R-mode Instability of Slowly Rotating Non-isentropic Relativistic Stars

We investigate properties of $r$-mode instability in slowly rotating relativistic polytropes. Inside the star slow rotation and low frequency formalism that was mainly developed by Kojima is employed to study axial oscillations restored by Coriolis force. At the stellar surface, in order to take account of gravitational radiation reaction effect, we use a near-zone boundary condition instead of the usually imposed boundary condition for asymptotically flat spacetime. Due to the boundary condition, complex frequencies whose imaginary part represents secular instability are obtained for discrete $r$-mode oscillations in some polytropic models. It is found that such discrete $r$-mode solutions can be obtained only for some restricted polytropic models. Basic properties of the solutions are similar to those obtained by imposing the boundary condition for asymptotically flat spacetime. Our results suggest that existence of a continuous part of spectrum cannot be avoided even when its frequency becomes complex due to the emission of gravitational radiation.Comment: 10 pages, 4 figures, accepted for publlication in PR

Quasilinear hyperbolic Fuchsian systems and AVTD behavior in T2-symmetric vacuum spacetimes

We set up the singular initial value problem for quasilinear hyperbolic Fuchsian systems of first order and establish an existence and uniqueness theory for this problem with smooth data and smooth coefficients (and with even lower regularity). We apply this theory in order to show the existence of smooth (generally not analytic) T2-symmetric solutions to the vacuum Einstein equations, which exhibit AVTD (asymptotically velocity term dominated) behavior in the neighborhood of their singularities and are polarized or half-polarized.Comment: 78 page

The rotational modes of relativistic stars: Numerical results

We study the inertial modes of slowly rotating, fully relativistic compact stars. The equations that govern perturbations of both barotropic and non-barotropic models are discussed, but we present numerical results only for the barotropic case. For barotropic stars all inertial modes are a hybrid mixture of axial and polar perturbations. We use a spectral method to solve for such modes of various polytropic models. Our main attention is on modes that can be driven unstable by the emission of gravitational waves. Hence, we calculate the gravitational-wave growth timescale for these unstable modes and compare the results to previous estimates obtained in Newtonian gravity (i.e. using post-Newtonian radiation formulas). We find that the inertial modes are slightly stabilized by relativistic effects, but that previous conclusions concerning eg. the unstable r-modes remain essentially unaltered when the problem is studied in full general relativity.Comment: RevTeX, 29 pages, 31 eps figure

The problem of a self-gravitating scalar field with positive cosmological constant

We study the Einstein-scalar field system with positive cosmological constant and spherically symmetric characteristic initial data given on a truncated null cone. We prove well-posedness, global existence and exponential decay in (Bondi) time, for small data. From this, it follows that initial data close enough to de Sitter data evolves to a causally geodesically complete spacetime (with boundary), which approaches a region of de Sitter asymptotically at an exponential rate; this is a non-linear stability result for de Sitter within the class under consideration, as well as a realization of the cosmic no-hair conjecture.We thank Pedro Girao, Marc Mars, Alan Rendall, Jorge Silva and Raul Vera for useful discussions. This work was supported by projects PTDC/MAT/108921/2008 and CERN/FP/116377/2010, and by CMAT, Universidade do Minho, and CAMSDG, Instituto Superior Tecnico, through FCT plurianual funding. AA thanks the Mathematics Department of Instituto Superior Tecnico (Lisbon), where this work was done, and the International Erwin Schrodinger Institute (Vienna), where the workshop "Dynamics of General Relativity: Analytical and Numerical Approaches" took place, for hospitality, and FCT for grant SFRH/BD/48658/2008

Rover Traverse Planning to Support a Lunar Polar Volatiles Mission

Studies of lunar polar volatile depositsare of interest for scientific purposes to understandthe nature and evolution of the volatiles, and alsofor exploration reasons as a possible in situ resource toenable long term exploration and settlement of theMoon. Both theoretical and observational studies havesuggested that significant quantities of volatiles exist inthe polar regions, although the lateral and horizontaldistribution remains unknown at the km scale and finerresolution. A lunar polar rover mission is required tofurther characterize the distribution, quantity, andcharacter of lunar polar volatile deposits at thesehigher spatial resolutions. Here we present two casestudies for NASAs Resource Prospector (RP) missionconcept for a lunar polar rover and utilize this missionarchitecture and associated constraints to evaluatewhether a suitable landing site exists to support an RPflight mission

Model Analysis of Time Reversal Symmetry Test in the Caltech Fe-57 Gamma-Transition Experiment

The CALTECH gamma-transition experiment testing time reversal symmetry via the E2/M1 mulipole mixing ratio of the 122 keV gamma-line in Fe-57 has already been performed in 1977. Extending an earlier analysis in terms of an effective one-body potential, this experiment is now analyzed in terms of effective one boson exchange T-odd P-even nucleon nucleon potentials. Within the model space considered for the Fe-57 nucleus no contribution from isovector rho-type exchange is possible. The bound on the coupling strength phi_A from effective short range axial-vector type exchange induced by the experimental bound on sin(eta) leads to phi_A < 10^{-2}.Comment: 5 pages, RevTex 3.

