Tuesday.
1405.7695
Three regimes of extrasolar planets inferred from host star metallicities
Buchhave, Bizzarro, ... Marcy, et al
Approximately half of the extrasolar planets with radii less than four Earth Radii are in orbits with short periods. Despite their sheer abundance, the compositions of such planets are largely unknown. The available evidence suggests that they range in composition from small, high-density rocky points to low-density planets consisting of rocky cores surrounded by thick hydrogen and He gas envelopes. Understanding the transition from the gaseous planets to Earth-like rocky worlds is important to estimate the number of potentially habitable planets in our Galaxy and provide constraints on planet formation theories. Report the abundances of heavy elements (metallicities) of more than 400 stars hosting 600 exoplanet candidates, and find that the exoplanets can be categorized into 3 populations defined by statistically distinct (~4.5 sigma) metallicity regions. Interpret these regions as reflecting the formation regimes of terrestrial-like planets (radii less than 1.7 Earth radii), gas dwarf planets with rocky cores and H-He envelopes (radii between 1.7 and 3.9 Earth radii) and ice or gas giant planets (>3.9 Earth radii). These transitions correspond well with those inferred from dynamical mass estimates, implying that host star metallicity, which is a proxy for the initial solid inventory of the protoplanetary disk, is a key ingredient regulating the structure of planetary systems.
1405.7860
What is the distance to the CMB? how relativistic corrections remove the tension with local H0 measurements
Clarkson, Umeh, Maartens, Durrer
The success of precision cosmology depends not only on accurate observations, but also on the theoretical model - which must be understood to at least the same level of precision. Subtle relativistic effects can lead to biased measurements if they are neglected. One such effect gives a systematic shift in the distance -redshift relation away from its background value, due to the accumulation of all possible lensing events. Estimate the expectation value of this aggregated lensing using second-order perturbations about a concordance background, and show that the distance to last scattering is shifted by several percent. Neglecting this shift leads to significant bias in the background cosmological parameters. Show that this removes the tension between local measurements of H0 and those measured through the CMB and favors a closed universe.
1405.7876
CLASH-X: a comparison of lensing and X-ray techniques for measuring the mass profiles of galaxy clusters
Donahue, Voit, Mahdavi, Umetsu, Ettori, .. Coe, .. Bartelmann, .. Broadhurst, .. et al
Present profile of temperature, gas mass, and hydrostatic mass estimated from X-ray observations of CLASH clusters. Compare measurements from XMM and Chandra and compare both sets to CLASH gravitational lensing mass profiles. Find that Chandra and XMM measurements of electron density and enclosed gas mass as functions of radius are nearly identical, indicating that any differences in hydrostatic masses inferred from X-ray observations arise from differences in gas-temperature estimates. Encouragingly, gas temperatures measured in clusters by XMM and Chandra are consistent with one another at ~100 kpc radii but XMM temperatures systematically decline relative to Chandra temperatures as the radius of the temperature measurement increases. One plausible reason for this trend is large-angle scattering of soft X-ray photons in excess of that amount expected from the standard XMM PSF correction. Present the CLASH-X mass-profile comparisons in the form of cosmology-independent and redshift-independent circular-velocity profiles, which are the most robust way to assess mass bias. Chandra HSE mass to CLASH lensing mass ratio profiles show no obvious radial dependence in the 0.3-0.8 Mpc range. However, the main mass biases inferred from the WL and SaWLens data are different, with a weighted-mean value at 0.5 Mpc of <b>=0.12 for the WL comparison and <b>=-0.11 for the SaWLens comparison. XMM HSE mass to CLASH lensing mass ratio profiles show a pronounced radial dependence in the 0.3-1.0 Mpc range, with a weighted-mean mass bias of value rising to b>0.3 at ~1 Mpc for the WL comparison and b~0.25 for the SaWLens comparison. The enclosed gas mass profiles from both Chandra and XMM rise to a value ~1/8 times the total-mass profiles inferred from lensing at ~0.5 Mpc, suggesting that 8 M_gas profiles may be an excellent proxy for total-mass profiles at >~0.5 Mpc in massive galaxy clusters.
1405.7654
Detecting non-relativistic cosmic neutrinos by capture on tritium: phenomenology and physics potential
Long, Lunardini, Sabancilar
Study the physics potential of the detection of the CNB via neutrino capture on tritium, taking the proposed PTOLEMY experiment as a case study. With the projected energy resolution of Delta ~ 0.15 eV, the experiment will be sensitive to neutrino masses with degenerate spectrum, m1~m2~m3=m_nu>0.1 eV. These neutrinos are non-relativistic today; detecting them would be a unique opportunity to probe this unexplored kinematical regime. The signature of neutrino capture is a peak in the electron spectrum that is displaced by 2 m_nu above the beta decay endpoint. The signal would exceed the BG from beta decay if the energy resolution of Delta < 0.7 m_nu. Interestingly, the total capture rate depends on the origin of the neutrino mass, with Gamma^D~4 and Gamma^M~8 events per year (for a 100g tritium target) for unclustered Dirac and Majorana neutrinos, respectively. An enhancement of the rate of up to O(1) is expected due to gravitational clustering, with the unique potential to probe the local overdensity of neutrinos. Turning to more exotic neutrino physics, PTOLEMY could be sensitive to a lepton asymmetry, and reveal the eV-scale sterile neutrino that is favored by short baseline oscillation searches. The experiment would also be sensitive to a neutrino lifetime on the order of the age of the universe and break the degeneracy between neutrino mass and lifetime which affects existing bounds.
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