3,367 research outputs found
Present Status of Chiral Perturbation Theory
The basic ideas and methods of chiral perturbation theory are briefly
reviewed. I discuss the recent attempts to build an effective Lagrangian in the
resonance region and summarize the known large-N_C constraints on the
low-energy chiral couplings.Comment: 6 pages. Invited talk at the 10th International Symposium on
Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2004), Beijing,
China, August 29 - September 4, 200
Form-factors and current correlators: chiral couplings L_10(mu) and C_87(mu) at NLO in 1/N(C)
Using the resonance chiral theory Lagrangian, we perform a calculation of the
vector and axial-vector two-point functions at the next-to-leading order (NLO)
in the 1/N(C) expansion. We have analyzed these correlators within the
single-resonance approximation and have also investigated the corrections
induced by a second multiplet of vector and axial-vector resonance states.
Imposing the correct QCD short-distance constraints, one determines the
difference of the two correlators Pi(t) = Pi_VV(t)- Pi_AA(t) in terms of the
pion decay constant and resonance masses. Its low momentum expansion fixes then
the low-energy chiral couplings L_10 and C_87 at NLO, keeping full control of
their renormalization scale dependence. At mu_0=0.77 GeV, we obtain L_10(mu_0)
= (-4.4 \pm 0.9)10^{-3} and C_87^r(mu_0)=(3.1 \pm 1.1)10^{-5}
Towards a determination of the chiral couplings at NLO in 1/N(C): L_8(mu) and C_38(mu)
We present a dispersive method which allows to investigate the low-energy
couplings of chiral perturbation theory at the next-to-leading order (NLO) in
the 1/N(C) expansion, keeping full control of their renormalization scale
dependence. Using the resonance chiral theory Lagrangian, we perform a NLO
calculation of the scalar and pseudoscalar two-point functions, within the
single-resonance approximation. Imposing the correct QCD short-distance
constraints, one determines their difference Pi(t)=Pi_S(t)-Pi_P(t) in terms of
the pion decay constant and resonance masses. Its low momentum expansion fixes
then the low-energy chiral couplings L_8 and C_38. At mu_0=0.77 GeV, we obtain
L_8(mu_0)^{SU(3)} = (0.6+-0.4)10^{-3} and C_{38}(mu_0)^{SU(3)}=(2+-6)10^{-6}.Comment: Extended version published at JHEP01(2007)039. A NLO prediction for
the O(p6) chiral coupling C_38 has been added. The original L_8 results
remain unchange
Pion and Kaon Decay Constants: Lattice vs. Resonance Chiral Theory
The Lattice results for the pion and kaon decay constants are analysed within
the Resonance Chiral Theory framework in the large NC limit. The approximately
linear behaviour of the observable at large light-quark mass is explained
through the interaction with the lightest multiplet of scalar resonances. The
analysis of the Lattice results allows to obtain the resonance mass MS=1049 +-
25 MeV and the Chiral Perturbation Theory parameters at leading order in 1/NC.Comment: 10 pages, 2 figure
Significación sedimentológica y paleogeográfica del nivel arcilloso con corales del Senonuense superior de los alrededores de la Pobla de Segur (Prov. Lérida)
There is in this note a facies description of the upper Cre- taceous clay levels with corals from Pobla de Segur surroundings and á sedimentological interpretation is give regardin, the regional paleogeographic evolution
Significado sedimentológico de los niveles con Assilinas de la Formación Armancies (Eoceno medio) y sus equivalentes laterales
En esta nota exponemos las características sedimentológicas de los niveles con Assilina de la Fm. Armancies y sus equivalentes laterales que permiten precisar algunos aspectos acerca de su génesis.Se llega a la conclusión de que las "barras de Assilinas" de la Fm. Armancies, en su extremo occidental (Bagà-Campdevànol), son canales de "grain flow" depositados originariamente al W de Terrades y deslizados, de E a W, en una cuenca turbidítica sin aportes de clásticos groseros
Observational Signatures of Massive Black Hole Progenitor Pathways: is Leo I a Smoking Gun?
