arXiv subjects

J. C. Jackson

Publications and source records attributed to J. C. Jackson.

9 recordsLinked to original sources

arXiv2012

Time and the Higgs (with apologies to J. B. Priestley)

A model of discrete space-time is presented which is, in a sense, both Lorentz invariant and has no restriction on the relative velocity between particles (except v < c). The space-time has an inbuilt indeterminacy. Published originally as 'A quantisation of time', J. Phys. A: Math. Gen., 10, 2115, 1977; identical to the original, apart from one or two minor corrections, and some simplification towards the end of Section 6. The paper presents a discrete model of time, in which the latter comprises a succession of instants which are identified as collisions with particles called chronons. Proper-time intervals are discrete; the structure of space-time is given by a radar map and has an inbuilt indeterminacy, which leads naturally to Heisenberg's uncertainty principle. If I were writing this paper today I would identify the chronon with the virtual Higgs boson. Without the latter all particles would be massless and would follow null paths; there would be no such thing as proper time. Time is an emergent phenomenon, and the Higgs boson is the agent of that emergence.

math-ph↗

arXiv2012

Ultra-compact radio sources and the isotropy and homogeneity of the Universe

A 2.29 GHz VLBI all-sky survey of ultra-compact radio sources has formed the basis of a number of cosmological investigations, which examine the relationship between angular-size and redshift. Here I use a sample of 468 such sources with 0.5<z<=3.787, to investigate the isotropy of the Universe. The sample is divided into hemispherical sub-samples, over an all-sky 5 degree x 5 degree array, each of which is allowed to determine a value of Omega_m, assuming that we are living in a spatially flat homogeneous isotropic LambdaCDM model. If we regard the latter as a null hypothesis, then it fails the test -- the results show significant anisotropy, the smallest value of Omega_m being towards (l,b)=(253.9,24.1) degrees, the largest in the opposite direction. This is close to the CMB dipole axis, but in the obverse sense. This is interpreted as meaning that the Universe is not spatially homogeneous on the largest scales, and is better represented at late times by a spherically symmetric model with a density enhancement at its centre.

astro-ph.CO↗

arXiv2008

Fingers of God

Very long wavelength universal gravitational waves cannot now produce in clusters of galaxies velocity dispersions greater than that which these systems would possess if they were expanding with the Universe, if the Universe is not younger than $10^{10}$ yr and Hubble's constant is not less than 50 km/sec/ Mpc. A diagram shows that actual velocity dispersions are significantly greater than this limit.

astro-ph↗

arXiv2008

Is there a standard measuring rod in the Universe?

The Caltech-Jodrell Bank very long baseline interferometry (VLBI) Surveys give detailed 5 GHz VLBI images of several hundred milliarcsecond (mas) radio sources, and the full width at half-maximum angular sizes of the corresponding compact cores. Using the latter, I have constructed an angular-diameter/redshift diagram comprising 271 objects, which shows clearly the expected features of such a diagram, without redshift binning. Cosmological parameters are derived which are compatible with existing concensus values, particularly when the VLBI data are combined with recent Baryon Accoustic Oscillations observations; the figures are presented as indications of what might be expected of larger samples of similar data. The importance of beaming and relativistic motion towards the observer is stressed; a model of the latter indicates that the emitting material is close to the observer's line of sight and moving with a velocity which brings it close to the observer's rest frame. With respect to linear size, these objects compare well in variance with type Ia supernovae; the efficacy of the latter is improved by the brighter-slower and brighter-bluer correlations, and by the inverse-square law.

astro-ph↗

arXiv2005

Tight Cosmological Constraints from the Angular-Size/Redshift Relation for Ultra-Compact Radio Sources

Some years ago (Jackson and Dodgson 1997) analysis of the angular-size/redshift relationship for ultra-compact radio sources indicted that for spatially flat universes the best choice of cosmological parameters was Omega_m=0.2 and Omega_Lambda=0.8. Here I present an astrophysical model of these sources, based upon the idea that for those with redshift z>0.5 each measured angular size corresponds to a single compact component which is moving relativistically towards the observer; this model gives a reasonable account of their behaviour as standard measuring rods. A new analysis of the original data set (Gurvits 1994), taking into account possible selection effects which bias against large objects, gives Omega_m=0.24+0.09/-0.07 for flat universes. The data points match the corresponding theoretical curve very accurately out to z~3, and there is clear and sustained indication of the switch from acceleration to deceleration, which occurs at z=0.85.

astro-ph↗

arXiv2001

Coherent Scalar Field Oscillations and the Epoch of Deceleration

The discovery of supernova SN 1997ff at z~1.7 has confirmed the expected switch from cosmological acceleration to deceleration, as predicted by the concordance Lambda/CDM model. However, its position in the SN Ia Hubble diagram suggestes that the switch is too pronounced, which here is taken to mean that a cosmological constant is not an adequate description of the state of the vacuum. An 'oscillessence' model is invoked, with a scalar field phi governed by a simple quadratic potential, which gives a better fit to the new data point. The field is undergoing coherent oscillations, and a key feature of the proposal is that we are towards the end of the second period of acceleration; a Lambda/phi mix replaces Lambda/CDM, with Omega_Lambda~0.4 and Omega_phi~0.6.

astro-ph↗

arXiv2001

Apocalypse soon

Based upon a simple vacuum Lagrangian, comprising cosmological and quadratic scalar field terms, a cosmological model is presented whose history is indistinguishable from that of an innocuous low-density cold dark matter (CDM) universe, but whose future is very much shorter. For sensible values of the deceleration parameter (0<q_0<1), its age is greater than 85% of the Hubble time, thus resolving the current version of the age crisis, which appears (appeared) to be that t_0 ~ H_0 while q_0 is significantly positive.

astro-ph↗

arXiv2001

Decelerating universes older than their Hubble times

Recent observations suggest that Hubble's constant is large, and hence that the Universe appears to be younger than some of its constituents. The traditional escape route, which assumes that the expansion is accelerating, appears to be blocked by observations of Type 1a supernovae, which suggest(ed) that the Universe is decelerating. These observations are reconciled in a model in which the Universe has experienced an inflationary phase in the recent past, driven by an ultra-light inflaton whose Compton wavelength is of the same order as the Hubble radius.

astro-ph↗

arXiv2001

Determination of cosmology and evolution from K-band magnitude-redshift and number count observations

We determine cosmological and evolutionary parameters from the 3CR K-band Hubble diagram and K-band number counts, assuming that the galaxies in question undergo pure luminosity evolution. Separately the two data sets are highly degenerate with respect to choice of cosmological and evolutionary parameters, but in combination the degeneracy is resolved. Of models which are either flat or have $Ω_Λ=0$, the preferred ones are close to the canonical case $Ω_\CdM=1$, $Ω_Λ=0$, with luminosity evolution amounting to one magnitude brighter at z=1.

astro-ph↗