arXiv subjects

John G. Hartnett

Publications and source records attributed to John G. Hartnett.

34 records · Page 2Linked to original sources

arXiv2010

Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures

We report on extremely sensitive measurements of changes in the microwave properties of high purity non-intentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide and 4H-silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors whilst they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping relaxation times have been evaluated from comparison with measured data.

physics.ins-det↗

arXiv2010

Microwave cavity light shining through a wall optimization and experiment

It has been proposed that microwave cavities can be used in a photon regeneration experiment to search for hidden sector photons. Using two isolated cavities, the presence of hidden sector photons could be inferred from a 'light shining through a wall' phenomenon. The sensitivity of the experiment has strong a dependence on the geometric construction and electromagnetic mode properties of the two cavities. In this paper we perform an in depth investigation to determine the optimal setup for such an experiment. We also describe the results of our first microwave cavity experiment to search for hidden sector photons. The experiment consisted of two cylindrical copper cavities stacked axially inside a single vacuum chamber. At a hidden sector photon mass of 37.78 micro eV we place an upper limit on the kinetic mixing parameter chi = 2.9 * 10^(-5). Whilst this result lies within already established limits our experiment validates the microwave cavity `light shining through a wall' concept. We also show that the experiment has great scope for improvement, potentially able to reduce the current upper limit on the mixing parameter chi by several orders of magnitude.

hep-ex↗

arXiv2010

Ultra-low vibration pulse-tube cryocooler stabilized cryogenic sapphire oscillator with 10^-16 fractional frequency stability

A low maintenance long-term operational cryogenic sapphire oscillator has been implemented at 11.2 GHz using an ultra-low-vibration cryostat and pulse-tube cryocooler. It is currently the world's most stable microwave oscillator employing a cryocooler. Its performance is explained in terms of temperature and frequency stability. The phase noise and the Allan deviation of frequency fluctuations have been evaluated by comparing it to an ultra-stable liquid-helium cooled cryogenic sapphire oscillator in the same laboratory. Assuming both contribute equally, the Allan deviation evaluated for the cryocooled oscillator is sigma_y = 1 x 10^-15 tau^-1/2 for integration times 1 < tau < 10 s with a minimum sigma_y = 3.9 x 10^-16 at tau = 20 s. The long term frequency drift is less than 5 x 10^-14/day. From the measured power spectral density of phase fluctuations the single side band phase noise can be represented by L_phi(f) = 10^-14.0/f^4+10^-11.6/f^3+10^-10.0/f^2+10^-10.2/f+ 10^-11.0 for Fourier frequencies 10^-3<f<10^3 Hz in the single oscillator. As a result L_phi approx -97.5 dBc/Hz at 1 Hz offset from the carrier.

physics.ins-det↗

arXiv2010

Cryogenic Sapphire Oscillator using a low-vibration design pulse-tube cryocooler: First results

A Cryogenic Sapphire Oscillator has been implemented at 11.2 GHz using a low-vibration design pulse-tube cryocooler. Compared with a state-of-the-art liquid helium cooled CSO in the same laboratory, the square root Allan variance of their combined fractional frequency instability is $σ_y = 1.4 \times 10^{-15}τ^{-1/2}$ for integration times $1 < τ< 10$ s, dominated by white frequency noise. The minimum $σ_y = 5.3 \times 10^{-16}$ for the two oscillators was reached at $τ= 20$ s. Assuming equal contributions from both CSOs, the single oscillator phase noise $S_ϕ \approx -96 \; dB \; rad^2/Hz$ at 1 Hz offset from the carrier.

physics.ins-det↗

arXiv2009

Rotating Odd-Parity Lorentz Invariance Test in Electrodynamics

We report the first operation of a rotating odd-parity Lorentz Invariance test in electrodynamics using a microwave Mach-Zehnder interferometer with permeable material in one arm. The experiment sets a direct bound to $ κ_{tr}$ of $-0.3\pm 3\times10^{-7}$. Using new power recycled waveguide interferometer techniques (with the highest spectral resolution ever achieved of $2\times10^{-11} rad/\sqrt{Hz}$) we show an improvement of several orders of magnitude is attainable in the future.

