Posts Tagged dimensionless

Recent Postings from dimensionless

Restricted Weyl invariance in four-dimensional curved spacetime

We discuss the physics and mathematics of {\it restricted Weyl invariance}, a spacetime symmetry of dimensionless actions in four dimensional curved space time. When we study a scalar field nonminimally coupled to gravity with Weyl(conformal) weight of $-1$ (i.e. scalar field with the usual two-derivative kinetic term), we find that dimensionless terms are either fully Weyl invariant or are Weyl invariant if the conformal factor $\Omega(x)$ obeys the condition $g^{\mu\nu}\nabla_{\mu}\nabla_{\nu}\Omega=0$. We refer to the latter as {\it restricted Weyl invariance}. We show that all the dimensionless geometric terms such as $R^2$, $R_{\mu\nu}R^{\mu\nu}$ and $R_{\mu\nu\sigma\tau}R^{\mu\nu\sigma\tau}$ are restricted Weyl invariant. Restricted Weyl transformations possesses nice mathematical properties such as the existence of a composition and an inverse in four dimensional space-time. We exemplify the distinction among rigid Weyl invariance, restricted Weyl invariance and the full Weyl invariance in dimensionless actions constructed out of scalar fields and vector fields with Weyl weight zero.

Restricted Weyl invariance in four-dimensional curved spacetime [Replacement]

We discuss the physics of {\it restricted Weyl invariance}, a symmetry of dimensionless actions in four dimensional curved space time. When we study a scalar field nonminimally coupled to gravity with Weyl(conformal) weight of $-1$ (i.e. scalar field with the usual two-derivative kinetic term), we find that dimensionless terms are either fully Weyl invariant or are Weyl invariant if the conformal factor $\Omega(x)$ obeys the condition $g^{\mu\nu}\nabla_{\mu}\nabla_{\nu}\Omega=0$. We refer to the latter as {\it restricted Weyl invariance}. We show that all the dimensionless geometric terms such as $R^2$, $R_{\mu\nu}R^{\mu\nu}$ and $R_{\mu\nu\sigma\tau}R^{\mu\nu\sigma\tau}$ are restricted Weyl invariant. Restricted Weyl transformations possesses nice mathematical properties such as the existence of a composition and an inverse in four dimensional space-time. We exemplify the distinction among rigid Weyl invariance, restricted Weyl invariance and the full Weyl invariance in dimensionless actions constructed out of scalar fields and vector fields with Weyl weight zero.

Restricted Weyl invariance in four-dimensional curved spacetime

We discuss the physics and mathematics of {\it restricted Weyl invariance}, a spacetime symmetry of dimensionless actions in four dimensional curved space time. When we study a scalar field nonminimally coupled to gravity with Weyl(conformal) weight of $-1$ (i.e. scalar field with the usual two-derivative kinetic term), we find that dimensionless terms are either fully Weyl invariant or are Weyl invariant if the conformal factor $\Omega(x)$ obeys the condition $g^{\mu\nu}\nabla_{\mu}\nabla_{\nu}\Omega=0$. We refer to the latter as {\it restricted Weyl invariance}. We show that all the dimensionless geometric terms such as $R^2$, $R_{\mu\nu}R^{\mu\nu}$ and $R_{\mu\nu\sigma\tau}R^{\mu\nu\sigma\tau}$ are restricted Weyl invariant. Restricted Weyl transformations possesses nice mathematical properties such as the existence of a composition and an inverse in four dimensional space-time. We exemplify the distinction among rigid Weyl invariance, restricted Weyl invariance and the full Weyl invariance in dimensionless actions constructed out of scalar fields and vector fields with Weyl weight zero.

Scaling of Magneto-Quantum-Radiative Hydrodynamic Equations: From Laser-produced Plasmas to Astrophysics

The relevant equations of magneto-quantum-radiative hydrodynamics are introduced and then written in a dimensionless form in order to extract a set of dimensionless parameters that describe scale-dependent ratios of all the characteristic hydrodynamic variables. Under the conditions where such dimensionless number are all large, the equations reduce to the usual ideal magnetohydrodynamics and thus they are scale invariant. We discuss this property with regards to the similarity between astrophysical observations and laboratory experiments. These similarity properties have been successfully exploited in a variety of laboratory experiments where radiative processes can be neglected. On the other hand, when radiation is important, laboratory experiments are much more difficult to scale to the corresponding astrophysical objects. As an example, a recent experiment related to break out shocks in supernova explosions is discussed.

Black hole remnant of black hole-neutron star coalescing binaries with arbitrary black hole spin

A model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with arbitrary initial black hole spin angular momentum, binary mass ratio, and neutron star mass and cold equation of state is formulated. Tests against numerical-relativity results are carried out, showing that both the dimensionless spin parameter and the final mass are accurately reproduced. For the first time, the behaviour of both quantities and of the l = 2, m = 2, n = 0 quasinormal mode frequency is inspected throughout the parameter space. Predictions of this frequency may be exploited to guide gravitational wave modelling and detection efforts, and to extract physical information from detected gravitational wave signals that would help us break degeneracies between binary black hole and black hole-neutron star systems, improve our understanding of compact binary formation, and constrain the neutron star equation of state.

Black hole remnant of black hole-neutron star coalescing binaries with arbitrary black hole spin [Cross-Listing]

A model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with arbitrary initial black hole spin angular momentum, binary mass ratio, and neutron star mass and cold equation of state is formulated. Tests against numerical-relativity results are carried out, showing that both the dimensionless spin parameter and the final mass are accurately reproduced. For the first time, the behaviour of both quantities and of the l = 2, m = 2, n = 0 quasinormal mode frequency is inspected throughout the parameter space. Predictions of this frequency may be exploited to guide gravitational wave modelling and detection efforts, and to extract physical information from detected gravitational wave signals that would help us break degeneracies between binary black hole and black hole-neutron star systems, improve our understanding of compact binary formation, and constrain the neutron star equation of state.

Black hole remnant of black hole-neutron star coalescing binaries with arbitrary black hole spin [Replacement]

A model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with arbitrary initial black hole spin angular momentum, binary mass ratio, and neutron star mass and cold equation of state is formulated. Tests against numerical-relativity results are carried out, showing that both the dimensionless spin parameter and the final mass are accurately reproduced. For the first time, the behaviour of both quantities and of the l = 2, m = 2, n = 0 quasinormal mode frequency is inspected throughout the parameter space. Predictions of this frequency may be exploited to guide gravitational wave modelling and detection efforts, and to extract physical information from detected gravitational wave signals that would help us break degeneracies between binary black hole and black hole-neutron star systems, improve our understanding of compact binary formation, and constrain the neutron star equation of state.

Black hole remnant of black hole-neutron star coalescing binaries with arbitrary black hole spin [Replacement]

A model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with arbitrary initial black hole spin angular momentum, binary mass ratio, and neutron star mass and cold equation of state is formulated. Tests against numerical-relativity results are carried out, showing that both the dimensionless spin parameter and the final mass are accurately reproduced. For the first time, the behaviour of both quantities and of the l = 2, m = 2, n = 0 quasinormal mode frequency is inspected throughout the parameter space. Predictions of this frequency may be exploited to guide gravitational wave modelling and detection efforts, and to extract physical information from detected gravitational wave signals that would help us break degeneracies between binary black hole and black hole-neutron star systems, improve our understanding of compact binary formation, and constrain the neutron star equation of state.

