Visualizing Spacetime Curvature via Frame-Drag Vortexes and Tidal Tendexes I. General Theory and Weak-Gravity Applications

When one splits spacetime into space plus time, the Weyl curvature tensor (vacuum Riemann tensor) gets split into two spatial, symmetric, and trace-free (STF) tensors: (i) the Weyl tensor's so-called "electric" part or tidal field, and (ii) the Weyl tensor's so-called "magnetic" part or frame-drag field. Being STF, the tidal field and frame-drag field each have three orthogonal eigenvector fields which can be depicted by their integral curves. We call the integral curves of the tidal field's eigenvectors tendex lines, we call each tendex line's eigenvalue its tendicity, and we give the name tendex to a collection of tendex lines with large tendicity. The analogous quantities for the frame-drag field are vortex lines, their vorticities, and vortexes. We build up physical intuition into these concepts by applying them to a variety of weak-gravity phenomena: a spinning, gravitating point particle, two such particles side by side, a plane gravitational wave, a point particle with a dynamical current-quadrupole moment or dynamical mass-quadrupole moment, and a slow-motion binary system made of nonspinning point particles. [Abstract is abbreviated; full abstract also mentions additional results.]Comment: 25 pages, 20 figures, matches the published versio

Momentum flow in black-hole binaries: II. Numerical simulations of equal-mass, head-on mergers with antiparallel spins

Research on extracting science from binary-black-hole (BBH) simulations has often adopted a "scattering matrix" perspective: given the binary's initial parameters, what are the final hole's parameters and the emitted gravitational waveform? In contrast, we are using BBH simulations to explore the nonlinear dynamics of curved spacetime. Focusing on the head-on plunge, merger, and ringdown of a BBH with transverse, antiparallel spins, we explore numerically the momentum flow between the holes and the surrounding spacetime. We use the Landau-Lifshitz field-theory-in-flat-spacetime formulation of general relativity to define and compute the density of field energy and field momentum outside horizons and the energy and momentum contained within horizons, and we define the effective velocity of each apparent and event horizon as the ratio of its enclosed momentum to its enclosed mass-energy. We find surprisingly good agreement between the horizons' effective and coordinate velocities. To investigate the gauge dependence of our results, we compare pseudospectral and moving-puncture evolutions of physically similar initial data; although spectral and puncture simulations use different gauge conditions, we find remarkably good agreement for our results in these two cases. We also compare our simulations with the post-Newtonian trajectories and near-field energy-momentum. [Abstract abbreviated; full abstract also mentions additional results.]Comment: Submitted to Phys. Rev.

Intensive swift and LCO monitoring of PG 1302–102 : active galactic nucleus disk reverberation mapping of a supermassive black hole binary candidate

This work is supported by the NANOGrav National Science Foundation Physics Frontiers Center award No. 2020265 and NASA grant 80NSSC24K0251. Research at UC Irvine was supported by NSF grant AST-1907290. E.M.C. gratefully acknowledges support from the NSF through grant No. AST-1909199.We present an intensive multiwavelength monitoring campaign of the quasar PG 1302−102 with Swift and the Las Cumbres Observatory network telescopes. At z ∼ 0.3, it tests the limits of the reverberation mapping (RM) technique in probing the accretion disk around a supermassive black hole (SMBH) and extends the parameter space to high masses and high accretion rates. This is also the first time the RM technique has been applied to test disk structures predicted in the SMBH binary model that has been suggested for this source. PG 1302−102 was observed at a ∼daily cadence for ∼9 months in 14 bands spanning from X-ray to UV and optical wavelengths, and it shows moderate to significant levels of variability correlated between wavelengths. We measure the interband time lags, which are consistent with a τ ∝ λ 4/3 relation as expected from standard disk reprocessing, albeit with large uncertainties. The disk size implied by the lag spectrum is consistent with the expected disk size for its black hole mass within uncertainties. While the source resembles other reverberation-mapped active galactic nuclei in many respects, and we do not find evidence supporting the prevalent hypothesis that it hosts an SMBH binary, we demonstrate the feasibility of studying SMBH binaries from this novel angle and suggest possibilities for the LSST Deep Drilling Fields.Peer reviewe