hep-ph↗

arXiv2008

Galaxy redshift abundance periodicity from Fourier analysis of number counts $N(z)$ using SDSS and 2dF GRS galaxy surveys

A Fourier analysis on galaxy number counts from redshift data of both the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey indicates that galaxies have preferred periodic redshift spacings of $Δz =$ 0.0102, 0.0246, and 0.0448 in the SDSS and strong agreement with the results from the 2dF GRS. The redshift spacings are confirmed by the mass density fluctuations, the power spectrum $P(z)$ and $N_{pairs}$ calculations. Application of the Hubble law results in galaxies preferentially located on co-moving concentric shells with periodic spacings. The combined results from both surveys indicate regular co-moving radial distance spacings of $31.7 \pm 1.8$ $h^{-1} Mpc$, $73.4 \pm 5.8$ $h^{-1} Mpc$ and $127 \pm 21$ $h^{-1} Mpc$. The results are consistent with oscillations in the expansion rate of the universe over past epochs.

astro-ph↗

arXiv2007

Extending the redshift-distance relation in Cosmological General Relativity to higher redshifts

The redshift-distance modulus relation, the Hubble Diagram, derived from Cosmological General Relativity has been extended to arbitrarily large redshifts. Numerical methods were employed and a density function was found that results in a valid solution of the field equations at all redshifts. The extension has been compared to 302 type Ia supernova data as well as to 69 Gamma-ray burst data. The latter however do not not truly represent a `standard candle' as the derived distance modulii are not independent of the cosmology used. Nevertheless the analysis shows a good fit can be achieved without the need to assume the existence of dark matter. The Carmelian theory is also shown to describe a universe that is always spatially flat. This results from the underlying assumption of the energy density of a cosmological constant $Ω_Λ = 1$, the result of vacuum energy. The curvature of the universe is described by a \textit{spacevelocity} metric where the energy content of the curvature at any epoch is $Ω_K = Ω_Λ - Ω= 1-Ω$, where $Ω$ is the matter density of the universe. Hence the total density is always $Ω_K + Ω= 1$

physics.gen-ph↗

arXiv2007

Spheroidal and elliptical galaxy radial velocity dispersion determined from Cosmological General Relativity

Radial velocity dispersion in spheroidal and elliptical galaxies, as a function of radial distance from the center of the galaxy, has been derived from Cosmological Special Relativity. For velocity dispersions in the outer regions of spherical galaxies, the dynamical mass calculated for a galaxy using Carmelian theory may be 10 to 100 times less than that calculated from standard Newtonian physics. This means there is no need to include halo dark matter. The velocity dispersion is found to be approximately constant across the galaxy after falling from an initial high value at the center.

physics.gen-ph↗

arXiv2007

Testing Cosmological General Relativity against high redshift observations

Several key relations are derived for Cosmological General Relativity which are used in standard observational cosmology. These include the luminosity distance, angular size, surface brightness and matter density. These relations are used to fit type Ia supernova (SNe Ia) data, giving consistent, well behaved fits over a broad range of redshift $0.1 < z < 2$. The best fit to the data for the local density parameter is $Ω_{m} = 0.0401 \pm 0.0199$. Because $Ω_{m}$ is within the baryonic budget there is no need for any dark matter to account for the SNe Ia redshift luminosity data. From this local density it is determined that the redshift where the universe expansion transitions from deceleration to acceleration is $z_{t}= 1.095 {}^{+0.264}_{-0.155}$. Because the fitted data covers the range of the predicted transition redshift $z_{t}$, there is no need for any dark energy to account for the expansion rate transition. We conclude that the expansion is now accelerating and that the transition from a closed to an open universe occurred about $8.54 {\rm Gyr}$ ago.

