass spectrum derived from Ward-Takahashi identities with composite fields,the vertex correction among fermions and σ meson is calculated beyond the leading order in 1/N expansion,and the change of vertex function with temperature and decoupling transition are discussed in (2+1) dimensional chiral Gross-Neveu model.It turns out that the critical temperature of decoupling transitionarises with increasing fermion mass and π meson mass at zero temperature;the vertex correction resulting from thermal fluctuation will affect the fermion dynamical mass and cannot be ignored at finite temperature.     

The U(1) problem and instantons on a lattice

Taking Wilson fermions for quarks, we derive the spectral representation of the quark propagator and investigate the relation between the spectrum and the topological charge of gauge configuration. Then we calculate the η and π propagators on an 8³ × 16 lattice and show that topologically non-trivial gauge configurations make the η meson much heavier than the π meson, when the hopping parameter is very close to the critical value.     

SU(2) Yang-Mills theory in (1 + 1) dimensions: A finite-lattice approach

Finite-lattice methods are used to calculate the masses of the lowest-lying baryon and meson states in the two-dimensional SU(2) Yang-Mills theory. No sign of a phase transition is seen at non-zero quark mass m. Both the meson and baryon mass vanish at m = 0: this is presumably a “chiral protection” mechanism.     

Applying the variational principle to (1+1)-dimensional quantum field theories

We extend the recently introduced continuous matrix product state variational class to the setting of (1+1)-dimensional relativistic quantum field theories. This allows one to overcome the difficulties highlighted by Feynman concerning the application of the variational procedure to relativistic theories, and provides a new way to regularize quantum field theories. A fermionic version of the continuous matrix product state is introduced which is manifestly free of fermion doubling and sign problems. We illustrate the power of the formalism by studying the momentum occupation for free massive Dirac fermions and the chiral symmetry breaking in the Gross-Neveu model.     

QUARK MASS RENORMALIZATION IN LATTICE GAUGE THEORY (Ⅱ) BARYON MASS CALCULATION

Using the renormalized quark mass m(g) obtained by fixing the ρ meson mass, we calculate the masses of the baryon states as a function of 1/g² in lattice gauge theory with fermions by variational method. The results are in agreement with experimental values in the range of 1/g² between 0.1 to 0.9.     

Mass spectrum and elastic scattering in the massive SU(2)f Schwinger model on the lattice

We calculate numerically scattering phases for elastic meson-meson scattering processes in the strongly coupled massive Schwinger model with an SU(2) flavor symmetry. These calculations are based on Lüscher's method in which finite size effects in two-particle energies are exploited. The results from Monte Carlo simulations with staggered fermions for the lightest meson (“pion”) are in good agreement with the analytical strong-coupling prediction. Furthermore, the mass spectrum of low-lying mesonic states is investigated numerically. We find a surprisingly rich spectrum in the mass region [m_π, 4m_π].     

Observation of e(+)e(-) annihilation into the C = +1 hadronic final states rho(0)rho(0) and phirho(0)

We report the first observation of e(+)e(-) annihilation into states of positive C parity, namely, rho(0)rho(0) and phirho(0). The two states are observed in the pi(+)pi(-)pi(+)pi(-) and K(+)K(-)pi(+)pi(-) final states, respectively, in a data sample of 225 fb(-1) collected by the BABAR experiment at the Positron-Electron Project II e(+)e(-) storage rings at energies near sqrt[s]=10.58 GeV. The distributions of costheta(*), where theta(*) is the center-of-mass polar angle of the phi meson or the forward rho(0) meson, suggest production by two-virtual-photon annihilation. We measure cross sections within the range |costheta(*)|<0.8 of sigma(e(+)e(-)-->rho(0)rho(0))=20.7+/-0.7(stat)+/-2.7(syst) fb and sigma(e(+)e(-)-->phirho(0))=5.7+/-0.5(stat)+/-0.8(syst) fb.     

Formation of eta'(958)-mesic nuclei and axial UA(1) anomaly at finite density

We discuss the possibility of producing the bound states of the eta'(958) meson in nuclei theoretically. We calculate the formation cross sections of the eta' bound states with the Green function method for the (gamma, p) reaction and discuss the experimental feasibility at photon facilities such as SPring-8. We conclude that we can expect to observe resonance peaks in (gamma, p) spectra for the formation of eta' bound states and we can deduce new information on eta' properties at finite density. These observations are believed to be essential to know the possible mass shift of eta' and deduce new information on the effective restoration of the chiral UA(1) anomaly in the nuclear medium.     

Semileptonic Decays of B_s~(**) Mesons into D_(s1) and D_(s2)~* in HQET

In the framework of the heavy quark effective theory,the leading order Isgur-Wise functions relevant to semileptonic decays of the orbitally P-wave excited B s meson states B**s,including the newly found narrow B s1(5830) and B**s2(5840) states,into the(D s1(2536),D*s2(2573)) doublet are calculated from QCD sum rules.With these universal form factors,the decay rates and branching ratios are also estimated.     

A minimalSU(2)×U(1)×U(1) electroweak model with mirror fermions

We present a minimal extension of the standard electroweak model, which accommodates mirror fermions, based onSU(2)×U(1)×U(1). Mirror mixing happens through sterile neutrino states and induces radiative mixing for charged leptons. Quarks and mirror quarks are not mixed with each other, consistent with the suppression of flavour changing neutral currents. Higgs sector, fermion masses and neutral currents are discussed. In this scheme there can be a secondZ boson as light as 0.2TeV.     

