4,339 research outputs found
Chiral extrapolation of light resonances from one and two-loop unitarized Chiral Perturbation Theory versus lattice results
We study the pion mass dependence of the rho(770) and f_0(600) masses and
widths from one and two-loop unitarized Chiral Perturbation Theory. We show the
consistency of one-loop calculations with lattice results for the M_rho, f_pi
and the isospin 2 scattering length a_20.Then, we develop and apply the
modified Inverse Amplitude Method formalism for two-loop ChPT. In contrast to
the f_0(600), the rho(770) is rather sensitive to the two-loop ChPT parameters
--our main source of systematic uncertainty. We thus provide two-loop
unitarized fits constrained by lattice information on M_rho, f_pi, by the qqbar
leading 1/N_c behavior of the rho and by existing estimates of low energy
constants. These fits yield relatively stable predictions up to m_pi\simeq
300-350 MeV for the rho coupling and width as well as for all the f_0(600)
parameters. We confirm, to two-loops, the weak m_pi dependence of the rho
coupling and the KSRF relation, and the existence of two virtual f_0(600) poles
for sufficiently high m_pi. At two loops one of these poles becomes a bound
state when m_pi is somewhat larger than 300 MeV.Comment: 15 pages, to appear in Phys. Rev.
Rotation curves and metallicity gradients from HII regions in spiral galaxies
In this paper we study long slit spectra in the region of H emission
line of a sample of 111 spiral galaxies with recognizable and well defined
spiral morphology and with a well determined environmental status, ranging from
isolation to non-disruptive interaction with satellites or companions. The form
and properties of the rotation curves are considered as a function of the
isolation degree, morphological type and luminosity. The line ratios are used
to estimate the metallicity of all the detected HII regions, thus producing a
composite metallicity profile for different types of spirals. We have found
that isolated galaxies tend to be of later types and lower luminosity than the
interacting galaxies. The outer parts of the rotation curves of isolated
galaxies tend to be flatter than in interacting galaxies, but they show similar
relations between global parameters. The scatter of the Tully-Fisher relation
defined by isolated galaxies is significantly lower than that of interacting
galaxies. The [NII]/H ratios, used as metallicity indicator, show a
clear trend between Z and morphological type, t, with earlier spirals showing
larger ratios; this trend is tighter when instead of t the gradient of the
inner rotation curve, G, is used; no trend is found with the interaction
status. The Z-gradient of the disks depends on the type, being almost flat for
early spirals, and increasing for later types. The [NII]/H ratios
measured for disk HII regions of interacting galaxies are higher than for
normal/isolated objects, even if all the galaxy families present similar
distributions of H Equivalent Width.Comment: accepted for publication in A&A (tables for HII region parameters
incomplete, contact [email protected] for the whole set of tables
Can Schools and Education Policy Make Children Happier? A Comparative Study in 33 Countries
Our understanding of child subjective well-being and how to promote it has improved substantially over the last decade. In relation to the role of education policy in shaping subjective well-being, although valuable research has been conducted, many questions remain unanswered. This paper aims to fill this gap by studying the links between education policy and students’ life satisfaction. We use linear and multilevel regression to analyse PISA 2015 data on 15-year-old students in 33 countries. Our interest is in within society differences and how these vary across societies. We find that (1) there is an association between multiple education policy-relevant factors and students’ life satisfaction, which is particularly prominent –and observed in a larger number of countries- in the domains of family relationships, schoolwork-related anxiety and bullying. Our models explain between one-fifth and one-third of the variation in students’ life satisfaction. Results also indicate that (2) schools may play an important role in shaping students’ life satisfaction. This is supported by evidence that these associations tend to vary by school; by evidence on the existence of school effects in all countries but two; and by the finding that a proportion - substantial in some countriesof the variation in students’ life satisfaction is explained by differences between schools. Finally, we find that (3) in relation to both questions, there are important differences across societies. Overall, these results provide evidence that an association between education policy and children’s subjective well-being seems to exist but is of a complex nature
Nesting Success of Kemp’s Ridley Sea Turtles, Lepidochelys kempi, at Rancho Nuevo, Tamaulipas, Mexico, 1982–2004
The Kemp’s ridley sea turtle, Lepidochelys kempi, was on the edge of extinction owing to a combination of intense
egg harvesting and incidental capture in commercial fishing trawls. Results from a cooperative conservation strategy initiated in 1978 between Mexico and the United States to protect and restore the Kemp’s ridley turtle at the main nesting beach at Rancho Nuevo, Tamaulipas, Mexico are
assessed. This strategy appears to be working as there are signs that the species is starting to make a recovery. Recovery indicators include: 1) increased numbers of nesting turtles, 2) increased numbers of 100+ turtle nesting aggregations (arribadas), 3) an expanding nesting season now extending from March to August, and 4) significant nighttime nesting since 2003. The population low point at Rancho Nuevo was in 1985 (706 nests) and the population began to significantly increase in 1997
(1,514 nests), growing to over 4,000 nests in 2004. The size and numbers of arribadas have increased each year since 1983 but have yet to exceed the 1,000+ mark; most
arribadas are still 200–800+ turtles
The Broad Line Radio Galaxy J2114+820
In the frame of the study of a new sample of large angular size radio
galaxies selected from the NRAO VLA Sky Survey, we have made radio observations
of J2114+820, a low power radio galaxy with an angular size of 6'. Its radio
structure basically consists of a prominent core, a jet directed in north-west
direction and two extended S-shaped lobes. We have also observed the optical
counterpart of J2114+820, a bright elliptical galaxy with a strong unresolved
central component. The optical spectrum shows broad emission lines. This fact,
together with its low radio power and FR-I type morphology, renders J2114+820 a
non-trivial object from the point of view of the current unification schemes of
radio loud active galactic nuclei.Comment: 6 pages, 5 figures. To appear in the proceedings of EVN/JIVE
Symposium No. 4, New Astronomy Reviews (eds. Garrett et al.
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