Published papers

We analyze the properties of mesons in (1+1)-dimensional QCD with bosonic and fermionic ''quarks'' in the large Nc limit. We study the spectrum in detail and show that it is impossible to obtain massless mesons including boson constituents in this model. We quantitatively show how the QCD mass inequality is realized in two-dimensional QCD. We find that the mass inequality is close to being an equality even when the quarks are light. Methods for obtaining the properties of ''mesons'' formed from boson and/or fermion constituents are formulated in an explicit manner convenient for further study. We also analyze how the physical properties of the mesons such as confinement and asymptotic freedom are realized. © 1995 The American Physical Society.

We describe a tabletop experiment for the direct measurement of the speed of light to an accuracy of a few percent. The experiment is accessible to students not majoring in science or engineering. The experiment can include a measurement of the index of refraction of a sample. We discuss the experimental apparatus and safety considerations. The results and limitations of the experiment are analyzed, based partly on our experience in employing the experiment in student laboratories. © 2008 American Association of Physics Teachers.

We derive the boson-fermion bound state equation in a two-dimensional gauge theory in the large-Nc limit. We analyze the properties of this equation and, in particular, find that the mass trajectory is linear with respect to the bound state level for the higher mass states. © 1994 The American Physical Society.

We study nonequilibrium properties of a one-dimensional lattice Hamiltonian with quartic interactions in strong thermal gradients. Nonequilibrium temperature profiles, T(x), are found to develop significant curvature and boundary jumps. From the determination of the bulk thermal conductivity, we develop a quantitative description of T(x) including the jumps. (C) 2000 Published by Elsevier Science B.V.

The correlation function of the ZN super twist fields is calculated on the sphere. Also, the degeneration behavior of the higher genus partition function is used to derive the spectrum of dimensions for the non-abelian super twist fields. © 1989.

We show how systematically incorporate back reaction into fermion number violating amplitudes in Yang-Mills theories. We discuss the possible recovery of unittarity at high energies for these processes. © 1991.

The temperature and size dependence of the thermal conductivity in the Fermi-Pasta-Ulam β model were computed. A quantitative understanding of these effects was obtained. Further, dynamical regimes were defined based on the interplay of surface and volume effects.

Heat kernels of Laplacians on superfields of arbitrary tensor weight on super Riemann surfaces are constructed, and are used to compute the super determinants of these operators in terms of the Selberg super zeta function. © 1988 Springer-Verlag.

We summarize recent work, in which we consider scattering amplitudes of non-critical strings in the limit where the energy of all external states is large compared to the string tension. We show that the high energy limit is dominated by a saddle point that can be mapped onto an electrostatic equilibrium configuration of an assembly of charges associated with the external states, together with a density of charges arising from the Liouville field. The Liouville charges accumulate on line segments, which produce quadratic branch cuts on the worldsheet. The electrostatics problem is solved for string tree level in terms of hyperelliptic integrals and is given explicitly for the 3- and 4-point functions. For generic values of the central charge, the high energy limit behaves in a string-like fashion, with exponential energy dependence. © World Scientific Publishing Company.

By enlarging the number of fermion species and sclar fields, we generalize the Yukawa-Higgs sector of the standard model. We solve this model to leading order in a 1NF expansion. We study the behavior of the fermion mass and the width when they are below the cutoff scale of the theory. Other Yukawa-Higgs models with different chiral structures are also studied. We find that the mass of the fermion is finite and is below the cutoff scale for any finite on-shell Yukawa coupling in the chiral models. © 1991 The American Physical Society.

We solve a model of a Higgs supermultiplet coupled to a quark (or a lepton) supermultiplet in the large-NF limit including the effects of soft supersymmetry-breaking terms. We find that the model needs to be defined with a cutoff and we obtian the spectrum of the model in the region where the masses of the particles remain below the cutoff scale of the model. The model corresponds to the quark-Higgs (or lepton-Higgs) sector of the supersymmetric versions of the standard model when the quantum corrections due to only the Yukawa-Higgs couplings are considered. © 1992 The American Physical Society.

We compute some nondecoupling effects in the standard model, such as the ρ parameter, to all orders in the coupling constant expansion. We analyze their large order behavior and explicitly show how they are related to the nonperturbative cutoff dependence of these nondecoupling effects due to the triviality of the theory. © 1994 The American Physical Society.

An explicit relation between the dimensional loss (δ), entropy production, and transport under thermal gradients was discussed. It was found that the extensivity of δD in systems with bulk behavior followed from the relation. It was found that the maximum Lyapunov exponents in thermal equilibrium and δD in nonequilibrium depended on the choice of heat baths while their prodcuts was unique and macroscopic. The statistical errors in the numerical computation of δD were also elaborated.

