71,379 research outputs found

### On zero-divisors in group rings of groups with torsion

Nontrivial pairs of zero-divisors in group rings are introduced and
discussed. A problem on the existence of nontrivial pairs of zero-divisors in
group rings of free Burnside groups of odd exponent $n \gg 1$ is solved in the
affirmative. Nontrivial pairs of zero-divisors are also found in group rings of
free products of groups with torsion.Comment: 8 pages, to appear in Canadian Math. Bul

### On the Form Factors of the $D_{s}^{+}\to \phi\mu^{+}\nu_{\mu} decay

We apply the infinite mass effective theory, when a heavy quark mass tends to
infinity, and Chiral perturbation theory at the quark level, based on the
extended Nambu -- Jona -- Lasinio model with linear realization of chiral
$U(3)\times U(3)$ symmetry, to calculate the form factors of the
$D^{\,+}_{\,s}\to\phi~\mu^+~\nu_{\,\mu}$ decay up to the first order in current
$s$ -- quark mass. The theoretical results are compared with experimental data
and found to be in good agreement.Comment: 7pages, latex, no figure

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### Using inventory to mitigate the Ripple effect

A single disruption at a single location within a supply chain may effect many other locations of a the supply chain through the Ripple effect (Ivanov et al., 2014). In this article we focus on the role of inventory to mitigate the Ripple effect. Our main finding states that operational decisions (such as safety inventory level or service level) are highly interrelated with decisions that mitigate the Ripple effect (such as a high Resilience of the supply chain). Specifically, we find: 1) An increase in demand volatility may lead a firm to invest more in operational safety stock as well as in dedicated Risk Mitigation Inventory. 2) A high service level and high resilience of a supply chain can be conflicting objectives

### Gauging N=4 supersymmetric mechanics II: (1,4,3) models from the (4,4,0) ones

Exploiting the gauging procedure developed by us in hep-th/0605211, we study
the relationships between the models of N=4 mechanics based on the off-shell
multiplets (4,4,0) and (1,4,3). We make use of the off-shell N=4, d=1 harmonic
superspace approach as most adequate for treating this circle of problems. We
show that the most general sigma-model type superfield action of the multiplet
(1,4,3) can be obtained in a few non-equivalent ways from the (4,4,0) actions
invariant under certain three-parameter symmetries, through gauging the latter
by the appropriate non-propagating gauge multiplets. We discuss in detail the
gauging of both the Pauli-Gursey SU(2) symmetry and the abelian three-generator
shift symmetry. We reveal the (4,4,0) origin of the known mechanisms of
generating potential terms for the multiplet (1,4,3), as well as of its
superconformal properties. A new description of this multiplet in terms of
unconstrained harmonic analytic gauge superfield is proposed. It suggests, in
particular, a novel mechanism of generating the (1,4,3) potential terms via
coupling to the fermionic off-shell N=4 multiplet (0,4,4).Comment: 27 page

### Finite-Difference Calculations for Atoms and Diatomic Molecules in Strong Magnetic and Static Electric Fields

Fully numerical mesh solutions of 2D quantum equations of Schroedinger and
Hartree-Fock type allow us to work with wavefunctions which possess a very
flexible geometry. This flexibility is especially important for calculations of
atoms and molecules in strong external fields where neither the external field
nor the internal interactions can be considered as a perturbation. The
applications of the present approach include calculations of atoms and diatomic
molecules in strong static electric and magnetic fields. For the latter we have
carried out Hartree-Fock calculations for He, Li, C and several other atoms.
This yields in particular the first comprehensive investigation of the ground
state configurations of the Li and C atoms in the whole range of magnetic
fields (0<B<10000 a.u.) and a study of the ground state electronic
configurations of all the atoms with 1<Z<11 and their ions A^+ in the
high-field fully spin-polarised regime. The results in a case of a strong
electric field relate to single-electron systems including the correct solution
of the Schroedinger equation for the H_2^+ ion (energies and decay rates) and
the hydrogen atom in strong parallel electric and magnetic fields.Comment: 20 pages, 7 figure

### Strongly interacting $\sigma$-electrons and MgB$_2$ superconductivity

MgB$(p^{n_{\sigma}}p^{n_{\pi}})_{2}$ is classified as a system with strongly
interacting $\sigma$-electrons and non-correlated $\pi$-electrons of boron
ions. The kinematic and Coulomb interaction V between the orbitally degenerated
$\sigma$-electrons provide the superconducting state with an anisotropic gap of
s*-wave symmetry. The critical temperature $T_c$ has a non-monotonic dependence
on the distance r between the centers of gravity of $\sigma$- and $\pi$-bands.
MgB$_2$ corresponds to r=0.085 eV and V=0.45 eV in our model with flat bands.
The derived superconducting density of electronic states is in good agreement
with available experimental and theoretical data. The possibilities for
increasing $T_c$ are discussed.Comment: 8 pages, 4 figure

### On kaonic deuterium. Quantum field theoretic and relativistic covariant approach

We study kaonic deuterium, the bound K^-d state A_(K d). Within a quantum
field theoretic and relativistic covariant approach we derive the energy level
displacement of the ground state of kaonic deuterium in terms of the amplitude
of K^-d scattering for arbitrary relative momenta. Near threshold our formula
reduces to the well-known DGBT formula. The S-wave amplitude of K^-d scattering
near threshold is defined by the resonances Lambda(1405), Sigma(1750) and a
smooth elastic background, and the inelastic channels K^- d -> NY and K^- d ->
NY pion, with Y = Sigma^(+/-), Sigma^0 and Lambda^0, where the final-state
interactions play an important role. The Ericson-Weise formula for the S-wave
scattering length of K^-d scattering is derived. The total width of the energy
level of the ground state of kaonic deuterium is estimated using the
theoretical predictions of the partial widths of the two-body decays A_(Kd) ->
NY and experimental data on the rates of the NY-pair production in the
reactions K^-d -> NY. We obtain Gamma_{1s} = (630 +/-100) eV. For the shift of
the energy level of the ground state of kaonic deuterium we predict
epsilon_(1s) = (353 +/-60)eV.Comment: 73 pages,10 figures, Latex, We have slightly corrected the
contribution of the double scattering. The change of the S-wave scattering
length of K^-d scattering does not go beyond the theoretical uncertainty,
which is about 18

### Universal Superfield Action for $N=8 \to N=4$ Partial Breaking of Global Supersymmetry in D=1

We explicitly construct N=4 worldline supersymmetric minimal off-shell
actions for five options of 1/2 partial spontaneous breaking of $N=8, d=1$
Poincar\'e supersymmetry. We demonstrate that the action for the N=4 Goldstone
supermultiplet with four fermions and four auxiliary components is a universal
one. The remaining actions for the Goldstone supermultiplets with physical
bosons are obtained from the universal one by off-shell duality
transformations.Comment: 9 pages, LaTeX file, PACS numbers: 11.30.Pb, 03.65.-

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