42,976 research outputs found
XMMPZCAT: A catalogue of photometric redshifts for X-ray sources
The third version of the XMM-Newton serendipitous catalogue (3XMM),
containing almost half million sources, is now the largest X-ray catalogue.
However, its full scientific potential remains untapped due to the lack of
distance information (i.e. redshifts) for the majority of its sources. Here we
present XMMPZCAT, a catalogue of photometric redshifts (photo-z) for 3XMM
sources. We searched for optical counterparts of 3XMM-DR6 sources outside the
Galactic plane in the SDSS and Pan-STARRS surveys, with the addition of near-
(NIR) and mid-infrared (MIR) data whenever possible (2MASS, UKIDSS, VISTA-VHS,
and AllWISE). We used this photometry data set in combination with a training
sample of 5157 X-ray selected sources and the MLZ-TPZ package, a supervised
machine learning algorithm based on decision trees and random forests for the
calculation of photo-z. We have estimated photo-z for 100,178 X-ray sources,
about 50% of the total number of 3XMM sources (205,380) in the XMM-Newton
fields selected to build this catalogue (4208 out of 9159). The accuracy of our
results highly depends on the available photometric data, with a rate of
outliers ranging from 4% for sources with data in the optical+NIR+MIR, up to
40% for sources with only optical data. We also addressed the reliability
level of our results by studying the shape of the photo-z probability density
distributions.Comment: 16 pages, 14 figures, A&A accepte
Multiplicative Lidskii's inequalities and optimal perturbations of frames
In this paper we study two design problems in frame theory: on the one hand,
given a fixed finite frame \cF for \hil\cong\C^d we compute those dual
frames \cG of \cF that are optimal perturbations of the canonical dual
frame for \cF under certain restrictions on the norms of the elements of
\cG. On the other hand, for a fixed finite frame \cF=\{f_j\}_{j\in\In} for
\hil we compute those invertible operators such that is a
perturbation of the identity and such that the frame V\cdot
\cF=\{V\,f_j\}_{j\in\In} - which is equivalent to \cF - is optimal among
such perturbations of \cF. In both cases, optimality is measured with respect
to submajorization of the eigenvalues of the frame operators. Hence, our
optimal designs are minimizers of a family of convex potentials that include
the frame potential and the mean squared error. The key tool for these results
is a multiplicative analogue of Lidskii's inequality in terms of
log-majorization and a characterization of the case of equality.Comment: 22 page
Anyonic statistics and large horizon diffeomorphisms for Loop Quantum Gravity Black Holes
We investigate the role played by large diffeomorphisms of quantum Isolated
Horizons for the statistics of LQG Black Holes by means of their relation to
the braid group. To this aim the symmetries of Chern-Simons theory are
recapitulated with particular regard to the aforementioned type of
diffeomorphisms. For the punctured spherical horizon, these are elements of the
mapping class group of , which is almost isomorphic to a corresponding
braid group on this particular manifold. The mutual exchange of quantum
entities in two dimensions is achieved by the braid group, rendering the
statistics anyonic. With this we argue that the quantum Isolated Horizon model
of LQG based on -Chern-Simons theory explicitly exhibits non-abelian
anyonic statistics. In this way a connection to the theory behind the
fractional quantum Hall effect and that of topological quantum computation is
established, where non-abelian anyons play a significant role.Comment: 20 pages, 8 figures, closest to published versio
Optimal dual frames and frame completions for majorization
In this paper we consider two problems in frame theory. On the one hand,
given a set of vectors we describe the spectral and geometrical
structure of optimal completions of by a finite family of vectors
with prescribed norms, where optimality is measured with respect to
majorization. In particular, these optimal completions are the minimizers of a
family of convex functionals that include the mean square error and the
Bendetto-Fickus' frame potential. On the other hand, given a fixed frame
we describe explicitly the spectral and geometrical structure of
optimal frames that are in duality with and such that
the Frobenius norms of their analysis operators is bounded from below by a
fixed constant. In this case, optimality is measured with respect to
submajorization of the frames operators. Our approach relies on the description
of the spectral and geometrical structure of matrices that minimize
submajorization on sets that are naturally associated with the problems above.Comment: 29 pages, with modifications related with the exposition of the
materia
Feynman-Hellmann theorem for resonances and the quest for QCD exotica
The generalization of the Feynman-Hellmann theorem for resonance states in
quantum field theory is derived. On the basis of this theorem, a criterion is
proposed to study the possible exotic nature of certain hadronic states
emerging in QCD. It is shown that this proposal is supported by explicit
calculations in Chiral Perturbation Theory and by large- arguments.
