Document Type


Date of Degree

Summer 2015

Degree Name

PhD (Doctor of Philosophy)

Degree In


First Advisor

Philip Kaaret


The search for a theory of quantum gravity has persisted through the last century. Although many beautiful theories such as string theory and loop quantum gravity have been proposed, experimental evidence to support or refute these theories has been difficult to obtain. Searching for Lorentz invariance violation (LIV) is one of a limited number of experimental tests which can be used to search for evidence of quantum gravity since new physics may only be observable at energies well beyond those present in the most energetic astrophysical objects, which are far greater than the energies accessible in a terrestrial laboratory.

One method of searching for LIV is to look for energy-dependent time delays in the arrival of high-energy photons from distant astrophysical sources. We search for Lorentz invariance violation (LIV) using VERITAS, an imaging atmospheric Cherenkov telescope (IACT) located in southern Arizona. Significant TeV gamma ray flaring activity was detected from the blazar Markarian 421 on the night of February 17, 2010 (MJD 55244), which presented a good opportunity to search for delays in the energetic emission. We demonstrate the performance of two different dispersion estimation algorithms and apply these algorithms to our data to search for LIV. We find that while the emission from Markarian 421 contains significant variability, a necessary condition for an LIV detection, the presence of a constant background flux severely limits our sensitivity. We expect our findings to be useful for guiding future LIV studies, especially those using IACT data.

In the latter part of this work we discuss the alignment of ground-based gamma-ray telescopes and present a digital autocollimator which will be used in the alignment system of a next-generation IACT. The configuration of our autocollimator enables measurement of the angle formed between the planar surface of a distant reflector and the line of sight over a range of ±0.126° with a precision better than 5 arcsec. We present a detailed description of the instrument and its data acquisition software that was used during laboratory testing.

Public Abstract

The speed at which light travels through vacuum is thought to be an immutable constant of nature, unchanging regardless of who observes it and where. Evidence accumulated over the past century indicates that the maximum speed of light is always the same regardless of its energy (wavelength or frequency). However, it is possible that at very high energies, the speed of light in vacuum may change.

I use observations of the most energetic light, gamma rays, made with a telescope called VERITAS to look for arrival time differences between high and low energy light emitted by a jet of material streaming out of a supermassive black hole. If a difference were observed, it could help us find a theory of quantum gravity and would provide insight into the physics of the early universe. The way in which the black hole jet was emitting light at the time we observed it does not allow me to place any useful constraints on the constancy of the speed of light. However, the reasons why I was not able to generate a constraint are themselves a useful result.

I also discuss an instrument I designed and constructed to measure the tilt of a mirror located 9 meters away. I show that the instrument is capable of measuring tilts of approximately 1/1000 of a degree. This instrument will be used to help align the mirrors of a next-generation gamma-ray telescope.


publicabstract, Autocollimator, Blazar, Lorentz invariance, Quantum gravity, VHE Astronomy


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Copyright 2015 Scott Tyler Griffiths

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