1,164 research outputs found
Asymptotic Behavior of the Wave Packet Propagation through a Barrier: the Green's Function Approach Revisited
To model the decay of a quasibound state we use the modified two-potential
approach introduced by Gurvitz and Kalbermann. This method has proved itself
useful in the past for calculating the decay width and the energy shift of an
isolated quasistationary state. We follow the same approach in order to
propagate the wave-packet in time with the ultimate goal of extracting the
momentum-distribution of emitted particles. The advantage of the method is that
it provides the time-dependent wave function in a simple semi-analytic form. We
intend to apply this method to the modeling of metastable states for which no
direct integration of the time-dependent Schroedinger equation is available
today.Comment: 7 page
An Estimate Of the Branching Fraction Of Tau -\u3e Pi Eta \u27Nu(Tau)
We calculate the expected branching fraction of the second-class-current decay tau -\u3e pi eta \u27nu(tau), motivated by a recent experimental upper-limit determination of this quantity. The largest contribution to the branching fraction is due to the intermediate a(0)(980) scalar meson, assuming it is a (u) over bard state. Smaller contributions arise from a(0)(1450), rho(770), and rho(1450). Our calculated values are substantially below the experimental upper limit, and are smaller still if the a(0)(980) is a four-quark state, as often suggested. Thus, a precise measurement or tight upper limit has the potential to determine the nature of the a(0)(980), as well as provide information about new scalar interactions
Graphs of Transportation Polytopes
This paper discusses properties of the graphs of 2-way and 3-way
transportation polytopes, in particular, their possible numbers of vertices and
their diameters. Our main results include a quadratic bound on the diameter of
axial 3-way transportation polytopes and a catalogue of non-degenerate
transportation polytopes of small sizes. The catalogue disproves five
conjectures about these polyhedra stated in the monograph by Yemelichev et al.
(1984). It also allowed us to discover some new results. For example, we prove
that the number of vertices of an transportation polytope is a
multiple of the greatest common divisor of and .Comment: 29 pages, 7 figures. Final version. Improvements to the exposition of
several lemmas and the upper bound in Theorem 1.1 is improved by a factor of
tw
Closed formula for the relative entropy of entanglement in all dimensions
The relative entropy of entanglement is defined in terms of the relative
entropy between an entangled state and its closest separable state (CSS). Given
a multipartite-state on the boundary of the set of separable states, we find a
closed formula for all the entangled state for which this state is a CSS. Quite
amazing, our formula holds for multipartite states in all dimensions. In
addition we show that if an entangled state is full rank, then its CSS is
unique. For the bipartite case of two qubits our formula reduce to the one
given in Phys. Rev. A 78, 032310 (2008).Comment: 8 pages, 1 figure, significantly revised; theorem 1 is now providing
necessary and sufficient conditions to determine if a state is CS
Opportunistic Information Dissemination in Mobile Ad-hoc Networks: adaptiveness vs. obliviousness and randomization vs. determinism
In this paper the problem of information dissemination in Mobile Ad-hoc
Networks (MANET) is studied. The problem is to disseminate a piece of
information, initially held by a distinguished source node, to all nodes in a
set defined by some predicate. We use a model of MANETs that is well suited for
dynamic networks and opportunistic communication. In this model nodes are
placed in a plane, in which they can move with bounded speed, and communication
between nodes occurs over a collision-prone single channel. In this setup
informed and uninformed nodes can be disconnected for some time (bounded by a
parameter alpha), but eventually some uninformed node must become neighbor of
an informed node and remain so for some time (bounded by a parameter beta). In
addition, nodes can start at different times, and they can crash and recover.
Under the above framework, we show negative and positive results for different
types of randomized protocols, and we put those results in perspective with
respect to previous deterministic results
Production of the X(3872) in B Meson Decay by the Coalescence of Charm Mesons
If the recently-discovered charmonium state X(3872) is a loosely-bound S-wave
molecule of the charm mesons \bar D^0 D^{*0} or \bar D^{*0} D^0, it can be
produced in B meson decay by the coalescence of charm mesons. If this
coalescence mechanism dominates, the ratio of the differential rate for B^+ \to
\bar D^0 D^{*0} K^+ near the \bar D^0 D^{*0} threshold and the rate for B^+ \to
X K^+ is a function of the \bar D^0 D^{*0} invariant mass and hadron masses
only. The identification of the X(3872) as a \bar D^0 D^{*0}/\bar D^{*0} D^0
molecule can be confirmed by observing an enhancement in the \bar D^0 D^{*0}
invariant mass distribution near the threshold. An estimate of the branching
fraction for B^+ \to X K^+ is consistent with observations if X has quantum
numbers J^{PC} = 1^{++} and if J/\psi \pi^+ \pi^- is one of its major decay
modes.Comment: 4 pages, 3 figures, revtex
Robust Detection of Ocular Dominance Columns in Humans using High Field HSE BOLD fMRI
The ability to reliably and reproducibility map high resolution functional architecture using fMRI techniques has been a point of debate in animal as well as human studies. Several animal and human studies have successfully mapped high resolution functional organizations, however, the robustness of the phenomenon (i.e. reproducibility and demonstration in multiple subjects), which would certainly improve the credibility of the data, has been a subject of debate. Here we demonstrate the spatial specificity of Hahn spin echo BOLD by robust mapping of ocular dominance columns in humans at the high magnetic field of 7 T
Some Aspects of New CDM Models and CDM Detection Methods
We briefly review some recent Cold Dark Matter (CDM) models. Our main focus
are charge symmetric models of WIMPs which are not the standard SUSY LSP's
(Lightest Supersymmetric Partners). We indicate which experiments are most
sensitive to certain aspects of the models. In particular we discuss the
manifestations of the new models in neutrino telescopes and other set-ups. We
also discuss some direct detection experiments and comment on measuring the
direction of recoil ions--which is correlated with the direction of the
incoming WIMP. This could yield daily variations providing along with the
annual modulation signatures for CDM.Comment: 14 page
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