1,598 research outputs found
A progressive diagonalization scheme for the Rabi Hamiltonian
A diagonalization scheme for the Rabi Hamiltonian, which describes a qubit
interacting with a single-mode radiation field via a dipole interaction, is
proposed. It is shown that the Rabi Hamiltonian can be solved almost exactly
using a progressive scheme that involves a finite set of one variable
polynomial equations. The scheme is especially efficient for lower part of the
spectrum. Some low-lying energy levels of the model with several sets of
parameters are calculated and compared to those provided by the recently
proposed generalized rotating-wave approximation and full matrix
diagonalization.Comment: 8pages, 1 figure, LaTeX. Accepted for publication in J. Phys. B: At.
Mol. Opt. Phy
Wigner Random Banded Matrices with Sparse Structure: Local Spectral Density of States
Random banded matrices with linearly increasing diagonal elements are
recently considered as an attractive model for complex nuclei and atoms. Apart
from early papers by Wigner \cite{Wig} there were no analytical studies on the
subject. In this letter we present analytical and numerical results for local
spectral density of states (LDOS) for more general case of matrices with a
sparsity inside the band. The crossover from the semicircle form of LDOS to
that given by the Breit-Wigner formula is studied in detail.Comment: Misprints are corrected and stylistic changes are made. To be
published in PR
RoboPol: Connection between optical polarization plane rotations and gamma-ray flares in blazars
We use results of our 3 year polarimetric monitoring program to investigate
the previously suggested connection between rotations of the polarization plane
in the optical emission of blazars and their gamma-ray flares in the GeV band.
The homogeneous set of 40 rotation events in 24 sources detected by {\em
RoboPol} is analysed together with the gamma-ray data provided by {\em
Fermi}-LAT. We confirm that polarization plane rotations are indeed related to
the closest gamma-ray flares in blazars and the time lags between these events
are consistent with zero. Amplitudes of the rotations are anticorrelated with
amplitudes of the gamma-ray flares. This is presumably caused by higher
relativistic boosting (higher Doppler factors) in blazars that exhibit smaller
amplitude polarization plane rotations. Moreover, the time scales of rotations
and flares are marginally correlated.Comment: 12 pages, 16 figures, accepted to MNRA
RoboPol: First season rotations of optical polarization plane in blazars
We present first results on polarization swings in optical emission of
blazars obtained by RoboPol, a monitoring program of an unbiased sample of
gamma-ray bright blazars specially designed for effective detection of such
events. A possible connection of polarization swing events with periods of high
activity in gamma rays is investigated using the dataset obtained during the
first season of operation. It was found that the brightest gamma-ray flares
tend to be located closer in time to rotation events, which may be an
indication of two separate mechanisms responsible for the rotations. Blazars
with detected rotations have significantly larger amplitude and faster
variations of polarization angle in optical than blazars without rotations. Our
simulations show that the full set of observed rotations is not a likely
outcome (probability ) of a random walk of the
polarization vector simulated by a multicell model. Furthermore, it is highly
unlikely () that none of our rotations is physically
connected with an increase in gamma-ray activity.Comment: 16 pages, 9 figure
ELPA: A parallel solver for the generalized eigenvalue problem
For symmetric (hermitian) (dense or banded) matrices the computation of eigenvalues and eigenvectors Ax = λBx is an important task, e.g. in electronic structure calculations. If a larger number of eigenvectors are needed, often direct solvers are applied. On parallel architectures the ELPA implementation has proven to be very efficient, also compared to other parallel solvers like EigenExa or MAGMA. The main improvement that allows better parallel efficiency in ELPA is the two-step transformation of dense to band to tridiagonal form. This was the achievement of the ELPA project. The continuation of this project has been targeting at additional improvements like allowing monitoring and autotuning of the ELPA code, optimizing the code for different architectures, developing curtailed algorithms for banded A and B, and applying the improved code to solve typical examples in electronic structure calculations. In this paper we will present the outcome of this project
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First measurement of neutrino oscillation parameters using neutrinos and antineutrinos by NOvA.
The NOvA experiment has seen a 4.4σ signal of ν[over ¯]_{e} appearance in a 2 GeV ν[over ¯]_{μ} beam at a distance of 810 km. Using 12.33×10^{20} protons on target delivered to the Fermilab NuMI neutrino beamline, the experiment recorded 27 ν[over ¯]_{μ}→ν[over ¯]_{e} candidates with a background of 10.3 and 102 ν[over ¯]_{μ}→ν[over ¯]_{μ} candidates. This new antineutrino data are combined with neutrino data to measure the parameters |Δm_{32}^{2}|=2.48_{-0.06}^{+0.11}×10^{-3}  eV^{2}/c^{4} and sin^{2}θ_{23} in the ranges from (0.53-0.60) and (0.45-0.48) in the normal neutrino mass hierarchy. The data exclude most values near δ_{CP}=π/2 for the inverted mass hierarchy by more than 3σ and favor the normal neutrino mass hierarchy by 1.9σ and θ_{23} values in the upper octant by 1.6σ
Defecting or not defecting: how to "read" human behavior during cooperative games by EEG measurements
Understanding the neural mechanisms responsible for human social interactions
is difficult, since the brain activities of two or more individuals have to be
examined simultaneously and correlated with the observed social patterns. We
introduce the concept of hyper-brain network, a connectivity pattern
representing at once the information flow among the cortical regions of a
single brain as well as the relations among the areas of two distinct brains.
Graph analysis of hyper-brain networks constructed from the EEG scanning of 26
couples of individuals playing the Iterated Prisoner's Dilemma reveals the
possibility to predict non-cooperative interactions during the decision-making
phase. The hyper-brain networks of two-defector couples have significantly less
inter-brain links and overall higher modularity - i.e. the tendency to form two
separate subgraphs - than couples playing cooperative or tit-for-tat
strategies. The decision to defect can be "read" in advance by evaluating the
changes of connectivity pattern in the hyper-brain network
RoboPol: the optical polarization of gamma-ray-loud and gamma-ray-quiet blazars
We present average R-band optopolarimetric data, as well as variability parameters, from the first and second RoboPol observing season. We investigate whether gamma-ray-loud and gamma-ray-quiet blazars exhibit systematic differences in their optical polarization properties. We find that gamma-ray-loud blazars have a systematically higher polarization fraction (0.092) than gamma-ray-quiet blazars (0.031), with the hypothesis of the two samples being drawn from the same distribution of polarization fractions being rejected at the 3σ level. We have not found any evidence that this discrepancy is related to differences in the redshift distribution, rest-frame R-band luminosity density, or the source classification. The median polarization fraction versus synchrotron-peak-frequency plot shows an envelope implying that high-synchrotron-peaked sources have a smaller range of median polarization fractions concentrated around lower values. Our gamma-ray-quiet sources show similar median polarization fractions although they are all low-synchrotron-peaked. We also find that the randomness of the polarization angle depends on the synchrotron peak frequency. For high-synchrotron-peaked sources, it tends to concentrate around preferred directions while for low-synchrotron-peaked sources, it is more variable and less likely to have a preferred direction. We propose a scenario which mediates efficient particle acceleration in shocks and increases the helical B-field component immediately downstream of the shock
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