Renormalization and asymptotic freedom in quantum gravity through symmetry of the functional measure [Cross-Listing]

A method of renormalization is developed for the Einstein action with a cosmological constant in four spacetime dimensions. In the method described, the Einstein action is obtained from the renormalizable action of higher-derivative gravity by performing a local field transformation and redefining the parameters. Since the Jacobian of a local transformation is one (assuming the use of dimensional regularization), the $S$-matrix elements on the Einstein shell are unaffected by the field redefinition. This allows the renormalization of the Einstein action to be calculated from the renormalization constants of the higher-derivative theory. It is shown that the resulting quantum theory of gravitation is asymptotically free in the essential dimensionless coupling constant $\Lambda G$, where $G$ is Newton’s constant and $\Lambda$ is the cosmological constant.

Inner Disc Obscuration in GRS 1915+105 Based on Relativistic Slim Disc Model

We study the observational signatures of the relativistic slim disc of 10 M_sun black hole, in a wide range of mass accretion rate, mdot, dimensionless spin parameter, a_ast, and viewing angle, i. In general, the innermost temperature, T_in increases with the increase of i for a fixed value of mdot and a_ast, due to the Doppler effect. However, for i > 50 and mdot > mdot_turn, T_in starts to decrease with the increase of mdot. This is a result of self-obscuration — the radiation from the innermost hot part of the disc is blocked by the surrounding cooler part. The value of mdot_turn and the corresponding luminosities depend on a_ast and i. Such obscuration effects cause an interesting behavior on the disc luminosity (L_disc) — T_in plane for high inclinations. In addition to the standard-disc branch which appears below mdot_turn and which obeys L_disc propto T_in^4 -relation, another branch above mdot_turn, which is nearly horizontal, may be observed at luminosities close to the Eddington luminosity. We show that these features are likely observed in a Galactic X-ray source, GRS 1915+105. We support a high spin parameter (a_ast > 0.9) for GRS 1915+105 since otherwise the high value of T_in and small size of the emitting region (r_in < 1r_S) cannot be explained.

CosMIn: The Solution to the Cosmological Constant Problem [Replacement]

The current acceleration of the universe can be modeled in terms of a cosmological constant. We show that the extremely small value of \Lambda L_P^2 ~ 3.4 x 10^{-122}, the holy grail of theoretical physics, can be understood in terms of a new, dimensionless, conserved number CosMIn (N), which counts the number of modes crossing the Hubble radius during the three phases of evolution of the universe. Theoretical considerations suggest that N ~ 4\pi. This single postulate leads us to the correct, observed numerical value of the cosmological constant! This approach also provides a unified picture of cosmic evolution relating the early inflationary phase to the late-time accelerating phase.

The closest black holes

Starting from the assumption that there is a large population (> 10^8) of isolated, stellar-mass black holes (IBH) distributed throughout our galaxy, we consider the detectable signatures of accretion from the interstellar medium (ISM) that may be associated with such a population. We simulate the nearby (radius 250 pc) part of this population, corresponding to the closest ~35 000 black holes, using current best estimates of the mass distribution of stellar mass black holes combined with two models for the velocity distribution of stellar-mass IBH which bracket likely possibilities. We distribute this population of objects appropriately within the different phases of the ISM and calculate the Bondi-Hoyle accretion rate, modified by a further dimensionless efficiency parameter \lambda. Assuming a simple prescription for radiatively inefficient accretion at low Eddington ratios, we calculate the X-ray luminosity of these objects, and similarly estimate the radio luminosity from relations found empirically for black holes accreting at low rates. The latter assumption depends crucially on whether or not the IBH accrete from the ISM in a manner which is axisymmetric enough to produce jets. Comparing the predicted X-ray fluxes with limits from hard X-ray surveys, we conclude that either the Bondi-Hoyle efficiency parameter \lambda, is rather small (< 0.01), the velocities of the IBH are rather high, or some combination of both. The predicted radio flux densities correspond to a population of objects which, while below current survey limits, should be detectable with the Square Kilometre Array (SKA). Converting the simulated space velocities into proper motions, we further demonstrate that such IBH could be identified as faint high proper motion radio sources in SKA surveys.

Quasi-periodical features in the distribution of Luminous Red Galaxies

A statistical analysis of radial distributions of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS DR7) catalogue within an interval $0.16 \leq z \leq 0.47$ is carried out. We found that the radial distribution of $\sim$ 106,000 LRGs incorporates a few quasi-periodical components relatively to a variable $\eta$, dimensionless line-of-sight comoving distance calculated for the $\Lambda$CDM cosmological model. The most significant peaks of the power spectra are obtained for two close periodicities corresponding to the spatial comoving scales $(135 \pm 12) h^{-1}$ Mpc and $(101 \pm 6)h^{-1}$ Mpc. The latter one is dominant and consistent with the characteristic scale of the baryon acoustic oscillations. We analyse also the radial distributions of two other selected LRG samples: $\sim$ 33,400 bright LRGs ($-23.2 < M \leq -21.8$) and $\sim$ 60,300 all LRGs within a rectangle region on the sky, and show differences of the quasi-periodical features characteristic for different samples. Being confirmed the results would allow to give preference of the spatial against temporal models which could explain the quasi-periodicities discussed here. As a caveat we show that estimations of the significance levels of the peaks strongly depend on a smoothed radial function (trend) as well as characteristics of random fluctuations.

The standard flare model in three dimensions. II. Upper limit on solar flare energy

Solar flares strongly affect the Sun’s atmosphere as well as the Earth’s environment. Quantifying the maximum possible energy of solar flares of the present-day Sun, if any, is thus a key question in heliophysics. The largest solar flares observed over the past few decades have reached energies of a few times 10^{32} ergs, possibly up to 10^{33} ergs. Flares in active Sun-like stars reach up to about 10^{36} ergs. In the absence of direct observations of solar flares within this range, complementary methods of investigation are needed. Using historical reports for solar active region, we scaled to observed solar values a realistic dimensionless 3D MHD simulation for eruptive flares, which originate from a highly sheared bipole. This enabled us to calculate the magnetic fluxes and flare energies in the model in a wide paramater space. Firstly, commonly observed solar conditions lead to modeled magnetic fluxes and flare energies that are comparable to those estimated from observations. Secondly, we evaluate from observations that 30% of the area of sunspot groups are typically involved in flares. This is related to the strong fragmentation of these groups, which naturally results from sub-photospheric convection. When the model is scaled to 30% of the area of the largest sunspot group ever reported, with its peak magnetic field being set to the strongest value ever measured in a sunspot, it produces a flare with a maximum energy of ~ 6×10^{33} ergs. The results of the model suggest that the Sun is able to produce flares up to about six times as energetic in total solar irradiance fluence as the strongest directly-observed flare from Nov 4, 2003. Sunspot groups larger than historically reported would yield superflares for spot pairs that would exceed tens of degrees in extent. We thus conjecture that superflare-productive Sun-like stars should have a much stronger dynamo than in the Sun.

