637 research outputs found
Gauge invariance in the presence of a cutoff
We use the method of gauging equations to construct the electromagnetic
current operator for the two-nucleon system in a theory with a finite cutoff.
The employed formulation ensures that the two-nucleon T-matrix and
corresponding five-point function, in the cutoff theory, are identical to the
ones formally defined by a reference theory without a cutoff. A feature of our
approach is that it effectively introduces a cutoff into the reference theory
in a way that maintains the long-range part of the exchange current operator;
for applications to effective field theory (EFT), this property is usually
sufficient to guarantee the predictive power of the resulting cutoff theory. In
addition, our approach leads to Ward-Takahashi (WT) identities that are linear
in the interactions.
From the point of view of EFT's where such a WT identity is satisfied in the
reference theory, this ensures that gauge invariance in the cutoff theory is
maintained order by order in the expansion.Comment: 15 pages, 2 figure
Renormalization of the Deuteron with One Pion Exchange
We analyze the deuteron bound state through the One Pion Exchange Potential.
We pay attention to the short distance peculiar singularity structure of the
bound state wave functions in coordinate space and the elimination of short
distance ambiguities by selecting the regular solution at the origin. We
determine the so far elusive amplitude of the converging exponential solutions
at the origin. All bound state deuteron properties can then be uniquely deduced
from the deuteron binding energy, the pion-nucleon coupling constant and pion
mass. This generates correlations among deuteron properties. Scattering phase
shifts and low energy parameters in the 3S1-3D1 channel are constructed by
requiring orthogonality of the positive energy states to the deuteron bound
state, yielding an energy independent combination of boundary conditions. We
also analyze from the viewpoint of short distance boundary conditions the weak
binding regime on the light of long distance perturbation theory and discuss
the approach to the chiral limit.Comment: 22 pages, 11 figure
Neutrino Oscillation Parameters: Future
The Neutrino Oscillation Workshop (NOW2018) included a session addressing neutrino oscillation parameters in the future. This session included discussion of planned and proposed experiments, detector technologies, and analysis techniques to better measure neutrino oscillation parameters. Constraint of systematic uncertainty in future precision measurements was a topic of particular interest. This proceedings is a brief summary of the presentations in the Oscillation Parameters: Future session; readers are directed to individual contributions to the proceedings for more detailed information
Renormalization of NN-Scattering with One Pion Exchange and Boundary Conditions
A non perturbative renormalization scheme for Nucleon-Nucleon interaction
based on boundary conditions at short distances is presented and applied to the
One Pion Exchange Potential. It is free of off-shell ambiguities and
ultraviolet divergences, provides finite results at any step of the calculation
and allows to remove the short distance cut-off in a suitable way. Low energy
constants and their non-perturbative evolution can directly be obtained from
experimental threshold parameters in a completely unique and model independent
way when the long range explicit pion effects are eliminated. This allows to
compute scattering phase shifts which are, by construction consistent with the
effective range expansion to a given order in the C.M. momentum . In the
singlet and triplet channels ultraviolet fixed points
and limit cycles are obtained respectively for the threshold parameters. Data
are described satisfactorily up to CM momenta of about .Comment: 22 pages, 10 figures, revte
CXCL12-induced neurotoxicity critically depends on NMDA receptor-gated and L-type Ca2+ channels upstream of p38 MAPK.
