Planck 2015 constraints on spatially-flat dynamical dark energy models [CEA]

We determine constraints on spatially-flat tilted dynamical dark energy XCDM and $\phi$CDM inflation models by analyzing Planck 2015 cosmic microwave background (CMB) anisotropy data and baryon acoustic oscillation (BAO) distance measurements. XCDM is a simple and widely used but physically inconsistent parameterization of dynamical dark energy, while the $\phi$CDM model is a physically consistent one in which a scalar field $\phi$ with an inverse power-law potential energy density powers the currently accelerating cosmological expansion. Both these models have one additional parameter compared to standard $\Lambda$CDM and both better fit the TT + lowP + lensing + BAO data than does the standard tilted flat-$\Lambda$CDM model, with $\Delta \chi^2 = -1.26\ (-1.60)$ for the XCDM ($\phi$CDM) model relative to the $\Lambda$CDM model. While this is a 1.1$\sigma$ (1.3$\sigma$) improvement over standard $\Lambda$CDM and so not significant, dynamical dark energy models cannot be ruled out. In addition, both dynamical dark energy models reduce the tension between the Planck 2015 CMB anisotropy and the weak lensing $\sigma_8$ constraints.

Read this paper on arXiv…

J. Ooba, B. Ratra and N. Sugiyama
Fri, 16 Feb 18

Comments: 9 pages, 12 figures, 3 tables. arXiv admin note: text overlap with arXiv:1712.08617

Strongly gravitational lensed SNe Ia as multi-messengers: Direct test of the Friedmann-Lemaître-Robertson-Walker metric [CEA]

We present a new idea of testing the validity of the Friedmann-Lema\^{\i}tre-Robertson-Walker metric, through the multiple measurements of galactic-scale strong gravitational lensing systems with type Ia supernova acting as background sources. Each individual lensing system will provides a model-independent measurement of the geometrical optics of the universe along the line of sight the SNe Ia located, which is independent of the matter content of the universe and the applicability of the Einstein equation. This will provide us the valuable possibility of directly measuring the FRW metric on cosmological scales. Moreover, our results show that LSST would produce robust constraints on the spacial curvature comparable to Planck 2014 results, with 500 strongly lensed SNe Ia observed in the future.

Read this paper on arXiv…

J. Qi, S. Cao, M. Biesiada, et. al.
Fri, 16 Feb 18

Comments: N/A

Reinterpreting Low Frequency LIGO/Virgo Events as Magnified Stellar-Mass Black Holes at Cosmological Distances [CEA]

Gravitational waves can be focussed by the gravity of an intervening galaxy, just like light, thereby magnifying binary merging events in the far Universe. High magnification by galaxies is found to be responsible for the brightest sources detected in sky surveys, but the low angular resolution of LIGO/Virgo is insufficient to check this lensing possibility directly. Here we find that the first six binary black hole (BBH) merging events reported by LIGO/Virgo show clear evidence for lensing in the plane of observed mass and source distance. The four lowest frequency events follow an apparent locus in this plane, which we can reproduce by galaxy lensing, where the higher the magnification, the generally more distant the source so the wave train is stretched more by the Universal expansion, by factors of 2-4. This revises the reported BBH distances upwards by an order of magnitude, equal to the square root of the magnification. Furthermore, the reported black hole masses must be decreased by 2-4 to counter the larger stretch factor, since the orbital frequency is used to derive the black hole masses. This lowers the masses to 5-15 solar, well below the puzzlingly high values of 20-35 solar masses otherwise estimated, with the attraction of finding agreement in mass with black holes orbiting stars in our own Galaxy, thereby implying a stellar origin for the low frequency events in the far Universe. We also show that the other two BBH events of higher frequency detected by LIGO/VIRGO, lie well below the lensing locus, consistent with being nearby and unlensed. If this apparent division between local and distant lensed events is reinforced by new detections then the spins and masses of stellar black holes can be compared over a timespan of 10 billion years by LIGO/Virgo.

