The inflationary origin of the Cold Spot anomaly

Single-field inflation, arguably the simplest and most compelling paradigm for the origin of our Universe, is strongly supported by the recent results of the Planck satellite and the BICEP2 experiment. The results from Planck, however, also confirm the presence of a number of anomalies in the Cosmic Microwave Background (CMB), whose origin becomes problematic in single-field inflation. Among the most prominent and well-tested of these anomalies is the Cold Spot, which constitutes the only significant deviation from gaussianity in the CMB. Planck's non-detection of primordial non-gaussianity on smaller scales thus suggests the existence of a physical mechanism whereby significant non-gaussianity is generated on large angular scales only. In this letter, we address this question by developing a localized version of the inhomogeneous reheating scenario, which postulates the existence of a scalar field able to modify the decay of the inflaton on localized spatial regions only. We demonstrate that if the Cold Spot is due to an overdensity in the last scattering surface, the localization mechanism offers a feasible explanation for it, thus providing a physical mechanism for the generation of localized non-gaussianity in the CMB. If, on the contrary, the Cold Spot is caused by a newly discovered supervoid (as recently claimed), we argue that the localization mechanism, while managing to enhance underdensities, may well shed light on the rarity of the discovered supervoid.Comment: 12 pages, 4 figures. v3 Comments and references added. It matches published versio

Regional growth and regional imbalances: Spain and USA

Regional and national incomes are determined by spatial and non spatial phenomena. Relative elasticities in Spain and U.S.A. for income explanatory variables, which were derivated from space models estimates, are 35 y 65%, respectively. External spatial economies, locational inertia of investment and urban expenditure multiplier -all of them typical spatial variables- are all concepts explaining the way space cooperates to income generation. Non spatial economic analysis therefore does not pay attention to phenomena which explain about a third of the produced national wealth. Regional income imbalances have not disappeared after decades or even centuries of economic development. Although they have indeed decreased dramatically, this reduction stopped around 1960 in the U.S.A. and 1980 in Spain. Since then regional per capita income imbalances have remained almost constant, ranging from 60 to 75 % between poor and rich regions. Interregional technological transfers, internal economies of scale, the urban expenditure multiplier, and decreasing external spatial economies explain the interregional “catching-up”. External spatial economies, locational inertia of investment and the end of regional labour migration are the reasons explaining the present steadiness in spatial imbalances.

Algorithms and structures for source separation based on the constant modulus property

We propose two structures and theirs associated algorithms designed to solve the blind source separation problem in the presence of noise and interferences. Both structures exploit the non convexity of the Constant Modulus cost function, finding its multiple local minima. A convergence analysis shows that both schemes achieve the desired solution, separately extracting the sources of interest while rejecting noise and interferences, provided that they do not share the constant modulus property.Peer ReviewedPostprint (published version

On the coupling of vector fields to the Gauss-Bonnet invariant

Inflationary models including vector fields have attracted a great deal of attention over the past decade. Such an interest owes to the fact that they might contribute to, or even be fully responsible for, the curvature perturbation imprinted in the CMB. However, the necessary breaking of the vector field's conformal invariance during inflation is not without problems. In recent years it has been realized that a number of instabilities endangering the consistency of the theory arise when the conformal invariance is broken by means of a non-minimal coupling to gravity. In this paper we consider a massive vector field non-minimally coupled to gravity through the Gauss-Bonnet invariant, and investigate whether the vector can obtain a nearly scale-invariant perturbation spectrum while evading the emergence of perturbative instabilities. We find that the strength of the coupling must be extremely small if the vector field is to have a chance to contribute to the total curvature perturbation.Comment: 8 pages, 1 figur