9,052 research outputs found
On the Birkhoff factorization problem for the Heisenberg magnet and nonlinear Schroedinger equations
A geometrical description of the Heisenberg magnet (HM) equation with
classical spins is given in terms of flows on the quotient space where
is an infinite dimensional Lie group and is a subgroup of . It is
shown that the HM flows are induced by an action of on ,
and that the HM equation can be integrated by solving a Birkhoff factorization
problem for . For the HM flows which are Laurent polynomials in the spectral
variable we derive an algebraic transformation between solutions of the
nonlinear Schroedinger (NLS) and Heisenberg magnet equations. The Birkhoff
factorization for is treated in terms of the geometry of the Segal-Wilson
Grassmannian . The solution of the problem is given in terms of a pair
of Baker functions for special subspaces of . The Baker functions are
constructed explicitly for subspaces which yield multisoliton solutions of NLS
and HM equations.Comment: To appear in Journal of Mathematical Physic
Lattice QCD and QCD Sum Rule determination of the decay constants of eta_c, J/psi and hc states
We compute the decay constants of the lowest ccbar-states with quantum
numbers J(PC)=0(-+) [eta_c], 1(--) [J/psi], and 1(+-) [hc] by using lattice QCD
and QCD sum rules. We consider the coupling of J/psi to both the vector and
tensor currents. Lattice QCD results are obtained from the unquenched (Nf=2)
simulations using twisted mass QCD at four lattice spacings, allowing us to
take the continuum limit. On the QCD sum rule side we use the moment sum rules.
The results are then used to discuss the rate of eta_c --> gamma gamma decay,
and to comment on the factorization in B --> X K decays, with X being either
eta_c or J/psi.Comment: 25 pages (published version
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