749 research outputs found
Magnetotransport in Sr3PbO antiperovskite with three-dimensional massive Dirac electrons
Novel topological phenomena are anticipated for three-dimensional (3D) Dirac
electrons. The magnetotransport properties of cubic
antiperovskite, theoretically proposed to be a 3D massive Dirac electron
system, are studied. The measurements of Shubnikov-de Haas oscillations and
Hall resistivity indicate the presence of a low density ( ) of holes with an extremely small cyclotron mass of
0.01-0.06. The magnetoresistance is linear in
magnetic field with the magnitude independent of temperature. These results
are fully consistent with the presence of 3D massive Dirac electrons in . The chemical flexibility of the antiperovskites and our findings
in the family member, , point to their potential as a model
system in which to explore exotic topological phases
Searching for nontensorial polarizations of stochastic gravitational waves with laser interferometers
Model-independent test of gravity with a network of ground-based gravitational-wave detectors
The observation of gravitational waves with a global network of
interferometric detectors such as advanced LIGO, advanced Virgo, and KAGRA will
make it possible to probe into the nature of space-time structure. Besides
Einstein's general theory of relativity, there are several theories of
gravitation that passed experimental tests so far. The gravitational-wave
observation provides a new experimental test of alternative theories of gravity
because a gravitational wave may have at most six independent modes of
polarization, of which properties and number of modes are dependent on theories
of gravity. This paper proposes a method to reconstruct the independent modes
of polarization in time-series data of an advanced detector network. Since the
method does not rely on any specific model, it gives model-independent test of
alternative theories of gravity
Searches for gravitational waves associated with pulsar glitches using a coherent network algorithm
Pulsar glitches are a potential source of gravitational waves for current and
future interferometric gravitational wave detectors. Some pulsar glitch events
were observed by radio and X-ray telescopes during the fifth LIGO science run.
It is expected that glitches from these same pulsars should also be seen in the
future. We carried out Monte Carlo simulations to estimate the sensitivity of
possible gravitational wave signals associated with a pulsar glitch using a
coherent network analysis method. We show the detection efficiency and evaluate
the reconstruction accuracy of gravitational waveforms using a matched filter
analysis on the estimated gravitational waveforms from the coherent analysis
algorithm.Comment: submitted to CQ
Inverse-perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) : a platform for control of Dirac and Weyl fermions
This work was partly supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI (Grant Nos. 24224010, 15K13523, JP15H05852, JP15K21717, and 17H01140), EPSRC (Grant No. EP/P024564/1), and the Alexander von Humboldt FoundationBulk Dirac electron systems have attracted strong interest for their unique magnetoelectric properties as well as their close relation to topological (crystalline) insulators. Recently, the focus has been shifting toward the role of magnetism in stabilizing Weyl fermions as well as chiral surface states in such materials. While a number of nonmagnetic systems are well known, experimental realizations of magnetic analogs are a key focus of current studies. Here, we report on the physical properties of a large family of inverse perovskites A3BO (A = Sr, Ca, Eu/B = Pb, Sn) in which we are able to not only stabilize 3D Dirac electrons at the Fermi energy but also chemically control their properties. In particular, it is possible to introduce a controllable Dirac gap, change the Fermi velocity, tune the anisotropy of the Dirac dispersion, and—crucially—introduce complex magnetism into the system. This family of compounds therefore opens up unique possibilities for the chemical control and systematic investigation of the fascinating properties of such topological semimetals.Publisher PDFPeer reviewe
Prospects for improving the sensitivity of KAGRA gravitational wave detector
KAGRA is a new gravitational wave detector which aims to begin joint observation with Advanced LIGO and Advanced Virgo from late 2019. Here, we present KAGRA's possible upgrade plans to improve the sensitivity in the decade ahead. Unlike other state-of-the-art detectors, KAGRA requires different investigations for the upgrade since it is the only detector which employs cryogenic cooling of the test mass mirrors. In this paper, investigations on the upgrade plans which can be realized by changing the input laser power, increasing the mirror mass, and injecting frequency dependent squeezed vacuum are presented. We show how each upgrade affects to the detector frequency bands and also discuss impacts on gravitational-wave science. We then propose an effective progression of upgrades based on technical feasibility and scientific scenarios
Report on the first round of the Mock LISA Data Challenges
The Mock LISA Data Challenges (MLDCs) have the dual purpose of fostering the
development of LISA data analysis tools and capabilities, and demonstrating the
technical readiness already achieved by the gravitational-wave community in
distilling a rich science payoff from the LISA data output. The first round of
MLDCs has just been completed: nine data sets containing simulated
gravitational wave signals produced either by galactic binaries or massive
black hole binaries embedded in simulated LISA instrumental noise were released
in June 2006 with deadline for submission of results at the beginning of
December 2006. Ten groups have participated in this first round of challenges.