Read this paper on arXiv…

T. Broadhurst, J. Diego and G. Smoot
Fri, 16 Feb 18

Comments: 16 pages, 3 figures

Maximum PBH Mass and Primordiality [CL]

In order to avoid unacceptable $\mu$-distortions inconsistent with observational data on the Cosmic Microwave Background, Primordial Black Holes (PBHs) must be less massive than $10^{12} M_{\odot}$, quite closely above the highest black hole mass yet observed. This comparableness leads us to posit that all supermassive black holes originate as PBHs.

Read this paper on arXiv…

P. Frampton
Fri, 16 Feb 18

Comments: 5 pages LaTeX

Dark-matter-like solutions to Einstein's unified field equations [CL]

Einstein originally proposed a nonsymmetric tensor field, with its symmetric part associated with the spacetime metric and its antisymmetric part associated with the electromagnetic field, as an approach to a unified field theory. Here we interpret it more modestly as an alternative to Einstein-Maxwell theory, approximating the coupling between the electromagnetic field and spacetime curvature in the macroscopic classical regime. Previously it was shown that the Lorentz force can be derived from this theory, albeit with deviation on the scale of a universal length constant $\ell$. Here we assume that $\ell$ is of galactic scale and show that the modified coupling of the electromagnetic field with charged particles allows a non-Maxwellian equilibrium of non-neutral plasma. The resulting electromagnetic field is “dark” in the sense that its modified Lorentz force on the plasma vanishes, yet through its modified coupling to the gravitational field it engenders a nonvanishing, effective mass density. We obtain a solution for which this mass density asymptotes approximately to that of the pseudo-isothermal model of dark matter. The resulting gravitational field produces radial acceleration, in the context of a post-Minkowskian approximation, which is negligible at small radius but yields a flat rotation curve at large radius. We further exhibit a family of such solutions which, like the pseudo-isothermal model, has a free parameter to set the mass scale (in this case related to the charge density) and a free parameter to set the length scale (in this case an integer multiple of $\ell$). Moreover, these solutions are members of a larger family with more general angular and radial dependence. They thus show promise as approximations of generalized pseudo-isothermal models, which in turn are known to fit a wide range of mass density profiles for galaxies and clusters.

Read this paper on arXiv…

J. Meter
Thu, 15 Feb 18

Comments: 13 pages, 2 figures

MOND and the dynamics of NGC 628 [GA]

Aniyan et al. (2018) have recently published direct measurements of the baryonic mass distribution and the rotation curve of the almost-face-on disc galaxy NGC 628. While its very low inclination makes this galaxy anything but ideal for rotation-curve analysis, these new results, taken at face value, have interesting ramifications for MOND. The methods employed afford a direct determination of the stellar mass in the disc, which, in turn, affords a parameter-free MOND prediction of the rotation curve, which I show. In comparison, the dark-matter fits that Aniyan et al. present have two free parameters. To boot, these results further negate an earlier claim deleterious to MOND. It is that stellar $M/L$ ratios deduced from vertical velocity dispersions in disc galaxies are rather lower than what is required by MOND fits to rotation curves. Specifically, it was claimed that even high-surface-density discs are, by and large, sub maximal; viz., that they show substantial mass discrepancies near their center. This is contrary to the prediction of MOND that in such high-acceleration regions only small discrepancies should appear, if any to speak of. Such claims of low $M/L$ values have been rebutted before, and the fallacy that may have led to them pointed out. The new results strongly buttress these rebuttals.

Read this paper on arXiv…

M. Milgrom
Thu, 15 Feb 18

Comments: 3 pages, 1 figure

Unimodular Gravity and the lepton anomalous magnetic moment at one-loop [CL]

We work out the one-loop contribution to the lepton anomalous magnetic moment coming from Unimodular Gravity. We use Dimensional Regularization and Dimensional Reduction to carry out the computations. In either case, we find that Unimodular Gravity gives rise to the same one-loop correction as that of General Relativity.

Read this paper on arXiv…

C. Martin
Thu, 15 Feb 18

Comments: 16 pages, 5 figures