3,423 research outputs found
The influence of grain growth in circumstellar dust envelopes on observed colors and polarization of some eruptive stars
R CrB stars are classical examples of stars where dust envelope formation takes place. Dust envelope formation was detected around the Kuwano-Honda object (PU Vul) in 1980 to 1981 when the star's brightness fell to 8(sup m). Such envelopes are also formed at nova outbursts. The process of dust envelope formation leads to appreciable variations in optical characteristics, which are seen in specific color and polarization variations in the course of light fading and the appearance of IR radiation. It is shown that the model of a circumstellar dust envelope with aligned particles of changing size can be successfully applied to explain most phenomena observed at the time of light minima for a number of eruptive stars. The polarization may arise in a nonspherical dust envelope or be produced by alignment of nonspherical particles
The few-body problem for trapped bosons with large scattering length
We calculate energy levels of two and three bosons trapped in a harmonic
oscillator potential with oscillator length . The atoms are
assumed to interact through a short-range potential with a scattering length
, and the short-distance behavior of the three-body wave function is
characterized by a parameter . For large positive ,
the energies of states which, in the absence of the trap, correspond to three
free atoms approach values independent of and . For other states
the dependence of the energy is strong, but the energy is independent
of for .Comment: 4 pages, 3 figure
Mass Dependence of Ultracold Three-Body Collision Rates
We show that many aspects of ultracold three-body collisions can be
controlled by choosing the mass ratio between the collision partners. In the
ultracold regime, the scattering length dependence of the three-body rates can
be substantially modified from the equal mass results. We demonstrate that the
only non-trivial mass dependence is due solely to Efimov physics. We have
determined the mass dependence of the three-body collision rates for all
heteronuclear systems relevant for two-component atomic gases with resonant
s-wave interspecies interactions, which includes only three-body systems with
two identical bosons or two identical fermions
Single-Particle Momentum Distribution of an Efimov trimer
Experimental progress in the study of strongly interacting ultracold atoms
has recently allowed the observation of Efimov trimers. We study theoretically
a non-conventional observable for these trimer states, that may be accessed
experimentally, the momentum distribution n(k) of the constitutive bosonic
particles. The large momentum part of the distribution is particularly
intriguing: In addition to the expected 1/k^4 tail associated to contact
interactions, it exhibits a subleading tail 1/k^5 which is a hall-mark of
Efimov physics and leads to a breakdown of a previously proposed expression of
the energy as a functional of the momentum distribution.Comment: This is a subpart of the (too long to be published) work
arXiv:1001.0774. This subpart has 11 pages and 2 figures. Revised version
correcting minor error
Three-boson problem near a narrow Feshbach resonance
We consider a three-boson system with resonant binary interactions and show
that three-body observables depend only on the resonance width and the
scattering length. The effect of narrow resonances is qualitatively different
from that of wide resonances revealing novel physics of three-body collisions.
We calculate the rate of three-body recombination to a weakly bound level and
the atom-dimer scattering length and discuss implications for experiments on
Bose-Einstein condensates and atom-molecule mixtures near Feshbach resonances.Comment: published versio
When a DNA Triple helix melts: An analog of the Efimov state
The base sequences of DNA contain the genetic code and to decode it a double
helical DNA has to open its base pairs. Recent studies have shown that one can
use a third strand to identify the base sequences without opening the double
helix but by forming a triple helix. It is predicted here that such a three
chain system exhibits the unusual behaviour of the existence of a three chain
bound state in the absence of any two being bound. This phenomenon is analogous
to the Efimov state in three particle quantum mechanics. A scaling theory is
used to justify the Efimov connection. Real space renormalization group (RG),
and exact numerical calculations are used to validate the prediction of a
biological Efimov effect.Comment: Replaced by the (almost) published version, except the word
"curiouser
(Anti-)self-dual homogeneous vacuum gluon field as an origin of confinement and symmetry breaking in QCD
It is shown that an (anti-)self-dual homogeneous vacuum gluon field appears
in a natural way within the problem of calculation of the QCD partition
function in the form of Euclidean functional integral with periodic boundary
conditions. There is no violation of cluster property within this formulation,
nor are parity, color and rotational symmetries broken explicitly. The massless
limit of the product of the quark masses and condensates, , is calculated to all loop orders. This quantity
does not vanish and is proportional to the gluon condensate appearing due to
the nonzero strength of the vacuum gluon field. We conclude that the gluon
condensate can be considered as an order parameter both for confinement and
chiral symmetry breaking.Comment: 16 pages, LaTe
Exact relations for quantum-mechanical few-body and many-body problems with short-range interactions in two and three dimensions
We derive relations between various observables for N particles with
zero-range or short-range interactions, in continuous space or on a lattice, in
two or three dimensions, in an arbitrary external potential. Some of our
results generalise known relations between large-momentum behavior of the
momentum distribution, short-distance behavior of the pair correlation function
and of the one-body density matrix, derivative of the energy with respect to
the scattering length or to time, and the norm of the regular part of the
wavefunction; in the case of finite-range interactions, the interaction energy
is also related to dE/da. The expression relating the energy to a functional of
the momentum distribution is also generalised, and is found to break down for
Efimov states with zero-range interactions, due to a subleading oscillating
tail in the momentum distribution. We also obtain new expressions for the
derivative of the energy of a universal state with respect to the effective
range, the derivative of the energy of an efimovian state with respect to the
three-body parameter, and the second order derivative of the energy with
respect to the inverse (or the logarithm in the two-dimensional case) of the
scattering length. The latter is negative at fixed entropy. We use exact
relations to compute corrections to exactly solvable three-body problems and
find agreement with available numerics. For the unitary gas, we compare exact
relations to existing fixed-node Monte-Carlo data, and we test, with existing
Quantum Monte Carlo results on different finite range models, our prediction
that the leading deviation of the critical temperature from its zero range
value is linear in the interaction effective range r_e with a model independent
numerical coefficient.Comment: 51 pages, 5 figures. Split into three articles: Phys. Rev. A 83,
063614 (2011) [arXiv:1103.5157]; Phys. Rev. A 86, 013626 (2012)
[arXiv:1204.3204]; Phys. Rev. A 86, 053633 (2012) [ arXiv:1210.1784
Effective Field Theory Program for Conformal Quantum Anomalies
The emergence of conformal states is established for any problem involving a
domain of scales where the long-range, SO(2,1) conformally invariant
interaction is applicable. Whenever a clear-cut separation of ultraviolet and
infrared cutoffs is in place, this renormalization mechanism produces binding
in the strong-coupling regime. A realization of this phenomenon, in the form of
dipole-bound anions, is discussed.Comment: 15 pages. Expanded, with additional calculational details. To be
published in Phys. Rev.
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