R-mode oscillations of differentially and rapidly rotating Newtonian polytropic stars

For the analysis of the r-mode oscillation of hot young neutron stars, it is necessary to consider the effect of it differential rotation, because viscosity is not strong enough for differentially rotating young neutron stars to be lead to uniformly rotating configurations on a very short time scale after their birth. In this paper, we have developed a numerical scheme to solve r-mode oscillations of differentially rotating polytropic inviscid stars. This is the extended version of the method which was applied to compute r-mode oscillations of uniformly rotating Newtonian polytropic stars. By using this new method, we have succeeded in obtaining eigenvalues and eigenfunctions of r-mode oscillations of differentially rotating polytropic stars. Our numerical results show that as the degree of differential rotation is increased, it becomes more difficult to solve r-mode oscillations for slightly deformed configurations from sphere compared to solving r-mode oscillations of considerably deformed stars. One reason for it seems that for slightly deformed stars corotation points appear near the surface region if the degree of differential rotation is strong enough. This is similar to the situation that the perturbational approach of r-mode oscillations for it slowly rotating stars in general relativity results in a singular eigenvalue problem.Comment: including 7 figures. submitted to PR

Finite-size scaling above the upper critical dimension in Ising models with long-range interactions

The correlation length plays a pivotal role in finite-size scaling and hyperscaling at continuous phase transitions. Below the upper critical dimension, where the correlation length is proportional to the system length, both finite-size scaling and hyperscaling take conventional forms. Above the upper critical dimension these forms break down and a new scaling scenario appears. Here we investigate this scaling behaviour in one-dimensional Ising ferromagnets with long-range interactions. We show that the correlation length scales as a non-trivial power of the linear system size and investigate the scaling forms. For interactions of sufficiently long range, the disparity between the correlation length and the system length can be made arbitrarily large, while maintaining the new scaling scenarios. We also investigate the behavior of the correlation function above the upper critical dimension and the modifications imposed by the new scaling scenario onto the associated Fisher relation.Comment: 16 pages, 5 figure

State of play and future direction with NOACs: An expert consensus.

Atrial fibrillation (AF) and venous thromboembolism (VTE) are cardiovascular conditions significant in contemporary practice. In both, the use of anticoagulation with vitamin K antagonists (VKAs) has been traditionally used to prevent adverse events. However, VKA therapy is associated with challenges relating to dose maintenance, the need to monitor anticoagulation, and bleeding risks. The non-vitamin K oral anticoagulants (NOACs) are becoming accepted as a clear alternative to VKA therapy for both AF and VTE management. The aim of this paper was to review contemporary evidence on the safety of NOACs in both conditions. A comprehensive literature review was conducted to explore key safety issues and expert consensus was achieved from eight professionals specialised in AF and VTE care. Consensus-based statements were formulated where available evidence was weak or contradictory. The expert statements in this paper form a key overview of the safety of NOACs compared with VKA therapy, and the comparative safety of different NOACs. It is apparent that a detailed patient work-up is required in order to identify and manage individual risk factors for bleeding and thrombosis prior to NOAC therapy. Additional measures, such as dose reductions, may also be used to maintain the safety of NOACs in practice

Fighting post-COVID and ME/CFS - development of curative therapies

The sequela of COVID-19 include a broad spectrum of symptoms that fall under the umbrella term post-COVID-19 condition or syndrome (PCS). Immune dysregulation, autoimmunity, endothelial dysfunction, viral persistence, and viral reactivation have been identified as potential mechanisms. However, there is heterogeneity in expression of biomarkers, and it is unknown yet whether these distinguish different clinical subgroups of PCS. There is an overlap of symptoms and pathomechanisms of PCS with postinfectious myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). No curative therapies are available for ME/CFS or PCS. The mechanisms identified so far provide targets for therapeutic interventions. To accelerate the development of therapies, we propose evaluating drugs targeting different mechanisms in clinical trial networks using harmonized diagnostic and outcome criteria and subgrouping patients based on a thorough clinical profiling including a comprehensive diagnostic and biomarker phenotyping