BackgroundThe chemokine receptor CXCR4 (CD184) and its natural ligand CXCL12 contribute to many physiological processes, including decisions about cell death and survival in the central nervous system. In addition, CXCR4 is a co-receptor for human immunodeficiency virus (HIV)-1 and mediates the neurotoxicity of the viral envelope protein gp120. However, we previously observed that CXCL12 also causes toxicity in cerebrocortical neurons but the cellular mechanism remained incompletely defined.MethodsPrimary neuronal-glial cerebrocortical cell cultures from rat were exposed to a neurotoxicity-inducing CXCL12 concentration for different times and the activity of the stress-associated mitogen-activated protein kinase p38 (p38 MAPK) was assessed using an in vitro kinase assay. Neurotoxicity of CXCL12 and cellular localization of p38 MAPK was analyzed by immunofluorescence microscopy. Pharmacological inhibition of NMDA-type glutamate receptor-gated ion channels (NMDAR) of L-type Ca2+ channels was employed during 12- and 24-h exposure to neurotoxic amounts of CXCL12 to study the effects on active p38 MAPK and neuronal survival by Western blotting and microscopy, respectively. Neurotoxicity of CXCL12 was also assessed during pharmacological inhibition of p38 MAPK.ResultsHere, we show that a neurotoxic amount of CXCL12 triggers a significant increase of endogenous p38 MAPK activity in cerebrocortical cells. Immunofluorescence and Western blotting experiments with mixed neuronal-glial and neuron-depleted glial cerebrocortical cells revealed that the majority of active/phosphorylated p38 MAPK was located in neurons. Blockade of NMDAR-gated ion channels or L-type Ca2+ channels both abrogated an increase of active p38 MAPK and toxicity of CXCL12 in cerebrocortical neurons. Inhibition of L-type Ca2+ channels with nimodipine kept the active kinase at levels not significantly different from baseline while blocking NMDAR with MK-801 strongly reduced phosphorylated p38 MAPK below baseline. Finally, we confirmed that directly blocking p38 MAPK also abrogated neurotoxicity of CXCL12.ConclusionsOur findings link CXCL12-induced neuronal death to the regulation of NMDAR-gated ion channels and L-type Ca2+ channels upstream of p38 MAPK activation
Cosmological perturbations in warm inflationary models with viscous pressure
Scalar and tensorial cosmological perturbations generated in warm
inflationary scenarios whose matter-radiation fluid is endowed with a viscous
pressure are considered. Recent observational data from the WMAP experiment are
employed to restrict the parameters of the model. Although the effect of this
pressure on the matter power spectrum is of the order of a few percent, it may
be detected in future experiments.Comment: 20 pages, to be published in the Physcal Review
Stability of inflationary solutions driven by a changing dissipative fluid
In this paper the second Lyapunov method is used to study the stability of
the de Sitter phase of cosmic expansion when the source of the gravitational
field is a viscous fluid. Different inflationary scenarios related with
reheating and decay of mini-blackholes into radiation are investigated using an
effective fluid described by time--varying thermodynamical quantities.Comment: 17 pages, LaTeX 2.09, 2 figures. To be published in Classical and
Quantum Gravit
Estudio de viaductos existentes: criterios para llevar a cabo la investigación estructural
El objeto de la presente comunicación es destacar la importancia de plantear
correctamente el estudio del estado actual de un viaducto existente de cara a analizar sus
condiciones de durabilidad. Para ello, partiendo de su inspección, deberemos establecer
los criterios para la localización y tipología de las calas a realizar sobre la estructura, definir
los ensayos complementarios necesarios en cada caso según se deduzca de los aspectos
observados en las inspecciones realizadas (tanto de los daños existentes como de las
calas que se practiquen), y así poder establecer un juicio técnico fundamentado sobre el
origen de las anomalías que se observen, valorar su trascendencia estructural, y poder
determinar las medidas de reparación y/ o refuerzo más adecuadas en cada caso. La
propuesta de actuación expuesta en el artículo destaca la importancia de los trabajos de
inspección (daños y calas) y de Laboratorio, sin entrar a valorar otros ensayos
(resistividad, medidas de potenciales de corrosión, etc.), que podrían resultar oportunos en
algunos casos
Big rip avoidance via black holes production
We consider a cosmological scenario in which the expansion of the Universe is
dominated by phantom dark energy and black holes which condense out of the
latter component. The mass of black holes decreases via Hawking evaporation and
by accretion of phantom fluid but new black holes arise continuously whence the
overall evolution can be rather complex. We study the corresponding dynamical
system to unravel this evolution and single out scenarios where the big rip
singularity does not occur.Comment: 16 pages, two figures. Key words. Cosmology, phantom energy, black
holes. Sligthly extended version to be published in Gravitation and Cosmolog
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