11,682 research outputs found
High-Energy Proton-Proton Forward Scattering and Derivative Analyticity Relations
We present the results of several parametrizations to two different ensemble
of data on total cross sections at the highest
center-of-mass energies (including cosmic-ray information). The results are
statistically consistent with two distinct scenarios at high energies. From one
ensemble the prediction for the LHC ( TeV) is mb and from the other, mb. From each
parametrization, and making use of derivative analyticity relations (DAR), we
determine (ratio between the forward real and imaginary parts of the
elastic scattering amplitude). A discussion on the optimization of the DAR in
terms of a free parameter is also presented.In all cases good descriptions of
the experimental data are obtained.Comment: One formula added, one unit changed, small misprints corrected, final
version to be published in Brazilian Journal of Physics; 13 pages, 8 figures,
aps-revte
Non-hermitian topology as a unifying framework for the Andreev versus Majorana states controversy
Zero-energy Andreev levels in hybrid semiconductor-superconductor nanowires mimic all expected Majorana phenomenology, including 2 e2∕ h conductance quantisation, even where band topology predicts trivial phases. This surprising fact has been used to challenge the interpretation of various transport experiments in terms of Majorana zero modes. Here we show that the Andreev versus Majorana controversy is clarified when framed in the language of non-Hermitian topology, the natural description for quantum systems open to the environment. This change of paradigm allows one to understand topological transitions and the emergence of zero modes in more general systems than can be described by band topology. This is achieved by studying exceptional point bifurcations in the complex spectrum of the system’s non-Hermitian Hamiltonian. Within this broader topological classification, Majoranas from both conventional band topology and a large subset of Andreev levels at zero energy are in fact topologically equivalent, which explains why they cannot be distinguishedWe thank J. Cayao for useful discussions in the early stages of this work. Research supported by the Spanish Ministry of Science, Innovation and Universities through Grants PGC2018-097018-B-I00, FIS2015-65706-P, FIS2015-64654-P, FIS2016-80434-P (AEI/FEDER, EU), the FPI programme BES-2016-078122, the Ramón y Cajal programme Grants RYC-2011-09345, RYC-2013-14645, the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), and the European Union’s Horizon 2020 research and innovation programme under the FETOPEN Grant Agreement No. 828948. We also acknowledge support from CSIC Research Platform on Quantum Technologies PTI-00
Holder continuity of absolutely continuous spectral measures for one-frequency Schrodinger operators
We establish sharp results on the modulus of continuity of the distribution
of the spectral measure for one-frequency Schrodinger operators with
Diophantine frequencies in the region of absolutely continuous spectrum. More
precisely, we establish 1/2-Holder continuity near almost reducible energies
(an essential support of absolutely continuous spectrum). For
non-perturbatively small potentials (and for the almost Mathieu operator with
subcritical coupling), our results apply for all energies.Comment: 16 page
BVRI Surface Photometry of Isolated Spiral Galaxies
A release of multicolor broad band (BVRI) photometry for a subsample of 44
isolated spirals drawn from the Catalogue of Isolated Galaxies (CIG) is
presented. Total magnitudes and colors at various circular apertures, as well
as some global structural/morphological parameters are estimated. Morphology is
reevaluated through optical and sharp/filtered R band images, (B-I) color index
maps, and archive near-IR JHK images from the Two-Micron Survey. The CAS
structural parameters (Concentration, Asymmetry, and Clumpiness) were
calculated from the images in each one of the bands. The fraction of galaxies
with well identified optical/near-IR bars (SB) is 63%, while a 17% more shows
evidence of weak or suspected bars (SAB). The sample average value of the
maximum bar ellipticity is 0.4. Half of the galaxies in the sample shows rings.
We identify two candidates for isolated galaxies with disturbed morphology. The
structural CAS parameters change with the observed band, and the tendencies
they follow with the morphological type and global color are more evident in
the redder bands. In any band, the major difference between our isolated
spirals and a sample of interacting spirals is revealed in the A-S plane. A
deep and uniformly observed sample of isolated galaxies is intended for various
purposes including (i) comparative studies of environmental effects, (ii)
confronting model predictions of galaxy evolution and (iii) evaluating the
change of galaxy properties with redshift.Comment: 44 pages, 9 figures and 7 tables included. To appear in The
Astronomical Journal. For the 43 appendix figures 4.1-4.43 see
http://www.astroscu.unam.mx/~avila/Figs4.1_4.43.tar.gz (7.2 Mb tar.gz file
Time reparametrization invariance in arbitrary range p-spin models: symmetric versus non-symmetric dynamics
We explore the existence of time reparametrization symmetry in p-spin models.
Using the Martin-Siggia-Rose generating functional, we analytically probe the
long-time dynamics. We perform a renormalization group analysis where we
systematically integrate over short timescale fluctuations. We find three
families of stable fixed points and study the symmetry of those fixed points
with respect to time reparametrizations. One of those families is composed
entirely of symmetric fixed points, which are associated with the low
temperature dynamics. The other two families are composed entirely of
non-symmetric fixed points. One of these two non-symmetric families corresponds
to the high temperature dynamics.
Time reparametrization symmetry is a continuous symmetry that is
spontaneously broken in the glass state and we argue that this gives rise to
the presence of Goldstone modes. We expect the Goldstone modes to determine the
properties of fluctuations in the glass state, in particular predicting the
presence of dynamical heterogeneity.Comment: v2: Extensively modified to discuss both high temperature
(non-symmetric) and low temperature (symmetric) renormalization group fixed
points. Now 16 pages with 1 figure. v1: 13 page
van der Waals epitaxy of monolayer hexagonal boron nitride on copper foil : growth, crystallography and electronic band structure
We investigate the growth of hexagonal boron nitride (h-BN) on copper foil by low pressure chemical vapour deposition (LP-CVD). At low pressure, h-BN growth proceeds through the nucleation and growth of triangular islands. Comparison between the orientation of the islands and the local crystallographic orientation of the polycrystalline copper foil reveals an epitaxial relation between the copper and h-BN, even on Cu(100) and Cu(110) regions whose symmetry is not matched to the h-BN. However, the growth rate is faster and the islands more uniformly oriented on Cu(111) grains. Angle resolved photoemission spectroscopy measurements reveal a well-defined band structure for the h-BN, consistent with a band gap of 6 eV, that is decoupled from the copper surface beneath. These results indicate that, despite a weak interaction between h-BN and copper, van der Waals epitaxy defines the long range ordering of h-BN even on polycrystalline copper foils and suggest that large area, single crystal, monolayer h-BN could be readily and cheaply produced
Eficiência relativa na avaliação de instituições de pesquisa agropecuária.
Apresenta-se um modelo que serve ao proposito de avaliacao das relacoes de producao em instituicoes de pesquisa agropecuaria. A nocao basica que permite avaliacoes comparativas entre unidades produtoras de pesquisa e a de medida radial de eficiencia relativa de producao. Esta medida de eficiencia, aplicada neste estudo aos centros de pesquisa da EMBRAPA, e geral e pode ser estendida a outros contextos. A abordagem que se utiliza na definicao do conceito de eficiencia e a do estudo de fronteiras economicas via envoltoria de dados - modelo DEA.Na publicação: Eliseu Alves
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