22 research outputs found
Deriving Spin within a discrete-time theory
We prove that the classical theory with a discrete time (chronon) is a
particular case of a more general theory in which spinning particles are
associated with generalized Lagrangians containing time-derivatives of any
order (a theory that has been called "Non-Newtonian Mechanics"). As a
consequence, we get, for instance, a classical kinematical derivation of
Hamiltonian and spin vector for the mentioned chronon theory (e.g., in
Caldirola et al.'s formulation).Comment: 10 pages; LaTeX fil
Coupled Dipole Method Determination of the Electromagnetic Force on a Particle over a Flat Dielectric Substrate
We present a theory to compute the force due to light upon a particle on a
dielectric plane by the Coupled Dipole Method (CDM). We show that, with this
procedure, two equivalent ways of analysis are possible, both based on
Maxwell's stress tensor. The interest in using this method is that the nature
and size or shape of the object, can be arbitrary. Even more, the presence of a
substrate can be incorporated. To validate our theory, we present an analytical
expression of the force due to the light acting on a particle either in
presence, or not, of a surface. The plane wave illuminating the sphere can be
either propagating or evanescent. Both two and three dimensional calculations
are studied.Comment: 10 pages, 8 figures and 3 table
A Tail of a Quark in N=4 SYM
We study the dynamics of a `composite' or `dressed' quark in strongly-coupled
large-N_c N=4 super-Yang-Mills, making use of the AdS/CFT correspondence. We
show that the standard string dynamics nicely captures the physics of the quark
and its surrounding non-Abelian field configuration, making it possible to
derive a relativistic equation of motion that incorporates the effects of
radiation damping. From this equation one can deduce a non-standard dispersion
relation for the composite quark, as well as a Lorentz covariant formula for
its rate of radiation. We explore the consequences of the equation in a few
simple examples.Comment: 26 pages, no figures. v2: added brief clarification on string
boundary conditions, version to be published in JHE