Curved Space or Curved Vacuum?

While the simple picture of a spatially flat, matter plus cosmological constant universe fits current observation of the accelerated expansion, strong consideration has also been given to models with dynamical vacuum energy. We examine the tradeoff of ``curving'' the vacuum but retaining spatial flatness, vs. curving space but retaining the cosmological constant. These different breakdowns in the simple picture could readily be distinguished by combined high accuracy supernovae and cosmic microwave background distance measurements. If we allow the uneasy situation of both breakdowns, the curvature can still be measured to 1%, but at the price of degrading estimation of the equation of state time variation by 60% or more, unless additional information (such as weak lensing data or a tight matter density prior) is included.Comment: 7 pages, 6 figures; minor changes to match version accepted to Astroparticle Physics and correct typo at bottom of page

Of Tourist Places: The Cultural Politics of Narrating Space in Thamel

Thamel—a bustling neighborhood of restaurants, shops, bars, dance clubs, street vendors, and hotels in Kathmandu, Nepal—is overwhelmingly portrayed as a ‘tourist place’ by Nepalis and foreigners alike. Despite this widespread reputation, many user-groups assign divergent and contradictory meanings to the space, and these cannot be so easily reduced to the machinations of foreign tourism. This article critically considers this common trope that relegates Thamel to a ‘foreign’ status within Kathmandu’s cultural landscape. After reviewing the history of Thamel, the article details the various modes of reiteration through which the ‘tourist place’ characterization finds continued articulation. Drawing on ethnographic fieldwork conducted between 2015-2016, it then offers contrary evidence to undermine the assertion that tourism represents the most salient aspect for understanding contemporary Thamel. It argues that prevailing narratives of the space eclipse other modes of meaning-making, thereby impoverishing scholarly understandings and simultaneously obscuring the ongoing contestations over Thamel’s cultural significance. In so doing, the article highlights the problematic cultural politics of continually positioning ‘tourism’ as Thamel’s sole (or central) referent. A discussion of Nepali cosmopolitan youth highlights the very real affective significance that Thamel holds for this particular user-group. Furthermore, it illustrates the implicit delegitimizing of youth experiences that occurs through reiterations of the ‘tourist place’ trope. The article concludes with a broader discussion of the theoretical, conceptual, and political stakes involved in critically engaging with attempts to fix spatial meaning in a neighborhood like Thamel

Improved Domain Wall Dynamics and Magnonic Torques using Topological Insulators

We investigate the magnetization dynamics that arise when a thin-film ferromagnet is deposited on a topological insulator (TI), focusing in particular on domain-wall motion via current and the possibility of a spin-wave torque acting on the magnetization. We show analytically that the coupling between the magnetic domain wall and the TI removes the degeneracy of the wall profile with respect to its chirality and topological charge. Moreover, we find that the threshold for Walker breakdown of domain wall motion is substantially increased and determined by the interaction with the TI, allowing for higher attainable wall velocities than in the conventional case where the hard axis anisotropy determines the Walker threshold. Finally, we show that the allowed modes of spin-wave excitations and the ensuing magnetization dynamics in the presence of a TI coupling enable a magnonic torque acting even on homogeneous magnetization textures. Our results indicate that the TI-ferromagnet interaction has a similar effect on the magnetization dynamics as an intrinsic Dzyaloshinskii-Moriya interaction in ferromagnets.Comment: 4 pages, 1 figure. Accepted for publication in PRB Rapid Communications. Chosen as Editors' Suggestio

Kendrick Lamar’s Collapsing of Hip Hop Realness and Christian Identity

In Danielle S. Macon’s To Pimp a Caterpillar: Hip Hop as Vehicle to Spiritual Liberation through the Decolonization of European Ideology about Kendrick Lamar’s To Pimp a Butterfly, she identifies Kendrick’s three-step process of liberation for African-Americans through spirituality: exhibition, revelation, and community orientation. I seek to place her analysis of Kendrick’s music within the context of Daniel White Hodge’s exploration of the neo-sacred secular in Hip Hop, a theological concept containing three elements: a belief that God is in all things, viewing life as having good and bad elements, and a rejection of religionism as the only way to God. Firstly, I will explore how Kendrick takes on himself the tropes of Hip Hop and African-American Street life, not to promote their virtues but to subvert them. Secondly, framing Kendrick’s presentation of an alternative identity built on his reframing of two Christian theological concepts: imago dei and identity as found in person and work of Jesus. Lastly, the process through which he bridges the gap between life in poor African-American urban spaces and Christianity to reconstruct Hip Hop realness in terms of sincerity and a common humanity, instead of the artificially-created litmus tests of Hip Hop authenticity. These three elements are then oriented in Kendrick’s music as the spiritual processes through which he strives to liberate himself, Compton, and his African-American community

Adam Reinhold Schiewe---A Cross-Border Man of Faith: A Baptist Trailblazer in Estonia, Poland, Ukraine, Germany, and Russia

This study aimed at compiling a biography of the preacher Adam Reinhold Schiewe (1843–1930). Schiewe ministered in the territories of present-day Poland, Germany, Ukraine, Russia, and Estonia. His historical significance lies primarily in the formal founding of the first Baptist congregation in Estonia. Schiewe wrote memoirs of his life and is featured in a large number of fragmentary, at times even contradictory, sources. The author pointed out the inaccuracies found therein and reconstructed a plausible biography. The study was originally written in Estonian and was supported by a single scholarship from the ESF programme DoRa activity 8

Chirality Sensitive Domain Wall Motion in Spin-Orbit Coupled Ferromagnets

Using the Lagrangian formalism, we solve analytically the equations of motion for current-induced domain-wall dynamics in a ferromagnet with Rashba spin-orbit coupling. An exact solution for the domain wall velocity is provided, including the effect of non-equilibrium conduction electron spin-density, Gilbert damping, and the Rashba interaction parameter. We demonstrate explicitly that the influence of spin-orbit interaction can be qualitatively different from the role of non-adiabatic spin-torque in the sense that the former is sensitive to the chirality of the domain wall whereas the latter is not: the domain wall velocity shows a reentrant behavior upon changing the chirality of the domain wall. This could be used to experimentally distinguish between the spin-orbit and non-adiabatic contribution to the wall speed. A quantitative estimate for the attainable domain wall velocity is given, based on an experimentally relevant set of parameters for the system.Comment: 7 pages, 2 figures. Accepted for publication in Phys. Rev.

Exploring the Expansion History of the Universe

Exploring the recent expansion history of the universe promises insights into the cosmological model, the nature of dark energy, and potentially clues to high energy physics theories and gravitation. We examine the extent to which precision distance-redshift observations can map out the history, including the acceleration-deceleration transition, and the components and equations of state of the energy density. We consider the ability to distinguish between various dynamical scalar field models for the dark energy, as well as higher dimension and alternate gravity theories. Finally, we present a new, advantageous parametrization for the study of dark energy.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Letter