Surface fluctuation spectra of liquids are measured to unprecedented precision, down to 3 orders of magnitude below the shot-noise level using averaged correlations of interferometry measurements. This allows us to investigate the limits in our current theoretical understanding of these phenomena. The spectrum derived from hydrodynamical considerations agrees well with the observed results for water. However, for oil, deviations are seen at high frequencies (1 MHz), perhaps indicating its more complex underlying physics. The measurements are made possible by dualizing the Michelson interferometry measurements and employing the averaged correlation of signals, in which the shot noise is statistically reduced. The method works in the presence of the quantum noise of a coherent state of light. The optical part of the experimental setup is essentially the same as that of Michelson interferometry so that the method can be applied when Michelson interferometry can be used. Furthermore, the measurement method requires a relatively low light power and a short time so that it has a wide range of applicability. © 2013 American Physical Society.

We developed a system for measurements of power spectra of transmitted light intensity fluctuations, in which the extraneous noise, including shot noise, is reduced. In essence, we just apply light, measure the power of the transmitted light, and derive its power spectrum. We use this to observe the spontaneous noise spectra of photon atom interactions. Applying light with frequency modulation, we can also observe the spontaneous noise reflecting the coherence between the hyperfine levels in the excited state. There are two main novel components in the measurement system, the noise reduction scheme and the stabilization of the laser system. The noise reduction mechanism can be used to reduce the shot noise contribution to arbitrarily low levels through averaging, in principle. This is combined with differential detection to keep unwanted noise at low levels. The laser system is stabilized to obtain spectral width below 1 kHz without high frequency (≳10 MHz) noise. These methods are described systematically and the performance of the measurement system is examined through experimental results. © 2014 Optical Society of America.

We consider scattering amplitudes in non-critical string theory of N external states in the limit where the energy of all external states is large compared to the string tension. We argue that the amplitudes are naturally complex analytic in the matter central charge c and we propose to define the amplitudes for arbitrary value of c by analytic continuation. We show that the high energy limit is dominated by a saddle point that can be mapped onto an equilibrium electrostatic energy configuration of an assembly of N pointlike (Minkowskian) charges, together with a density of charges arising from the Liouville field. We argue that the Liouville charges accumulate on segments of curves, and produce quadratic branch cuts on the world-sheet. The electrostatics problem is solved for string tree level in terms of hyper-elliptic integrals and is given explicitly for three-and four-point functions. We show that the high energy limit should behave in a string-like fashion with exponential dependence on the energy scale for generic values of c. © 1997 Elsevier Science B.V.

We show that the dimensionful scalar cubic coupling in 3 + 1 dimensions gives rise to non-decoupling effects and analyze the behavior of these effects. In the process, we clarify how it is perturbatively consistent to construct theories in which the cubic coupling is dominant. We use the scalar sector of the Supersymmetric Standard Model as an example. We discuss how the non-decoupling effects may be analyzed systematically. © 1998 Elsevier Science B.V.

The dependence of the ρ{variant} parameter on the mass of the Higgs scalar and the top quark is computed non-perturbatively using the 1/NF expansion in the standard model. We find an explicit expression for the ρ{variant} parameter that requires the presence of a physical cutoff. This should come as no surprise since the theory is presumably trivial. By taking this cutoff into account, we find that the ρ{variant} parameter can take values only within a limited range and has finite ambiguities that are suppressed by inverse powers of the cutoff scale, the so called "scaling-violations". We find that large deviations from the perturbative results are possible, but only when the cutoff effects are also large. © 1994 Springer-Verlag.

We study the classical non-equilibrium statistical mechanics of scalar field theory on the lattice. Steady states are analyzed near and far from equilibrium. The bulk thermal conductivity is computed, including its temperature dependence. We examine the validity of linear response predictions, as well as properties of the non-equilibrium steady state. We find that the linear response theory applies to visibly curved temperature profiles as long as the thermal gradients are not too strong. We also examine the transition from local equilibrium to local non-equilibrium. (C) 2000 Elsevier Science B.V.

We study the nonequilibrium statistical mechanics of classical lattice 4 theory in thermal gradients of arbitrary strength. The steady-state physics of the theory in (1 + 1) dimensions is investigated from first principles and classified into dynamical regimes. The bulk properties associated with thermal transport are derived. Starting with thermal equilibrium, we examine the relation to the kinetic theory description of the behavior of the system. Green-Kubo transport coefficients are computed and compared to measured transport near and far from equilibrium, defining the scope of linear response and including an analysis of long-time tails. Local equilibrium is investigated and seen to explicitly break down under sufficiently strong gradients. Additional measures of the nonequilibrium steady state are also discussed as well as the connections to irreversible thermodynamics. © 2002 Elsevier Science (USA).