Rossby Wave Instability with Self-Gravity

The Rossby wave instability (RWI) in non-self-gravitating discs can be triggered by a bump at a radius $r_0$ in the disc surface mass-density (which is proportional to the inverse potential vorticity). It gives rise to a growing non-axisymmetric perturbation [$\propto \exp(im\phi)$, $m=1,2..$] in the vicinity of $r_0$ consisting of anticyclonic vortices which may facilitate planetesimal growth in protoplanetary discs. Here, we analyze a continuum of thin disc models ranging from self-gravitating to non-selfgravitating. The key quantities determining the stability/instability are: (1) the parameters of the bump (or depression) in the disc surface density, (2) the Toomre $Q$ parameter of the disc (a non-self-gravitating disc has $Q\gg1$), and (3) the dimensionless azimuthal wavenumber of the perturbation $\bar{k}_\phi =mQh/r_0$, where $h$ is the half-thickness of the disc. For discs stable to axisymmetric perturbations ($Q>1$), the self-gravity has a significant role for $\bar{k}_\phi < \pi/2$ or $m<(\pi/2) (r_0/h)Q^{-1}$; instability may occur for a depression or groove in the surface density if $Q\lesssim 2$. For $\bar{k}_\phi > \pi/2$ the self-gravity is not important, and instability may occur at a bump in the surface density. Thus, for all mode numbers $m \ge 1$, the self-gravity is unimportant for $Q > (\pi/2)(r_0/h)$. We suggest that the self-gravity be included in simulations for cases where $Q< (r_0/h)$.

Scheme dependence of quantum gravity on de Sitter background [Cross-Listing]

We extend our investigation of the IR effects on the local dynamics of matter fields in quantum gravity. Specifically we clarify how the IR effects depend on the change of the quantization scheme: different parametrization of the metric and the matter field redefinition. An arbitrary choice of the parametrization of the metric and the matter field redefinition do not preserve the Lorentz invariance of the local dynamics. As for the effect of different parametrization of the metric alone, the Lorentz symmetry breaking term can be eliminated by shifting the background metric. In contrast, we cannot compensate the matter field redefinition dependence by such a way. The Lorentz invariance can be retained only when we adopt the specific matter field redefinitions where all dimensionless couplings become scale invariant at the classical level.

Scheme dependence of quantum gravity on de Sitter background [Replacement]

We extend our investigation of the IR effects on the local dynamics of matter fields in quantum gravity. Specifically we clarify how the IR effects depend on the change of the quantization scheme: different parametrization of the metric and the matter field redefinition. Conformal invariance implies effective Lorentz invariance of the matter system in de Sitter space. An arbitrary choice of the parametrization of the metric and the matter field redefinition does not preserve the effective Lorentz invariance of the local dynamics. As for the effect of different parametrization of the metric alone, the effective Lorentz symmetry breaking term can be eliminated by shifting the background metric. In contrast, we cannot compensate the matter field redefinition dependence by such a way. The effective Lorentz invariance can be retained only when we adopt the specific matter field redefinitions where all dimensionless couplings become scale invariant at the classical level. This scheme is also singled out by unitarity as the kinetic terms are canonically normalized.

Magnetization Degree of Gamma-Ray Burst Fireballs: Numerical Study

The relative strength between forward and reverse shock emission in early gamma-ray burst afterglow reflects that of magnetic energy densities in the two shock regions. We numerically show that with the current standard treatment, the fireball magnetization is underestimated by up to two orders of magnitude. This discrepancy is especially large in the sub-relativistic reverse shock regime (i.e. the thin shell and intermediate regime) where most optical flashes were detected. We provide new analytic estimates of the reverse shock emission based on a better shock approximation, which well describe numerical results in the intermediate regime. We show that the reverse shock temperature at the onset of afterglow is constant, $(\bar{\Gamma}_d-1)\sim 8\times10^{-2}$, when the dimensionless parameter $\xi_{0}$ is more than several. Our approach is applied to case studies of GRB 990123 and 090102, and we find that magnetic fields in the fireballs are even stronger than previously believed.

Magnetization Degree of Gamma-Ray Burst Fireballs: Numerical Study [Replacement]

The relative strength between forward and reverse shock emission in early gamma-ray burst afterglow reflects that of magnetic energy densities in the two shock regions. We numerically show that with the current standard treatment, the fireball magnetization is underestimated by up to two orders of magnitude. This discrepancy is especially large in the sub-relativistic reverse shock regime (i.e. the thin shell and intermediate regime) where most optical flashes were detected. We provide new analytic estimates of the reverse shock emission based on a better shock approximation, which well describe numerical results in the intermediate regime. We show that the reverse shock temperature at the onset of afterglow is constant, $(\bar{\Gamma}_d-1)\sim 8\times10^{-2}$, when the dimensionless parameter $\xi_{0}$ is more than several. Our approach is applied to case studies of GRB 990123 and 090102, and we find that magnetic fields in the fireballs are even stronger than previously believed.

The Black Hole Remnant of Black Hole-Neutron Star Coalescing Binaries [Replacement]

We present a model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with parallel orbital angular momentum and initial black hole spin. This approach is based on the Buonanno, Kidder, and Lehner method for binary black holes, and it is successfully tested against the results of numerical-relativity simulations: the dimensionless spin parameter is predicted with absolute error $\lesssim 0.02$, whereas the relative error on the final mass is $\lesssim 2$%, its distribution in the tests being pronouncedly peaked at $1$%. Our approach and the fit to the torus remnant mass reported in Foucart (2012) thus constitute an easy-to-use analytical model that accurately describes the remnant of black hole-neutron star mergers. The space of parameters consisting of the binary mass ratio, the initial black hole spin, and the neutron star mass and equation of state is investigated. We provide indirect support to the cosmic censorship conjecture for black hole remnants of black hole-neutron star mergers. We show that the presence of a neutron star affects the quasinormal mode frequency of the black hole remnant, thus suggesting that the ringdown epoch of the gravitational wave signal may virtually be used to (1) distinguish black hole-black hole from black hole-neutron star mergers and to (2) constrain the neutron star equation of state.

The Black Hole Remnant of Black Hole-Neutron Star Coalescing Binaries [Replacement]

We present a model for determining the dimensionless spin parameter and mass of the black hole remnant of black hole-neutron star mergers with parallel orbital angular momentum and initial black hole spin. This approach is based on the Buonanno, Kidder, and Lehner method for binary black holes, and it is successfully tested against the results of numerical-relativity simulations: the dimensionless spin parameter is predicted with absolute error $\lesssim 0.02$, whereas the relative error on the final mass is $\lesssim 2$%, its distribution in the tests being pronouncedly peaked at $1$%. Our approach and the fit to the torus remnant mass reported in Foucart (2012) thus constitute an easy-to-use analytical model that accurately describes the remnant of black hole-neutron star mergers. The space of parameters consisting of the binary mass ratio, the initial black hole spin, and the neutron star mass and equation of state is investigated. We provide indirect support to the cosmic censorship conjecture for black hole remnants of black hole-neutron star mergers. We show that the presence of a neutron star affects the quasinormal mode frequency of the black hole remnant, thus suggesting that the ringdown epoch of the gravitational wave signal may virtually be used to (1) distinguish black hole-black hole from black hole-neutron star mergers and to (2) constrain the neutron star equation of state.

Detecting binary neutron star systems with spin in advanced gravitational-wave detectors [Replacement]

The detection of gravitational waves from binary neutron stars is a major goal of the gravitational-wave observatories Advanced LIGO and Advanced Virgo. Previous searches for binary neutron stars with LIGO and Virgo neglected the component stars’ angular momentum (spin). We demonstrate that neglecting spin in matched-filter searches causes advanced detectors to lose more than 3% of the possible signal-to-noise ratio for 59% (6%) of sources, assuming that neutron star dimensionless spins, $c\mathbf{J}/GM^2$, are uniformly distributed with magnitudes between 0 and 0.4 (0.05) and that the neutron stars have isotropically distributed spin orientations. We present a new method for constructing template banks for gravitational wave searches for systems with spin. We present a new metric in a parameter space in which the template placement metric is globally flat. This new method can create template banks of signals with non-zero spins that are (anti-)aligned with the orbital angular momentum. We show that this search loses more than 3% of the maximium signal-to-noise for only 9% (0.2%) of BNS sources with dimensionless spins between 0 and 0.4 (0.05) and isotropic spin orientations. Use of this template bank will prevent selection bias in gravitational-wave searches and allow a more accurate exploration of the distribution of spins in binary neutron stars.

