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Hidden unity in the quantum description of matter
We introduce an algebraic framework for interacting quantum systems that
enables studying complex phenomena, characterized by the coexistence and
competition of various broken symmetry states of matter. The approach unveils
the hidden unity behind seemingly unrelated physical phenomena, thus
establishing exact connections between them. This leads to the fundamental
concept of {\it universality} of physical phenomena, a general concept not
restricted to the domain of critical behavior. Key to our framework is the
concept of {\it languages} and the construction of {\it dictionaries} relating
them.Comment: 10 pages 2 psfigures. Appeared in Recent Progress in Many-Body
Theorie
Heating and thermal squeezing in parametrically-driven oscillators with added noise
In this paper we report a theoretical model based on Green functions, Floquet
theory and averaging techniques up to second order that describes the dynamics
of parametrically-driven oscillators with added thermal noise. Quantitative
estimates for heating and quadrature thermal noise squeezing near and below the
transition line of the first parametric instability zone of the oscillator are
given. Furthermore, we give an intuitive explanation as to why heating and
thermal squeezing occur. For small amplitudes of the parametric pump the
Floquet multipliers are complex conjugate of each other with a constant
magnitude. As the pump amplitude is increased past a threshold value in the
stable zone near the first parametric instability, the two Floquet multipliers
become real and have different magnitudes. This creates two different effective
dissipation rates (one smaller and the other larger than the real dissipation
rate) along the stable manifolds of the first-return Poincare map. We also show
that the statistical average of the input power due to thermal noise is
constant and independent of the pump amplitude and frequency. The combination
of these effects cause most of heating and thermal squeezing. Very good
agreement between analytical and numerical estimates of the thermal
fluctuations is achieved.Comment: Submitted to Phys. Rev. E, 29 pages, 12 figures. arXiv admin note:
substantial text overlap with arXiv:1108.484
Renormalization of chiral nuclear forces with multiple subtractions in peripheral channels
We analyse the renormalization of the of two-nucleon interaction with
multiple subtractions in peripheral waves considering two chiral forces at
N3LO. Phase shifts at low energies are then computed with several subtraction
points below \mu = 10 / fm. We show that for most peripheral waves the phase
shifts have nearly no dependence on the renormalization scale. In two cases the
phase shifts converge slowly as the renormalization scale approaches \mu = 1 /
fm and in one case the phase shifts presented oscillations with respect to the
subtraction point \mu.Comment: 21 pages, 12 figures, to appear in the special issue "Few-Body
Systems in High Energy Physics" (AHEP
Parallel structurally-symmetric sparse matrix-vector products on multi-core processors
We consider the problem of developing an efficient multi-threaded
implementation of the matrix-vector multiplication algorithm for sparse
matrices with structural symmetry. Matrices are stored using the compressed
sparse row-column format (CSRC), designed for profiting from the symmetric
non-zero pattern observed in global finite element matrices. Unlike classical
compressed storage formats, performing the sparse matrix-vector product using
the CSRC requires thread-safe access to the destination vector. To avoid race
conditions, we have implemented two partitioning strategies. In the first one,
each thread allocates an array for storing its contributions, which are later
combined in an accumulation step. We analyze how to perform this accumulation
in four different ways. The second strategy employs a coloring algorithm for
grouping rows that can be concurrently processed by threads. Our results
indicate that, although incurring an increase in the working set size, the
former approach leads to the best performance improvements for most matrices.Comment: 17 pages, 17 figures, reviewed related work section, fixed typo
Spectral function and quasiparticle weight in the generalized t-J model
We extend to the spectral function an approach which allowed us to calculate
the quasiparticle weight for destruction of a real electron Z_c sigma (k) (in
contrast to that of creation of a spinless holon Z_h(k) in a generalized
model, using the self-consistent Born approximation (SCBA). We compare our
results with those obtained using the alternative approach of Sushkov et al.,
which also uses the SCBA. The results for Z_c sigma (k) are also compared with
results obtained using the string picture and with exact diagonalizations of a
32-site square cluster. While on a qualitative level, all results look similar,
our SCBA approach seems to compare better with the ED one. The effect of
hopping beyond nearest neighbors, and that of the three-site term are
discussed.Comment: 7 pages, 6 figure
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