164 research outputs found
Search for photons at the Pierre Auger Observatory
The Pierre Auger Observatory has a unique potential to search for ultra-high
energy photons (above ~1 EeV). First experimental limits on photons were
obtained during construction of the southern part of the Observatory.
Remarkably, already these limits have proven useful to falsify proposals about
the origin of cosmic rays, and to perform fundamental physics by constraining
Lorentz violation. A final discovery of photons at the upper end of the
electromagnetic spectrum is likely to impact various branches of physics and
astronomy.Comment: 5 pages, 5 figures. Presented at CRIS 2008, Malfa, Ital
Cosmological birefringence constraints from CMB and astrophysical polarization data
Cosmological birefringence is a rotation of the polarization plane of photons
coming from sources of astrophysical and cosmological origin. The rotation can
also depend on the energy of the photons and not only on the distance of the
source and on the cosmological evolution of the underlying theoretical model.
In this work, we constrain few selected models for cosmological birefringence,
combining CMB and astrophysical data at radio, optical, X and gamma
wavelengths, taking into account the specific energy and distance dependences.Comment: 12 pages, 2 figure
Light Bending as a Probe of the Nature of Dark Energy
We study the bending of light for static spherically symmetric (SSS)
space-times which include a dark energy contribution. Geometric dark energy
models generically predict a correction to the Einstein angle written in terms
of the distance to the closest approach, whereas a cosmological constant
does not. While dark energy is associated with a repulsive force in
cosmological context, its effect on null geodesics in SSS space-times can be
attractive as for the Newtonian term. This dark energy contribution may be not
negligible with respect to the Einstein prediction in lensing involving
clusters of galaxies. Strong lensing may therefore be useful to distinguish
from other dark energy models.Comment: 5 pages, 2 figures, 1 table. References added, final version appeared
in Physical Review
Multilocus Detection of Wolf x Dog Hybridization in Italy, and Guidelines for Marker Selection
Hybridization and introgression can impact the evolution of natural populations. Several wild canid species hybridize in nature, sometimes originating new taxa. However, hybridization with free-ranging dogs is threatening the genetic integrity of grey wolf populations (Canis lupus), or even the survival of endangered species (e.g., the Ethiopian wolf C. simensis). Efficient molecular tools to assess hybridization rates are essential in wolf conservation strategies. We evaluated the power of biparental and uniparental markers (39 autosomal and 4 Y-linked microsatellites, a melanistic deletion at the \u3b2-defensin CBD103 gene, the hypervariable domain of the mtDNA control-region) to identify the multilocus admixture patterns in wolf x dog hybrids. We used empirical data from 2 hybrid groups with different histories: 30 presumptive natural hybrids from Italy and 73 Czechoslovakian wolfdogs of known hybrid origin, as well as simulated data. We assessed the efficiency of various marker combinations and reference samples in admixture analyses using 69 dogs of different breeds and 99 wolves from Italy, Balkans and Carpathian Mountains. Results confirmed the occurrence of hybrids in Italy, some of them showing anomalous phenotypic traits and exogenous mtDNA or Y-chromosome introgression. Hybridization was mostly attributable to village dogs and not strictly patrilineal. The melanistic \u3b2-defensin deletion was found only in Italian dogs and in putative hybrids. The 24 most divergent microsatellites (largest wolf-dog FST values) were equally or more informative than the entire panel of 39 loci. A smaller panel of 12 microsatellites increased risks to identify false admixed individuals. The frequency of F1 and F2 was lower than backcrosses or introgressed individuals, suggesting hybridization already occurred some generations in the past, during early phases of wolf expansion from their historical core areas. Empirical and simulated data indicated the identification of the past generation backcrosses is always uncertain, and a larger number of ancestry-informative markers is needed
Novel Harmonization Method for Multi-Centric Radiomic Studies in Non-Small Cell Lung Cancer
