Search results for "electrodynamics"

Nonlocal effects in superfluid turbulence: Application to the low-density- to high-density-state transition and to vortex decay

2005

We discuss a phenomenological equation for the evolution of vortex tangle in counterflow superfluid turbulence, which takes into account the influence of the nonlocal effects, introducing into the original equation of Vinen two simple corrective terms dependent on a nonvanishing ratio between the average separation between vortex lines and the diameter of the channel. The equation allows one to describe, in relatively good agreement with experimental results, the two turbulent regimes present in counterflow superfluid turbulence and the transition between them. The decay rate of the vortex line density L, when the heat flux is suddenly turned off, is also investigated; due to the simplicity…

Preservation of quantum coherence after exciton-exciton interaction in quantum wells

2003

The dynamics of exciton-exciton interaction in quantum wells has been investigated by monitoring the time-resolved resonant secondary emission that follows excitation with linearly and circularly polarized light. Preservation of quantum beating in the cross-polarized emission demonstrates that spin relaxation can take place, for some scattering channels, without total quantum coherence loss. Interexciton electron exchange is the scattering mechanism that explains the persistence of the beating and, since it is sensitive to the fine structure of excitons, the shift by pi in the phase of the beating observed in the experiment.

Three physical quantum manifolds from the conformal group

1987

Low-frequency internal waves in magnetized rotating stellar radiation zones

2012

Context. With the progress of observational constraints on dynamical processes in stars, it becomes necessary to understand the angular momentum and the rotation profile history. In this context, internal waves constitute an efficient transport mechanism over long distances in stellar radiation zones. Indeed, they could be one of the mechanisms responsible for the quasi-flat rotation profile of the solar radiative region up to 0.2 R ⊙ .Aims. Angular momentum transport induced by internal waves depends on the properties of their excitation regions and of their dissipation during propagation. Then, the bottom of convective envelopes (the top of convective cores, respectively) are differential…

General treatment of vortical, toroidal, and compression modes

2011

The multipole vortical, toroidal, and compression modes are analyzed. Following the vorticity concept of Ravenhall and Wambach, the vortical operator is derived and related in a simple way to the toroidal and compression operators. The strength functions and velocity fields of the modes are analyzed in $^{208}$Pb within the random-phase-approximation using the Skyrme force SLy6. Both convection and magnetization nuclear currents are taken into account. It is shown that the isoscalar (isovector) vortical and toroidal modes are dominated by the convection (magnetization) nuclear current while the compression mode is fully convective. The relation between the above concept of the vorticity to …

Maximum Entropy Limit of Small-scale Magnetic Field Fluctuations in the Quiet Sun

2017

The observed magnetic field on the solar surface is characterized by a very complex spatial and temporal behavior. Although feature-tracking algorithms have allowed us to deepen our understanding of this behavior, subjectivity plays an important role in the identification and tracking of such features. In this paper, we continue studies Gorobets, A. Y., Borrero, J. M., & Berdyugina, S. 2016, ApJL, 825, L18 of the temporal stochasticity of the magnetic field on the solar surface without relying either on the concept of magnetic features or on subjective assumptions about their identification and interaction. We propose a data analysis method to quantify fluctuations of the line-of-sight …

Poincaré's role in the Crémieu-Pender controversy over electric convection

1989

Summary In the course of 1901, V. Cremieu published the results of some experiments carried out to test the magnetic effects of electric convection currents. According to Cremieu, his experiments had proved that convection currents had no magnetic effects and consequently they were not equivalent to conduction currents, that is they were not ‘real’ electric currents. These negative results conflicted with those of well-known experiments carried out by other researchers, in particular with Rowland's experiments, and with Maxwell's, Hertz's and Lorentz's theories, which was more shocking. The publication of Cremieu's experiments raised a controversy which involved directly or indirectly some …

2021-$H_0$ Odyssey: Closed, Phantom and Interacting Dark Energy Cosmologies

2021

Up-to-date cosmological data analyses have shown that \textit{(a)} a closed universe is preferred by the Planck data at more than $99\%$ CL, and \textit{(b)} interacting scenarios offer a very compelling solution to the Hubble constant tension. In light of these two recent appealing scenarios, we consider here an interacting dark matter-dark energy model with a non-zero spatial curvature component and a freely varying dark energy equation of state in both the quintessential and phantom regimes. When considering Cosmic Microwave Background data only, a phantom and closed universe can perfectly alleviate the Hubble tension, without the necessity of a coupling among the dark sectors. Accountin…

Sub-MeV dark matter and the Goldstone modes of superfluid helium

2019

We show how the relativistic effective field theory for the superfluid phase of helium-4 can replace the standard methods used to compute the production rates of low momentum excitations due to the interaction with an external probe. This is done by studying the scattering problem of a light dark matter particle in the superfluid, and comparing to some existing results. We show that the rate of emission of two phonons, the Goldstone modes of the effective theory, gets strongly suppressed for sub-MeV dark matter particles due to a fine cancellation between two different tree-level diagrams in the limit of small exchanged momenta. This phenomenon is found to be a consequence of the particular…

Gravitational Wave Echo of Relaxion Trapping

2021

To solve the hierarchy problem, the relaxion must remain trapped in the correct minimum, even if the electroweak symmetry is restored after reheating. In this scenario, the relaxion starts rolling again until the backreaction potential, with its set of local minima, reappears. Depending on the time of barrier reappearance, Hubble friction alone may be insufficient to retrap the relaxion in a large portion of the parameter space. Thus, an additional source of friction is required, which might be provided by coupling to a dark photon.The dark photon experiences a tachyonic instability as the relaxion rolls, which slows down the relaxion by backreacting to its motion, and efficiently creates a…