astro-ph↗

arXiv2007

Finite bounded expanding white hole universe without dark matter

The solution of Einstein's field equations in Cosmological General Relativity (CGR), where the Galaxy is at the center of a finite yet bounded spherically symmetrical isotropic gravitational field, is identical with the unbounded solution. This leads to the conclusion that the Universe may be viewed as a finite expanding white hole. The fact that CGR has been successful in describing the distance modulus verses redshift data of the high-redshift type Ia supernovae means that the data cannot distinguish between unbounded models and those with finite bounded radii of at least $c τ$. Also it is shown that the Universe is spatially flat at the current epoch and has been at all past epochs where it was matter dominated.

astro-ph↗

arXiv2006

Spiral galaxy rotation curves determined from Carmelian general relativity

Equations of motion, in cylindrical co-ordinates, for the observed rotation of gases within the gravitational potential of spiral galaxies have been derived from Carmeli's Cosmological General Relativity theory. A Tully-Fisher type relation results and rotation curves are reproduced without the need for non-baryonic halo dark matter. Two acceleration regimes are discovered that are separated by a critical accleration $\approx 4.75 \times 10^{-10}$ $m.s^{-2}$. For accelerations larger than the critical value the Newtonian force law applies, but for accelerations less than the critical value the Carmelian regime applies. In the Newtonian regime the accelerations fall off as $r^{-2}$, but in the Carmelian regime the accelerations fall off as $r^{-1}$. This is new physics but is exactly what is suggested by Migrom's phenomenological MOND theory.

astro-ph↗

arXiv2006

Properties of gravitational waves in Cosmological General Relativity

The 5D Cosmological General Relativity theory developed by Carmeli reproduces all of the results that have been successfully tested for Einstein's 4D theory. However the Carmeli theory because of its fifth dimension, the velocity of the expanding universe, predicts something different for the propagation of gravity waves on cosmological distance scales. This analysis indicates that gravitational radiation may not propagate as an unattenuated wave where effects of the Hubble expansion are felt. In such cases the energy does not travel over such large length scales but is evanescent and dissipated into the surrounding space as heat.

gr-qc↗

arXiv2006

On the anomalous acceleration of Pioneer spacecraft

The anomalous acceleration of Pioneer 10 and 11 spacecraft of (8.74 \pm 1.33) \times 10^{-8} cm. s^{-2} fits with a theoretical prediction of a minimal acceleration in nature of about 7.61 \times 10^{-8} cm. s^{-2}

gr-qc↗

arXiv2005

The distance modulus determined from Carmeli's cosmology fits the accelerating universe data of the high-redshift type Ia supernovae without dark matter

The velocity of the Hubble expansion has been added to General Relativity by Moshe Carmeli and this resulted in new equations of motion for the expanding universe. For the first time the observational magnitude-redshift data derived from the high-$z$ supernova teams has been analysed in the framework of the Carmeli theory and the fit to that theory is achieved without the inclusion of any dark matter. Best fits to the data yield an averaged matter density for the universe at the present epoch $Ω_{m} \approx 0.021$, which falls well within the measured values of the baryonic matter density. And the best estimate of $Ω_Λ + Ω_{m} \approx 1.021$ at the present epoch. The analysis also clearly distinguishes that the Hubble expansion of the universe is speed-limited.

astro-ph↗

arXiv2005

The Cosmic Time in Terms of the Redshift

In cosmology one labels the time t since the Big Bang in terms of the redshift of light emitted at t, as we see it now. In this Note we derive a formula that relates t to z which is valid for all redshifts. One can go back in time as far as one wishes, but not to the Big Bang at which the redshift tends to infinity.

gr-qc↗

arXiv2004

New methods of testing Lorentz violation in electrodynamics

We investigate experiments that are sensitive to the scalar and parity-odd coefficients for Lorentz violation in the photon sector of the Standard Model Extension (SME). We show that of the classic tests of special relativity, Ives-Stilwell (IS) experiments are sensitive to the scalar coefficient, but at only parts in 10^5 for the state-of-the-art experiment. We then propose asymmetric Mach-Zehnder interferometers with different electromagnetic properties in the two arms, including recycling techniques based on travelling wave resonators to improve the sensitivity. With present technology we estimate that the scalar and parity odd coefficients may be measured at sensitivity better than parts in 10^11 and 10^15 respectively.

hep-ph↗