13,679 research outputs found
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
Optimal State-Contingent Unemployment Insurance
Since the probability of finding a job is affected not only by individual effort but also by the aggregate state of the economy, designing unemployment insurance payments conditional on the business cycle could be valuable. This paper answers a fundamental question related to this issue: How should the payments vary with the aggregate state of the economy?Unemployment Insurance; Aggregate Fluctuations; Recursive Contracts and Moral Hazard
Invisibility and PT Symmetry: A Simple Geometrical Viewpoint
We give a simplified account of the properties of the transfer matrix for a
complex one-dimensional potential, paying special attention to the particular
instance of unidirectional invisibility. In appropriate variables, invisible
potentials appear as performing null rotations, which lead to the
helicity-gauge symmetry of massless particles. In hyperbolic geometry, this can
be interpreted, via M\"{o}bius transformations, as parallel displacements, a
geometric action that has no Euclidean analogy.Comment: 13 pages. No figure. Accepted for publication in Symmetr
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