A pilot ASKAP survey for radio transients towards the Galactic Centre

We present the results of a radio transient and polarisation survey towards the Galactic Centre, conducted as part of the Australian Square Kilometre Array Pathfinder Variables and Slow Transients pilot survey. The survey region consisted of five fields covering $\sim265\,{\rm deg}^2$ ($350^\circ\lesssim l\lesssim10^\circ$, $\vert b\vert \lesssim 10^\circ$). Each field was observed for 12\,minutes, with between 7 and 9 repeats on cadences of between one day and four months. We detected eight highly variable sources and seven highly circularly-polarised sources (14 unique sources in total). Seven of these sources are known pulsars including the rotating radio transient PSR~J1739--2521 and the eclipsing pulsar PSR~J1723--2837. One of them is a low mass X-ray binary, 4U 1758--25. Three of them are coincident with optical or infrared sources and are likely to be stars. The remaining three may be related to the class of Galactic Centre Radio Transients (including a highly likely one, VAST~J173608.2--321634, that has been reported previously), although this class is not yet understood. In the coming years, we expect to detect $\sim$40 bursts from this kind of source with the proposed four-year VAST survey if the distribution of the source is isotropic over the Galactic fields.Comment: 17 pages, 13 figures, Accepted for publication in MNRA

Manacled to Identity: Cosmopolitanism, Class, and ‘The Culture Concept’ in Stephen Crane

This article begins with a close reading of Stephen Crane’s short story ‘Manacled’ from 1900, which situates this rarely considered short work within the context of contemporary debates about realism. I then proceed to argue that many of the debates raised by the tale have an afterlife in our own era of American literary studies, which has frequently focused on questions of ‘identity’ and ‘culture’ in its reading of realism and naturalism to the exclusion of the importance of cosmopolitan discourses of diffusion and exchange across national borders. I then offer a brief reading of Crane’s novel George’s Mother, which follows Walter Benn Michaels in suggesting that the recent critical attention paid to particularities of cultural difference in American studies have come to conflate ideas of class and social position with ideas of culture in ways that have ultimately obscured the presence of genuine historical inequalities in US society. In order to challenge this critical commonplace, I situate Crane’s work within a history of transatlantic cosmopolitanism associated with the ideas of Franz Boas and Matthew Arnold to demonstrate the ways in which Crane’s narratives sought out an experience of the universal within their treatments of the particular

Atomic Dark Matter

We propose that dark matter is dominantly comprised of atomic bound states. We build a simple model and map the parameter space that results in the early universe formation of hydrogen-like dark atoms. We find that atomic dark matter has interesting implications for cosmology as well as direct detection: Protohalo formation can be suppressed below $M_{proto} \sim 10^3 - 10^6 M_{\odot}$ for weak scale dark matter due to Ion-Radiation interactions in the dark sector. Moreover, weak-scale dark atoms can accommodate hyperfine splittings of order 100 \kev, consistent with the inelastic dark matter interpretation of the DAMA data while naturally evading direct detection bounds.Comment: 17 pages, 3 figure

Intermediate scale as a source of lepton flavor violation in SUSY SO(10)

In supersymmetric SO(10) grand unified models, we examine the lepton flavor violation process $\mu \rightarrow e\gamma$ from having the SU(2)$_R\times$U(1)$_{B-L}$ gauge symmetry broken at an intermediate scale $M_I$ below the SO(10) grand unification scale $M_G$. Even in the case that supersymmetry is broken by universal soft terms introduced at the scale $M_G$, we find significant rates for $\mu\rightarrow e\gamma$ with $M_I \sim 10^{12}$ GeV or less. These rates are further enhanced if the universal soft terms appear at a scale greater than $M_G$.Comment: 12 pages (Latex), 3 PS Figures (uuencoded, epsf.tex), small addition to discussion in the text, as to appear in Phys. Rev. D Rapid Communication

