10,435 research outputs found
Fermi Gases in Slowly Rotating Traps: Superfluid vs Collisional Hydrodynamics
The dynamic behavior of a Fermi gas confined in a deformed trap rotating at
low angular velocity is investigated in the framework of hydrodynamic theory.
The differences exhibited by a normal gas in the collisional regime and a
superfluid are discussed. Special emphasis is given to the collective
oscillations excited when the deformation of the rotating trap is suddenly
removed or when the rotation is suddenly stopped. The presence of vorticity in
the normal phase is shown to give rise to precession and beating phenomena
which are absent in the superfluid phase.Comment: 4 pages, 2 figure
Universal low-energy properties of three two-dimensional particles
Universal low-energy properties are studied for three identical bosons
confined in two dimensions. The short-range pair-wise interaction in the
low-energy limit is described by means of the boundary condition model. The
wave function is expanded in a set of eigenfunctions on the hypersphere and the
system of hyper-radial equations is used to obtain analytical and numerical
results. Within the framework of this method, exact analytical expressions are
derived for the eigenpotentials and the coupling terms of hyper-radial
equations. The derivation of the coupling terms is generally applicable to a
variety of three-body problems provided the interaction is described by the
boundary condition model. The asymptotic form of the total wave function at a
small and a large hyper-radius is studied and the universal logarithmic
dependence in the vicinity of the triple-collision point is
derived. Precise three-body binding energies and the scattering length
are calculated.Comment: 30 pages with 13 figure
"Universal" Distribution of Inter-Earthquake Times Explained
We propose a simple theory for the ``universal'' scaling law previously
reported for the distributions of waiting times between earthquakes. It is
based on a largely used benchmark model of seismicity, which just assumes no
difference in the physics of foreshocks, mainshocks and aftershocks. Our
theoretical calculations provide good fits to the data and show that
universality is only approximate. We conclude that the distributions of
inter-event times do not reveal more information than what is already known
from the Gutenberg-Richter and the Omori power laws. Our results reinforces the
view that triggering of earthquakes by other earthquakes is a key physical
mechanism to understand seismicity.Comment: 4 pages with two figure
Existence of two-channel Kondo regime for tunneling impurities with resonant scattering
Dynamical tunneling systems have been proposed earlier to display a
two-channel Kondo effect, the orbital index of the particle playing the role of
a pseudospin in the equivalent Kondo problem, and the spin being a silent
channel index. However, as shown recently by Aleiner et al. [Phys. Rev. Lett.
86, 2629 (2001)], the predicted two-channel Kondo behavior can never be
observed in the weak coupling regime, where the tunneling induced splitting of
the levels of the tunneling system always dominates the physics. Here we show
that the above scenario changes completely if the conduction electrons are
scattered by resonant scattering off the tunneling impurity; Then - as a
non-perturbative analysis reveals - the two-channel Kondo regime can easily be
reached.Comment: 10 PRB page
Origin of type-2 thermal-ion upflows in the auroral ionosphere
International audienceThe origin of thermal ion outflows exceeding 1km/s in the high-latitude F-region has been a subject of considerable debate. For cases with strong convection electric fields, the "evaporation" of the ions due to frictional heating below 400-500km has been shown to provide some satisfactory answers. By contrast, in the more frequent subclass of outflow events observed over auroral arcs, called type-2, there is no observational evidence for ion frictional heating. Instead, an electron temperature increase of up to 6000° K is observed over the outflow region. In this case, field-aligned electric fields have long been suspected to be involved, but this explanation did not seem to agree with expectations from the ion momentum balance. In the present work we provide a consistent scenario for the type-2 ion upflows based on our case study of an event that occurred on 20 February 1990. We introduce, for the first time, the electron energy balance in the analysis. We couple this equation with the ion momentum balance to study the salient features of the observations and conclude that type-2 ion outflows and the accompanying electron heating events are indeed consistent with the existence of a field-aligned electric field. However, for our explanation to work, we have to require that an allowance be made for electron scattering by high frequency turbulence. This turbulence could be generated at first by the very fast response of the electrons themselves to a newly imposed electric field that would be partly aligned with the geomagnetic field. The high frequencies of the waves would make it impossible for the ions to react to the waves. We have found the electron collision frequency associated with scattering from the waves to be rather modest, i.e. comparable to the ambient electron-ion collision frequency. The field-aligned electric field inferred from the observations is likewise of the same order of magnitude as the normal ambipolar field, at least for the case that we have studied in detail. We propose that the field-aligned electric field is maintained by the north-south motion of an east-west arc. The magnetic perturbation associated with the arc itself converts a small fraction of the perpendicular electric field into a field parallel to the total magnetic field, while the north-south motion ensures that the conversion never stops
