40,838 research outputs found
Evidence for non-Gaussianity in the COBE DMR Four Year Sky Maps
We introduce and study the distribution of an estimator for the normalized
bispectrum of the Cosmic Microwave Background (CMB) anisotropy. We use it to
construct a goodness of fit statistic to test the coadded 53 and 90 GHz
COBE-DMR 4 year maps for non-Gaussianity. Our results indicate that Gaussianity
is ruled out at the confidence level in excess of 98%. This value is a lower
bound, given all the investigated systematics. The dominant non-Gaussian
contribution is found near the multipole of order . Our attempts to
explain this effect as caused by the diffuse foreground emission from the
Galaxy have failed. We conclude that unless there exists a microwave foreground
emission which spatially correlates neither with the DIRBE nor Haslam maps, the
cosmological CMB anisotropy is genuinely non-Gaussian.Comment: 16 pages, 3 figs uses aasms4.tex, revised and accepted to Ap. J. Let
The 4 Year COBE DMR data is non-Gaussian
I review our recent claim that there is evidence of non-Gaussianity in the 4
Year COBE DMR data. I describe the statistic we apply, the result we obtain and
make a detailed list of the systematics we have analysed. I finish with a
qualitative understanding of what it might be and its implications.Comment: Proceedings of Rome 3K conference, 5 pages, 3 figure
Where is the COBE maps' non-Gaussianity?
We review our recent claim that there is evidence of non-Gaussianity in the 4
Year COBE DMR data. We present some new results concerning the effect of the
galactic cut upon the non-Gaussian signal. These findings imply a localization
of the non-Gaussian signal on the Northern galactic hemisphere.Comment: Proceedings of COSMO98 Asiloma
Discrete and continuous symmetries in multi-Higgs-doublet models
We consider the Higgs sector of multi-Higgs-doublet models in the presence of
simple symmetries relating the various fields. We construct basis invariant
observables which may in principle be used to detect these symmetries for any
number of doublets. A categorization of the symmetries into classes is
required, which we perform in detail for the case of two and three Higgs
doublets.Comment: 13 pages, RevTex, references adde
Charge breaking bounds in the Zee model
We study the possibility that charge breaking minima occur in the Zee model.
We reach very different conclusions from those attained in simpler, two Higgs
doublet models, and the reason for this is traced back to the existence of
cubic terms in the potential. A scan of the Zee model's parameter space shows
that CB is restricted to a narrow region of values of the parameters
Continuous and discontinuous absorbing-state phase transitions on Voronoi-Delaunay random lattices
We study absorbing-state phase transitions in two-dimensional
Voronoi-Delaunay (VD) random lattices with quenched coordination disorder.
Quenched randomness usually changes the criticality and destroys discontinuous
transitions in low-dimensional nonequilibrium systems. We performed extensive
simulations of the Ziff-Gulari-Barshad (ZGB) model, and verified that the VD
disorder does not change the nature of its discontinuous transition. Our
results corroborate recent findings of Barghatti and Vojta [Phys. Rev. Lett.
{\bf 113}, 120602 (2014)] stating the irrelevance of topological disorder in a
class of random lattices that includes VD and raise the interesting possibility
that disorder in nonequilibrium APT may, under certain conditions, be
irrelevant for the phase coexistence. We also verify that the VD disorder is
irrelevant for the critical behavior of models belonging to the directed
percolation and Manna universality classes.Comment: 7 pages, 6 figure
Unified Superfluid Dark Sector
We present a novel theory of a unified dark sector, where late-time cosmic
acceleration emerges from the dark matter superfluid framework. The system is
described by a superfluid mixture consisting of two distinguishable states with
a small energy gap, such as the ground state and an excited state of dark
matter. Given their contact in the superfluid, interaction between those states
can happen, converting one state into the other. This long range interaction
within the superfluid couples the two superfluid phonon species through a
cosine potential motivated by Josephson/Rabi interactions. As a consequence of
this potential, a new dynamics of late-time accelerated expansion emerges in
this system, without the need of dark energy, coming from a universe containing
only this two-state DM superfluid. Because the superfluid species are
non-relativistic, their sound speeds remain suitably small throughout the
evolution. We calculate the expansion history and growth of linear
perturbations, and compare the results to CDM cosmology. For the
fiducial parameters studied here, the predicted expansion and growth function
are close to those of CDM, but the difference in the predicted growth
rate is significant at late times. The present theory nicely complements the
recent proposal of dark matter superfluidity to explain the empirical success
of MOdified Newtonian Dynamics (MOND) on galactic scales, thus offering a
unified framework for dark matter, dark energy, and MOND phenomenology.Comment: 27 pages, 4 figures. v2: Version accepted in JCA
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