Analyzing recent lattice data on the quark mass dependence in the pseudoscalar,
vector meson, baryon octet and baryon decuplet sectors, we conclude that, as
expected, these are predominately quark-model states, albeit the corrections
are non-negligible.Comment: 26 pages, 2 figure
Real-time reverse transcription polymerase chain reaction development for rapid detection of Tomato brown rugose fruit virus and comparison with other techniques
Background: Tomato brown rugose fruit virus (ToBRFV) is a highly infectious tobamovirus that causes severe disease in tomato (Solanum lycopersicum L.) crops. In Italy, the first ToBRFV outbreak occurred in 2018 in several provinces of the Sicily region. ToBRFV outbreak represents a serious threat for tomato crops in Italy and the Mediterranean Basin. Methods: Molecular and biological characterisation of the Sicilian ToBRFV ToB-SIC01/19 isolate was performed, and a sensitive and specific Real-time RT-PCR TaqMan minor groove binder probe method was developed to detect ToBRFV in infected plants and seeds. Moreover, four different sample preparation procedures (immunocapture, total RNA extraction, direct crude extract and leaf-disk crude extract) were evaluated. Results: The Sicilian isolate ToB-SIC01/19 (6,391 nt) showed a strong sequence identity with the isolates TBRFV-P12-3H and TBRFV-P12-3G from Germany, Tom1-Jo from Jordan and TBRFV-IL from Israel. The ToB-SIC01/19 isolate was successfully transmitted by mechanical inoculations in S. lycopersicum L. and Capsicum annuum L., but no transmission occurred in S. melongena L. The developed real-time RT-PCR, based on the use of a primer set designed on conserved sequences in the open reading frames3, enabled a reliable quantitative detection. This method allowed clear discrimination of ToBRFV from other viruses belonging to the genus Tobamovirus, minimising false-negative results. Using immunocapture and total RNA extraction procedures, the real-time RT-PCR and end-point RT-PCR gave the same comparable results. Using direct crude extracts and leaf-disk crude extracts, the end-point RT-PCR was unable to provide a reliable result. This developed highly specific and sensitive real-time RT-PCR assay will be a particularly valuable tool for early ToBRFV diagnosis, optimising procedures in terms of costs and time
Sterile neutrino decay and the LSND experiment
We propose a new explanation of the intriguing LSND evidence for electron
antineutrino appearance in terms of heavy (mostly sterile) neutrino decay via a
coupling with a light scalar and light (mostly active) neutrinos. We perform a
fit to the LSND data, as well as all relevant null-result experiments, taking
into account the distortion of the spectrum due to decay. By requiring a
coupling g ~ 10^{-5}, a heavy neutrino mass m_4 ~ 100 keV and a mixing with
muon neutrinos |U_{mu 4}|^2 ~ 10^{-2}, we show that this model explains all
existing data evading constraints that disfavor standard (3+1) neutrino models.Comment: 3pp. Talk given at 9th International Conference on Astroparticle and
Underground Physics (TAUP 2005), Zaragoza, Spain, 10-14 Sep 200
An obscured AGN population hidden in the VIPERS galaxies: identification through spectral energy distribution decomposition
The detection of X-ray emission constitutes a reliable and efficient tool for
the selection of Active Galactic Nuclei (AGNs), although it may be biased
against the most heavily absorbed AGNs. Simple mid-IR broad-band selection
criteria identify a large number of luminous and absorbed AGNs, yet again host
contamination could lead to non-uniform and incomplete samples. Spectral Energy
Distribution (SED) decomposition is able to decouple the emission from the AGN
versus that from star-forming regions, revealing weaker AGN components. We aim
to identify the obscured AGN population in the VIPERS survey in the CFHTLS W1
field through SED modelling. We construct SEDs for 6,860 sources and identify
160 AGNs at a high confidence level using a Bayesian approach. Using optical
spectroscopy, we confirm the nature of ~85% of the AGNs. Our AGN sample is
highly complete (~92%) compared to mid-IR colour selected AGNs, including a
significant number of galaxy-dominated systems with lower luminosities. In
addition to the lack of X-ray emission (80%), the SED fitting results suggest
that the majority of the sources are obscured. We use a number of diagnostic
criteria in the optical, infrared and X-ray regime to verify these results.
Interestingly, only 35% of the most luminous mid-IR selected AGNs have X-ray
counterparts suggesting strong absorption. Our work emphasizes the importance
of using SED decomposition techniques to select a population of type II AGNs,
which may remain undetected by either X-ray or IR colour surveys.Comment: Accepted for publication in MNRAS in May 4, 2020. 18 figures, 3
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