34 research outputs found
Could the primordial radiation be responsible for vanishing of topological defects?
We study the motion of topological defects in 1+1 and 2+1 d relativistic
model with three equal vacua in the presence of radiation. We show
that even small fluctuations can trigger a chain reaction leading to vanishing
of topological defects. Only one vacuum remains stable and domains containing
other vacua vanish. We explain this phenomenon in terms of radiation pressure
(both positive and negative). We construct an effective model which translates
the fluctuations into additional term in the field theory potential. In case of
two dimensional model we find a relation between the critical size of the bulk
and amplitude of the perturbation.Comment: 5 pages, 3 figures, additional 3 movies (simulations
Oscillons in the presence of external potential
We discuss similarity between oscillons and oscillational mode in perturbed . For small depths of the perturbing potential it is difficult to distinguish between oscillons and the mode in moderately long time evolution, moreover one can transform one into the other by adiabatically switching on and off the potential. Basins of attraction are presented in the parameter space describing the potential and initial conditions
Negative radiation pressure exerted on kinks
The interaction of a kink and a monochromatic plane wave in one dimensional
scalar field theories is studied. It is shown that in a large class of models
the radiation pressure exerted on the kink is negative, i.e. the kink is {\sl
pulled} towards the source of the radiation. This effect has been observed by
numerical simulations in the model, and it is explained by a
perturbative calculation assuming that the amplitude of the incoming wave is
small. Quite importantly the effect is shown to be robust against small
perturbations of the model. In the sine-Gordon (sG) model the time
averaged radiation pressure acting on the kink turns out to be zero. The
results of the perturbative computations in the sG model are shown to be in
full agreement with an analytical solution corresponding to the superposition
of a sG kink with a cnoidal wave. It is also demonstrated that the acceleration
of the kink satisfies Newton's law.Comment: 23 pages, 8 figures, LaTeX/RevTe
Simplest oscillon and its sphaleron
Oscillons in a simple, one-dimensional scalar field theory with a cubic potential are discussed. The theory has a classical sphaleron, whose decay generates a version of the oscillon. A good approximation to the small-amplitude oscillon is constructed explicitly using the asymptotic expansion of Fodor et al., but for larger amplitudes a better approximation uses the discrete, unstable, and stable deformation modes of the sphaleron
Quantum Oscillons May be Long-Lived
Hertzberg has constructed a quantum oscillon that decays into pairs of
relativistic mesons with a power much greater than the radiation from classical
oscillon decay. This result is often construed as a proof that quantum
oscillons decay quickly, and so are inconsequential. We apply a construction
similar to Hertzberg's to the quantum kink. Again it leads to a rapid decay via
the emission of relativistic mesons. However, we find that this is the decay of
a squeezed kink state to a stable kink state, and so it does not imply that the
quantum kink is unstable. We then consider a time-dependent solution, which may
be an oscillon, and we see that the argument proceeds identically.Comment: 19 pages, no figure
Plane waves as tractor beams
It is shown that in a large class of systems plane waves can act as tractor
beams: i.e., an incident plane wave can exert a pulling force on the scatterer.
The underlying physical mechanism for the pulling force is due to the
sufficiently strong scattering of the incoming wave into another mode having a
larger wave number, in which case excess momentum is created behind the
scatterer. Such a tractor beam or negative radiation pressure effect arises
naturally in systems where the coupling between the scattering channels is due
to Aharonov-Bohm (AB) gauge potentials. It is demonstrated that this effect is
also present if the AB potential is an induced, ("artificial") gauge potential
such as the one found in J. March-Russell, J. Preskill, F. Wilczek, Phys. Rev.
Lett. 58 2567 (1992).Comment: 6 pages, 4 figure
Negative radiation pressure in Bose-Einstein condensates
In two-component non-linear Schr\"odinger equations, the force exerted by
incident monochromatic plane waves on an embedded dark soliton and on
dark-bright-type solitons is investigated, both perturbatively and by numerical
simulations. When the incoming wave is non-vanishing only in the orthogonal
component to that of the embedded dark soliton, its acceleration is in the
opposite direction to that of the incoming wave. This somewhat surprising
phenomenon can be attributed to the well known "negative effective mass" of the
dark soliton. When a dark-bright soliton, whose effective mass is also
negative, is hit by an incoming wave non-vanishing in the component
corresponding to the dark soliton, the direction of its acceleration coincides
with that of the incoming wave. This implies that the net force acting on it is
in the opposite direction to that of the incoming wave. This rather
counter-intuitive effect is a yet another manifestation of negative radiation
pressure exerted by the incident wave, observed in other systems. When a
dark-bright soliton interacts with an incoming wave in the component of the
bright soliton, it accelerates in the opposite direction, hence the force is
"pushing" it now. We expect that these remarkable effects, in particular the
negative radiation pressure, can be experimentally verified in Bose-Einstein
condensates.Comment: 31 pages, 16 figure
Negative radiation pressure in Bose-Einstein condensates.
In two-component nonlinear Schrödinger equations, the force exerted by incident monochromatic plane waves on an embedded dark soliton and on dark-bright-type solitons is investigated, both perturbatively and by numerical simulations. When the incoming wave is nonvanishing only in the orthogonal component to that of the embedded dark soliton, its acceleration is in the opposite direction to that of the incoming wave. This somewhat surprising phenomenon can be attributed to the well-known negative effective mass of the dark soliton. When a dark-bright soliton, whose effective mass is also negative, is hit by an incoming wave nonvanishing in the component corresponding to the dark soliton, the direction of its acceleration coincides with that of the incoming wave. This implies that the net force acting on it is in the opposite direction to that of the incoming wave. This rather counterintuitive effect is a yet another manifestation of negative radiation pressure exerted by the incident wave, observed in other systems. When a dark-bright soliton interacts with an incoming wave in the component of the bright soliton, it accelerates in the opposite direction; hence the force is pushing it now. We expect that these remarkable effects, in particular the negative radiation pressure, can be experimentally verified in Bose-Einstein condensates
Kink moduli spaces : collective coordinates reconsidered
Moduli spaces - finite-dimensional, collective coordinate manifolds - for
kinks and antikinks in theory and sine-Gordon theory are reconsidered.
The field theory Lagrangian restricted to moduli space defines a reduced
Lagrangian, combining a potential with a kinetic term that can be interpreted
as a Riemannian metric on moduli space. Moduli spaces should be metrically
complete, or have an infinite potential on their boundary. Examples are
constructed for both kink-antikink and kink-antikink-kink configurations. The
naive position coordinates of the kinks and antikinks sometimes need to be
extended from real to imaginary values, although the field remains real. The
previously discussed null-vector problem for the shape modes of kinks
is resolved by a better coordinate choice. In sine-Gordon theory, moduli spaces
can be constructed using exact solutions at the critical energy separating
scattering and breather (or wobble) solutions; here, energy conservation
relates the metric and potential. The reduced dynamics on these moduli spaces
accurately reproduces properties of the exact solutions over a range of
energies.Comment: presentation improved, new plots adde