Detecting binary neutron star systems with spin in advanced gravitational-wave detectors [Cross-Listing]

The detection of gravitational waves from binary neutron stars is a major goal of the gravitational-wave observatories Advanced LIGO and Advanced Virgo. Previous searches for binary neutron stars with LIGO and Virgo neglected the component stars’ angular momentum (spin). We demonstrate that neglecting spin in matched-filter searches causes advanced detectors to lose more than 3% of the possible signal-to-noise ratio for 59% (6%) of sources, assuming that neutron star dimensionless spins, $cJ/GM^2$, are uniformly distributed with magnitudes between 0 and 0.4 (0.05) and that the neutron stars have isotropically distributed spin orientations. We present a new method of constructing filter banks for advanced-detector searches, which can create template banks of signals with non-zero spins that are (anti-)aligned with the orbital angular momentum. We show that this search loses more than 3% of the maximium signal-to-noise for only 9% (0.2%) of BNS sources with dimensionless spins between 0 and 0.4 (0.05) and isotropic spin orientations. Use of this template bank will prevent selection bias in gravitational-wave searches and allow a more accurate exploration of the distribution of spins in binary neutron stars.

Exact Hairy Black Holes and their Modification to the Universal Law of Gravitation [Cross-Listing]

In this paper two things are done. First, it is pointed out the existence of exact asymptotically flat, spherically symmetric black holes when a self interacting, minimally coupled scalar field is the source of the energy momentum of the Einstein equations in four dimensions. The scalar field potential is the recently found to be compatible with the hairy generalization of the Plebanski-Demianski solution of general relativity. This paper describes the spherically symmetric solutions that smoothly connect the Schwarzschild black hole with its hairy counterpart. The geometry and scalar field are everywhere regular except at the usual Schwarzschild like singularity inside the black hole. The scalar field energy momentum tensor satisfies the null energy condition in the static region of the spacetime. The first law holds when the parameters of the scalar field potential are fixed under thermodynamical variation. Secondly, it is shown that an extra, dimensionless parameter, present in the hairy solution, allows to modify the gravitational field of a spherically symmetric black hole in a remarkable way. When the dimensionless parameter is increased, the scalar field generates a flat gravitational potential, that however asymptotically matches the Schwarzschild gravitational field. Finally, it is shown that a positive cosmological constant can render the scalar field potential convex if the parameters are within a specific rank.

Exact Hairy Black Holes and their Modification to the Universal Law of Gravitation [Replacement]

In this paper two things are done. First, it is pointed out the existence of exact asymptotically flat, spherically symmetric black holes when a self interacting, minimally coupled scalar field is the source of the energy momentum of the Einstein equations in four dimensions. The scalar field potential is the recently found to be compatible with the hairy generalization of the Plebanski-Demianski solution of general relativity. This paper describes the spherically symmetric solutions that smoothly connect the Schwarzschild black hole with its hairy counterpart. The geometry and scalar field are everywhere regular except at the usual Schwarzschild like singularity inside the black hole. The scalar field energy momentum tensor satisfies the null energy condition in the static region of the spacetime. The first law holds when the parameters of the scalar field potential are fixed under thermodynamical variation. Secondly, it is shown that an extra, dimensionless parameter, present in the hairy solution, allows to modify the gravitational field of a spherically symmetric black hole in a remarkable way. When the dimensionless parameter is increased, the scalar field generates a flat gravitational potential, that however asymptotically matches the Schwarzschild gravitational field. Finally, it is shown that a positive cosmological constant can render the scalar field potential convex if the parameters are within a specific rank.

On the aerodynamic redistribution of chondrite components in protoplanetary disks

Despite being all roughly of solar composition, primitive meteorites (chondrites) present a diversity in their chemical, isotopic and petrographic properties, and in particular a first-order dichotomy between carbonaceous and non-carbonaceous chondrites. We investigate here analytically the dynamics of their components (chondrules, refractory inclusions, metal/sulfide and matrix grains) in protoplanetary disks prior to their incorporation in chondrite parent bodies. We find the dynamics of the solids, subject to gas drag, to be essentially controlled by the “gas-solid decoupling parameter” $S\equiv \textrm{St}/\alpha$, the ratio of the dimensionless stopping time to the turbulence parameter. The decoupling of the solid particles relative to the gas is significant when $S$ exceeds unity. $S$ is expected to increase with time and heliocentric distance. On the basis of (i) abundance of refractory inclusions (ii) proportion of matrix (iii) lithophile element abundances and (iv) oxygen isotopic composition of chondrules, we propose that non-matrix chondritic components had $S1$ when the other chondrites accreted. This suggests that accretion of carbonaceous chondrites predated on average that of the other chondrites and that refractory inclusions are genetically related to their host carbonaceous chondrites.

Prograde and Retrograde Black Holes: Whose Jet is More Powerful?

We study prograde and retrograde disc accretion on rapidly spinning black holes (BHs) via global 3D time-dependent non-radiative general relativistic magnetohydrodynamic simulations. Our discs contain more large-scale vertical magnetic flux than the accreting gas can push into the BH. As a result, the BH becomes saturated with flux, and strong centrally concentrated large-scale magnetic fields form that obstruct the accretion and lead to a magnetically arrested disc. We show that the efficiency with which such accretion systems generate steady outflows depends only on the dimensionless BH spin, a, and accretion disc angular thickness, h/r. Prograde BHs with thick discs (h/r ~ 0.3-0.6) generate jets and outflows several times more efficiently than retrograde BHs, for the same absolute value of spin. Both orientations can reach high values of outflow efficiency, eta ~ 100%, with higher efficiency values for thicker discs.

General Relativistic Magnetohydrodynamic Simulations of Magnetically Choked Accretion Flows around Black Holes [Replacement]

Black hole (BH) accretion flows and jets are qualitatively affected by the presence of ordered magnetic fields. We study fully three-dimensional global general relativistic magnetohydrodynamic (MHD) simulations of radially extended and thick (height $H$ to cylindrical radius $R$ ratio of $|H/R|\sim 0.2$-1) accretion flows around BHs with various dimensionless spins ($a/M$, with BH mass $M$) and with initially toroidally-dominated ($\phi$-directed) and poloidally-dominated ($R-z$ directed) magnetic fields. Firstly, for toroidal field models and BHs with high enough $|a/M|$, coherent large-scale (i.e. $\gg H$) dipolar poloidal magnetic flux patches emerge, thread the BH, and generate transient relativistic jets. Secondly, for poloidal field models, poloidal magnetic flux readily accretes through the disk from large radii and builds-up to a natural saturation point near the BH. For sufficiently high $|a/M|$ or low $|H/R|$ the polar magnetic field compresses the inflow into a geometrically thin highly non-axisymmetric “magnetically choked accretion flow” (MCAF) within which the standard linear magneto-rotational instability is suppressed. The condition of a highly-magnetized state over most of the horizon is optimal for the Blandford-Znajek mechanism that generates persistent relativistic jets with $\gtrsim 100$% efficiency for $|a/M|\gtrsim 0.9$. A magnetic Rayleigh-Taylor and Kelvin-Helmholtz unstable magnetospheric interface forms between the compressed inflow and bulging jet magnetosphere, which drives a new jet-disk oscillation (JDO) type of quasi-periodic oscillation (QPO) mechanism. The high-frequency QPO has spherical harmonic $|m|=1$ mode period of $\tau\sim 70GM/c^3$ for $a/M\sim 0.9$ with coherence quality factors $Q\gtrsim 10$. [abridged]

