2,479 research outputs found
Dimer-atom scattering between two identical fermions and a third particle
We use the diagrammatic -matrix approach to analyze the three-body
scattering problem between two identical fermions and a third particle (which
could be a different species of fermion or a boson). We calculate the s-wave
dimer-atom scattering length for all mass ratios, and our results exactly match
the results of Petrov. In particular, we list the exact dimer-atom scattering
lengths for all available two-species Fermi-Fermi and Bose-Fermi mixtures. In
addition, unlike that of the equal-mass particles case where the three-body
scattering -matrix decays monotonically as a function of the outgoing
momentum, we show that, after an initial rapid drop, this function changes sign
and becomes negative at large momenta and then decays slowly to zero when the
mass ratio of the fermions to the third particle is higher than a critical
value (around 6.5). As the mass ratio gets higher, modulations of the
-matrix become more apparent with multiple sign changes, related to the
"fall of a particle to the center" phenomenon and to the emergence of
three-body Efimov bound states.Comment: 6 pages, 3 figures, and 2 table
Observation of heteronuclear atomic Efimov resonances
The Efimov effect represents a cornerstone in few-body physics. Building on
the recent experimental observation with ultracold atoms, we report the first
experimental signature of Efimov physics in a heteronuclear system. A mixture
of K and Rb atoms was cooled to few hundred nanoKelvins and
stored in an optical dipole trap. Exploiting a broad interspecies Feshbach
resonance, the losses due to three-body collisions were studied as a function
of the interspecies scattering length. We observe an enhancement of the
three-body collisions for three distinct values of the interspecies scattering
lengths, both positive and negative. We attribute the two features at negative
scattering length to the existence of two kind of Efimov trimers, namely KKRb
and KRbRb.Comment: 4 pages, 4 figure
N-body Efimov states from two-particle noise
The ground state energies of universal N-body clusters tied to Efimov
trimers, for N even, are shown to be encapsulated in the statistical
distribution of two particles interacting with a background auxiliary field at
large Euclidean time when the interaction is tuned to the unitary point.
Numerical evidence that this distribution is log-normal is presented, allowing
one to predict the ground-state energies of the N-body system.Comment: Extended discussion of results; published versio
Strong and radiative decays of the Ds0*(2317) meson in the DK-molecule picture
We consider a possible interpretation of the new charm-strange meson
Ds0*(2317) as a hadronic molecule - a bound state of D and K mesons. Using an
effective Lagrangian approach we calculate the strong Ds0* to Ds pi0 and
radiative Ds0* to Ds* gamma decays. A new impact related to the DK molecular
structure of the Ds0*(2317) meson is that the presence of u(d) quarks in the D
and K mesons gives rise to a direct strong isospin-violating transition Ds0* to
Ds pi0 in addition to the decay mechanism induced by eta-pi0 mixing considered
previously. We show that the direct transition dominates over the eta-pi0
mixing transition in the Ds0* to Ds pi0 decay. Our results for the partial
decay widths are consistent with previous calculations.Comment: 22 pages, 4 figures, accepted for publication in Phys. Rev.
Production of three-body Efimov molecules in an optical lattice
We study the possibility of associating meta-stable Efimov trimers from three
free Bose atoms in a tight trap realised, for instance, via an optical lattice
site or a microchip. The suggested scheme for the production of these molecules
is based on magnetically tunable Feshbach resonances and takes advantage of the
Efimov effect in three-body energy spectra. Our predictions on the energy
levels and wave functions of three pairwise interacting 85Rb atoms rely upon
exact solutions of the Faddeev equations and include the tightly confining
potential of an isotropic harmonic atom trap. The magnetic field dependence of
these energy levels indicates that it is the lowest energetic Efimov trimer
state that can be associated in an adiabatic sweep of the field strength. We
show that the binding energies and spatial extents of the trimer molecules
produced are comparable, in their magnitudes, to those of the associated
diatomic Feshbach molecule. The three-body molecular state follows Efimov's
scenario when the pairwise attraction of the atoms is strengthened by tuning
the magnetic field strength.Comment: 21 pages, 8 figures (final version
Analytic Confinement and Regge Trajectories
A simple relativistic quantum field model with the Yukawa-type interaction is
considered to demonstrate that the analytic confinement of the constituent
("quarks") and carrier ("gluons") particles explains qualitatively the basic
dynamical properties of the spectrum of mesons considered as two-particle
stable bound states of quarks and gluons: the quarks and gluons are confined,
the glueballs represent bound states of massless gluons, the masses of mesons
are larger than the sum of the constituent quark masses and the Regge
trajectories of mesonic orbital excitations are almost linear.Comment: RevTeX, 16 pages, 3 figures and 2 table
Rare decay pi0 -> e+e-: theory confronts KTeV data
Within the dispersive approach to the amplitude of the rare decay pi0 -> e+e-
the nontrivial dynamics is contained only in the subtraction constant. We
express this constant, in the leading order in (m_e/\Lambda)^2 perturbative
series, in terms of the inverse moment of the pion transition form factor given
in symmetric kinematics. By using the CELLO and CLEO data on the pion
transition form factor given in asymmetric kinematics the lower bound on the
decay branching ratio is found. The restrictions following from QCD allow us to
make a quantitative prediction for the branching B(pi0 -> e+e-) =(6.2\pm
0.1)*10^{-8} which is 3\sigma below the recent KTeV measurement. We confirm our
prediction by using the quark models and phenomenological approaches based on
the vector meson dominance. The decays \eta -> l^+l^- are also discussed.Comment: 7 pages, 1 figur
A non-perturbative method of calculation of Green functions
A new method for non-perturbative calculation of Green functions in quantum
mechanics and quantum field theory is proposed. The method is based on an
approximation of Schwinger-Dyson equation for the generating functional by
exactly soluble equation in functional derivatives. Equations of the leading
approximation and the first step are solved for -model. At
(anharmonic oscillator) the ground state energy is calculated. The
renormalization program is performed for the field theory at . At
the renormalization of the coupling involves a trivialization of the theory.Comment: 13 pages, Plain LaTex, no figures, some discussion of results for
anharmonic oscillator and a number of references are added, final version
published in Journal of Physics
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
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