Scattering processes could distinguish Majorana from Dirac neutrinos

It is well known that Majorana neutrinos have a pure axial neutral current interaction while Dirac neutrinos have the standard vector-axial interaction. In spite of this crucial difference, usually Dirac neutrino processes differ from Majorana processes by a term proportional to the neutrino mass, resulting in almost unmeasurable observations of this difference. In the present work we show that once the neutrino polarization evolution is considered, there are clear differences between Dirac and Majorana scattering on electrons. The change of polarization can be achieved in astrophysical environments with strong magnetic fields. Furthermore, we show that in the case of unpolarized neutrino scattering onto polarized electrons, this difference can be relevant even for large values of the neutrino energy.Comment: 12 pages, 5 figure

Science with an ngVLA: Resolved Substructures in Protoplanetary Disks

Terrestrial planets and the cores of giant planets are thought to be built by the collisional agglomeration of solids spanning over 20 orders of magnitude in size within a few million years. However, there is tension between this basic picture of planet formation and standard theoretical assumptions associated with the migration of "pebbles" ($\sim$mm/cm-sized particles) in gas-rich disks and the presumably much longer timescales necessary to assemble ($\sim$km-scale) "planetesimals". To confront these potential theoretical discrepancies with observational constraints, the ideal tracer of the solids concentrated in protoplanetary disk substructures is the 30-100 GHz continuum, which strikes the best balance in sensitivity (emission still bright), optical depth (low enough to reliably estimate densities), and angular resolution (high enough to resolve fine-scale features at disk radii as small as 1 au). With its combination of sensitivity, frequency coverage, and angular resolution, the next-generation VLA will be the only facility that has the capabilities to open up this new window into the physics of planetesimal formation.Comment: To be published in the ASP Monograph Series, Science with a Next-Generation VLA, ed. E. J. Murphy (ASP, San Francisco, CA

Imaging the Inner and Outer Gaps of the Pre-Transitional Disk of HD 169142 at 7 mm

We present Very Large Array observations at 7 mm that trace the thermal emission of large dust grains in the HD 169142 protoplanetary disk. Our images show a ring of enhanced emission of radius ~25-30 AU, whose inner region is devoid of detectable 7 mm emission. We interpret this ring as tracing the rim of an inner cavity or gap, possibly created by a planet or a substellar companion. The ring appears asymmetric, with the western part significantly brighter than the eastern one. This azimuthal asymmetry is reminiscent of the lopsided structures that are expected to be produced as a consequence of trapping of large dust grains. Our observations also reveal an outer annular gap at radii from ~40 to ~70 AU. Unlike other sources, the radii of the inner cavity, the ring, and the outer gap observed in the 7 mm images, which trace preferentially the distribution of large (mm/cm sized) dust grains, coincide with those obtained from a previous near-infrared polarimetric image, which traces scattered light from small (micron- sized) dust grains. We model the broad-band spectral energy distribution and the 7 mm images to constrain the disk physical structure. From this modeling we infer the presence of a small (radius ~0.6 AU) residual disk inside the central cavity, indicating that the HD 169142 disk is a pre-transitional disk. The distribution of dust in three annuli with gaps in between them suggests that the disk in HD 169142 is being disrupted by at least two planets or substellar objects.Comment: Accepted by ApJ Letters, 16 pages, 3 figures, ApJ Letters 201

Characterizing the dust content of disk substructures in TW Hya

We present Atacama Large Millimeter Array (ALMA) observations of TW Hya at 3.1 mm with $\sim50$ milliarcsecond resolution. These new data were combined with archival high angular resolution ALMA observations at 0.87 mm, 1.3 mm, and 2.1 mm. We analyze these multi-wavelength data to infer a disk radial profile of the dust surface density, maximum particle size, and slope of the particle size distribution. Most previously known annular substructures in the disk of TW Hya are resolved at the four wavelengths. Inside the inner 3 au cavity, the 2.1 mm and 3.1 mm images show a compact source of free-free emission, likely associated with an ionized jet. Our multi-wavelength analysis of the dust emission shows that the maximum particle size in the disk of TW Hya is $>1$ mm. The inner 20 au are completely optically thick at all four bands, which results in the data tracing different disk heights at different wavelengths. Coupled with the effects of dust settling, this prevents the derivation of accurate density and grain size estimates in these regions. At $r>20$ au, we find evidence of the accumulation of large dust particle at the position of the bright rings, indicating that these are working as dust traps. The total dust mass in the disk is between 250 and 330 $M_{\oplus}$, which represents a gas-to-dust mass ratio between 50 and 70. Our mass measurement is a factor of 4.5-5.9 higher than the mass that one would estimate using the typical assumptions of large demographic surveys. Our results indicate that the ring substructures in TW Hya are ideal locations to trigger the streaming instability and form new generations of planetesimals.Comment: 22 pages, 17 figures, accepted for publication in A&A. Language edited versio

The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA and VLA Observations

Understanding planet formation requires one to discern how dust grows in protoplanetary disks. An important parameter to measure in disks is the maximum dust grain size present. This is usually estimated through measurements of the dust opacity at different millimeter wavelengths assuming optically thin emission and dust opacity dominated by absorption. However, Atacama Large Millimeter/submillimeter Array (ALMA) observations have shown that these assumptions might not be correct in the case of protoplanetary disks, leading to overestimation of particle sizes and to underestimation of the disk\u27s mass. Here, we present an analysis of high-quality ALMA and Very Large Array images of the HL Tau protoplanetary disk, covering a wide range of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of ~7.35 au. We describe a procedure to analyze a set of millimeter images without any assumption about the optical depth of the emission, and including the effects of absorption and scattering in the dust opacity. This procedure allows us to obtain the dust temperature, the dust surface density, and the maximum particle size at each radius. In the HL Tau disk, we found that particles have already grown to a few millimeters in size. We detect differences in the dust properties between dark and bright rings, with dark rings containing low dust density and small dust particles. Different features in the HL Tau disk seem to have different origins. Planet–disk interactions can explain substructure in the external half of the disk, but the internal rings seem to be associated with the presence of snow lines of several molecules

Circulating vitamin D levels and colorectal cancer risk: a meta-analysis and systematic review of case-control and prospective cohort studies

The associations between circulating vitamin D concentrations and total and site-specific colorectal cancer (CRC) incidence have been examined in several epidemiological studies with overall inconclusive findings. The aim of this systematic review and meta-analysis of both case-control and prospective cohort studies was to evaluate the association between CRC and circulating levels of vitamin D. The main exposure and outcome were circulating total 25(OH)D and CRC, respectively, in the overall population (i.e., all subjects). Two reviewers, working independently, screened all the literature available to identify studies that met the inclusion criteria (e.g., case-control or prospective cohort studies, published in English, and excluding non-original papers). Data were pooled by the generic inverse variance method using a random or fixed effect model, as approriate. Heterogeneity was identified using the Cochran's Q-test and quantified by the I2 statistic. Results were stratified by study design, sex, and metabolite of vitamin D. Sensitivity and subgroup analyses were also performed. A total of 28 original studies were included for the quantitative meta-analysis. Meta-analyses comparing the highest vs lowest categories, showed a 39% lower risk between levels of total 25(OH)D and CRC risk (OR (95% CI): 0.61 (0.52; 0.71); 11 studies) in case-control studies; whereas a 20% reduced CRC risk in prospective cohort studies (HR (95% CI): 0.80 (0.66; 0.97); 6 studies). Results in women mirrored main results, whereas results in men were non-significant in both analyses. Our findings support an inverse association between circulating vitamin D levels and CRC risk