The Densities of Planets in Multiple Stellar Systems

We analyze the effect of companion stars on the bulk density of 29 planets orbiting 15 stars in the Kepler field. These stars have at least one stellar companion within 2", and the planets have measured masses and radii, allowing an estimate of their bulk density. The transit dilution by the companion star requires the planet radii to be revised upward, even if the planet orbits the primary star; as a consequence, the planetary bulk density decreases. We find that, if planets orbited a faint companion star, they would be more volatile-rich, and in several cases their densities would become unrealistically low, requiring large, inflated atmospheres or unusually large mass fractions in a H/He envelope. In addition, for planets detected in radial velocity data, the primary star has to be the host. We can exclude 14 planets from orbiting the companion star; the remaining 15 planets in seven planetary systems could orbit either the primary or the secondary star, and for five of these planets the decrease in density would be substantial even if they orbited the primary, since the companion is of almost equal brightness as the primary. Substantial follow-up work is required in order to accurately determine the radii of transiting planets. Of particular interest are small, rocky planets that may be habitable; a lower mean density might imply a more volatile-rich composition. Reliable radii, masses, and thus bulk densities will allow us to identify which small planets are truly Earth-like.Comment: Accepted by AJ; 22 page

A Higgs Conundrum with Vector Fermions

Many models of Beyond the Standard Model physics involve heavy colored fermions. We study models where the new fermions have vector interactions and examine the connection between electroweak precision measurements and Higgs production. In particular, for parameters which are allowed by precision measurements, we show that the gluon fusion Higgs cross section and the Higgs decay branching ratios must be close to those predicted by the Standard Model. The models we discuss thus represent scenarios with new physics which will be extremely difficult to distinguish from the minimal Standard Model. We pay particular attention to the decoupling properties of the vector fermions.Comment: 34 pages, 15 figures. Version accepted for publication in Phys. Rev.

John Wheeler Between Cold Matter and Frozen Stars: The Road Towards Black Holes

One of the truly decisive figures in the flourishing of general relativity that began in the 1950s, the eminent physicist John A. Wheeler (1911-2008) is best known today to the general public because of the adoption of the phrase ‘black hole’. Still, that seems quite a thin reason for scientific fame – the question, then, is: what did Wheeler actually do in that field? A proper answer has to take into account a plurality of levels, from Wheeler's peculiarly visual style to his interactions with his own school and other groups, from the pioneering uses of computers to his early visions of quantum gravity. That is what this paper offers, while tracing Wheeler's evolving positions – from rejection to enthusiastic acceptance and popularisation – during the fifteen years (ca 1952-1967) preceding the moment black holes became ‘black holes’

Ab initio simulations of Cu binding sites in the N-terminal region of PrP

The prion protein (PrP) binds Cu2+ ions in the octarepeat domain of the N-terminal tail up to full occupancy at pH=7.4. Recent experiments show that the HGGG octarepeat subdomain is responsible for holding the metal bound in a square planar coordination. By using first principle ab initio molecular dynamics simulations of the Car-Parrinello type, the Cu coordination mode to the binding sites of the PrP octarepeat region is investigated. Simulations are carried out for a number of structured binding sites. Results for the complexes Cu(HGGGW)+(wat), Cu(HGGG) and the 2[Cu(HGGG)] dimer are presented. While the presence of a Trp residue and a H2O molecule does not seem to affect the nature of the Cu coordination, high stability of the bond between Cu and the amide Nitrogens of deprotonated Gly's is confirmed in the case of the Cu(HGGG) system. For the more interesting 2[Cu(HGGG)] dimer a dynamically entangled arrangement of the two monomers, with intertwined N-Cu bonds, emerges. This observation is consistent with the highly packed structure seen in experiments at full Cu occupancy.Comment: 4 pages, conference proceedin

Far from the Particle Crowd: Shugyosha Nambu and Michizane Wheeler

In the late 1940s many physicists embrace the surging particle physics regarding it as potentially resolutive of the crisis of nuclear physics. Against this backdrop, two thinkers of peculiar taste choose otherwise. Here we trace the roots and consequences of their decisions

Looking Stereoscopically at Goethe vs. Newton: Heisenberg and Pauli on the Future of Physics

Goethe’s polemics against Newtonian optics is not rarely men- tioned as a singular instance of incompetent stubbornness, or quickly dis- posed of as an embarrassing incident, not worthy of Goethe’s stature. None- theless, Goethe’s presence in the mind of 20th-century physicists is not a neg- ligible chapter, not only due to the pre-eminence of his literary work but to a suffused Naturphilosophie as well. Even more significantly, physicists of the calibre of Heisenberg and Pauli, while openly recognizing the ‘mistakes’ of the Goethean polemics in optics, tried to extract from that episode important lessons and expectations about the future of science

Unresolved Binary Exoplanet Host Stars Fit as Single Stars: Effects on the Stellar Parameters

In this work, we quantify the effect of an unresolved companion star on the derived stellar parameters of the primary star if a blended spectrum is fit assuming the star is single. Fitting tools that determine stellar parameters from spectra typically fit for a single star, but we know that up to half of all exoplanet host stars may have one or more companion stars. We use high-resolution spectra of planet host stars in the Kepler field from the California-Kepler Survey to create simulated binaries; we select eight stellar pairs and vary the contribution of the secondary star, then determine stellar parameters with SpecMatch-Emp and compare them to the parameters derived for the primary star alone. We find that, in most cases, the effective temperature, surface gravity, metallicity, and stellar radius derived from the composite spectrum are within 2–3σ of the values determined from the unblended spectrum, but the deviations depend on the properties of the two stars. Relatively bright companion stars that are similar to the primary star have the largest effect on the derived parameters; in these cases, the stellar radii can be overestimated by up to 60%. We find that metallicities are generally underestimated, with values up to eight times smaller than the typical uncertainty in [Fe/H]. Our study shows that follow-up observations are necessary to detect or set limits on stellar companions of planetary host stars so that stellar (and planet) parameters are as accurate as possible