General Relativistic Magnetohydrodynamic Simulations of Magnetically Choked Accretion Flows around Black Holes [Replacement]

Black hole (BH) accretion flows and jets are qualitatively affected by the presence of ordered magnetic fields. We study fully three-dimensional global general relativistic magnetohydrodynamic (MHD) simulations of radially extended and thick (height $H$ to cylindrical radius $R$ ratio of $|H/R|\sim 0.2–1$) accretion flows around BHs with various dimensionless spins ($a/M$, with BH mass $M$) and with initially toroidally-dominated ($\phi$-directed) and poloidally-dominated ($R-z$ directed) magnetic fields. Firstly, for toroidal field models and BHs with high enough $|a/M|$, coherent large-scale (i.e. $\gg H$) dipolar poloidal magnetic flux patches emerge, thread the BH, and generate transient relativistic jets. Secondly, for poloidal field models, poloidal magnetic flux readily accretes through the disk from large radii and builds-up to a natural saturation point near the BH. For sufficiently high $|a/M|$ or low $|H/R|$ the polar magnetic field compresses the inflow into a geometrically thin highly non-axisymmetric “magnetically choked accretion flow” (MCAF) within which the standard linear magneto-rotational instability is suppressed. The condition of a highly-magnetized state over most of the horizon is optimal for the Blandford-Znajek mechanism that generates persistent relativistic jets with $\gtrsim 100$% efficiency for $|a/M|\gtrsim 0.9$. A magnetic Rayleigh-Taylor and Kelvin-Helmholtz unstable magnetospheric interface forms between the compressed inflow and bulging jet magnetosphere, which drives a new jet-disk quasi-periodic oscillation (JD-QPO) mechanism. The high-frequency QPO has spherical harmonic $|m|=1$ mode period of $\tau\sim 70GM/c^3$ for $a/M\sim 0.9$ with coherence quality factors $Q\gtrsim 10$. [abridged]

General Relativistic Magnetohydrodynamic Simulations of Magnetically Choked Accretion Flows around Black Holes

Black hole (BH) accretion flows and jets are qualitatively affected by the presence of ordered magnetic fields. We describe fully three-dimensional global general relativistic magnetohydrodynamic (MHD) simulations of radially extended and thick (height $H$ to cylindrical radius $R$ ratio of $|H/R|\sim 0.2–1$) accretion flows around BHs with various dimensionless spins ($a/M$, with BH mass $M$) and with initially toroidally-dominated ($\phi$-directed) and poloidally-dominated ($R-z$ directed) magnetic fields. For initially toroidally-dominated magnetic field models, patches of spontaneously generated coherent large-scale dipolar magnetic flux do reach the BH but only lead to transient mildly relativistic winds and weak relativistic jets. For initially poloidally-dominated magnetic field models, poloidal magnetic flux readily accretes through the disk from large radii and builds-up to a natural saturation point near the BH. For sufficiently high $|a/M|$ or low $|H/R|$ the polar magnetic field compresses the thick flow into a geometrically thin highly non-axisymmetric magnetically choked accretion flow (MCAF) within which the magneto-rotational instability is suppressed. The condition of a highly-magnetized state over most of the horizon is optimal for the Blandford-Znajek mechanism that generates persistent relativistic jets with $\gtrsim 100$% efficiency for $|a/M|\gtrsim 0.9$. The compressed disk inflow interacts with the jet magnetosphere driving a new jet-disk oscillation (JDO) type of quasi-periodic oscillation (QPO) mechanism leading to high-frequency QPOs with spherical harmonic $|m|=1$ mode period of $\tau\sim 70GM/c^3$ for $a/M\sim 0.9$ with quality factor $Q\sim 100$ in the jet, $Q\sim 10$ at one disk scale-height, and $Q\sim 3$ in the disk plane [abridged].

The kinetic Sunyaev-Zel'dovich signal from inhomogeneous reionization: a parameter space study [Replacement]

[ABRIDGED] Inhomogeneous reionization acts as a source of arcminute-scale anisotropies in the cosmic microwave background (CMB), the most important of which is the kinetic Sunyaev-Zel’dovich (kSZ) effect. Observational efforts with the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) are poised to detect this signal for the first time. Indeed, recent SPT measurements place a bound on the dimensionless kSZ power spectrum around a multipole of l=3000 of P_tot < 2.8 (6) micro K^2 at 95% C.L., by ignoring (allowing) correlations between the thermal Sunyaev-Zel'dovich (tSZ) effect and the cosmic infrared background (CIB). To interpret these and upcoming observations, we compute the kSZ signal from a suite of ~ 100 reionization models using the publicly available code 21cmFAST. Our physically motivated reionization models are parameterized by the ionizing efficiency of high-redshift galaxies, the minimum virial temperature of halos capable of hosting stars, and the ionizing photon mean free path. We predict the contribution of patchy reionization to be P_patchy = 1.5-3.5 micro K^2. Therefore, even when conservatively adopting a low estimate of the post-reionization signal, P_OV ~ 2 micro K^2, none of our models are consistent with the aggressive 2sigma SPT bound that does not include correlations. This implies that either: (i) the early stages of reionization occurred in a much more homogeneous manner than suggested by the stellar-driven scenarios we explore, such as would be the case if, e.g., very high energy X-rays or exotic particles contributed significantly; and/or (ii) that there is a significant correlation between the CIB and the tSZ. On the other hand, the conservative SPT bound is compatible with all of our models, and is on the boarder of constraining reionization.

The kinetic Sunyaev-Zel'dovich signal from inhomogeneous reionization: a parameter space study

[ABRIDGED] Inhomogeneous reionization acts as a source of arcminute-scale anisotropies in the cosmic microwave background (CMB), the most important of which is the kinetic Sunyaev-Zel’dovich (kSZ) effect. Observational efforts with the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT) are poised to detect this signal for the first time. Indeed, recent SPT measurements place a bound on the dimensionless kSZ power spectrum around a multipole of l=3000 of P_tot < 2.8 (6) micro K^2 at 95% C.L., by ignoring (allowing) correlations between the thermal Sunyaev-Zel'dovich (tSZ) effect and the cosmic infrared background (CIB). To interpret these and upcoming observations, we compute the kSZ signal from a suite of ~ 100 reionization models using the publicly available code 21cmFAST. Our physically motivated reionization models are parameterized by the ionizing efficiency of high-redshift galaxies, the minimum virial temperature of halos capable of hosting stars, and the ionizing photon mean free path. We predict the contribution of patchy reionization to be P_patchy = 1.5-3.5 micro K^2. Therefore, even when conservatively adopting a low estimate of the post-reionization signal, P_OV ~ 2 micro K^2, none of our models are consistent with the aggressive 2sigma SPT bound that does not include correlations. This implies that either: (i) the early stages of reionization occurred in a much more homogeneous manner than suggested by the stellar-driven scenarios we explore, such as would be the case if, e.g., very high energy X-rays or exotic particles contributed significantly; and/or (ii) that there is a significant correlation between the CIB and the tSZ. On the other hand, the conservative SPT bound is compatible with all of our models, and is on the boarder of constraining reionization.

