365 research outputs found
Controlled delocalization of electronic states in a multi-strand quasiperiodic lattice
Finite strips, composed of a periodic stacking of infinite quasiperiodic
Fibonacci chains, have been investigated in terms of their electronic
properties. The system is described by a tight binding Hamiltonian. The
eigenvalue spectrum of such a multi-strand quasiperiodic network is found to be
sensitive on the mutual values of the intra-strand and inter-strand tunnel
hoppings, whose distribution displays a unique three-subband self-similar
pattern in a parameter subspace. In addition, it is observed that special
numerical correlations between the nearest and the next-nearest neighbor
hopping integrals can render a substantial part of the energy spectrum
absolutely continuous. Extended, Bloch like functions populate the above
continuous zones, signalling a complete delocalization of single particle
states even in such a non-translationally invariant system, and more
importantly, a phenomenon that can be engineered by tuning the relative
strengths of the hopping parameters. A commutation relation between the
potential and the hopping matrices enables us to work out the precise
correlation which helps to engineer the extended eigenfunctions and determine
the band positions at will.Comment: 8 pages, 6 figure
Implementation and characterization of BinaryWeave: A new search pipeline for continuous gravitational waves from Scorpius X-1
Scorpius X-1 (Sco X-1) has long been considered one of the most promising
targets for detecting continuous gravitational waves with ground-based
detectors. Observational searches for Sco X-1 have achieved substantial
sensitivity improvements in recent years, to the point of starting to rule out
emission at the torque-balance limit in the low-frequency range \sim 40--180
Hz. In order to further enhance the detection probability, however, there is
still much ground to cover for the full range of plausible signal frequencies
\sim 20--1500 Hz, as well as a wider range of uncertainties in binary orbital
parameters. Motivated by this challenge, we have developed BinaryWeave, a new
search pipeline for continuous waves from a neutron star in a known binary
system such as Sco X-1. This pipeline employs a semi-coherent StackSlide
F-statistic using efficient lattice-based metric template banks, which can
cover wide ranges in frequency and unknown orbital parameters. We present a
detailed timing model and extensive injection-and-recovery simulations that
illustrate that the pipeline can achieve high detection sensitivities over a
significant portion of the parameter space when assuming sufficiently large
(but realistic) computing budgets. Our studies further underline the need for
stricter constraints on the Sco X-1 orbital parameters from electromagnetic
observations, in order to be able to push sensitivity below the torque-balance
limit over the entire range of possible source parameters.Comment: 19 pages, 7 figures, 3 table
Flux driven and geometry controlled spin filtering for arbitrary spins in aperiodic quantum networks
We demonstrate that an aperiodic array of certain quantum networks comprising magnetic and non-magnetic atoms can act as perfect spin filters for particles with arbitrary spin state. This can be achieved by introducing minimal quasi-one dimensionality in the basic structural units building up the array, along with an appropriate tuning of the potential of the non-magnetic atoms, the tunnel hopping integral between the non-magnetic atoms and the backbone, and, in some cases, by tuning an external magnetic field. This latter result opens up the interesting possibility of designing a flux controlled spin demultiplexer using quantum networks. The proposed networks have close resemblance with a family of recently developed photonic lattices, and the scheme for spin filtering can thus be linked, in principle, to a possibility of suppressing any one of the two states of polarization of a single photon, almost at will. We use transfer matrices and a real space renormalization group scheme to unravel the conditions under which any aperiodic arrangement of such topologically different structures will filter out any given spin projection. Our results are analytically exact, and corroborated by extensive numerical calculations of the spin polarized transmission and the density of states of such systems
Constraining the neutron-matter equation of state with gravitational waves
We show how observations of gravitational waves from binary neutron star
(BNS) mergers over the next few years can be combined with insights from
nuclear physics to obtain useful constraints on the equation of state (EoS) of
dense matter, in particular, constraining the neutron-matter EoS to within 20%
between one and two times the nuclear saturation density $n_0\approx 0.16\
{\text{fm}^{-3}}$. Using Fisher information methods, we combine observational
constraints from simulated BNS merger events drawn from various population
models with independent measurements of the neutron star radii expected from
x-ray astronomy (the Neutron Star Interior Composition Explorer (NICER)
observations in particular) to directly constrain nuclear physics parameters.
To parameterize the nuclear EoS, we use a different approach, expanding from
pure nuclear matter rather than from symmetric nuclear matter to make use of
recent quantum Monte Carlo (QMC) calculations. This method eschews the need to
invoke the so-called parabolic approximation to extrapolate from symmetric
nuclear matter, allowing us to directly constrain the neutron-matter EoS. Using
a principal component analysis, we identify the combination of parameters most
tightly constrained by observational data. We discuss sensitivity to various
effects such as different component masses through population-model
sensitivity, phase transitions in the core EoS, and large deviations from the
central parameter values.Comment: 13 pages, 9 figures + supplement 11 page
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