3,032 research outputs found
CMB statistical isotropy confirmation at all scales using multipole vectors
We present an efficient numerical code and conduct, for the first time, a
null and model-independent CMB test of statistical isotropy using Multipole
Vectors (MVs) at all scales. Because MVs are insensitive to the angular power
spectrum , our results are independent from the assumed cosmological
model. We avoid a posteriori choices and use pre-defined ranges of scales
, and in our analyses. We
find that all four masked Planck maps, from both 2015 and 2018 releases, are in
agreement with statistical isotropy for , . For
we detect anisotropies but this is indicative of simply the
anisotropy in the noise: there is no anisotropy for and an
increasing level of anisotropy at higher multipoles. Our findings of no
large-scale anisotropies seem to be a consequence of avoiding \emph{a
posteriori} statistics. We also find that the degree of anisotropy in the full
sky (i.e. unmasked) maps vary enormously (between less than 5 and over 1000
standard deviations) among the different mapmaking procedures and data
releases.Comment: v4: additional analysis which increased statistical sensitivity,
including new plots and tables; extended discussion; 15 pages, 14 figures, 7
tables. Matches published versio
Cosmological Signatures of Anisotropic Spatial Curvature
If one is willing to give up the cherished hypothesis of spatial isotropy,
many interesting cosmological models can be developed beyond the simple
anisotropically expanding scenarios. One interesting possibility is presented
by shear-free models in which the anisotropy emerges at the level of the
curvature of the homogeneous spatial sections, whereas the expansion is
dictated by a single scale factor. We show that such models represent viable
alternatives to describe the large-scale structure of the inflationary
universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the
definition of a complete set of spatial eigenfunctions we compute the two-point
correlation function of scalar perturbations in these models. In addition, we
show how such scenarios would modify the spectrum of the CMB assuming that the
observations take place in a small patch of a universe with anisotropic
curvature.Comment: 21 pages, 1 figure. To appear in JCA
Angular-planar CMB power spectrum
Gaussianity and statistical isotropy of the Universe are modern cosmology's
minimal set of hypotheses. In this work we introduce a new statistical test to
detect observational deviations from this minimal set. By defining the
temperature correlation function over the whole celestial sphere, we are able
to independently quantify both angular and planar dependence (modulations) of
the CMB temperature power spectrum over different slices of this sphere. Given
that planar dependence leads to further modulations of the usual angular power
spectrum , this test can potentially reveal richer structures in the
morphology of the primordial temperature field. We have also constructed an
unbiased estimator for this angular-planar power spectrum which naturally
generalizes the estimator for the usual 's. With the help of a chi-square
analysis, we have used this estimator to search for observational deviations of
statistical isotropy in WMAP's 5 year release data set (ILC5), where we found
only slight anomalies on the angular scales and . Since this
angular-planar statistic is model-independent, it is ideal to employ in
searches of statistical anisotropy (e.g., contaminations from the galactic
plane) and to characterize non-Gaussianities.Comment: Replaced to match the published version. Journal-ref: Phys.Rev. D80
063525 (2009
Inflationary Perturbations in Anisotropic, Shear-Free Universes
In this work, the linear and gauge-invariant theory of cosmological
perturbations in a class of anisotropic and shear-free spacetimes is developed.
After constructing an explicit set of complete eigenfunctions in terms of which
perturbations can be expanded, we identify the effective degrees of freedom
during a generic slow-roll inflationary phase. These correspond to the
anisotropic equivalent of the standard Mukhanov-Sasaki variables. The
associated equations of motion present a remarkable resemblance to those found
in perturbed Friedmann-Robertson-Walker spacetimes with curvature, apart from
the spectrum of the Laplacian, which exhibits the characteristic frequencies of
the underlying geometry. In particular, it is found that the perturbations
cannot develop arbitrarily large super-Hubble modes.Comment: 24 pages, 2 figure
Nonviolation of Bell's Inequality in Translation Invariant Systems
The nature of quantum correlations in strongly correlated systems has been a
subject of intense research. In particular, it has been realized that
entanglement and quantum discord are present at quantum phase transitions and
able to characterize it. Surprisingly, it has been shown for a number of
different systems that qubit pairwise states, even when highly entangled, do
not violate Bell's inequalities, being in this sense local. Here we show that
such a local character of quantum correlations is in fact general for
translation invariant systems and has its origins in the monogamy trade-off
obeyed by tripartite Bell correlations. We illustrate this result in a quantum
spin chain with a soft breaking of translation symmetry. In addition, we extend
the monogamy inequality to the -qubit scenario, showing that the bound
increases with and providing examples of its saturation through uniformly
generated random pure states.Comment: Published erratum added at the en
Overcoming ambiguities in classical and quantum correlation measures
We identify ambiguities in the available frameworks for defining quantum,
classical, and total correlations as measured by discordlike quantifiers. More
specifically, we determine situations for which either classical or quantum
correlations are not uniquely defined due to degeneracies arising from the
optimization procedure over the state space. In order to remove such
degeneracies, we introduce a general approach where correlations are
independently defined, escaping therefore from a degenerate subspace. As an
illustration, we analyze the trace-norm geometric quantum discord for two-qubit
Bell-diagonal states.Comment: 5 pages, 2 figures. v2: Minor corrections. Published versio
Local roughness exponent in the nonlinear molecular-beam-epitaxy universality class in one-dimension
We report local roughness exponents, , for three
interface growth models in one dimension which are believed to belong the
non-linear molecular-beam-epitaxy (nMBE) universality class represented by the
Villain-Lais-Das Sarma (VLDS) stochastic equation. We applied an optimum
detrended fluctuation analysis (ODFA) [Luis et al., Phys. Rev. E 95, 042801
(2017)] and compared the outcomes with standard detrending methods. We observe
in all investigated models that ODFA outperforms the standard methods providing
exponents in the narrow interval consistent
with renormalization group predictions for the VLDS equation. In particular,
these exponent values are calculated for the Clarke-Vvdensky and Das
Sarma-Tamborenea models characterized by very strong corrections to the
scaling, for which large deviations of these values had been reported. Our
results strongly support the absence of anomalous scaling in the nMBE
universality class and the existence of corrections in the form
of the one-loop renormalization group analysis
of the VLDS equation
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