The nuclear Yukawa model on a lattice

We present the results of the quantum field theory approach to the nuclear Yukawa model obtained by standard lattice techniques. We have considered the simplest case of two identical fermions interacting via a scalar meson exchange. Calculations have been performed using Wilson fermions in the quenched approximation. We found the existence of a critical coupling constant above which the model cannot be numerically solved. The range of the accessible coupling constants is below the threshold value for producing two-body bound states. Two-body scattering lengths have been obtained and compared to the non-relativistic results.     

Meson supercurrent state in high-density QCD

The ground state of three flavor quark matter at asymptotically large density is believed to be the color-flavor-locked (CFL) phase. At nonasymptotic density the effect of the nonzero strange quark mass cannot be neglected. If the strange quark mass exceeds m(s) approximately m(u)(1/3)delta(2/3), the CFL state becomes unstable toward the formation of a neutral kaon condensate. Recently, several authors discovered that for m(s) approximately (2deltap(F))(1/2) the CFL state contains gapless fermions, and that the gapless modes lead to an instability in current-current correlation functions. Using an effective theory of the CFL state, we demonstrate that this instability can be resolved by the formation of a meson supercurrent, analogous to Migdal's p-wave pion condensate. This state has a nonzero meson current that is canceled by a backflow of gapless fermions.     

Properties of L=1 B(1) and B(2)* mesons

This Letter presents the first strong evidence for the resolution of the excited B mesons B(1) and B(2)* as two separate states in fully reconstructed decays to B(+)(*)pi(-). The mass of B(1) is measured to be 5720.6+/-2.4+/-1.4 MeV/c(2) and the mass difference DeltaM between B(2)* and B(1) is 26.2+/-3.1+/-0.9 MeV/c;{2}, giving the mass of the B(2)* as 5746.8+/-2.4+/-1.7 MeV/c(2). The production rate for B(1) and B(2)* mesons is determined to be a fraction (13.9+/-1.9+/-3.2)% of the production rate of the B+ meson.     

Strong coupling expansion of meson propagator in finite temperature lattice gauge theories

We consider Susskind fermions on a (d+1)-dimensional lattice interacting with aU(n) gauge field at finite temperature. We calculate the meson propagator in an expansion in 1/g ² and 1/d and determine the meson masses. To the order considered the results are identical to those obtained at zero temperature.     

Topological Superconductivity in Cu(x)Bi(2)Se(3)

A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator Cu(x)Bi(2)Se(3), which superconducts below ～3 K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting Cu(x)Bi(2)Se(3) present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in Cu(x)Bi(2)Se(3). In addition, we found an unusual pseudogap that develops below ～20 K and coexists with the topological superconducting state.     

UNITARY TRAPJSFORMATIOPJS IN LATTICE GAUGE THEORY WITH FEPMIONS AND THE MESON SPECTRUM

The Hamiltonian of lattice gauge theory with fermions is diagonalized in the one-link approximation and the meson spectrum of SU(N) theory with one flavor is derived.     

Chiral Ring Structure in the N = 2 Superconformal Field Theory Based on the Coset Construction with SU(1,1)/U(1)

In this paper, we carefully analyze the unitarity of the simplest Kazama-Suzuki model based on the noncompact group. The chiral ring structure in this N = 2 theory is clarified. In general, it is infinitely dimensional and innumerable. The primary chiral states belonging to the ring can be constructed by means of the direct products of the highest weight states of the coset SU(1,1)/ U(1) and the scalar representation of U(1) for the fermions. The primary chird and anti-chiral states Jive individually in the positive discrete series D⁺ and negative discrete series D^- of SU(1,1), respectively. With appropriate restrictions, this theory can be regarded as one at the fixed point of a Landau-Ginzburg theory, in which the superpotential is given by S₁₂ in the fourteen exceptional singularities.     

带有质量的Wilson费米子的格点Schwinger模型中M_V对m的变化率的计算

用变分法计算带有质量的Ｗｉｌｓｏｎ费米子的格点Ｓｃｈｗｉｎｇｅｒ模型中矢量介子的质量Ｍ，从而求出Ｍ、对费米子质量ｍ的变化率Ｍｖ／ｍ（ｍ＝０处），结果与连续理论的准确解十分接近．     

A possible interpretation of the \pi_1(1400) exotic meson

I will discuss the current theoretical and experimental status of exotic mesons and a possible interpretation of the light, exotic meson as a final state interaction effect.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.39.Mk Glueball and nonstandard multi-quark/gluon states - 13.60.Le Meson productionA.P. Szczepaniak: Present address: Department of Physics, Indiana University, Bloomington, IN 47405, USA     

A study of SU(3) × SU(2) × U(1) × U(1) as an intermediate energy subgroup of SO(10)

We analyze several patterns of symmetry breaking of SO(10) where SU(3)_c × SU(2) × U(1) × U(1) is an intermediate energy subgroup. Using constraints from the renormalization group and data from neutral-current experiments we show that if the only Higgs used in the low-energy breaking of the theory are those which can give mass to fermions then the possibility of a low intermediate mass scale is ruled out.