WIMPless Dark Matter from an AMSB Hidden Sector with No New Mass Parameters [Cross-Listing]

We present a model with dark matter in an anomaly-mediated supersymmetry breaking hidden sector with a U(1)xU(1) gauge symmetry. The symmetries of the model stabilize the dark matter and forbid the introduction of new mass parameters. As a result, the thermal relic density is completely determined by the gravitino mass and dimensionless couplings. Assuming non-hierarchical couplings, the thermal relic density is ~ 0.1, independent of the dark matter’s mass and interaction strength, realizing the WIMPless miracle. The model has several striking features. For particle physics, stability of the dark matter is completely consistent with R-parity violation in the visible sector, with implications for superpartner collider signatures; also the thermal relic’s mass may be ~ 10 GeV or lighter, which is of interest given recent direct detection results. Interesting astrophysical signatures are dark matter self-interactions through a long-range force, and massless hidden photons and fermions that contribute to the number of relativistic degrees of freedom at BBN and CMB. The latter are particularly interesting, given current indications for extra degrees of freedom and near future results from the Planck observatory.

Global GRMHD Simulations of Black Hole Accretion Flows: a Convergence Study

Global, general relativistic magnetohydrodynamic (GRMHD) simulations of nonradiative, magnetized disks are widely used to model accreting black holes. We have performed a convergence study of GRMHD models computed with HARM3D. The models span a factor of 4 in linear resolution, from 96x96x64 to 384x384x256. We consider three diagnostics of convergence: (1) dimensionless shell-averaged quantities such as plasma \beta; (2) the azimuthal correlation length of fluid variables; and (3) synthetic spectra of the source including synchrotron emission, absorption, and Compton scattering. Shell-averaged temperature is, except for the lowest resolution run, nearly independent of resolution; shell-averaged plasma \beta\ decreases steadily with resolution but shows signs of convergence. The azimuthal correlation lengths of density, internal energy, and temperature decrease steadily with resolution but show signs of convergence. In contrast, the azimuthal correlation length of magnetic field decreases nearly linearly with grid size. We argue by analogy with local models, however, that convergence should be achieved with another factor of 2 in resolution. Synthetic spectra are, except for the lowest resolution run, nearly independent of resolution. The convergence behavior is consistent with that of higher physical resolution local model (shearing box) calculations and with the recent nonrelativistic global convergence studies of Hawley et al. (2011).

Vertical Structure of Stationary Accretion Disks with a Large-Scale Magnetic Field

In earlier works we pointed out that the disk’s surface layers are non-turbulent and thus highly conducting (or non-diffusive) because the hydrodynamic and/or magnetorotational (MRI) instabilities are suppressed high in the disk where the magnetic and radiation pressures are larger than the plasma thermal pressure. Here, we calculate the vertical profiles of the {\it stationary} accretion flows (with radial and azimuthal components), and the profiles of the large-scale, magnetic field taking into account the turbulent viscosity and diffusivity and the fact that the turbulence vanishes at the surface of the disk. Also, here we require that the radial accretion speed be zero at the disk’s surface and we assume that the ratio of the turbulent viscosity to the turbulent magnetic diffusivity is of order unity. Thus at the disk’s surface there are three boundary conditions. As a result, for a fixed dimensionless viscosity $\alpha$-value, we find that there is a definite relation between the ratio ${\cal R}$ of the accretion power going into magnetic disk winds to the viscous power dissipation and the midplane plasma-$\beta$, which is the ratio of the plasma to magnetic pressure in the disk. For a specific disk model with ${\cal R}$ of order unity we find that the critical value required for a stationary solution is $\beta_c \approx 2.4r/(\alpha h)$, where $h$ the disk’s half thickness. For weaker magnetic fields, $\beta > \beta_c$, we argue that the poloidal field will advect outward while for $\beta< \beta_c$ it will advect inward. Alternatively, if the disk wind is negligible (${\cal R} \ll 1$), there are stationary solutions with $\beta \gg \beta_c$.

Asteroseismic diagrams from a survey of solar-like oscillations with Kepler

Photometric observations made by the NASA Kepler Mission have led to a dramatic increase in the number of main-sequence and subgiant stars with detected solar-like oscillations. We present an ensemble asteroseismic analysis of 76 solar-type stars. Using frequencies determined from the Kepler time-series photometry, we have measured three asteroseismic parameters that characterize the oscillations: the large frequency separation (\Delta \nu), the small frequency separation between modes of l=0 and l=2 (\delta \nu_02), and the dimensionless offset (\epsilon). These measurements allow us to construct asteroseismic diagrams, namely the so-called C-D diagram of \delta \nu_02 versus \Delta \nu, and the recently re-introduced {\epsilon} diagram. We compare the Kepler results with previously observed solar-type stars and with theoretical models. The positions of stars in these diagrams places constraints on their masses and ages. Additionally, we confirm the observational relationship between {\epsilon} and T_eff that allows for the unambiguous determination of radial order and should help resolve the problem of mode identification in F stars.

Evolution of [OIII]5007 emission-line profiles in narrow emission-line galaxies

The AGN-host co-evolution issue is investigated here by focusing on the evolution of the [\ion{O}{3}]$\lambda5007$ emission-line profile. In order to simultaneously measure both [\ion{O}{3}] line profile and circumnuclear stellar population in individual spectrum, a large sample of narrow emission-line galaxies is selected from the MPA/JHU SDSS DR7 catalog. By requiring that 1) the [\ion{O}{3}] line signal-to-noise ratio is larger than 30, 2) the [\ion{O}{3}] line width is larger than the instrumental resolution by a factor of 2, our sample finally contains 2,333 Seyfert galaxies/LINERs (AGNs), 793 transition galaxies, and 190 starforming galaxies. In additional to the commonly used profile parameters (i.e., line centroid, relative velocity shift and velocity dispersion), two dimensionless shape parameters, skewness and kurtosis, are used to quantify the line shape deviation from a pure Gaussian function. We show that the transition galaxies are systematically associated with narrower line widths and weaker [\ion{O}{3}] broad wings than the AGNs, which implies that the kinematics of the emission-line gas is different in the two kinds of objects. By combining the measured host properties and line shape parameters, we find that the AGNs with stronger blue asymmetries tend to be associated with younger stellar populations. However, the similar trend is not identified in the transition galaxies. The failure is likely resulted from a selection effect in which the transition galaxies are systematically associated with younger stellar populations than the AGNs. The evolutionary significance revealed here suggests that both NLR kinematics and outflow feedback in AGNs co-evolve with their host galaxies.

Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU

Magnetic Clouds (MCs) are a particular subset of Interplanetary Coronal Mass Ejections (ICMEs), forming large scale magnetic flux ropes. In this work we analyze the evolution of a particular MC (observed on March 1998) using {\it in situ} observations made by two spacecraft approximately aligned with the Sun, the first one at 1 AU from the Sun and the second one at 5.4 AU. We study the MC expansion, its consequent decrease of magnetic field intensity and mass density, and the possible evolution of the so-called global ideal-MHD nvariants. We describe the magnetic configuration of the MC at both spacecraft using different models and compute relevant global quantities (magnetic fluxes, helicity and energy) at both helio-distances. We also track back this structure to the Sun, in order to find out its solar source. We find that the flux rope is significantly distorted at 5.4 AU. However, we are able to analyze the data before the flux rope center is over-passed and compare it with observations at 1 AU. From the observed decay of magnetic field and mass density, we quantify how anisotropic is the expansion, and the consequent deformation of the flux rope in favor of a cross section with an aspect ratio at 5.4 AU of $\approx 1.6$ (larger in the direction perpendicular to the radial direction from the Sun). We quantify the ideal-MHD invariants and magnetic energy at both locations, and find that invariants are almost conserved, while the magnetic energy decays as expected with the expansion rate found. The use of MHD invariants to link structures at the Sun and the interplanetary medium is supported by the results of this multispacecraft study. We also conclude that the local dimensionless expansion rate, that is computed from the velocity profile observed by a single spacecraft, is very accurate for predicting the evolution of flux ropes in the solar wind.

Future weak lensing constraints in a dark coupled universe

Coupled cosmologies can predict values for the cosmological parameters at low redshifts which may differ substantially from the parameters values within non-interacting cosmologies. Therefore, low redshift probes, as the growth of structure and the dark matter distribution via galaxy and weak lensing surveys constitute a unique tool to constrain interacting dark sector models. We focus here on weak lensing forecasts from future Euclid and LSST-like surveys combined with the ongoing Planck cosmic microwave background experiment. We find that these future data could constrain the dimensionless coupling to be smaller than a few $\times 10^{-2}$. The coupling parameter $\xi$ is strongly degenerate with the cold dark matter energy density $\Omega_{c}h^2$ and the Hubble constant $H_0$.These degeneracies may cause important biases in the cosmological parameter values if in the universe there exists an interaction among the dark matter and dark energy sectors.

Disentangling galaxy environment and host halo mass [Replacement]

[Abridged] The properties of observed galaxies and dark matter haloes in simulations depend on their environment. The term environment has been used to describe a wide variety of measures that may or may not correlate with each other. Popular measures of environment include the distance to the N’th nearest neighbour, the number density of objects within some distance, or the mass of the host dark matter halo. We use results from the Millennium simulation and a semi-analytic model for galaxy formation to quantify the relations between environment and halo mass. We show that the environmental parameters used in the observational literature are in effect measures of halo mass, even if they are measured for a fixed stellar mass. The strongest correlation between environment and halo mass arises when the number of objects is counted out to a distance of 1.5-2 times the virial radius of the host halo and when the galaxies/haloes are required to be relatively bright/massive. For observational studies the virial radius is not easily determined, but the number of neighbours out to 1-2 Mpc/h gives a similarly strong correlation. For the distance to the N’th nearest neighbour the correlation with halo mass is nearly as strong provided N>2. We demonstrate that this environmental parameter becomes insensitive to halo mass if it is constructed from dimensionless quantities. This can be achieved by scaling the minimum luminosity/mass of neighbours to that of the object in question and by dividing the distance to a length scale associated with either the neighbour or the galaxy under consideration. We show how such a halo mass independent environmental parameter can be defined for observational and numerical studies. The results presented here will help future studies to disentangle the effects of halo mass and external environment on the properties of galaxies and dark matter haloes.

Disentangling galaxy environment and host halo mass

[Abridged] The properties of observed galaxies and dark matter haloes in simulations depend on their environment. The term environment has been used to describe a wide variety of measures that may or may not correlate with each other. Popular measures of environment include the distance to the N’th nearest neighbour, the number density of objects within some distance, or the mass of the host dark matter halo. We use results from the Millennium simulation and a semi-analytic model for galaxy formation to quantify the relations between environment and halo mass. We show that the environmental parameters used in the observational literature are in effect measures of halo mass, even if they are measured for a fixed stellar mass. The strongest correlation between environment and halo mass arises when the number of objects is counted out to a distance of 1.5-2 times the virial radius of the host halo and when the galaxies/haloes are required to be relatively bright/massive. For observational studies the virial radius is not easily determined, but the number of neighbours out to 1-2 Mpc/h gives a similarly strong correlation. For the distance to the N’th nearest neighbour the correlation with halo mass is nearly as strong provided N>2. We demonstrate that this environmental parameter becomes insensitive to halo mass if it is constructed from dimensionless quantities. This can be achieved by scaling the minimum luminosity/mass of neighbours to that of the object in question and by dividing the distance to a length scale associated with either the neighbour or the galaxy under consideration. We show how such a halo mass independent environmental parameter can be defined for observational and numerical studies. The results presented here will help future studies to disentangle the effects of halo mass and external environment on the properties of galaxies and dark matter haloes.

Instabilities in neutrino systems induced by interactions with scalars

If there are scalar particles of small or moderate mass coupled very weakly to Dirac neutrinos, in a minimal way, then neutrino-anti-neutrino clouds of sufficient number density can experience an instability in which helicities are suddenly reversed. The predicted collective evolution is many orders of magnitude faster than given by cross-section calculations. The instabilities are the analogue of the “flavor-angle” instabilities (enabled by the Z exchange force) that may drive very rapid flavor exchange among the neutrinos that emerge from a supernova. Operating in the mode of putting limits on the coupling constant of the scalar field, for the most minimal coupling scheme, with independent couplings to all three neutrinos, we find a rough limit on the dimensionless coupling constant for a neutrino-flavor independent coupling of $G<10^{-10}$, to avoid the effective number of light neutrinos in the early universe being essentially six. If, on the other hand, we wish to fine-tune the model to give a more modest excess (over three) in the effective neutrino number, as may be needed according to recent WMAP analyses, it is easy to do so.

Instabilities in neutrino systems induced by interactions with scalars [Replacement]

If there are scalar particles of small or moderate mass coupled very weakly to Dirac neutrinos, in a minimal way, then neutrino-anti-neutrino clouds of sufficient number density can experience an instability in which helicities are suddenly reversed. The predicted collective evolution is many orders of magnitude faster than given by cross-section calculations. The instabilities are the analogue of the “flavor-angle” instabilities (enabled by the Z exchange force) that may drive very rapid flavor exchange among the neutrinos that emerge from a supernova. These exchanges do require a tiny seed in addition to the scalar couplings, but the transition time is proportional to the negative of the logarithm of the seed strength, so that the size of this parameter is comparatively unimportant. For our actual estimates we use a tiny non-conservation of leptons; an alternative would be a neutrino magnetic moment in a small magnetic field. The possibility of a quantum fluctuation as a seed is also discussed. Operating in the mode of putting limits on the coupling constant of the scalar field, for the most minimal coupling scheme, with independent couplings to all three $\nu$, we find a rough limit on the dimensionless coupling constant for a neutrino-flavor independent coupling of $G<10^{-10}$, to avoid the effective number of light neutrinos in the early universe being essentially six. If, on the other hand, we wish to fine-tune the model to give a more modest excess (over three) in the effective neutrino number, as may be needed according to recent WMAP analyses, it is easy to do so. \pacs{13.15.+g}

Simulating merging binary black holes with nearly extremal spins [Cross-Listing]

Astrophysically realistic black holes may have spins that are nearly extremal (i.e., close to 1 in dimensionless units). Numerical simulations of binary black holes—important tools both for calibrating analytical templates for gravitational-wave detection and for exploring the nonlinear dynamics of curved spacetime—are particularly challenging when the holes’ spins are nearly extremal. Typical initial data methods cannot yield simulations with nearly extremal spins; e.g., Bowen-York data cannot produce simulations with spins larger than about 0.93. In this paper, we present the first binary black hole inspiral, merger, and ringdown with initial spins larger than the Bowen-York limit. Specifically, using the Spectral Einstein Code (SpEC), we simulate the inspiral (through 12.5 orbits), merger and ringdown of two equal-mass black holes with equal spins of magnitude 0.95 antialigned with the orbital angular momentum.