b --> s g g decay in the two and three Higgs doublet models with CP violating effects
We study the decay width and CP-asymmetry of the inclusive process b--> s g g
(g denotes gluon) in the three and two Higgs doublet models with complex Yukawa
couplings. We analyse the dependencies of the differential decay width and
CP-asymmetry to the s- quark energy E_s and CP violating parameter \theta. We
observe that there exist a considerable enhancement in the decay width and CP
asymmetry is at the order of 10^{-2}. Further, it is possible to predict the
sign of C_7^{eff} using the CP asymmetry.Comment: 15 pages, 7 Figures (required epsf style
Long-Term Clustering, Scaling, and Universality in the Temporal Occurrence of Earthquakes
Scaling analysis reveals striking regularities in earthquake occurrence. The
time between any one earthquake and that following it is random, but it is
described by the same universal-probability distribution for any spatial region
and magnitude range considered. When time is expressed in rescaled units, set
by the averaged seismic activity, the self-similar nature of the process
becomes apparent. The form of the probability distribution reveals that
earthquakes tend to cluster in time, beyond the duration of aftershock
sequences. Furthermore, if aftershock sequences are analysed in an analogous
way, yet taking into account the fact that seismic activity is not constant but
decays in time, the same universal distribution is found for the rescaled time
between events.Comment: short paper, only 2 figure
CP violation and the 4th generation
Within the Standard model with the 4th generation quarks b' and t' we have
analyzed CP-violating flavor changing neutral current processes t -> cX; b'->
sX, b'-> bX,t'-> cX, and t'-> tX, with X=Z,H,gamma,g, by constructing and
employing global, unique fit for the 4th generation mass mixing matrix CKM4 at
300 < m_t' < 700 GeV. All quantities appearing in the CKM4 were subject to our
fitting procedure. We have found that our fit produces the following CP partial
rate asymmetry dominance: a_CP(b'-> s(Z,H,gamma,g))= (90,73,52,30)%, at m_t' ~
300,300,380,400 GeV, respectively. From the experimental point of view the best
decay mode, out of the above four, is certainly b'-> s gamma, because of the
presence of a clean high energy single final state photon. We have also
obtained relatively large a_CP(t -> c g) ~ 15 (10)% for t' running in the loops
with the mass m_t'= 650(500) GeV. There are fair chances that the 4th
generation quarks will be discovered at Tevatron or LHC and that some of their
decay rates shall be measured. If b' and t' exist at energies we assumed, with
well executed tagging, large a_CP could be found too.Comment: 19 pages, 12 figures, some of them new, references added, minor
corrections in the text, version to appear in PR
Magnetic polarons in doped 1D antiferromagnetic chain
The structure of magnetic polarons (ferrons) is studied for an 1D
antiferromagnetic chain doped by non-magnetic donor impurities. The conduction
electrons are assumed to be bound by the impurities. Such a chain can be
described as a set of ferrons at the antiferromagnetic background. We found
that two types of ferrons can exist in the system. The ground state of the
chain corresponds to the ferrons with the sizes of the order of the
localization length of the electron near the impurity. The ferrons of the
second type produce a more extended distortion of spins in the chain. They are
stable within a finite domain of the system parameters and can be treated as
excitations above the ground state. The ferrons in the excited states can
appear in pairs only. The energy of the excited states decreases with the
growth in density of impurities. This can be interpreted as a manifestation of
an attractive interaction between ferrons.Comment: 6 pages, 5 figures, RevTex4, submitted to PR
On the influence of time and space correlations on the next earthquake magnitude
A crucial point in the debate on feasibility of earthquake prediction is the
dependence of an earthquake magnitude from past seismicity. Indeed, whilst
clustering in time and space is widely accepted, much more questionable is the
existence of magnitude correlations. The standard approach generally assumes
that magnitudes are independent and therefore in principle unpredictable. Here
we show the existence of clustering in magnitude: earthquakes occur with higher
probability close in time, space and magnitude to previous events. More
precisely, the next earthquake tends to have a magnitude similar but smaller
than the previous one. A dynamical scaling relation between magnitude, time and
space distances reproduces the complex pattern of magnitude, spatial and
temporal correlations observed in experimental seismic catalogs.Comment: 4 Figure
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