Here we describe the challenges, summarise the results, and provide a first
critical assessment of the entries.Comment: Proceedings report from GWDAW 11. Added author, added reference,
clarified some text, removed typos. Results unchanged; Removed author, minor
edits, reflects submitted versio
Networks of gravitational wave detectors and three figures of merit
This paper develops a general framework for studying the effectiveness of
networks of interferometric gravitational wave detectors and then uses it to
show that enlarging the existing LIGO-VIRGO network with one or more planned or
proposed detectors in Japan (LCGT), Australia, and India brings major benefits,
including much larger detection rate increases than previously thought... I
show that there is a universal probability distribution function (pdf) for
detected SNR values, which implies that the most likely SNR value of the first
detected event will be 1.26 times the search threshold. For binary systems, I
also derive the universal pdf for detected values of the orbital inclination,
taking into account the Malmquist bias; this implies that the number of
gamma-ray bursts associated with detected binary coalescences should be 3.4
times larger than expected from just the beaming fraction of the gamma burst.
Using network antenna patterns, I propose three figures of merit that
characterize the relative performance of different networks... Adding {\em any}
new site to the planned LIGO-VIRGO network can dramatically increase, by
factors of 2 to 4, the detected event rate by allowing coherent data analysis
to reduce the spurious instrumental coincident background. Moving one of the
LIGO detectors to Australia additionally improves direction-finding by a factor
of 4 or more. Adding LCGT to the original LIGO-VIRGO network not only improves
direction-finding but will further increase the detection rate over the
extra-site gain by factors of almost 2, partly by improving the network duty
cycle... Enlarged advanced networks could look forward to detecting three to
four hundred neutron star binary coalescences per year.Comment: 38 pages, 7 figures, 2 tables. Accepted for publication in Classical
and Quantum Gravit
Determination of the angular momentum distribution of supernovae from gravitational wave observations
Significant progress has been made in the development of an international
network of gravitational wave detectors, such as TAMA300, LIGO, VIRGO, and
GEO600. For these detectors, one of the most promising sources of gravitational
waves are core collapse supernovae especially in our Galaxy. Recent simulations
of core collapse supernovae, rigorously carried out by various groups, show
that the features of the waveforms are determined by the rotational profiles of
the core, such as the rotation rate and the degree of the differential rotation
prior to core-collapse. Specifically, it has been predicted that the sign of
the second largest peak in the gravitational wave strain signal is negative if
the core rotates cylindrically with strong differential rotation. The sign of
the second peak could be a nice indicator that provides us with information
about the angular momentum distribution of the core, unseen without
gravitational wave signals. Here we present a data analysis procedure aiming at
the detection of the second peak using a coherent network analysis and estimate
the detection efficiency when a supernova is at the sky location of the
Galactic center. The simulations showed we were able to determine the sign of
the second peak under an idealized condition of a network of gravitational wave
detectors if a supernova occurs at the Galactic center.Comment: 9 pages, 11 figures, add references and some sentenses. To appear on
CQ
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