Simulating merging binary black holes with nearly extremal spins [Replacement]

Astrophysically realistic black holes may have spins that are nearly extremal (i.e., close to 1 in dimensionless units). Numerical simulations of binary black holes are important tools both for calibrating analytical templates for gravitational-wave detection and for exploring the nonlinear dynamics of curved spacetime. However, all previous simulations of binary-black-hole inspiral, merger, and ringdown have been limited by an apparently insurmountable barrier: the merging holes’ spins could not exceed 0.93, which is still a long way from the maximum possible value in terms of the physical effects of the spin. In this paper, we surpass this limit for the first time, opening the way to explore numerically the behavior of merging, nearly extremal black holes. Specifically, using an improved initial-data method suitable for binary black holes with nearly extremal spins, we simulate the inspiral (through 12.5 orbits), merger and ringdown of two equal-mass black holes with equal spins of magnitude 0.95 antialigned with the orbital angular momentum.

Simulating merging binary black holes with nearly extremal spins [Replacement]

Astrophysically realistic black holes may have spins that are nearly extremal (i.e., close to 1 in dimensionless units). Numerical simulations of binary black holes are important tools both for calibrating analytical templates for gravitational-wave detection and for exploring the nonlinear dynamics of curved spacetime. However, all previous simulations of binary-black-hole inspiral, merger, and ringdown have been limited by an apparently insurmountable barrier: the merging holes’ spins could not exceed 0.93, which is still a long way from the maximum possible value in terms of the physical effects of the spin. In this paper, we surpass this limit for the first time, opening the way to explore numerically the behavior of merging, nearly extremal black holes. Specifically, using an improved initial-data method suitable for binary black holes with nearly extremal spins, we simulate the inspiral (through 12.5 orbits), merger and ringdown of two equal-mass black holes with equal spins of magnitude 0.95 antialigned with the orbital angular momentum.

Tidal Excitation of Oscillation Modes in Compact White Dwarf Binaries: I. Linear Theory

We study the tidal excitation of gravity modes (g-modes) in compact white dwarf binary systems with periods ranging from minutes to hours. As the orbit of the system decays via gravitational radiation, the orbital frequency increases and sweeps through a series of resonances with the g-modes of the white dwarf. At each resonance, the tidal force excites the g-mode to a relatively large amplitude, transferring the orbital energy to the stellar oscillation. We calculate the eigenfrequencies of g-modes and their coupling coefficients with the tidal field for realistic non-rotating white dwarf models. Using these mode properties, we numerically compute the excited mode amplitude in the linear approximation as the orbit passes though the resonance, including the backreaction of the mode on the orbit. We also derive analytical estimates for the mode amplitude and the duration of the resonance, which accurately reproduce our numerical results for most binary parameters. We find that the g-modes can be excited to a dimensionless (mass-weighted) amplitude up to 0.1, with the mode energy approaching $10^{-3}$ of the gravitational binding energy of the star. This suggests that thousands of years prior to the binary merger, the white dwarf may be heated up significantly by tidal interactions. However, more study is needed since the physical amplitudes of the excited oscillation modes become highly nonlinear in the outer layer of the star, which can reduce the mode amplitude attained by tidal excitation.

Tidal Excitation of Oscillation Modes in Compact White Dwarf Binaries: I. Linear Theory [Replacement]

We study the tidal excitation of gravity modes (g-modes) in compact white dwarf binary systems with periods ranging from minutes to hours. As the orbit of the system decays via gravitational radiation, the orbital frequency increases and sweeps through a series of resonances with the g-modes of the white dwarf. At each resonance, the tidal force excites the g-mode to a relatively large amplitude, transferring the orbital energy to the stellar oscillation. We calculate the eigenfrequencies of g-modes and their coupling coefficients with the tidal field for realistic non-rotating white dwarf models. Using these mode properties, we numerically compute the excited mode amplitude in the linear approximation as the orbit passes though the resonance, including the backreaction of the mode on the orbit. We also derive analytical estimates for the mode amplitude and the duration of the resonance, which accurately reproduce our numerical results for most binary parameters. We find that the g-modes can be excited to a dimensionless (mass-weighted) amplitude up to 0.1, with the mode energy approaching $10^{-3}$ of the gravitational binding energy of the star. This suggests that thousands of years prior to the binary merger, the white dwarf may be heated up significantly by tidal interactions. However, more study is needed since the physical amplitudes of the excited oscillation modes become highly nonlinear in the outer layer of the star, which can reduce the mode amplitude attained by tidal excitation.

Tidal Excitation of Oscillation Modes in Compact White Dwarf Binaries: I. Linear Theory [Replacement]

We study the tidal excitation of gravity modes (g-modes) in compact white dwarf binary systems with periods ranging from minutes to hours. As the orbit of the system decays via gravitational radiation, the orbital frequency increases and sweeps through a series of resonances with the g-modes of the white dwarf. At each resonance, the tidal force excites the g-mode to a relatively large amplitude, transferring the orbital energy to the stellar oscillation. We calculate the eigenfrequencies of g-modes and their coupling coefficients with the tidal field for realistic non-rotating white dwarf models. Using these mode properties, we numerically compute the excited mode amplitude in the linear approximation as the orbit passes though the resonance, including the backreaction of the mode on the orbit. We also derive analytical estimates for the mode amplitude and the duration of the resonance, which accurately reproduce our numerical results for most binary parameters. We find that the g-modes can be excited to a dimensionless (mass-weighted) amplitude up to 0.1, with the mode energy approaching $10^{-3}$ of the gravitational binding energy of the star. This suggests that thousands of years prior to the binary merger, the white dwarf may be heated up significantly by tidal interactions. However, more study is needed since the physical amplitudes of the excited oscillation modes become highly nonlinear in the outer layer of the star, which can reduce the mode amplitude attained by tidal excitation.

Tidal Excitation of Oscillation Modes in Compact White Dwarf Binaries: I. Linear Theory [Replacement]

We study the tidal excitation of gravity modes (g-modes) in compact white dwarf binary systems with periods ranging from minutes to hours. As the orbit of the system decays via gravitational radiation, the orbital frequency increases and sweeps through a series of resonances with the g-modes of the white dwarf. At each resonance, the tidal force excites the g-mode to a relatively large amplitude, transferring the orbital energy to the stellar oscillation. We calculate the eigenfrequencies of g-modes and their coupling coefficients with the tidal field for realistic non-rotating white dwarf models. Using these mode properties, we numerically compute the excited mode amplitude in the linear approximation as the orbit passes though the resonance, including the backreaction of the mode on the orbit. We also derive analytical estimates for the mode amplitude and the duration of the resonance, which accurately reproduce our numerical results for most binary parameters. We find that the g-modes can be excited to a dimensionless (mass-weighted) amplitude up to 0.1, with the mode energy approaching $10^{-3}$ of the gravitational binding energy of the star. This suggests that thousands of years prior to the binary merger, the white dwarf may be heated up significantly by tidal interactions. However, more study is needed since the physical amplitudes of the excited oscillation modes become highly nonlinear in the outer layer of the star, which can reduce the mode amplitude attained by tidal excitation.

 

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