1,040 research outputs found
Non-Gaussianity as a Particle Detector
We study the imprints of massive particles with spin on cosmological
correlators. Using the framework of the effective field theory of inflation, we
classify the couplings of these particles to the Goldstone boson of broken time
translations and the graviton. We show that it is possible to generate
observable non-Gaussianity within the regime of validity of the effective
theory, as long as the masses of the particles are close to the Hubble scale
and their interactions break the approximate conformal symmetry of the
inflationary background. We derive explicit shape functions for the scalar and
tensor bispectra that can serve as templates for future observational searches.Comment: 55 pages, 10 figure
Bibliometric Networks and financing in Brazilian Physical Education Research
In this paper, we looked at citations, major institutions, research themes and funding in physical education and sports studies from Brazilian authors to evaluate their impact and insertion worldwide. A bibliometric analysis using data from international (Web of Science and Scopus) and national (Sucupira) databases followed by visualization of similarities. Data was downloaded from Scopus and SciVal (Elsevier) and Web of Science (Clarivate Analytics) databases as well as Sucupira in the area of Physical Education as defined by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior in Brazil. Data were analysed using Visualisation of Similarities (Vosviewer), correlation, regression and variance analyses to examine the relationship between quantity and quality indicators. Major topics researched include obesity, exercise, joints, cartilage, tendons and muscles (ankle, knee, hip, shoulder) as well as factors linked to age (child, adolescent and ageing), in line with those researched worldwide. The correlation between the number of publications per topic worldwide and in Brazil is 0.79. There was a concentration of publishing in the area of physical education in Brazil with 80% of papers being published by only 12% of the institutions that publish on this subject. Brazilian authors in physical education cooperate with, and receive financing from, institutions and funding agencies worldwide, but papers funded by Brazilian agencies have lower impact. Brazilian researchers are researching similar topics to international researchers, but citation analysis shows relatively closed clusters of researchers with little interaction between them
A Characterization of Deterministic Sampling Patterns for Low-Rank Matrix Completion
Low-rank matrix completion (LRMC) problems arise in a wide variety of
applications. Previous theory mainly provides conditions for completion under
missing-at-random samplings. This paper studies deterministic conditions for
completion. An incomplete matrix is finitely rank- completable
if there are at most finitely many rank- matrices that agree with all its
observed entries. Finite completability is the tipping point in LRMC, as a few
additional samples of a finitely completable matrix guarantee its unique
completability. The main contribution of this paper is a deterministic sampling
condition for finite completability. We use this to also derive deterministic
sampling conditions for unique completability that can be efficiently verified.
We also show that under uniform random sampling schemes, these conditions are
satisfied with high probability if entries per column are
observed. These findings have several implications on LRMC regarding lower
bounds, sample and computational complexity, the role of coherence, adaptive
settings and the validation of any completion algorithm. We complement our
theoretical results with experiments that support our findings and motivate
future analysis of uncharted sampling regimes.Comment: This update corrects an error in version 2 of this paper, where we
erroneously assumed that columns with more than r+1 observed entries would
yield multiple independent constraint
Partially Massless Fields During Inflation
The representation theory of de Sitter space allows for a category of
partially massless particles which have no flat space analog, but could have
existed during inflation. We study the couplings of these exotic particles to
inflationary perturbations and determine the resulting signatures in
cosmological correlators. When inflationary perturbations interact through the
exchange of these fields, their correlation functions inherit scalings that
cannot be mimicked by extra massive fields. We discuss in detail the squeezed
limit of the tensor-scalar-scalar bispectrum, and show that certain partially
massless fields can violate the tensor consistency relation of single-field
inflation. We also consider the collapsed limit of the scalar trispectrum, and
find that the exchange of partially massless fields enhances its magnitude,
while giving no contribution to the scalar bispectrum. These characteristic
signatures provide clean detection channels for partially massless fields
during inflation.Comment: 48 pages, 5 figures. v2: references added, published versio
Tightness for the interface of the one-dimensional contact process
We consider a symmetric, finite-range contact process with two types of
infection; both have the same (supercritical) infection rate and heal at rate
1, but sites infected by Infection 1 are immune to Infection 2. We take the
initial configuration where sites in have Infection 1 and sites
in have Infection 2, then consider the process defined as
the size of the interface area between the two infections at time . We show
that the distribution of is tight, thus proving a conjecture posed by