The purpose of this multi-centric work was to investigate the relationship between radiomic features extracted from pre-treatment computed tomography (CT), positron emission tomography (PET) imaging, and clinical outcomes for stereotactic body radiation therapy (SBRT) in early-stage non-small cell lung cancer (NSCLC). One-hundred and seventeen patients who received SBRT for early-stage NSCLC were retrospectively identified from seven Italian centers. The tumor was identified on pre-treatment free-breathing CT and PET images, from which we extracted 3004 quantitative radiomic features. The primary outcome was 24-month progression-free-survival (PFS) based on cancer recurrence (local/non-local) following SBRT. A harmonization technique was proposed for CT features considering lesion and contralateral healthy lung tissues using the LASSO algorithm as a feature selector. Models with harmonized CT features (B models) demonstrated better performances compared to the ones using only original CT features (C models). A linear support vector machine (SVM) with harmonized CT and PET features (A1 model) showed an area under the curve (AUC) of 0.77 (0.63-0.85) for predicting the primary outcome in an external validation cohort. The addition of clinical features did not enhance the model performance. This study provided the basis for validating our novel CT data harmonization strategy, involving delta radiomics. The harmonized radiomic models demonstrated the capability to properly predict patient prognosis
Lorentz breaking Effective Field Theory and observational tests
Analogue models of gravity have provided an experimentally realizable test
field for our ideas on quantum field theory in curved spacetimes but they have
also inspired the investigation of possible departures from exact Lorentz
invariance at microscopic scales. In this role they have joined, and sometime
anticipated, several quantum gravity models characterized by Lorentz breaking
phenomenology. A crucial difference between these speculations and other ones
associated to quantum gravity scenarios, is the possibility to carry out
observational and experimental tests which have nowadays led to a broad range
of constraints on departures from Lorentz invariance. We shall review here the
effective field theory approach to Lorentz breaking in the matter sector,
present the constraints provided by the available observations and finally
discuss the implications of the persisting uncertainty on the composition of
the ultra high energy cosmic rays for the constraints on the higher order,
analogue gravity inspired, Lorentz violations.Comment: 47 pages, 4 figures. Lecture Notes for the IX SIGRAV School on
"Analogue Gravity", Como (Italy), May 2011. V.3. Typo corrected, references
adde
On Horava-Lifshitz "Black Holes"
The most general spherically symmetric solution with zero shift is found in
the non-projectable Horava-Lifshitz class of theories with general coupling
constants. It contains as special cases, spherically symmetric solutions found
by other authors earlier. It is found that the generic solution has
conventional (AdS, dS or flat) asymptotics with a universal 1/r tail. There are
several special cases where the asymptotics differ, including the detailed
balance choice of couplings. The conventional thermodynamics of this general
class of solutions is established by calculating the energy, temperature and
entropy. Although several of the solutions have conventional horizons, for
particles with ultra-luminal dispersion relations such solutions appear to be
horizonless.Comment: Latex 41 pages, 5 figure
Genome sequencing highlights the dynamic early history of dogs
To identify genetic changes underlying dog domestication and reconstruct their early evolutionary history, we generated high-quality genome sequences from three gray wolves, one from each of the three putative centers of dog domestication, two basal dog lineages (Basenji and Dingo) and a golden jackal as an outgroup. Analysis of these sequences supports a demographic model in which dogs and wolves diverged through a dynamic process involving population bottlenecks in both lineages and post-divergence gene flow. In dogs, the domestication bottleneck involved at least a 16-fold reduction in population size, a much more severe bottleneck than estimated previously. A sharp bottleneck in wolves occurred soon after their divergence from dogs, implying that the pool of diversity from which dogs arose was substantially larger than represented by modern wolf populations. We narrow the plausible range for the date of initial dog domestication to an interval spanning 11-16 thousand years ago, predating the rise of agriculture. In light of this finding, we expand upon previous work regarding the increase in copy number of the amylase gene (AMY2B) in dogs, which is believed to have aided digestion of starch in agricultural refuse. We find standing variation for amylase copy number variation in wolves and little or no copy number increase in the Dingo and Husky lineages. In conjunction with the estimated timing of dog origins, these results provide additional support to archaeological finds, suggesting the earliest dogs arose alongside hunter-gathers rather than agriculturists. Regarding the geographic origin of dogs, we find that, surprisingly, none of the extant wolf lineages from putative domestication centers is more closely related to dogs, and, instead, the sampled wolves form a sister monophyletic clade. This result, in combination with dog-wolf admixture during the process of domestication, suggests that a re-evaluation of past hypotheses regarding dog origins is necessary
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