University of California, Santa Cruz

About: University of California, Santa Cruz is a education organization based out in Santa Cruz, California, United States. It is known for research contribution in the topics: Galaxy & Population. The organization has 15541 authors who have published 44120 publications receiving 2759983 citations. The organization is also known as: UCSC & UC, Santa Cruz.

The minimum-mass extrasolar nebula: in situ formation of close-in super-Earths

Abstract: Close-in super-Earths, with radii R = 2-5 R_Earth and orbital periods P < 100 days, orbit more than half, and perhaps nearly all Sun-like stars in the universe. We use this omnipresent population to construct the minimum-mass extrasolar nebula (MMEN), the circumstellar disk of solar-composition solids and gas from which such planets formed, if they formed near their current locations and did not migrate. In a series of back-of-the-envelope calculations, we demonstrate how in-situ formation in the MMEN is fast, efficient, and can reproduce many of the observed properties of close-in super-Earths, including their gas-to-rock fractions. Testable predictions are discussed.

Supernova 2007bi as a pair-instability explosion.

Abstract: Stars with initial masses such that 10 M_☉ ≤ M_(initial) ≤ 100M_☉, where is the solar mass, fuse progressively heavier elements in their centres, until the core is inert iron. The core then gravitationally collapses to a neutron star or a black hole, leading to an explosion—an iron-core-collapse supernova. By contrast, extremely massive stars with M_(initial) ≥ 140M_☉(if such exist) develop oxygen cores with masses, M_(core), that exceed 50M_☉, where high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron–positron pairs occurs before oxygen ignition and leads to a violent contraction which triggers a nuclear explosion that unbinds the star in a pair-instability supernova. Transitional objects with 100M_☉ 3M_☉ of radioactive ^(56)Ni was synthesized during the explosion and that our observations are well fitted by models of pair-instability supernovae. This indicates that nearby dwarf galaxies probably host extremely massive stars, above the apparent Galactic stellar mass limit11, which perhaps result from processes similar to those that created the first stars in the Universe.

FCC-ee: The Lepton Collider: Future Circular Collider Conceptual Design Report Volume 2

Abstract: In response to the 2013 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) study was launched, as an international collaboration hosted by CERN. This study covers a highest-luminosity high-energy lepton collider (FCC-ee) and an energy-frontier hadron collider (FCC-hh), which could, successively, be installed in the same 100 km tunnel. The scientific capabilities of the integrated FCC programme would serve the worldwide community throughout the 21st century. The FCC study also investigates an LHC energy upgrade, using FCC-hh technology. This document constitutes the second volume of the FCC Conceptual Design Report, devoted to the electron-positron collider FCC-ee. After summarizing the physics discovery opportunities, it presents the accelerator design, performance reach, a staged operation scenario, the underlying technologies, civil engineering, technical infrastructure, and an implementation plan. FCC-ee can be built with today’s technology. Most of the FCC-ee infrastructure could be reused for FCC-hh. Combining concepts from past and present lepton colliders and adding a few novel elements, the FCC-ee design promises outstandingly high luminosity. This will make the FCC-ee a unique precision instrument to study the heaviest known particles (Z, W and H bosons and the top quark), offering great direct and indirect sensitivity to new physics.

Cosmology of brane models with radion stabilization

Abstract: We analyze the cosmology of the Randall-Sundrum model and that of compact brane models in general in the presence of a radius stabilization mechanism. We find that the expansion of our Universe is generically in agreement with the expected effective four dimensional description. The constraint (which is responsible for the appearance of nonconventional cosmologies in these models) that must be imposed on the matter densities on the two branes in the theory without a stabilized radius is a consequence of requiring a static solution even in the absence of stabilization. Such constraints disappear in the presence of a stablizing potential, and the ordinary Friedmann-Robertson-Walker (FRW) equations are reproduced, with the expansion driven by the sum of the physical values of the energy densities on the two branes and in the bulk. For the case of the Randall-Sundrum model we examine the kinematics of the radion field, and find that corrections to the standard FRW equations are small for temperatures below the weak scale. We find that the radion field has renormalizable and unsuppressed couplings to standard model particles after electroweak symmetry breaking. These couplings may have important implications for collider searches. We comment on the possibility that matter off the TeV brane could serve as a dark matter candidate.

The role of the Earth's mantle in controlling the frequency of geomagnetic reversals

Abstract: A series of computer simulations of the Earth's dynamo illustrates how the thermal structure of the lowermost mantle might affect convection and magnetic-field generation in the fluid core. Eight different patterns of heat flux from the core to the mantle are imposed over the core–mantle boundary. Spontaneous magnetic dipole reversals and excursions occur in seven of these cases, although sometimes the field only reverses in the outer part of the core, and then quickly reverses back. The results suggest correlations among the frequency of reversals, the duration over which the reversals occur, the magnetic-field intensity and the secular variation. The case with uniform heat flux at the core–mantle boundary appears most ‘Earth-like’. This result suggests that variations in heat flux at the core–mantle boundary of the Earth are smaller than previously thought, possibly because seismic velocity anomalies in the lowermost mantle might have more of a compositional rather than thermal origin, or because of enhanced heat flux in the mantle's zones of ultra-low seismic velocity.