1,882 research outputs found
Massive photons and Lorentz violation
All quadratic translation- and gauge-invariant photon operators for Lorentz
breakdown are included into the Stueckelberg Lagrangian for massive photons in
a generalized \xi-gauge. The corresponding dispersion relation and tree-level
propagator are determined exactly, and some leading-order results are derived.
The question of how to include such Lorentz-violating effects into a
perturbative quantum-field expansion is addressed. Applications of these
results within Lorentz-breaking quantum field theories include the
regularization of infrared divergences as well as the free propagation of
massive vector bosons.Comment: 12 pages, 1 figur
Vacuum Cherenkov radiation
Within the classical Maxwell-Chern-Simons limit of the Standard-Model
Extension (SME), the emission of light by uniformly moving charges is studied
confirming the possibility of a Cherenkov-type effect. In this context, the
exact radiation rate for charged magnetic point dipoles is determined and found
in agreement with a phase-space estimate under certain assumptions.Comment: 4 pages, REVTeX
Classical kinematics for Lorentz violation
Classical point-particle relativistic lagrangians are constructed that
generate the momentum-velocity and dispersion relations for quantum wave
packets in Lorentz-violating effective field theory.Comment: 6 pages, accepted for publication in Physics Letters
Non-local on-shell field redefinition for the SME
This work instigates a study of non-local field mappings within the Lorentz-
and CPT-violating Standard-Model Extension (SME). An example of such a mapping
is constructed explicitly, and the conditions for the existence of its inverse
are investigated. It is demonstrated that the associated field redefinition can
remove b-type Lorentz violation from free SME fermions in certain situations.
These results are employed to obtain explicit expressions for the corresponding
Lorentz-breaking momentum-space eigenspinors and their orthogonality relations.Comment: 12 pages, REVTeX
Alpha Channeling in a Rotating Plasma
The wave-particle alpha-channeling effect is generalized to include rotating
plasma. Specifically, radio frequency waves can resonate with alpha particles
in a mirror machine with ExB rotation to diffuse the alpha particles along
constrained paths in phase space. Of major interest is that the alpha-particle
energy, in addition to amplifying the RF waves, can directly enhance the
rotation energy which in turn provides additional plasma confinement in
centrifugal fusion reactors. An ancillary benefit is the rapid removal of alpha
particles, which increases the fusion reactivity.Comment: 4 pages and 3 figure
Adaptive Tuning of Feedback Gain in Time-Delayed Feedback Control
We demonstrate that time-delayed feedback control can be improved by
adaptively tuning the feedback gain. This adaptive controller is applied to the
stabilization of an unstable fixed point and an unstable periodic orbit
embedded in a chaotic attractor. The adaptation algorithm is constructed using
the speed-gradient method of control theory. Our computer simulations show that
the adaptation algorithm can find an appropriate value of the feedback gain for
single and multiple delays. Furthermore, we show that our method is robust to
noise and different initial conditions.Comment: 7 pages, 6 figure
Coherence resonance in a network of FitzHugh-Nagumo systems: interplay of noise, time-delay and topology
We systematically investigate the phenomena of coherence resonance in
time-delay coupled networks of FitzHugh-Nagumo elements in the excitable
regime. Using numerical simulations, we examine the interplay of noise,
time-delayed coupling and network topology in the generation of coherence
resonance. In the deterministic case, we show that the delay-induced dynamics
is independent of the number of nearest neighbors and the system size. In the
presence of noise, we demonstrate the possibility of controlling coherence
resonance by varying the time-delay and the number of nearest neighbors. For a
locally coupled ring, we show that the time-delay weakens coherence resonance.
For nonlocal coupling with appropriate time-delays, both enhancement and
weakening of coherence resonance are possible
Quantum nano-electromechanics with electrons, quasiparticles and Cooper pairs: effective bath descriptions and strong feedback effects
Using a quantum noise approach, we discuss the physics of both normal metal
and superconducting single electron transistors (SET) coupled to mechanical
resonators. Particular attention is paid to the regime where transport occurs
via incoherent Cooper-pair tunneling (either via the Josephson quasiparticle
(JQP) or double Josephson quasiparticle (DJQP) process). We show that,
surprisingly, the back-action of tunneling Cooper pairs (or superconducting
quasiparticles) can be used to significantly cool the oscillator. We also
discuss the physical origin of negative damping effects in this system, and how
they can lead to a regime of strong electro-mechanical feedback, where despite
a weak SET - oscillator coupling, the motion of the oscillator strongly effects
the tunneling of the Cooper pairs. We show that in this regime, the oscillator
is characterized by an energy-dependent effective temperature. Finally, we
discuss the strong analogy between back-action effects of incoherent
Cooper-pair tunneling and ponderomotive effects in an optical cavity with a
moveable mirror; in our case, tunneling Cooper pairs play the role of the
cavity photons.Comment: 27 pages, 7 figures; submitted to the New Journal of Physics focus
issue on Nano-electromechanical Systems; error in references correcte
- …