1,207 research outputs found
Scalar diagrammatic rules for Born amplitudes in QCD
We show that all Born amplitudes in QCD can be calculated from scalar
propagators and a set of three- and four-valent vertices. In particular, our
approach includes amplitudes with any number of quark pairs. The quarks may be
massless or massive. The proof of the formalism is given entirely within
quantum field theory.Comment: 20 pages, references adde
One-Loop MHV Amplitudes in Supersymmetric Gauge Theories
Using CSW rules for constructing scalar Feynman diagrams from MHV vertices,
we compute the contribution of chiral multiplet to one-loop
MHV gluon amplitude. The result agrees with the one obtained previously using
unitarity-based methods, thereby demonstrating the validity of the MHV-diagram
technique, in the case of one-loop MHV amplitudes, for all massless
supersymmetric theories.Comment: 20 pages, 5 figure
Recursion relations, Helicity Amplitudes and Dimensional Regularization
Using the method of on-shell recursion relations we compute tree level
amplitudes including D-dimensional scalars and fermions. These tree level
amplitudes are needed for calculations of one-loop amplitudes in QCD involving
external quarks and gluons.Comment: 28 pages, 6 figures, clarifications adde
Guided Modes in Negative Refractive Index Waveguides
We study linear guided waves propagating in a slab waveguide made of a
negative-refraction- index material, the so-called left-handed waveguide. We
reveal that the guided waves in left-handed waveguides possess a number of
peculiar properties, such as the absence of the fundamental modes, mode double
degeneracy, and sign-varying energy ux. In particular, we predict the existence
of novel types of guided waves with a dipole-vortex structure of the Pointing
vector.Comment: 4 pages, 4 figure
Plane waves with negative phase velocity in Faraday chiral mediums
The propagation of plane waves in a Faraday chiral medium is investigated.
Conditions for the phase velocity to be directed opposite to the direction of
power flow are derived for propagation in an arbitrary direction; simplified
conditions which apply to propagation parallel to the distinguished axis are
also established. These negative phase-velocity conditions are explored
numerically using a representative Faraday chiral medium, arising from the
homogenization of an isotropic chiral medium and a magnetically biased ferrite.
It is demonstrated that the phase velocity may be directed opposite to power
flow, provided that the gyrotropic parameter of the ferrite component medium is
sufficiently large compared with the corresponding nongyrotropic permeability
parameters.Comment: accepted for publication in Phys. Rev.
Nonlinear surface waves in left-handed materials
We study both linear and nonlinear surface waves localized at the interface
separating a left-handed medium (i.e. the medium with both negative dielectric
permittivity and negative magnetic permeability) and a conventional (or
right-handed) dielectric medium. We demonstrate that the interface can support
both TE- and TM-polarized surface waves - surface polaritons, and we study
their properties. We describe the intensity-dependent properties of nonlinear
surface waves in three different cases, i.e. when both the LH and RH media are
nonlinear and when either of the media is nonlinear. In the case when both
media are nonlinear, we find two types of nonlinear surface waves, one with the
maximum amplitude at the interface, and the other one with two humps. In the
case when one medium is nonlinear, only one type of surface wave exists, which
has the maximum electric field at the interface, unlike waves in right-handed
materials where the surface-wave maximum is usually shifted into a
self-focussing nonlinear medium. We discus the possibility of tuning the wave
group velocity in both the linear and nonlinear cases, and show that
group-velocity dispersion, which leads to pulse broadening, can be balanced by
the nonlinearity of the media, so resulting in soliton propagation.Comment: 9 pages, 10 figure
The staggered domain wall fermion method
A different lattice fermion method is introduced. Staggered domain wall
fermions are defined in 2n+1 dimensions and describe 2^n flavors of light
lattice fermions with exact U(1) x U(1) chiral symmetry in 2n dimensions. As
the size of the extra dimension becomes large, 2^n chiral flavors with the same
chiral charge are expected to be localized on each boundary and the full
SU(2^n) x SU(2^n) flavor chiral symmetry is expected to be recovered. SDWF give
a different perspective into the inherent flavor mixing of lattice fermions and
by design present an advantage for numerical simulations of lattice QCD
thermodynamics. The chiral and topological index properties of the SDWF Dirac
operator are investigated. And, there is a surprise ending...Comment: revtex4, 7 figures, minor revisions, 2 references adde
An Analytic Variational Study of the Mass Spectrum in 2+1 Dimensional SU(3) Hamiltonian Lattice Gauge Theory
We calculate the masses of the lowest lying eigenstates of improved SU(2) and
SU(3) lattice gauge theory in 2+1 dimensions using an analytic variational
approach. The ground state is approximated by a one plaquette trial state and
mass gaps are calculated in the symmetric and antisymmetric sectors by
minimising over a suitable basis of rectangular states
Low-lying meson spectrum of large strongly coupled lattice QCD
We compute the low energy mass spectrum of lattice QCD in the large
limit. Expanding around a gauge-invariant ground state, which spontaneously
breaks the discrete chiral symmetry, we derive an improved strong-coupling
expansion and evaluate, for any value of , the masses of the low-lying
states in the unflavored meson spectrum. We then take the 't Hooft limit by
rescaling ; the 't Hooft limit is smooth and no arbitrary
parameters are needed. We find, already at the fourth order of the strong
coupling perturbation theory, a very good agreement between the results of our
lattice computation and the known continuum values.Comment: 43 pages, 1 figure. Minor corrections. One reference added in section
Correlation functions for 1d interacting fermions with spin-orbit coupling
We compute correlation functions for one-dimensional electron systems which
spin and charge degrees of freedom are coupled through spin-orbit coupling.
Charge density waves, spin density waves, singlet- triplet- superconducting
fluctuations are studied. We show that the spin-orbit interaction modify the
exponents and the phase diagram of the system, changing the dominant
fluctuations and making new susceptibilities diverge for low temperature.Comment: 5 pages, 3 figures. Accepted for publication in Phys. Rev.
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