Hubble expansion and structure formation in the "running FLRW model" of the cosmic evolution

A new class of FLRW cosmological models with time-evolving fundamental parameters should emerge naturally from a description of the expansion of the universe based on the first principles of quantum field theory and string theory. Within this general paradigm, one expects that both the gravitational Newton's coupling, G, and the cosmological term, Lambda, should not be strictly constant but appear rather as smooth functions of the Hubble rate. This scenario ("running FLRW model") predicts, in a natural way, the existence of dynamical dark energy without invoking the participation of extraneous scalar fields. In this paper, we perform a detailed study of these models in the light of the latest cosmological data, which serves to illustrate the phenomenological viability of the new dark energy paradigm as a serious alternative to the traditional scalar field approaches. By performing a joint likelihood analysis of the recent SNIa data, the CMB shift parameter, and the BAOs traced by the Sloan Digital Sky Survey, we put tight constraints on the main cosmological parameters. Furthermore, we derive the theoretically predicted dark-matter halo mass function and the corresponding redshift distribution of cluster-size halos for the "running" models studied. Despite the fact that these models closely reproduce the standard LCDM Hubble expansion, their normalization of the perturbation's power-spectrum varies, imposing, in many cases, a significantly different cluster-size halo redshift distribution. This fact indicates that it should be relatively easy to distinguish between the "running" models and the LCDM cosmology using realistic future X-ray and Sunyaev-Zeldovich cluster surveys.Comment: Version published in JCAP 08 (2011) 007: 1+41 pages, 6 Figures, 1 Table. Typos corrected. Extended discussion on the computation of the linearly extrapolated density threshold above which structures collapse in time-varying vacuum models. One appendix, a few references and one figure adde

How does the cosmic large-scale structure bias the Hubble diagram?

The Hubble diagram is one of the cornerstones of observational cosmology. It is usually analysed assuming that, on average, the underlying relation between magnitude and redshift matches the prediction of a Friedmann-Lema\^itre-Robertson-Walker model. However, the inhomogeneity of the Universe generically biases these observables, mainly due to peculiar velocities and gravitational lensing, in a way that depends on the notion of average used in theoretical calculations. In this article, we carefully derive the notion of average which corresponds to the observation of the Hubble diagram. We then calculate its bias at second-order in cosmological perturbations, and estimate the consequences on the inference of cosmological parameters, for various current and future surveys. We find that this bias deeply affects direct estimations of the evolution of the dark-energy equation of state. However, errors in the standard inference of cosmological parameters remain smaller than observational uncertainties, even though they reach percent level on some parameters; they reduce to sub-percent level if an optimal distance indicator is used.Comment: 19+7 pages, 10 figures, v2 accepted by JCAP; minor changes to improve clarit

Determination of optimal doses of glyphosate for controlling weeds at several stages in southwestern Buenos Aires province (Argentina)

Efficient weed management is essential for avoiding competition for water, light, and nutrient resources in semiarid zones. Chemical weed control with glyphosate was evaluated on perennial wall-rocket (Diplotaxis tenuifolia), artichoke thistle (Cynara cardunculus), slender wild oat (Avena barbata), and perennial ryegrass (Lolium perenne). Plants at early, middle and advanced vegetative stages were used in this study. Glyphosate potassium salt was applied at rates of 0.0675 (1/16x), 0.135 (1/8x), 0.27 (1/4x), 0.54 (1/2x), 1.08 (x) and 2.16 (2x) kg acid equivalent (ae) ⋅ ha–1. Glyphosate combined with 2,4-D amine salt was evaluated at rates of 1.08 kg ae ⋅ ha–1 and 0.53 kg active ingredient (ai) ⋅ ha–1, respectively. The volume of the spray was 100 l ⋅ ha–1 with 86 droplets ⋅ cm–2 and a Volume Median Diameter (VMD) of 421.19 μm. In general, all the tested weeds were controlled with a quarter of the label rate. Three sizes of tested plants were controlled in a similar way at the same glyphosate dose rate. Moreover, the addition of 2,4-D to glyphosate did not produce an increase in the control of broadleaf weeds. The results showed that glyphosate was effective in controlling the tested weed species, including low application rates for all the growth stages in the southwestern Buenos Aires province

ENVIRONMENTAL FACTORS AFFECTING SEED GERMINATION OF COMMON TEASEL (Dipsacus fullonum)

<div><p>ABSTRACT Common teasel is a widespread, invasive species that has been introduced in Buenos Aires province, Argentina, where it alters the species composition of protected areas and native grasslands. A better understanding of seed germination behavior is essential for predicting its invasion potential in new areas and would be useful for developing effective management strategies. This research, conducted under laboratory conditions, evaluated the influence of several environmental factors such as pH, constant temperature, osmotic stress, salt stress and dry storage, on germination and rate of germination of common teasel seed. Between-year variation in germination responses was also examined. Seed germination was not affected by different pH levels. Although common teasel seeds germinated over a range of temperatures from 6 to 36 oC, the optimum temperature was 22 oC. Common teasel seed germination showed moderate tolerance to osmotic stress and a relatively high tolerance to salt stress. No seed germination was observed at - 1 MPa and 640 mM of osmotic potential and salt concentration, respectively. Seed germination remained high (> 90%) after all the dry storage treatments. Besides, the response of seeds to germination parameters showed between-year variation. It was shown that common teasel is able to germinate over a broad range of environmental conditions. This capacity would explain, at least partially, why this species is so widely distributed and its great potential to invade new areas.</p></div