arXiv subjects

S. Kim

Publications and source records attributed to S. Kim.

206 records · Page 12Linked to original sources

arXiv1998

Phonon Scattering by Breathers in the Discrete Nonlinear Schroedinger Equation

Linear theory for phonon scattering by discrete breathers in the discrete nonlinear Schroedinger equation using the transfer matrix approach is presented. Transmission and reflection coefficients are obtained as a function of the wave vector of the input phonon. The occurrence of a nonzero transmission, which in fact becomes perfect for a symmetric breather, is shown to be connected with localized eigenmodes thresholds. In the weak-coupling limit, perfect reflection are shown to exist, which requires two scattering channels. A necessary condition for a system to have a perfect reflection is also considered in a general context.

solv-int↗

arXiv1996

Thermodynamics of lattice QCD with two light quark flavours on a 16^3 x 8 lattice II

We have extended our earlier simulations of the high temperature behaviour of lattice QCD with two light flavours of staggered quarks on a $16^3 \times 8$ lattice to lower quark mass (m_q=0.00625). The transition from hadronic matter to a quark-gluon plasma is observed at $6/g^2=5.49(2)$ corresponding to a temperature of $T_c \approx 140$MeV. We present measurements of observables which probe the nature of the quark-gluon plasma and serve to distinguish it from hadronic matter. Although the transition is quite abrupt, we have seen no indications that it is first order.

hep-lat↗

arXiv1996

Lattice Calculation of Quarkonium Decay Matrix Elements

We calculate the NRQCD matrix elements for the decays of the lowest-lying S- and P-wave states of charmonium and bottomonium in quenched lattice QCD. We also compute the one-loop relations between the lattice and continuum matrix elements.

hep-ph↗

arXiv1996

Quarkonium Decay Matrix Elements from Quenched Lattice QCD

We calculate the long-distance matrix elements for the decays of the lowest-lying S- and P-wave states of charmonium and bottomonium in quenched lattice QCD, using a nonrelativistic formulation for the heavy quarks. (The short-distance coefficients are known from perturbation theory.) In particular, we present the first calculation from QCD first principles of the color-octet contribution to P-wave decay---a contribution that is absent in potential models. We also give the relations between the lattice matrix elements and their continuum counterparts through one-loop order in perturbation theory.

hep-lat↗

arXiv1995

The U(1) Gross-Neveu Model at Non-Zero Chemical Potential

The four-fermi model with continuous chiral symmetry is studied in three dimensions at non-zero chemical potential $μ$ using both the $1/N_f$ expansion and computer simulations. For strong coupling this model spontaneously breaks its U(1) chiral symmetry at zero chemical potential and the Goldstone mechanism is realized through massless pions. The computer simulation predicts a critical chemical potential $μ_c$ close to the lightest fermion mass in the model. As $μ$ is increased beyond $μ_c$, the pion screening mass increases rapidly from zero to a nonvanishing value indicating symmetry restoration. Some lessons are drawn relevant to lattice QCD simulations at non-zero $μ$.

hep-lat↗

arXiv1994

Decays rates for S- and P-wave bottomonium

We use the Bodwin-Braaten-Lepage factorization scheme to separate the long- and short-distance factors that contribute to the decay rates of $Υ$, $η_b$ (S-wave) and $χ_b$,$h_b$ (P-wave). The long distance matrix elements are calculated on the lattice in the quenched approximation using a non-relativistic formulation of the $b$ quark dynamics.

hep-lat↗

arXiv1994

The Phases and Triviality of Scalar Quantum Electrodynamics

The phase diagram and critical behavior of scalar quantum electrodynamics are investigated using lattice gauge theory techniques. The lattice action fixes the length of the scalar (``Higgs'') field and treats the gauge field as non-compact. The phase diagram is two dimensional. No fine tuning or extrapolations are needed to study the theory's critical behovior. Two lines of second order phase transitions are discovered and the scaling laws for each are studied by finite size scaling methods on lattices ranging from $6^4$ through $24^4$. One line corresponds to monopole percolation and the other to a transition between a ``Higgs'' and a ``Coulomb'' phase, labelled by divergent specific heats. The lines of transitions cross in the interior of the phase diagram and appear to be unrelated. The monopole percolation transition has critical indices which are compatible with ordinary four dimensional percolation uneffected by interactions. Finite size scaling and histogram methods reveal that the specific heats on the ``Higgs-Coulomb'' transition line are well-fit by the hypothesis that scalar quantum electrodynamics is logarithmically trivial. The logarithms are measured in both finite size scaling of the specific heat peaks as a function of volume as well as in the coupling constant dependence of the specific heats measured on fixed but large lattices. The theory is seen to be qualitatively similar to $λϕ^{4}$. The standard CRAY random number generator RANF proved to be inadequate

hep-lat↗

arXiv1993

On the Logarithmic Triviality of Scalar Quantum Electrodynamics

Using finite size scaling and histogram methods we obtain numerical results from lattice simulations indicating the logarithmic triviality of scalar quantum electrodynamics, even when the bare gauge coupling is chosen large. Simulations of the non-compact formulation of the lattice abelian Higgs model with fixed length scalar fields on $L^{4}$ lattices with $L$ ranging from $6$ through $20$ indicate a line of second order critical points. Fluctuation-induced first order transitions are ruled out. Runs of over ten million sweeps for each $L$ produce specific heat peaks which grow logarithmically with $L$ and whose critical couplings shift with $L$ picking out a correlation length exponent of $0.50(5)$ consistent with mean field theory. This behavior is qualitatively similar to that found in pure $λϕ^{4}$.

hep-lat↗