Predictive fermion mass matrix ansatzes in non-supersymmetric SO(10) grand unification

We investigate the status of predictive fermion mass ansatzes which make use of the grand unification scale conditions $m_e=m_d/3$, $m_\mu =3m_s$, and $\mid V_{cb}\mid =\sqrt{m_{c}/m_{t}}$ in non-supersymmetric SO(10) grand unification. The gauge symmetry below an intermediate symmetry breaking scale $M_I$ is assumed to be that of the standard model with either one Higgs doublet or two Higgs doublets . We find in both cases that a maximum of 5 standard model parameters may be predicted within $1\sigma$ experimental ranges. We find that the standard model scenario predicts the low energy $\mid V_{cb}\mid$ to be in a range which includes its experimental mid-value 0.044 and which for a large top mass can extend to lower values than the range resulting in the supersymmetric case. In the two Higgs standard model case, we identify the regions of parameter space for which unification of the bottom quark and tau lepton Yukawa couplings is possible at grand unification scale. In fact, we find that unification of the top, bottom and tau Yukawa couplings is possible with the running b-quark mass within the $1\sigma$ preferred range $m_b=4.25\pm 0.1\, GeV$ provided $\alpha_{3c}(M_Z)$ is near the low end of its allowed range. In this case, one may make 6 predictions which include $\mid V_{cb}\mid$ within its $90\%$ confidence limits. However unless the running mass $m_b>4.4\, GeV$, third generation Yukawa coupling unification requires the top mass to be greater thanComment: 30 pages, 8 figures available on request from [email protected], Late

Dialectics and difference: against Harvey's dialectical post-Marxism

David Harvey`s recent book, Justice, nature and the geography of difference (JNGD), engages with a central philosophical debate that continues to dominate human geography: the tension between the radical Marxist project of recent decades and the apparently disempowering relativism and `play of difference' of postmodern thought. In this book, Harvey continues to argue for a revised `post-Marxist' approach in human geography which remains based on Hegelian-Marxian principles of dialectical thought. This article develops a critique of that stance, drawing on the work of Jacques Derrida, Gilles Deleuze and Felix Guattari. I argue that dialectical thinking, as well as Harvey's version of `post-Marxism', has been undermined by the wide-ranging `post-' critique. I suggest that Harvey has failed to appreciate the full force of this critique and the implications it has for `post-Marxist' ontology and epistemology. I argue that `post-Marxism', along with much contemporary human geography, is constrained by an inflexible ontology which excessively prioritizes space in the theory produced, and which implements inflexible concepts. Instead, using the insights of several `post-' writers, I contend there is a need to develop an ontology of `context' leading to the production of `contextual theories'. Such theories utilize flexible concepts in a multilayered understanding of ontology and epistemology. I compare how an approach which produces a `contextual theory' might lead to more politically empowering theory than `post-Marxism' with reference to one of Harvey's case studies in JNGD

Timing Observations of Rotating Radio Transients

We present radio timing measurements of six rotating radio transient (RRAT) sources discovered in the Parkes Multibeam Pulsar Survey. These provide four new phase-connected timing solutions and two updated ones, making a total of seven of the original 11 reported RRATs now with high-precision rotational and astrometric parameters. Three of these seven RRATs have magnetic fields greater than 10^13 G, with spin-down properties similar to those of the magnetars and X-ray detected isolated neutron stars. Another two of these RRATs have long periods and large characteristic ages, and lie near the `death-line' for radio pulsar emission. The remaining two RRATs with timing solutions have properties typical of the bulk of the pulsar population. The new solutions offer insights into what might be responsible for the unusual emission properties. We demonstrate that the RRATs have significantly longer periods and higher magnetic fields than normal radio pulsars, and find no correlation with other spin-down parameters. These solutions also provide precise positions, which will facilitate follow-up studies at high energies, crucial for relating these sources with other neutron star populations.Comment: 9 pages, 5 figures, 4 tables, accepted by MNRA