817,914 research outputs found
Nonassociative Weyl star products
Deformation quantization is a formal deformation of the algebra of smooth
functions on some manifold. In the classical setting, the Poisson bracket
serves as an initial conditions, while the associativity allows to proceed to
higher orders. Some applications to string theory require deformation in the
direction of a quasi-Poisson bracket (that does not satisfy the Jacobi
identity). This initial condition is incompatible with associativity, it is
quite unclear which restrictions can be imposed on the deformation. We show
that for any quasi-Poisson bracket the deformation quantization exists and is
essentially unique if one requires (weak) hermiticity and the Weyl condition.
We also propose an iterative procedure that allows to compute the star product
up to any desired order.Comment: discussion extended, tipos corrected, published versio
Two-body relaxation of spin-polarized fermions in reduced dimensionalities near a p-wave Feshbach resonance
We study inelastic two-body relaxation in a spin-polarized ultracold Fermi
gas in the presence of a p-wave Feshbach resonance. It is shown that in reduced
dimensionalities, especially in the quasi-one-dimensional case, the enhancement
of the inelastic rate constant on approach to the resonance is strongly
suppressed compared to three dimensions. This may open promising paths for
obtaining novel many-body states.Comment: 14 pages, 12 figure
Non-Markovian dynamics with fermions
Employing the quadratic fermionic Hamiltonians for the collective and
internal subsystems with a linear coupling, we studied the role of fermionic
statistics on the dynamics of the collective motion. The transport coefficients
are discussed as well as the associated fluctuation-dissipation relation. Due
to different nature of the particles, the path to equilibrium is slightly
affected. However, in the weak coupling regime, the time-scale for approaching
equilibrium is found to be globally unchanged. The Pauli-blocking effect can
modify the usual picture in open quantum system. In some limits, contrary to
boson, this effect can strongly hinder the influence of the bath by blocking
the interacting channels.Comment: 13 pages, 6 figures. Submitted to PR
Neutron pair transfer in sub-barrier capture process
The sub-barrier capture reactions following the neutron pair transfer are
proposed to be used for the indirect study of neutron-neutron correlation in
the surface region of nucleus. The strong effect of the dineutron-like clusters
transfer stemming from the surface of magic and non-magic nuclei O,
Ca, Ni, Mo, Ru, Pd, and
Sn is demonstrated. The dominance of
two-neutron transfer channel at the vicinity of the Coulomb barrier is further
supported by time-dependent mean-field approaches.Comment: 17 pages, 7 figures, accepted in PR
Spaceability in Banach and quasi-Banach sequence spaces
Let be a Banach space. We prove that, for a large class of Banach or
quasi-Banach spaces of -valued sequences, the sets , where is any subset of , and
contain closed infinite-dimensional subspaces of (if
non-empty, of course). This result is applied in several particular cases and
it is also shown that the same technique can be used to improve a result on the
existence of spaces formed by norm-attaining linear operators.Comment: 9 page
On perturbations of the isometric semigroup of shifts on the semiaxis
We study perturbations of the semigroup of shifts
on with the property that belongs to a certain Schatten-von Neumann class \gS_p with .
We show that, for the unitary component in the Wold-Kolmogorov decomposition of
the cogenerator of the semigroup , {\it any singular}
spectral type may be achieved by \gS_1 perturbations. We provide an explicit
construction for a perturbation with a given spectral type based on the theory
of model spaces of the Hardy space . Also we show that we may obtain {\it
any} prescribed spectral type for the unitary component of the perturbed
semigroup by a perturbation from the class \gS_p with
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