Cox and Durrett in [Bernoulli 1 (1995) 343--370].Comment: Published in at http://dx.doi.org/10.3150/09-BEJ236 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
The Cosmological Bootstrap: Inflationary Correlators from Symmetries and Singularities
Scattering amplitudes at weak coupling are highly constrained by Lorentz
invariance, locality and unitarity, and depend on model details only through
coupling constants and particle content. In this paper, we develop an
understanding of inflationary correlators which parallels that of flat-space
scattering amplitudes. Specifically, we study slow-roll inflation with weak
couplings to extra massive particles, for which all correlators are controlled
by an approximate conformal symmetry on the boundary of the spacetime. After
classifying all possible contact terms in de Sitter space, we derive an
analytic expression for the four-point function of conformally coupled scalars
mediated by the tree-level exchange of massive scalars. Conformal symmetry
implies that the correlator satisfies a pair of differential equations with
respect to spatial momenta, encoding bulk time evolution in purely boundary
terms. The absence of unphysical singularities completely fixes this
correlator. A spin-raising operator relates it to the correlators associated
with the exchange of particles with spin, while weight-shifting operators map
it to the four-point function of massless scalars. We explain how these de
Sitter four-point functions can be perturbed to obtain inflationary three-point
functions. We reproduce many classic results in the literature and provide a
complete classification of all inflationary three- and four-point functions
arising from weakly broken conformal symmetry. The inflationary bispectrum
associated with the exchange of particles with arbitrary spin is completely
characterized by the soft limit of the simplest scalar-exchange four-point
function of conformally coupled scalars and a series of contact terms. Finally,
we demonstrate that the inflationary correlators contain flat-space scattering
amplitudes via a suitable analytic continuation of the external momenta.Comment: 110 pages, 13 figures, 1 table; V3: minor corrections and references
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The Publication Facts Label: Ascertaining a Publication’s Adherence to Scholarly Standards
This is a case study of a digital innovation aimed at increasing researchers’, professionals’, and the general public’s ability to approach research publications with a ready method of checking its compliance with the features that set scholarly publishing apart from other sources of information. More specifically, the innovation consists of generating a “publication facts label” (PFL) for articles and journals, which records their adherence to eight elements that reflect scholarly publishing standards. The label conveys data and links for publisher identity, scholarly editorial oversight, article acceptance rates, journal indexing, expert peer review, competing interests, data availability, and research funding (Fig. 1). The PFL is modeled on the United States nutrition facts label that, since 1996, has appeared on food products, proving itself an effective science communication strategy with adoptions around the world in different formats (Christof et al., 2018; Post et al., 2010). At this point, the PFL is being developed as an open source software project by the Public Knowledge Project (PKP) at Simon Fraser University for use with its Open Journal Systems. In this case study, we present the rationale, design, and assessment strategies involved in PFL development and piloting. Although the PFL is still at an early stage, we consider the lessons already learned from this approach worth introducing into the industry’s current emphasis on ways to improve research integrity
The Cosmological Bootstrap: Spinning Correlators from Symmetries and Factorization
We extend the cosmological bootstrap to correlators involving massless
particles with spin. In de Sitter space, these correlators are constrained both
by symmetries and by locality. In particular, the de Sitter isometries become
conformal symmetries on the future boundary of the spacetime, which are
reflected in a set of Ward identities that the boundary correlators must
satisfy. We solve these Ward identities by acting with weight-shifting
operators on scalar seed solutions. Using this weight-shifting approach, we
derive three- and four-point correlators of massless spin-1 and spin-2 fields
with conformally coupled scalars. Four-point functions arising from tree-level
exchange are singular in particular kinematic configurations, and the
coefficients of these singularities satisfy certain factorization properties.
We show that in many cases these factorization limits fix the structure of the
correlators uniquely, without having to solve the conformal Ward identities.
The additional constraint of locality for massless spinning particles manifests
itself as current conservation on the boundary. We find that the four-point
functions only satisfy current conservation if the s, t, and u-channels are
related to each other, leading to nontrivial constraints on the couplings
between the conserved currents and other operators in the theory. For spin-1
currents this implies charge conservation, while for spin-2 currents we recover
the equivalence principle from a purely boundary perspective. For multiple
spin-1 fields, we recover the structure of Yang-Mills theory. Finally, we apply
our methods to slow-roll inflation and derive a few phenomenologically relevant
scalar-tensor three-point functions.Comment: 128 pages, 15 figures; V3: minor corrections and references adde
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