24,595 research outputs found
A comment on "Ab initio calculations of pressure-dependence of high-order elastic constants using finite deformations approach" by I. Mosyagin, A.V. Lugovskoy, O.M. Krasilnikov, Yu.Kh. Vekilov, S.I. Simak and I.A. Abrikosov
Recently, I. Mosyagin, A.V. Lugovskoy, O.M. Krasilnikov, Yu.Kh. Vekilov, S.I.
Simak and I.A. Abrikosov in the paper: "Ab initio calculations of
pressure-dependence of high-order elastic constants using finite deformations
approach"[Computer Physics Communications 220 (2017) 2030] presented a
description of a technique for ab initio calculations of the pressure
dependence of second- and third-order elastic constants. Unfortunately, the
work contains serious and fundamental flaws in the field of finite-deformation
solid mechanics.Comment: 3 pages, 0 figure
Quantum fluctuations of spacetime generate quantum entanglement between gravitationally polarizable subsystems
There should be quantum vacuum fluctuations of spacetime itself, if we accept
that the basic quantum principles we are already familiar with apply as well to
a quantum theory of gravity. In this paper, we study, in linearized quantum
gravity, the quantum entanglement generation at the neighborhood of the initial
time between two independent gravitationally polarizable two-level subsystems
caused by fluctuating quantum vacuum gravitational fields in the framework of
open quantum systems. A bath of fluctuating quantum vacuum gravitational fields
serves as an environment that provides indirect interactions between the two
gravitationally polarizable subsystems, which may lead to entanglement
generation. We find that the entanglement generation is crucially dependent on
the polarizations, i.e, they cannot get entangled in certain circumstances when
the polarizations of the subsystems are different while they always can when
the polarizations are the same. We also show that the presence of a boundary
may render parallel aligned subsystems entangled which are otherwise
unentangled in a free space. However, the presence of the boundary does not
help in terms of entanglement generation if the two subsystems are vertically
aligned.Comment: 18 pages, 4 figure
Full analytic expression of overlap reduction function for gravitational wave background with pulsar timing arrays
Pulsar timing array (PTA) is expected to detect gravitational wave background
(GWB) in the nanohertz band within the next decade. This provides an
opportunity to test the gravity theory and cosmology. A typical data analysis
method to detect GWB is cross-correlation analysis. The overlap reduction
function (ORF) plays an important role in the correlation data analysis of GWB.
The present approach to dealing with the intricate integration in ORF is to use
short-wave approximation to drop out the tricky terms. In this paper, we
provide the full analytic expression of the ORF for PTA without any
approximation for all possible polarizations allowed by modifications of
general relativity. Compared with the numerical simulation and short-wave
approximation, our results are more efficient and widely applicable. Especially
for the scalar-longitudinal mode where the short-wave approximation is not
available, our analytical expression is particularly significant
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