27,187 research outputs found
Quaternary glacial evolution in the Central Cantabrian Mountains (Northern Spain)
Peer reviewedPostprin
An explanation of the as a bound state
We use the interaction in the hidden gauge formalism to
dynamically generate and resonances. We show,
through a comparison of the results from this analysis and from a quark model
study with data, that the
and resonances can be assigned to bound
states. More precisely the can be interpreted as a
bound state whereas the and
may contain an important component. This
interpretation allows for a solution of a long-standing puzzle concerning the
description of these resonances in constituent quark models. In addition we
also obtain degenerate states but their
assignment to experimental resonances is more uncertain.Comment: 19 pags, 8 fig
On the void explanation of the Cold Spot
The integrated Sachs-Wolfe (ISW) contribution induced on the cosmic microwave
background by the presence of a supervoid as the one detected by Szapudi et al.
(2015) is reviewed in this letter in order to check whether it could explain
the Cold Spot (CS) anomaly. Two different models, previously used for the same
purpose, are considered to describe the matter density profile of the void: a
top hat function and a compensated profile produced by a Gaussian potential.
The analysis shows that, even enabling ellipticity changes or different values
for the dark-energy equation of state parameter , the ISW contribution
due to the presence of the void does not reproduce the properties of the CS.
Finally, the probability of alignment between the void and the CS is also
questioned as an argument in favor of a physical connection between these two
phenomena
Non-Gaussianity analysis on local morphological measures of WMAP data
The decomposition of a signal on the sphere with the steerable wavelet
constructed from the second Gaussian derivative gives access to the
orientation, signed-intensity, and elongation of the signal's local features.
In the present work, the non-Gaussianity of the WMAP temperature data of the
cosmic microwave background (CMB) is analyzed in terms of the first four
moments of the statistically isotropic random fields associated with these
local morphological measures, at wavelet scales corresponding to angular sizes
between 27.5 arcminutes and 30 degrees on the celestial sphere. While no
detection is made neither in the orientation analysis nor in the elongation
analysis, a strong detection is made in the excess kurtosis of the
signed-intensity of the WMAP data. The non-Gaussianity is observed with a
significance level below 0.5% at a wavelet scale corresponding to an angular
size around 10 degrees, and confirmed at neighbour scales. This supports a
previous detection of an excess of kurtosis in the wavelet coefficient of the
WMAP data with the axisymmetric Mexican hat wavelet (Vielva et al. 2004).
Instrumental noise and foreground emissions are not likely to be at the origin
of the excess of kurtosis. Large-scale modulations of the CMB related to some
unknown systematics are rejected as possible origins of the detection. The
observed non-Gaussianity may therefore probably be imputed to the CMB itself,
thereby questioning the basic inflationary scenario upon which the present
concordance cosmological model relies. Taking the CMB temperature angular power
spectrum of the concordance cosmological model at face value, further analysis
also suggests that this non-Gaussianity is not confined to the directions on
the celestial sphere with an anomalous signed-intensity.Comment: 10 pages, 3 figures. Version 2 includes minor changes to match
version accepted for publication in MNRA
Searching for a dipole modulation in the large-scale structure of the Universe
Several statistical anomalies in the CMB temperature anisotropies seem to
defy the assumption of a homogeneous and isotropic universe. In particular, a
dipole modulation has been detected both in WMAP and Planck data. We adapt the
methodology proposed by Eriksen et al. (2007) on CMB data to galaxy surveys,
tracing the large-scale structure. We analyse the NRAO VLA Sky Survey (NVSS)
data at a resolution of ~2 degrees for three different flux thresholds: 2.5,
5.0 and 10.0 mJy respectively. No evidence of a dipole modulation is found.
This result suggests that the origin of the dipole asymmetry found in the CMB
cannot be assigned to secondary anisotropies produced at redshifts around z =
1. However, it could still have been generated at redshifts higher or lower,
such as the integrated Sachs-Wolfe effect produced by the local structures.
Other all-sky surveys, like the infrared WISE catalogue, could help to explore
with a high sensitivity a redshift interval closer than the one probed with
NVSS.Comment: 6 pages, 2 figures. Some minor changes have been done from the
original manuscript. This paper is accepted by MNRA
Evidence of several dipolar quasi-invariants in Liquid Crystals
In a closed quantum system of N coupled spins with magnetic quantum number I,
there are about (2I + 1)^N constants of motion. However, the possibility of
observing such quasi-invariant (QI) states in solid-like spin systems in
Nuclear Magnetic Resonance (NMR) is not a strictly exact prediction. The aim of
this work is to provide experimental evidence of several QI, in the proton NMR
of small spin clusters, besides those already known Zeeman, and dipolar orders
(strong and weak). We explore the spin states prepared with the
Jeener-Broekaert pulse sequence by analyzing the time-domain signals yielded by
this sequence as a function of the preparation times, in a variety of dipolar
networks. We observe that the signals can be explained with two dipolar QIs
only within a range of short preparation times. At longer times the time-domain
signals have an echo-like behaviour. We study their multiple quantum coherence
content on a basis orthogonal to the z-basis and see that such states involve a
significant number of correlated spins. Then we show that the whole preparation
time-scale can only be reconstructed by assuming the occurrence of multiple QI
which we isolate experimentally
- …