739 research outputs found
Heavy meson semileptonic differential decay rate in two dimensions in the large Nc
We study QCD in 1+1 dimensions in the large limit using light-front
Hamiltonian perturbation theory in the expansion. We use this formalism
to exactly compute hadronic transition matrix elements for arbitrary currents
at leading order in . We compute the semileptonic differential decay
rate of a heavy meson, , and its moments, , using the hadronic
matrix elements obtained previously. We put some emphasis in trying to
understand parity invariance. We also study with special care the kinematic
region where the operator product expansion () or
non-local effective field theories () can
be applied. We then compare with the results obtained using an effective field
theory approach based on perturbative factorization, with the focus to better
understand quark-hadron duality. At the end of the day, using effective field
theories, we have been able to obtain expressions for the moments with relative
accuracy of in the kinematic region where the
operator product expansion can be applied, and with relative accuracy of
in the kinematic region where non-local effective field
theories can be applied. These expressions agree, within this precision, with
those obtained from the hadronic result using the layer-function approximation
plus Euler-McLaurin expansion. Very good numerical agreement for the moments is
obtained between the exact result and the result using effective field
theories.Comment: 52 pages, 30 figures, references added, small modifications, some
discussion of the four dimensional case changed, journal versio
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1/N_c and 1/n preasymptotic corrections to Current-Current correlators
We obtain the corrections in and in ( is the principal
quantum number of the bound state) of the decay constants of scalar and
pseudoscalar currents in two and four dimensions in the large . We obtain
them from the operator product expansion provided a model for the large
mass spectrum is given. In the two-dimensional case the spectrum is known and
the corrections obtained in this paper are model independent. We confirm these
results by confronting them with the numerical solution of the 't Hooft model.
We also consider a model at finite and obtain the associated decay
constants that are consistent with perturbation theory. This example shows that
that the inclusion of perturbative corrections, or finite effects, to the
OPE does not constrain the slope of the Regge trajectories, which remain a free
parameter for each different channel.Comment: 29 pages, 11 figures. Two references adde
Impact of Social Media on TV Content Consumption: New Market Strategies, Scenarios and Trends
The mass adoption of Social Media together with the proliferation and widely usage of multi-connected companion devices have tremendously transformed the TV/video consumption paradigm, opening the door to a new range of possibilities. This Special Issue has aimed at analyzing, from different point of views, the impact of Social Media and social interaction tools on the TV/video consumption area. The targeted topics of this Special Issue and a general overview of the accepted articles are provided in this Guest Editorial
Leading Chiral Logarithms to the Hyperfine Splitting of the Hydrogen and Muonic Hydrogen
We study the hydrogen and muonic hydrogen within an effective field theory
framework. We perform the matching between heavy baryon effective theory
coupled to photons and leptons and the relevant effective field theory at
atomic scales. This matching can be performed in a perturbative expansion in
alpha, 1/m_p and the chiral counting. We then compute the O(m_{l_i}^3
alpha^5/m_p^2 x logarithms) contribution (including the leading chiral
logarithms) to the Hyperfine splitting and compare with experiment. They can
explain about 2/3 of the difference between experiment and the pure QED
prediction when setting the renormalization scale at the rho mass. We give an
estimate of the matching coefficient of the spin-dependent proton-lepton
operator in heavy baryon effective theory.Comment: 17 pages, LaTeX, minor changes, one reference adde
Expansion of bound state energies in powers of m/M and (1-m/M)
Elaborating on a previous letter, we use a new approach to compute energy
levels of a non-relativistic bound-state of two constituents, with masses m and
M, by systematic expansions - one in powers of m/M and another in powers of
(1-m/M). Technical aspects of the calculations are described in detail.
