Weak-field approximation of effective gravitational theory with local Galilean invariance

We examine the weak-field approximation of locally Galilean invariant gravitational theories with general covariance in a $(4+1)$-dimensional Galilean framework. The additional degrees of freedom allow us to obtain Poisson, diffusion, and Schr\"odinger equations for the fluctuation field. An advantage of this approach over the usual $(3+1)$-dimensional General Relativity is that it allows us to choose an ansatz for the fluctuation field that can accommodate the field equations of the Lagrangian approach to MOdified Newtonian Dynamics (MOND) known as AQUAdratic Lagrangian (AQUAL). We investigate a wave solution for the Schr\"odinger equations.Comment: 15 page

Cosmic distance-duality as probe of exotic physics and acceleration

In cosmology, distances based on standard candles (e.g. supernovae) and standard rulers (e.g. baryon oscillations) agree as long as three conditions are met: (1) photon number is conserved, (2) gravity is described by a metric theory with (3) photons travelling on unique null geodesics. This is the content of distance-duality (the reciprocity relation) which can be violated by exotic physics. Here we analyse the implications of the latest cosmological data sets for distance-duality. While broadly in agreement and confirming acceleration we find a 2-sigma violation caused by excess brightening of SN-Ia at z > 0.5, perhaps due to lensing magnification bias. This brightening has been interpreted as evidence for a late-time transition in the dark energy but because it is not seen in the d_A data we argue against such an interpretation. Our results do, however, rule out significant SN-Ia evolution and extinction: the "replenishing" grey-dust model with no cosmic acceleration is excluded at more than 4-sigma despite this being the best-fit to SN-Ia data alone, thereby illustrating the power of distance-duality even with current data sets.Comment: 6 pages, 4 colour figures. Version accepted as a Rapid Communication in PR

Gamma-Ray Bursts: The Underlying Model

A pedagogical derivation is presented of the ``fireball'' model of gamma-ray bursts, according to which the observable effects are due to the dissipation of the kinetic energy of a relativistically expanding wind, a ``fireball.'' The main open questions are emphasized, and key afterglow observations, that provide support for this model, are briefly discussed. The relativistic outflow is, most likely, driven by the accretion of a fraction of a solar mass onto a newly born (few) solar mass black hole. The observed radiation is produced once the plasma has expanded to a scale much larger than that of the underlying ``engine,'' and is therefore largely independent of the details of the progenitor, whose gravitational collapse leads to fireball formation. Several progenitor scenarios, and the prospects for discrimination among them using future observations, are discussed. The production in gamma- ray burst fireballs of high energy protons and neutrinos, and the implications of burst neutrino detection by kilometer-scale telescopes under construction, are briefly discussed.Comment: In "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture Notes in Physics, Springer-Verlag (in press); 26 pages, 2 figure

Gravitational Radiation from Compact Binary Pulsars

An outstanding question in modern Physics is whether general relativity (GR) is a complete description of gravity among bodies at macroscopic scales. Currently, the best experiments supporting this hypothesis are based on high-precision timing of radio pulsars. This chapter reviews recent advances in the field with a focus on compact binary millisecond pulsars with white-dwarf (WD) companions. These systems - if modeled properly - provide an unparalleled test ground for physically motivated alternatives to GR that deviate significantly in the strong-field regime. Recent improvements in observational techniques and advances in our understanding of WD interiors have enabled a series of precise mass measurements in such systems. These masses, combined with high-precision radio timing of the pulsars, result to stringent constraints on the radiative properties of gravity, qualitatively very different from what was available in the past.Comment: Short review chapter to appear in "Gravitational Wave Astrophysics" by Springer-Verlag, edited by Carlos F. Sopuerta; v3: a few major corrections and updated references. Comments are welcome

Tides in colliding galaxies

Long tails and streams of stars are the most noticeable upshots of galaxy collisions. Their origin as gravitational, tidal, disturbances has however been recognized only less than fifty years ago and more than ten years after their first observations. This Review describes how the idea of galactic tides emerged, in particular thanks to the advances in numerical simulations, from the first ones that included tens of particles to the most sophisticated ones with tens of millions of them and state-of-the-art hydrodynamical prescriptions. Theoretical aspects pertaining to the formation of tidal tails are then presented. The third part of the review turns to observations and underlines the need for collecting deep multi-wavelength data to tackle the variety of physical processes exhibited by collisional debris. Tidal tails are not just stellar structures, but turn out to contain all the components usually found in galactic disks, in particular atomic / molecular gas and dust. They host star-forming complexes and are able to form star-clusters or even second-generation dwarf galaxies. The final part of the review discusses what tidal tails can tell us (or not) about the structure and content of present-day galaxies, including their dark components, and explains how tidal tails may be used to probe the past evolution of galaxies and their mass assembly history. On-going deep wide-field surveys disclose many new low-surface brightness structures in the nearby Universe, offering great opportunities for attempting galactic archeology with tidal tails.Comment: 46 pages, 13 figures, Review to be published in "Tidal effects in Astronomy and Astrophysics", Lecture Notes in Physics. Comments are most welcom

Early communication in preterm infants following intervention in the NICU

Background: Despite ongoing improvements in clinical care, preterm infants experience a variety of stressors in the first weeks of life, including necessary medical procedures, which may affect development. Some stress-reduction programmes based in the Neonatal Intensive Care Unit (NICU) have reported a positive impact on development. In particular, trials of the Mother–Infant Transaction Program (MITP) have shown positive short and longer term effects, and are based on training parents to recognise and minimise stress responses in preterm infants. Aims: To evaluate the impact on early developmental milestones of an enhanced MITP (PremieStart) delivered over an extended period in the NICU. Study design: This was a parallel 2-group randomised controlled trial involving 109 women with 123 infants born at < 30 weeks gestation assessed initially at term-equivalent age and then at 6 months' corrected-age. Results: Intervention mothers were more sensitive in providing infant care, stressed their infants less, showed greater awareness of, and responded more appropriately to, negative infant cues (p < 0.05 in each case). Intervention infants displayed significantly lower stress when being bathed by mothers at term-equivalent age (p < 0.05). At 6 months corrected-age, intervention infants showed higher mean scores on the Communication and Symbolic Behavior Scales Developmental Profile Infant–Toddler Checklist. The strongest effects appeared in Symbolic behaviour (p = 0.05) and this was reflected in the Total score (p < 0.05). Conclusions: As significant cognitive and language deficits are reported in longitudinal studies of preterm children, an intervention that improves early infant communication abilities is promising, especially since previous research suggests that the strongest benefits may emerge at later ages.Jeannette Milgrom, Carol Newnham, Paul R.Martin, Peter J.Anderson, Lex W.Doyle, Rod W.Hunt ... et al

Communication compatible voting rules

We reassess the possibility of full information pooling in a Condorcet jury environment featuring heterogeneous and privately known preference types. We find that in general, with uncorrelated preference types, only very limited heterogeneity is compatible with full pooling. We provide a sufficient condition, based on a simple measure of preference misalignment, under which the set of voting rules compatible with full pooling is at most a singleton. As a caveat to any simplistic conclusions, we identify a case in which an increase in heterogeneity (i.e. polarization) systematically generates the possibility of full pooling. Increased jury size, in contrast, is shown to always render full pooling more difficult

Characterizing the Vickrey combinatorial auction by induction

Vickrey auction, Strategy-proofness, Induction, Heterogenous commodities, D44, C78, D71, D61, D82,