3,950 research outputs found
Excitation and control of large amplitude standing magnetization waves
A robust approach to excitation and control of large amplitude standing
magnetization waves in an easy axis ferromagnetic by starting from a ground
state and passage through resonances with chirped frequency microwave or spin
torque drives is proposed. The formation of these waves involves two stages,
where in the first stage, a spatially uniform, precessing magnetization is
created via passage through a resonance followed by a self-phase-locking
(autoresonance) with a constant amplitude drive. In the second stage, the
passage trough an additional resonance with a spatial modulation of the driving
amplitude yields transformation of the uniform solution into a doubly
phase-locked standing wave, whose amplitude is controlled by the variation of
the driving frequency. The stability of this excitation process is analyzed
both numerically and via Whitham's averaged variational principle
Autoresonant excitation of Bose-Einstein condensates
Controlling the state of a Bose-Einstein condensate driven by a chirped
frequency perturbation in a one-dimensional anharmonic trapping potential is
discussed. By identifying four characteristic time scales in this
chirped-driven problem, three dimensionless parameters are defined
describing the driving strength, the anharmonicity of the trapping potential,
and the strength of the particles interaction, respectively. As the driving
frequency passes the linear resonance in the problem, and depending on the
location in the parameter space, the system may exhibit two very
different evolutions, i.e. the quantum energy ladder climbing (LC) and the
classical autoresonance (AR). These regimes are analysed both in theory and
simulations with the emphasis on the effect of the interaction parameter
. In particular, the transition thresholds on the driving parameter
and their width in in both the AR and LC regimes are discussed.
Different driving protocols are also illustrated, showing efficient control of
excitation and de-excitation of the condensate
Flavor Gauge Models Below the Fermi Scale
The mass and weak interaction eigenstates for the quarks of the third
generation are very well aligned, an empirical fact for which the Standard
Model offers no explanation. We explore the possibility that this alignment is
due to an additional gauge symmetry in the third generation. Specifically, we
construct and analyze an explicit, renormalizable model with a gauge boson,
, corresponding to the symmetry of the third family. Having a
relatively light (in the MeV to multi-GeV range), flavor-nonuniversal gauge
boson results in a variety of constraints from different sources. By
systematically analyzing 20 different constraints, we identify the most
sensitive probes: kaon, , and Upsilon decays, mixing,
atomic parity violation, and neutrino scattering and oscillations. For the new
gauge coupling in the range the model is shown to
be consistent with the data. Possible ways of testing the model in physics,
top and decays, direct collider production and neutrino oscillation
experiments, where one can observe nonstandard matter effects, are outlined.
The choice of leptons to carry the new force is ambiguous, resulting in
additional phenomenological implications, such as non-universality in
semileptonic bottom decays. The proposed framework provides interesting
connections between neutrino oscillations, flavor and collider physics.Comment: 44 pages, 7 figures, 3 tables; B physics constraints and references
added, conclusions unchange
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