Theoretical predictions are given for O(alpha(Z*alpha)^5) radiative recoil and
O((Z*alpha)^6) pure recoil corrections to the average energy shift and
hyperfine splitting relevant for hydrogen, muonic hydrogen, and muonium.Comment: 9 pages, revte
BCI-Based Navigation in Virtual and Real Environments
A Brain-Computer Interface (BCI) is a system that enables people to control an external device with their brain activity, without the need of any muscular activity. Researchers in the BCI field aim to develop applications to improve the quality of life of severely disabled patients, for whom a BCI can be a useful channel for interaction with their environment. Some of these systems are intended to control a mobile device (e. g. a wheelchair). Virtual Reality is a powerful tool that can provide the subjects with an opportunity to train and to test different applications in a safe environment. This technical review will focus on systems aimed at navigation, both in virtual and real environments.This work was partially supported by the Innovation, Science and Enterprise Council of the Junta de Andalucía (Spain), project P07-TIC-03310, the Spanish Ministry of Science and Innovation, project TEC 2011-26395 and by the European fund ERDF
Heavy quark mass determination from the quarkonium ground state energy: a pole mass approach
The heavy quark pole mass in perturbation theory suffers from a renormalon
caused, inherent uncertainty of . This fundamental
difficulty of determining the pole mass to an accuracy better than the inherent
uncertainty can be overcome by direct resummation of the first infrared
renormalon. We show how a properly defined pole mass as well as the mass for the top and bottom quarks can be determined accurately from the
quarkonium ground state energy.Comment: 16 pages; published versio
Preventing and addressing the stress reactions of health care workers caring for patients with COVID-19: Development of a digital platform (Be + against COVID)
Background: COVID-19 became a major public health concern in March 2020. Due to the high rate of hospitalizations for COVID-19 in a short time, health care workers and other involved staff are subjected to a large workload and high emotional distress.
Objective: The objective of this study is to develop a digital tool to provide support resources that might prevent and consider acute stress reactions in health care workers and other support staff due to the COVID-19 pandemic.
Methods: The contents of the digital platform were created through an evidence-based review and consensus conference. The website was built using the Google Blogger tool. The Android version of the app was developed in the Java and XML languages using Android Studio version 3.6, and the iOS version was developed in the Swift language using Xcode version 11.5. The app was evaluated externally by the Andalusian Agency for Healthcare Quality.
Results: We detected the needs and pressing situations of frontline health care workers, and then, we proposed a serial of recommendations and support resources to address them. These resources were redesigned using the feedback received. A website in three different languages (Spanish, English, and Portuguese) and a mobile app were developed with these contents, and the AppSaludable Quality Seal was granted to the app. A specific self-report scale to measure acute stress and additional tools were included to support the health care workforce. This instrument has been used in several Latin American countries and has been adapted considering cultural differences. The resources section of the website was the most visited with 18, 516 out of 68, 913 (26.9%) visits, and the “Self-Report Acute Stress Scale” was the most visited resource with 6468 out of 18, 516 (34.9%) visits.
Conclusions: The Be + against COVID platform (website and app) was developed and launched to offer a pool of recommendations and support resources, which were specifically designed to protect the psychological well-being and the work morale of health care workers. This is an original initiative different from the usual psychological assistance hotlines
Cross-country migration linked to people who inject drugs challenges the long-term impact of national HCV elimination programmes
To the Editor:
As of 2018, the majority of Western European countries – including Spain – have lifted restrictions to therapy based on disease severity in the context of HCV infections.1 Long overdue, most national elimination programmes now also include access to care for people who inject drugs (PWID), 2 who are at the core of ongoing HCV transmission.3 Macías et al.4 have recently shown in this Journal that high viral cure rates can be achieved in this group, hereby providing evidence that targeting PWID in treatment programmes is worthwhile. However, the extent to which such national efforts can reduce the HCV burden not only depends on the uptake into care and treatment success rates, it is also determined by the relative importance of within-country transmission and virus importation from elsewhere.
As the chronic nature of most HCV infections hampers reliably reconstructing contact networks from patient interviews, virus genetic data can be a valuable alternative source of information for elucidating the geographic history of virus lineages (e.g. [5], [6]). Using such data, we have recently shown that for the most prevalent subtype among PWID in Spain (40%, 7), HCV1a, infections often link to infections abroad – in recent years >50% link to Western European countries, mostly European Union (EU) member states – as opposed to other infections ..
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