1,324 research outputs found
A Comparative Study of Pentaquark Interpolating Currents
In a diquark-diquark-antiquark picture of pentaquarks, we use two
interpolating currents to calculate the mass of the recently measured
state in the framework of QCD sum rules. We show that, even though
yielding similar values for (and close to the experimental
value), these currents differ from each other in what concerns the strength of
the pole, convergence of the OPE and sensitivity to the continuum threshold
parameter.Comment: 19 pages, 8 figures, replaced version accepted for publication in
Phys. Lett.
Revisiting consistency conditions for quantum states of systems on closed timelike curves: an epistemic perspective
There has been considerable recent interest in the consequences of closed
timelike curves (CTCs) for the dynamics of quantum mechanical systems. A vast
majority of research into this area makes use of the dynamical equations
developed by Deutsch, which were developed from a consistency condition that
assumes that mixed quantum states uniquely describe the physical state of a
system. We criticise this choice of consistency condition from an epistemic
perspective, i.e., a perspective in which the quantum state represents a state
of knowledge about a system. We demonstrate that directly applying Deutsch's
condition when mixed states are treated as representing an observer's knowledge
of a system can conceal time travel paradoxes from the observer, rather than
resolving them. To shed further light on the appropriate dynamics for quantum
systems traversing CTCs, we make use of a toy epistemic theory with a strictly
classical ontology due to Spekkens and show that, in contrast to the results of
Deutsch, many of the traditional paradoxical effects of time travel are
present.Comment: 10 pages, 6 figures, comments welcome; v2 added references and
clarified some points; v3 published versio
The Vertex in QCD Sum Rules
The form factor is evaluated in a QCD sum rule calculation for
both and off-shell mesons. We study the double Borel sum rule for
the three point function of two pseudoscalar and one vector meson current. We
find that the momentum dependence of the form factors is different if the
or the meson is off-shell, but they lead to the same coupling constant
in the vertex.Comment: 11 pages, Latex, 4 eps figure
Are and the Roper resonance diquark-diquark-antiquark states?
We consider a current in the QCD sum rule framework to study
the mass of the recently observed pentaquark state , obtaining
good agreement with the experimental value. We also study the mass of the
pentaquark . Our results are compatible with the interpretation
of the state as being the Roper resonance N(1440), as suggested
by Jaffe and Wilczek.Comment: 9 pages RevTex4 and 3 eps figures. Revised version accepted for
publication in Phys. Lett.
Institutions and the uneven geography of the first wave of the COVID-19 pandemic
This paper examines the uneven geography of COVID-19-related excess mortality during the first wave of the pandemic in Europe, before assessing the factors behind the geographical differences in impact. The analysis of 206 regions across 23 European countries reveals a distinct COVID-19 geography. Excess deaths were concentrated in a limited number of regions âexpected deaths exceeded 20% in just 16 regionsâ with more than 40% of the regions considered experiencing no excess mortality during the first six months of 2020. Highly connected regions, in colder and dryer climates, with high air pollution levels, and relatively poorly endowed health systems witnessed the highest incidence of excess mortality. Institutional factors also played an important role. The first wave hit regions with a combination of weak and declining formal institutional quality and fragile informal institutions hardest. Low and declining national government effectiveness, together with a limited capacity to reach out across societal divides, and a frequent tendency to meet with friends and family were powerful drivers of regional excess mortality
Intervalo de confiança "bootstrap" como ferramenta para classificar raças do nematóide de cisto da soja
Discrete symmetries, invisible axion and lepton number symmetry in an economic 3-3-1 model
We show that Peccei-Quinn and lepton number symmetries can be a natural
outcome in a 3-3-1 model with right-handed neutrinos after imposing a Z_11 x
Z_2 symmetry. This symmetry is suitably accommodated in this model when we
augmented its spectrum by including merely one singlet scalar field. We work
out the breaking of the Peccei-Quinn symmetry, yielding the axion, and study
the phenomenological consequences. The main result of this work is that the
solution to the strong CP problem can be implemented in a natural way, implying
an invisible axion phenomenologically unconstrained, free of domain wall
formation and constituting a good candidate for the cold dark matter.Comment: 17 pages, Revtex
The seesaw mechanism at TeV scale in the 3-3-1 model with right-handed neutrinos
We implement the seesaw mechanism in the 3-3-1 model with right-handed
neutrinos. This is accomplished by the introduction of a scalar sextet into the
model and the spontaneous violation of the lepton number. We identify the
Majoron as a singlet under symmetry, which makes it
safe under the current bounds imposed by electroweak data. The main result of
this work is that the seesaw mechanism works already at TeV scale with the
outcome that the right-handed neutrino masses lie in the electroweak scale, in
the range from MeV to tens of GeV. This window provides a great opportunity to
test their appearance at current detectors, though when we contrast our results
with some previous analysis concerning detection sensitivity at LHC, we
conclude that further work is needed in order to validate this search.Comment: about 13 pages, no figure
REVISITANDO A NOĂĂO DE JUSTIĂA CURRICULAR: PROBLEMATIZAĂĂES AO PROCESSO DE SELEĂĂO DOS CONHECIMENTOS ESCOLARES
Electrical conductivity and mineral composition of the imbibition solution of bean seeds during storage
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