9,429 research outputs found
Acquiring foreign firms far away might be hazardous to your share price: evidence from Germany
This paper examines shareholder wealth effects of cross-border acquisitions. In a sample of 155 large acquisitions by German corporations from 1985–2006 international transactions in total do not lead to significant announcement returns. Geography, however, makes a difference: Shareholders of acquiring firms gain 6.5% in cross-border transactions into countries that have a common border with Germany but lose 4.4% in other international transactions. We find proximity to be one of the most important success factors in cross-border mergers and acquisitions, even when we control for firm, deal and country characteristics
Spin-orbit coupling and anisotropic exchange in two-electron double quantum dots
The influence of the spin-orbit interactions on the energy spectrum of
two-electron laterally coupled quantum dots is investigated. The effective
Hamiltonian for a spin qubit pair proposed in F. Baruffa et al., Phys. Rev.
Lett. 104, 126401 (2010) is confronted with exact numerical results in single
and double quantum dots in zero and finite magnetic field. The anisotropic
exchange Hamiltonian is found quantitatively reliable in double dots in
general. There are two findings of particular practical importance: i) The
model stays valid even for maximal possible interdot coupling (a single dot),
due to the absence of a coupling to the nearest excited level, a fact following
from the dot symmetry. ii) In a weak coupling regime, the Heitler-London
approximation gives quantitatively correct anisotropic exchange parameters even
in a finite magnetic field, although this method is known to fail for the
isotropic exchange. The small discrepancy between the analytical model (which
employes the linear Dresselhaus and Bychkov-Rashba spin-orbit terms) and the
numerical data for GaAs quantum dots is found to be mostly due to the cubic
Dresselhaus term.Comment: 15 pages, 11 figure
Dynamics in the Ising field theory after a quantum quench
We study the real-time dynamics of the order parameter . Our main result is the development of
a method for treating divergences associated with working directly in the field
theory limit. We recover the scaling limit of the corresponding result by
Calabrese et al. [Phys. Rev. Lett. \textbf{106}, 227203 (2011)], which was
obtained for the lattice model. Our formalism generalizes to integrable quantum
quenches in other integrable models
Spectrum of Low-Lying Excitations in a Supersymmetric Extended Hubbard Model
We continue the study of the -supersymmetric extension of the Hubbard
model in one dimension. We determine the excitation spectrum at zero
temperature even in the sectors where the ground states are
-descendants of Bethe states. The excitations include spinons, holons,
electrons, localons (local electrons pairs, moving coherently through the
lattice) and their bound states. The spectra are found to be very different for
repulsive and attractive on-site interaction. We also study the thermodynamics
of the model.Comment: 37 pages, uuencoded compressed postscript fil
Applications of Massive Integrable Quantum Field Theories to Problems in Condensed Matter Physics
We review applications of the sine-Gordon model, the O(3) non-linear sigma
model, the U(1) Thirring model, and the O(N) Gross--Neveu model to quasi
one-dimensional quantum magnets, Mott insulators, and carbon nanotubes. We
focus upon the determination of dynamical response functions for these
problems. These quantities are computed by means of form factor expansions of
quantum correlation functions in integrable quantum field theories. This
approach is reviewed here in some detail.Comment: 150 pages, 35 figures, published in the I. Kogan Memorial Volume by
World Scientifi
Dynamical Magnetic Susceptibilities in Cu Benzoate
Recent experiments on the quasi 1-D antiferromagnet Cu Benzoate revealed a
magentic field induced gap coexisting with (ferro)magnetic order. A theory
explaining these findings has been proposed by Oshikawa and Affleck. In the
present work we discuss consequences of this theory for inelastic neutron
scattering experiments by calculating the dynamical magnetic susceptibilities
close to the antiferromagnetic wave vector by the formfactor method.Comment: 6 pages of revtex, 9 figures, extended comparison with experimen
Time evolution of local observables after quenching to an integrable model
We consider quantum quenches in integrable models. We argue that the
behaviour of local observables at late times after the quench is given by their
expectation values with respect to a single representative Hamiltonian
eigenstate. This can be viewed as a generalization of the eigenstate
thermalization hypothesis to quantum integrable models. We present a method for
constructing this representative state by means of a generalized Thermodynamic
Bethe Ansatz (GTBA). Going further, we introduce a framework for calculating
the time dependence of local observables as they evolve towards their
stationary values. As an explicit example we consider quantum quenches in the
transverse-field Ising chain and show that previously derived results are
recovered efficiently within our framework.Comment: 7 page
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