Search results for "descriptive"
showing 10 items of 494 documents
Large‐Scale Vector Modes and the First CMB Temperature Multipoles
2008
Recent observations have pointed out various anomalies in some multipoles (small $\ell $) of the cosmic microwave background (CMB). In this paper, it is proved that some of these anomalies could be explained in the framework of a modified concordance model, in which, there is an appropriate distribution of vector perturbations with very large spatial scales. Vector modes are associated with divergenceless (vortical) velocity fields. Here, the generation of these modes is not studied in detail (it can be done "a posteriori"); on the contrary, we directly look for the distributions of these vector modes which lead to both alignments of the second and third multipoles and a planar octopole. A …
Recovering the real-space correlation function from photometric redshift surveys
2008
Measurements of clustering in large-scale imaging surveys that make use of photometric redshifts depend on the uncertainties in the redshift determination. We have used light-cone simulations to show how the deprojection method successfully recovers the real space correlation function when applied to mock photometric redshift surveys. We study how the errors in the redshift determination affect the quality of the recovered two-point correlation function. Considering the expected errors associated to the planned photometric redshift surveys, we conclude that this method provides information on the clustering of matter useful for the estimation of cosmological parameters that depend on the la…
Physical and Chemical Inhomogeneities Inside the Vela SNR Shell: Indications of Ejecta Shrapnels
2007
We present the results of the combined analysis of three XMM-Newton EPIC observations of the northern rim of the Vela SNR. The three pointings cover an area of ~10 pc^2 (at 250 pc) behind the main shock front and we aim at studying with high resolution the spatial distribution of the physical and chemical properties of the X-ray emitting plasma on this large scale. We produce count-rate images and equivalent width maps of the Ne IX and Mg XI emission blends. We also perform a spatially resolved spectral analysis of a set of physically homogeneous regions. We reveal physical and chemical inhomogeneities in the X-ray emitting plasma. In particular, we find large variations of the O, Ne, Mg, a…
A weakly random Universe?
2010
The cosmic microwave background (CMB) radiation is characterized by well-established scales, the 2.7 K temperature of the Planckian spectrum and the $10^{-5}$ amplitude of the temperature anisotropy. These features were instrumental in indicating the hot and equilibrium phases of the early history of the Universe and its large scale isotropy, respectively. We now reveal one more intrinsic scale in CMB properties. We introduce a method developed originally by Kolmogorov, that quantifies a degree of randomness (chaos) in a set of numbers, such as measurements of the CMB temperature in some region. Considering CMB as a composition of random and regular signals, we solve the inverse problem of …
Bounding effective operators at the one-loop level: the case of four-fermion neutrino interactions
1994
The contributions of non-standard four-neutrino contact interactions to electroweak observables are considered at the one-loop level by using the effective quantum field theory. The analysis is done in terms of three unknown parameters: the strength of the non-standard neutrino interactions, $\tilde{F}$, an additional derivative coupling needed to renormalize the divergent contributions that appear when the four-neutrino interactions are used at the loop level and a non-standard non-derivative $Z$-${\bar\nu} \nu$ coupling. Then, the precise measurements of the invisible width of the $Z$-boson at LEP and the data on the neutrino deep-inelastic scattering yield the result $\tilde{F} = (-100 \…
Nucleon-to-Delta transition form factors in chiral effective field theory using the complex-mass scheme
2018
We calculate the form factors of the electromagnetic nucleon-to-$\Delta$-resonance transition to third chiral order in manifestly Lorentz-invariant chiral effective field theory. For the purpose of generating a systematic power counting, the complex-mass scheme is applied in combination with the small-scale expansion. We fit the results to available empirical data.
Comparing estimators of the galaxy correlation function
1999
We present a systematic comparison of some usual estimators of the 2--point correlation function, some of them currently used in Cosmology, others extensively employed in the field of the statistical analysis of point processes. At small scales, it is known that the correlation function follows reasonably well a power--law expression $\xi(r) \propto r^{-\gamma}$. The accurate determination of the exponent $\gamma$ (the order of the pole) depends on the estimator used for $\xi(r)$; on the other hand, its behavior at large scale gives information on a possible trend to homogeneity. We study the concept, the possible bias, the dependence on random samples and the errors of each estimator. Erro…
Relaxation of periodic and nonstandard growth integrals by means of two-scale convergence
2019
An integral representation result is obtained for the variational limit of the family functionals $\int_{\Omega}f\left(\frac{x}{\varepsilon}, Du\right)dx$, as $\varepsilon \to 0$, when the integrand $f = f (x,v)$ is a Carath\'eodory function, periodic in $x$, convex in $v$ and with nonstandard growth.
EFFECTIVE FIELD THEORY APPROACH TO THE NUCLEON–NUCLEON INTERACTION REVISITED
2006
It is argued that Weinberg's approach to the nucleon–nucleon (NN) interaction problem within effective field theory provides a consistent power counting for renormalized diagrams. Within this scheme the NN potential is organized as an expansion in terms of small quantities like small external momenta and the pion mass (divided by the characteristic large scale of the effective theory). Physical observables to any given order in these small quantities are calculated from the solutions of the Lippmann–Schwinger (or Schrödinger) equation.
K -> pi pi Electroweak Penguins in the Chiral Limit
2002
We report on dispersive and finite energy sum rule analyses of the electroweak penguin matrix elements in the chiral limit. We accomplish the correct perturbative matching (scale and scheme dependence) at NLO in alpha_s, and we describe two different strategies for numerical evaluation.