9,329 research outputs found
Isospin-dependent pion in-medium effects on charged pion ratio in heavy ion collisions
Using results from the chiral perturbation theory for the s-wave interaction
and the delta-resonance model for the p-wave interaction of pions with
nucleons, we have evaluated the spectral functions of pions in asymmetric
nuclear matter with unequal proton and neutron densities. We find that in hot
dense neutron-rich matter the strength of the spectral function of positively
charged pion at low energies is somewhat larger than that of negatively charged
pion. In a thermal model, this isospin-dependent effect slightly reduces the
ratio of negatively charged to positively charged pions that are produced in
heavy ion collisions induced by radioactive beams. Relevance of our results to
the determination of the nuclear symmetry energy from measured ratio of
negatively to positively charged pions produced in heavy ion collisions is
discussed.Comment: 7 pages, 4 figures, pion-nucleon s-wave interaction include
Entanglement distribution over the subsystems and its invariance
We study the entanglement dynamics of two qubits, each of which is embedded
into its local amplitude-damping reservoir, and the entanglement distribution
among all the bipartite subsystems including qubit-qubit, qubit-reservoir, and
reservoir-reservoir. It is found that the entanglement can be stably
distributed among all components, which is much different to the result
obtained under the Born-Markovian approximation by C. E. L\'{o}pez {\it et al.}
[Phys. Rev. Lett. \textbf{101}, 080503 (2008)], and particularly it also
satisfies an identity. Our unified treatment includes the previous results as
special cases. The result may give help to understand the physical nature of
entanglement under decoherence.Comment: 6 pages, 5 figure
Fractality of profit landscapes and validation of time series models for stock prices
We apply a simple trading strategy for various time series of real and
artificial stock prices to understand the origin of fractality observed in the
resulting profit landscapes. The strategy contains only two parameters and
, and the sell (buy) decision is made when the log return is larger
(smaller) than (). We discretize the unit square into the square grid and the profit is
calculated at the center of each cell. We confirm the previous finding that
local maxima in profit landscapes are scattered in a fractal-like fashion: The
number M of local maxima follows the power-law form , but the
scaling exponent is found to differ for different time series. From
comparisons of real and artificial stock prices, we find that the fat-tailed
return distribution is closely related to the exponent observed
for real stock markets. We suggest that the fractality of profit landscape
characterized by can be a useful measure to validate time
series model for stock prices.Comment: 10pages, 6figure
Generating Many Majorana Modes via Periodic Driving: A Superconductor Model
Realizing Majorana modes (MMs) in condensed-matter systems is of vast
experimental and theoretical interests, and some signatures of MMs have been
measured already. To facilitate future experimental observations and to explore
further applications of MMs, generating many MMs at ease in an experimentally
accessible manner has become one important issue. This task is achieved here in
a one-dimensional -wave superconductor system with the nearest- and
next-nearest-neighbor interactions. In particular, a periodic modulation of
some system parameters can induce an effective long-range interaction (as
suggested by the Baker-Campbell-Hausdorff formula) and may recover
time-reversal symmetry already broken in undriven cases. By exploiting these
two independent mechanisms at once we have established a general method in
generating many Floquet MMs via periodic driving.Comment: 5 pages, 3 figures. To appear in Phys. Rev. B as a Rapid
Communicatio
Medium effects on charged pion ratio in heavy ion collisions
We have recently studied in the delta-resonance--nucleon-hole model the
dependence of the pion spectral function in hot dense asymmetric nuclear matter
on the charge of the pion due to the pion p-wave interaction in nuclear medium.
In a thermal model, this isospin-dependent effect enhances the ratio of
negatively charged to positively charged pions in neutron-rich nuclear matter,
and the effect is comparable to that due to the uncertainties in the
theoretically predicted stiffness of nuclear symmetry energy at high densities.
This effect is, however, reversed if we also take into account the s-wave
interaction of the pion in nuclear medium as given by chiral perturbation
theory, resulting instead in a slightly reduced ratio of negatively charged to
positively charged pions. Relevance of our results to the determination of the
nuclear symmetry energy from the ratio of negatively to positively charged
pions produced in heavy ion collisions is discussed.Comment: 11 pages, 4 figures, contribution to The International Workshop on
Nuclear Dynamics in Heavy-Ion Reactions and the Symmetry Energy (IWND2009),
Shanghai, China, 22-25 August, 200
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