Basic ground and space-based observations of the highest-energy gamma-rays can provide insight into the very nature of time, matter, energy and space at scales extremely far below the subatomic level. High-energy observations of cosmic gamma rays can place strict constraints on extra dimensions and quantum gravity. GUTs such as loop quantum gravity or string theory may involve invoking extra dimensions of space and also violations of Einstein's special theory of relativity, such as the speed of light being the maximum attainable velocity for all objects.

According to the uncertainty principle, subatomic level virtual particles pop in and out of existence. Spacetime itself may be made up of these quantum fluctuations which, when viewed up close, resemble a"foam." A quantum foam of spacetime can slow the passage of light. The foam would slow higher energy X-ray and gamma-ray photons more than lower energy photons. Such a fundamental variation in the speed of light, different for photons of different energies, would violate Lorentz invariance (LIV), the basic principle of the special theory of relativity. Gamma-rays coming from very distant sources such as gamma-ray bursts or blazars would produce differences in the speeds of photons depending on their energy. With the advent of the Fermi gamma-ray telescope, there should be a plethora of high redshift objects to try and observe this effect and place strong constraints on the amount of LIV.

Additionally, gamma-rays from distant sources will collide with the ambient infrared photons in the Universe. Through pair production, the gamma-rays are destroyed. If Lorentz invariance were violated, the gamma rays would pass right through the extragalactic infrared fog without pair-producing as the reaction threshold for this reaction would be shifted to a higher energy. This would significantly alter calculations on the transparency of the universe (detailed in that section). Again the Fermi Gamma-ray Space Telescope should provide enough sources to test this transparency and place a strong constraint on LIV.

Above a few times 1019 eV, the number of cosmic rays should drop off quite sharply due to pion production from their interaction with the CMB - the so-called the Greisen-Zatsepin-Kuzmin (GZK) effect. The state of the art experiment in high energy cosmic rays is the Pierre Auger array. This instrument has taken data and produced the best spectrum of cosmic rays above 1018 eV. The spectrum hints at a GZK cutoff but the severity and location of the cutoff are still debatable meaning the high energy events observed by other experiments such as AGASA and HiRes may indeed be real and require some non-standard physics to explain them. This could include string or quantum gravity effects which can change the interactions between these particles and the microwave background. I am currently working on a detailed calculation of the effects of LIV which could be present in both string and loop quantum gravity models on the cosmic ray spectrum. The effect would manifest itself by supressing the photopion production or possibly the lower enrgy pair production process.

A key component in deciphering the origin of these particles or indeed add some degeneracy to the potential of LIV is the spectrum of neutrinos that would accompany the high energy particle events. Neutrinos could be produced by the source of the high energy cosmic rays or through the decay of pions left over from the high energy cosmic ray interactions with the microwave background. Thus the spectrum of neutrinos observed at the highest energies should be a signature of the processes which created them and/or affected them as they traversed to the Earth. The ICECUBE experiment promises to have the sensitivity to at least eliminate a few of the competing scenarios but a lot of work must be done in identifying these signatures.

Blazars, Gamma-ray bursts and other distant gamma-ray sources will experience significant absoption via pair production with abient photons in intergalactic space. We (Stecker, Malkan, & Scully 2006) modeled the intergalactic background light (IBL) from 0.03 eV up to the Lyman limit of 13.6 eV with the goal of determining optical depths of gamma-rays from 0 ≤ z ≤ 6 from .1 TeV to 100 TeV. We consider two different evolutionary models: The Baseline model with (1 + z)3.1 for 0 < z < 1.4 then flat until z = 6 and zero thereafter which is consistent with HST deep survey results and our Fast Evolution model with (1 + z)4 for 0 < z < 0.8 then (1 + z)2 for 0.8 < z < 1.5 then flat and again zero after z = 6 based on mid-IR LFs (derived from Spitzer results). The function τ(Eγ, z) is excellently approximated by the analytic form Log τ = Ax4+Bx3+Cx2+Dx+E over the range 0.01 < τ < 100 where x ≡Log Eγ (eV). The upper row is the baseline and the lower is the fast evolution model coefficients (for the various redshifts).

Measurements of the cosmic microwave background made by WMAP possibly provide support for a supersymmetric neutralino. In order to retrieve the cosmological data from the WMAP satellite, one must very carefully remove any "foregrounds" or processes other than the CMB that contribute to microwave and far-infrared wavelengths such as dust, synchrotron, and free-free. Finkbeiner (2004) has suggested an excess of microwaves from near the galactic center are not accounted for by these foregrounds and is termed the "WMAP haze." He proposed that it could be due to the self-annihilation of neutralinos into relativistic electrons and positrons.

I am doing a more careful analysis of the WMAP 5 year data to see if this haze really persists. The WMAP foreground removal processes is not geared to find new foregrounds but only remove excess emission to find the Planckian CMB spectrum. Should a more careful analysis conclude that this haze can not be explained by standard foregrounds, this would be exciting news for dark matter searches and could possibly even be improved upon by co-observations from the Fermi Gamma-Ray Space Telescope.

CMB maps from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite show an apparent coincident alignment between the quadrupole and octopole. I have examined multipoles 2 through 15 to determine if other alignments exist and their potential statistical significance. I constructed an ensemble of 25,000 random CMB realizations based on the ΛCDM fit to the first year WMAP results. I have determined that some of the individual poles in the real data show some unlikely structure that may be a result of topological effects, foreground residuals from the removal process, or unknown physical processes operating in the early universe and warrant further study.