Observational evidence is mounting regarding the population demographics of
Massive Black Holes (MBHs), from the most massive cluster galaxies down to the
dwarf galaxy regime. However, the progenitor pathways from which these central
MBHs formed remain unclear. Here we report a potentially powerful observational
signature of MBH formation in dwarf galaxies. We argue that a continuum in the
mass spectrum of MBHs in (fossil) dwarf galaxies would be a unique signature of
a heavy seed formation pathway. Under the robust assumption of initial
fragmentation of the parent gas cloud resulting in a burst of heavy seed
production, a significant fraction of these seeds will survive to the present
day as off-nuclear MBHs with masses less than that of the central object.
Motivated by the recent discovery of a MBH in the relatively low central
density Leo I galaxy, we show that such a continuum in MBH seed masses should
persist from the lightest black hole masses up to the mass of the central MBH
in contrast to the light seeding scenario where no such continuum should exist.
The detection of off-centered MBHs and a central MBH would represent strong
evidence of a heavy seeding pathway.Comment: Submitted to MNRAS Letters. 6 pages, 2 figures. Comments welcom
Influence of water availability in the distributions of branched glycerol dialkyl glycerol tetraether in soils of the Iberian Peninsula
The combined application of the MBT (degree of methylation) and CBT (degree
of cyclization) indices, based on the distribution of branched glycerol
dialkyl glycerol tetraethers (brGDGTs) in soils, has been proposed as a
paleoproxy to estimate mean annual temperature (MAT). CBT quantifies the
degree of cyclization of brGDGTs and relates to soil pH. MBT and the
simplified version MBT' quantify the degree of methylation of brGDGTs and
relate to MAT and soil pH. However, other factors such as soil water
availability have also been suggested to influence MBT' and possibly restrict
the combined application of the MBT' and CBT indices as a paleotemperature
proxy. To assess the effect of hydrological conditions on MBT' and CBT, a set
of 23 Iberian Peninsula soil samples, covering a MAT range from
10 to 18 °C and a mean annual precipitation (MAP) range of 405 mm to
1455 mm, was analyzed. We found that the CBT was indeed significantly
correlated with soil pH in our sample set. In contrast, MBT' was not correlated
with MAT but had a significant correlation with the aridity index (AI), a
parameter related to water availability in soils. The AI can explain 50%
of the variation of the MBT', and 70% of the residuals of MAT estimated
with the MBT/CBT proxy as compared to instrumentally measured MAT. We propose
that, in arid settings, where water may be an ecologically limiting factor,
MBT' is influenced by hydrological conditions rather than temperature. Thus,
our results suggest that the combination of MBT' and CBT indices should be
applied with caution in paleotemperature reconstructions in soils from dry
subhumid to hyperarid environments
Protecting biodiversity and economic returns in resource-rich tropical forests.
In pursuit of socioeconomic development, many countries are expanding oil and mineral extraction into tropical forests. These activities seed access to remote, biologically rich areas, thereby endangering global biodiversity. Here we demonstrate that conservation solutions that effectively balance the protection of biodiversity and economic revenues are possible in biologically valuable regions. Using spatial data on oil profits and predicted species and ecosystem extents, we optimise the protection of 741 terrestrial species and 20 ecosystems of the Ecuadorian Amazon, across a range of opportunity costs (i.e. sacrifices of extractive profit). For such an optimisation, giving up 5% of a year's oil profits (US 1.7 billion), and uses only marginally less land, to achieve equivalent levels of ecological protection. Applying spatial statistics to remotely sensed, historic deforestation data, we further focus the optimisation to areas most threatened by imminent forest loss. We identify Emergency Conservation Targets: areas that are essential to a cost-effective conservation reserve network and at imminent risk of destruction, thus requiring urgent and effective protection. Governments should employ the methods presented here when considering extractive led development options, to responsibly manage the associated ecological-economic trade-offs and protect natural capital. Article Impact Statement: Governments controlling resource extraction from tropical forests can arrange production and conservation to retain biodiversity and profits. This article is protected by copyright. All rights reserved
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