1,868 research outputs found
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
Functional renormalisation group for few-nucleon systems: SU(4) symmetry and its breaking
We apply the functional renormalisation group to few-nucleon systems. Our
starting point is a local effective action that includes three- and
four-nucleon interactions, expressed in terms of nucleon and two-nucleon boson
fields. The evolution of the coupling constants in this action is described by
a renormalisation group flow. We derive these flow equations both in the limit
of exact Wigner SU(4) symmetry and in the realistic case of broken symmetry. In
the symmetric limit we find that the renormalisation flow equations decouple,
and can be combined into two sets, one of which matches the known results for
bosons, and the other result matches the one for fermions with spin degrees
only. The equations show universal features in the unitary limit, which is
obtained when the two-body scattering length tends to infinity. We calculate
the spin-quartet neutron-deuteron scattering length and the deuteron-deuteron
scattering lengths in the spin-singlet and quintet channels
Light baryon magnetic moments and N -> Delta gamma transition in a Lorentz covariant chiral quark approach
We calculate magnetic moments of light baryons and N -> Delta gamma
transition characteristics using a manifestly Lorentz covariant chiral quark
approach for the study of baryons as bound states of constituent quarks dressed
by a cloud of pseudoscalar mesons.Comment: 29 pages, 10 figures, accepted for publication in Phys. Rev.
Higgsless Electroweak Model and Contraction of Gauge Group
A modified formulation of the Electroweak Model with 3-dimensional spherical
geometry in the target space is suggested. The {\it free} Lagrangian in the
spherical field space along with the standard gauge field Lagrangian form the
full Higgsless Lagrangian of the model, whose second order terms reproduce the
same experimentally verified fields with the same masses as the Standard
Electroweak Model. The vector bosons masses are automatically generated, so
there is no need in special mechanism of spontaneous symmetry breaking.
The limiting case of the modified Higgsless Electroweak Model, which
corresponds to the contracted gauge group is discussed.
Within framework of the limit model Z-boson, electromagnetic and electron
fields are interpreted as an external ones with respect to W-bosons and
neutrino fields. The W-bosons and neutrino fields do not effect on these
external fields. The masses of all particles remain the same, but the field
interactions in contracted model are more simple as compared with the standard
Electroweak Model due to nullification of some terms.Comment: Talk at the International Workshop "`Supersymmetries and Quantum
Symmetries"' (SQS-09), Dubna, Russia, July 29 -- August 3, 2009, 11
Anomalous Dimers in Quantum Mixtures near Broad Resonances: Pauli Blocking, Fermi Surface Dynamics and Implications
We study the energetics and dispersion of anomalous dimers that are induced
by the Pauli blocking effect in a quantum Fermi gas of majority atoms near
interspecies resonances. Unlike in vacuum, we find that both the sign and
magnitude of the dimer masses are tunable via Feshbach resonances. We also
investigate the effects of particle-hole fluctuations on the dispersion of
dimers and demonstrate that the particle-hole fluctuations near a Fermi surface
(with Fermi momentum ) generally reduce the effective two-body
interactions and the binding energy of dimers. Furthermore, in the limit of
light minority atoms the particle-hole fluctuations disfavor the formation of
dimers with a total momentum , because near the modes
where the dominating particle-hole fluctuations appear are the softest. Our
calculation suggests that near broad interspecies resonances when the
minority-majority mass ratio is smaller than a critical value
(estimated to be 0.136), dimers in a finite-momentum channel are energetically
favored over dimers in the zero-momentum channel. We apply our theory to
quantum gases of LiK, LiRb, KRb and
LiNa near broad interspecies resonances, and discuss the
limitations of our calculations and implications.Comment: 15 pages, 10 figures, published versio
Functional renormalization for trion formation in ultracold fermion gases
The energy spectrum for three species of identical fermionic atoms close to a
Feshbach resonance is computed by use of a nonperturbative flow equation.
Already a simple truncation shows that for large scattering length the
lowest energy state is a "trion" (or trimer) bound state of three atoms. At the
location of the resonance, for , we find an infinite set of
trimer bound states, with exponentially decreasing binding energy. This feature
was pointed out by Efimov. It arises from limit cycle scaling, which also leads
to a periodic dependence of the three body scattering coupling on .
Extending our findings by continuity to nonzero density and temperature we find
that a "trion phase" separates a BEC and a BCS phase, with interesting quantum
phase transitions for T=0.Comment: 9 pages, 4 figures, minor changes, reference adde
Efimov states and their Fano resonances in a neutron-rich nucleus
Asymmetric resonances in elastic n+C scattering are attributed to
Efimov states of such neutron-rich nuclei, that is, three-body bound states of
the n+n+C system when none of the pairs is bound or some of them only
weakly bound. By fitting to the general resonance shape described by Fano, we
extract resonance position, width, and the "Fano profile index". While Efimov
states have been discussed extensively in many areas of physics, there is only
one very recent experimental observation in trimers of cesium atoms. The
conjunction that we present of the Efimov and Fano phenomena may lead to
experimental realization in nuclei.Comment: 4 double-column pages, 3 figure
Bogolyubov-Hartree-Fock approach to studying the QCD ground state
The quark's behaviour while influenced by a strong stochastic gluon field is
analyzed. An approximate procedure for calculating the effective Hamiltonian is
developed and the corresponding ground state within the Hartree-Fock-Bogolyubov
approach is found. The comparative analysis of various Hamiltonian models is
given and transition to the chiral limit in the Keldysh model is discussed in
detail.Comment: 18 pages, 4 figures, new version of the manuscrip
Ultra-High Energy Cosmic Rays and Stable H-dibaryon
It is shown that an instanton induced interaction between quarks produces a
very deeply bound H-dibaryon with mass below 2M_N, M_H=1718 MeV. Therefore the
H-dibaryon is predicted to be a stable particle. The reaction of
photodisintegration of H-dibaryon to in during of its penetration
into cosmic microwave background will result in a new possible cut-off in the
cosmic-ray spectrum. This provides an explanation of ultra-high energy cosmic
ray events observed above the GZK cut-off as a result of the strong interaction
of high energy H-dibaryons from cosmic rays with nuclei in Earth's atmosphere.Comment: 5 pages, Late
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