2,953 research outputs found
The Four-Boson System with Short-Range Interactions
We consider the non-relativistic four-boson system with short-range forces
and large scattering length in an effective quantum mechanics approach. We
construct the effective interaction potential at leading order in the large
scattering length and compute the four-body binding energies using the
Yakubovsky equations. Cutoff independence of the four-body binding energies
does not require the introduction of a four-body force. This suggests that two-
and three-body interactions are sufficient to renormalize the four-body system.
We apply the equations to 4He atoms and calculate the binding energy of the 4He
tetramer. We observe a correlation between the trimer and tetramer binding
energies similar to the Tjon line in nuclear physics. Over the range of binding
energies relevant to 4He atoms, the correlation is approximately linear.Comment: 23 pages, revtex4, 5 PS figures, discussion expanded, results
unchange
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.
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
The structure of the atomic helium trimers: Halos and Efimov states
The Faddeev equations for the atomic helium-trimer systems are solved
numerically with high accuracy both for the most sophisticated realistic
potentials available and for simple phenomenological potentials. An efficient
numerical procedure is described. The large-distance asymptotic behavior,
crucial for weakly bound three-body systems, is described almost analytically
for arbitrary potentials. The Efimov effect is especially considered. The
geometric structures of the bound states are quantitatively investigated. The
accuracy of the schematic models and previous computations is comparable, i.e.
within 20% for the spatially extended states and within 40% for the smaller
^4He-trimer ground state.Comment: 32 pages containing 7 figures and 6 table
Atom-Dimer Scattering in a Three-Component Fermi Gas
Ultracold gases of three distinguishable particles with large scattering
lengths are expected to show rich few-body physics related to the Efimov
effect. We have created three different mixtures of ultracold 6Li atoms and
weakly bound 6Li2 dimers consisting of atoms in three different hyperfine
states and studied their inelastic decay via atom-dimer collisions. We have
found resonant enhancement of the decay due to the crossing of Efimov-like
trimer states with the atom-dimer continuum in one mixture as well as minima of
the decay in another mixture, which we interpret as a suppression of exchange
reactions of the type |12>+|3> -> |23>+|1>. Such a suppression is caused by
interference between different decay paths and demonstrates the possiblity to
use Efimov physics to control the rate constants for molecular exchange
reactions in the ultracold regime.Comment: 5 pages, 3 figure
The Renormalization Group Limit Cycle for the 1/r^2 Potential
Previous work has shown that if an attractive 1/r^2 potential is regularized
at short distances by a spherical square-well potential, renormalization allows
multiple solutions for the depth of the square well. The depth can be chosen to
be a continuous function of the short-distance cutoff R, but it can also be a
log-periodic function of R with finite discontinuities, corresponding to a
renormalization group (RG) limit cycle. We consider the regularization with a
delta-shell potential. In this case, the coupling constant is uniquely
determined to be a log-periodic function of R with infinite discontinuities,
and an RG limit cycle is unavoidable. In general, a regularization with an RG
limit cycle is selected as the correct renormalization of the 1/r^2 potential
by the conditions that the cutoff radius R can be made arbitrarily small and
that physical observables are reproduced accurately at all energies much less
than hbar^2/mR^2.Comment: 11 pages, 4 figure
An Infinite Number of Closed FLRW Universes for Any Value of the Spatial Curvature
The Friedman-Lemaitre-Robertson-Walker (FLRW) cosmological models are based
on the assumptions of large-scale homogeneity and isotropy of the distribution
of matter and energy. They are usually taken to have spatial sections that are
simply connected; they have finite volume in the positive curvature case, and
infinite volume in the null and negative curvature ones. I want to call the
attention to the existence of an infinite number of models, which are based on
these same metrics, but have compact, finite volume, multiply connected spatial
sections. Some observational implications are briefly mentioned.Comment: 4 pages. Contribution to the 5th International Workshop on Astronomy
and Relativistic Astrophysics (Joao Pessoa, PB, Brazil, October 10-12, 2011)
and to the 1o. Simposio Jayme Tiomno (Brasilia, DF, Brazil, October 27-28,
2011). In version 2: a few minor corrections; two new references added. In
this version: title correction in Ref. 3; dedication paragraph at the en
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
Differential Form of the Skornyakov--Ter-Martirosyan Equations
The Skornyakov--Ter-Martirosyan three-boson integral equations in momentum
space are transformed into differential equations. This allows us to take into
account quite directly the Danilov condition providing self-adjointness of the
underlying three-body Hamiltonian with zero-range pair interactions. For the
helium trimer the numerical solutions of the resulting differential equations
are compared with those of the Faddeev-type AGS equations.Comment: 4 pages, 2 figure
The Cleo III Ring Imaging Cherenkov Detector
The CLEO detector has been upgraded to include a state of the art particle
identification system, based on the Ring Imaging Cherenkov Detector (RICH)
technology, in order to take data at the upgraded CESR electron positron
collider. The expected performance is reviewed, as well as the preliminary
results from an engineering run during the first few months of operation of the
CLEO III detector.Comment: 5 pages, 2 Figures Talk given by M. Artuso at 8th Pisa Meeting on
Advanced Detectors, May 200
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