Cosmology, Relativity, and Gravity Commons^™

Gamma-Rays From The Quasar Pks 1441+25: Story Of An Escape, P. T. Reynolds, Et Al

Physical Sciences Publications

Outbursts from gamma-ray quasars provide insights on the relativistic jets of active galactic nuclei and constraints on the diffuse radiation fields that fill the universe. The detection of significant emission above 100 GeV from a distant quasar would show that some of the radiated gamma-rays escape pair-production interactions with low-energy photons, be it the extragalactic background light (EBL), or the radiation near the supermassive black hole lying at the jet's base. VERITAS detected gamma-ray emission up to ~200 GeV from PKS 1441+25 (z = 0.939) during 2015 April, a period of high activity across all wavelengths. This observation of …

Differentialgeometry In Brno, Ian M. Anderson

Presentations

This page will provide files supporting Ian Anderson's presentations in Brno, December 2015. The files can be found and downloaded from "Additional Files", below.

The files include:

(1) DifferentialGeometryUSU.mla: This is the Maple Library Archive file which provides all the DifferentialGeometry functionality. Here are Installation Instructions.

(2) DifferentialGeometry.help : this is the latest version of the DifferentialGeometry documentation. Copy this file to the same directory used for DifferentialGeometryUSU.mla (from step (1)).

The Impact Of Terrestrial Noise On The Detectability And Reconstruction Of Gravitational Wave Signals From Core-Collapse Supernovae, Jessica Mciver

Doctoral Dissertations

Among of the wide range of potentially interesting astrophysical sources for gravitational wave detectors Advanced LIGO and Advanced Virgo are galactic core-collapse supernovae. Although detectable core-collapse supernovae have a low expected rate (a few per century, or less) these signals would yield a wealth of new physics. Of particular interest is the insight into the explosion mechanism driving core-collapse supernovae that can be gleaned from the reconstructed gravitational wave signal. A well-reconstructed waveform will allow us to assess the likelihood of different explosion models, perform model selection, and potentially map unexpected features to new physics. This dissertation presents a series …

Gravitational Wave Astrophysics: Instrumentation, Detector Characterization, And A Search For Gravitational Signals From Gamma-Ray Bursts, Daniel Hoak

Doctoral Dissertations

In the coming years, the second generation of interferometric gravitational wave detectors are widely expected to observe the gravitational radiation emitted by compact, energetic events in the nearby universe. The field of gravitational wave astrophysics has grown into a large international endeavor with a global network of kilometer-scale observatories. The work presented in this thesis spans the field, from optical metrology, to instrument commissioning, to detector characterization and data analysis. The principal results are a method for the precise characterization of optical cavities, the commissioning of the advanced LIGO Output Mode Cleaner at the Hanford observatory, and a search for …

Exact Solutions In Gravity: A Journey Through Spacetime With The Kerr-Schild Ansatz, Benjamin Ett

Doctoral Dissertations

The Kerr-Schild metric ansatz can be expressed in the form $g_{ab} = \gbar_{ab}+\lambda k_ak_b$, where $\gbar_{ab}$ is a background metric satisfying Einstein's equations, $k_a$ is a null-vector, and $\lambda$ is a free parameter. It was discovered in 1963 while searching for the elusive rotating black hole solutions to Einstein's equations, fifty years after the static solution was found and Einstein first formulated his theory of general relativity. While the ansatz has proved an excellent tool in the search for new exact solutions since then, its scope is limited, particularly with respect to higher dimensional theories. In this thesis, we present …

Gravitons To Photons--Attenuation Of Gravitational Waves, Preston Jones, Douglas Singleton

Publications

In this essay, we examine the response of an Unruh–DeWitt (UD) detector (a quantum two-level system) to a gravitational wave background. The spectrum of the UD detector is of the same form as some scattering processes or three body decays such as muon-electron scattering or muon decay. Based on this similarity, we propose that the UD detector response implies a “decay” or attenuation of gravitons, G, into photons, γ, via G+G→γ+γ or G→γ+γ+G. Over large distances such a decay/attenuation may have consequences in regard to the detection of gravitational waves.

Probabilistic Reasoning In Cosmology, Yann Benétreau-Dupin

Electronic Thesis and Dissertation Repository

Cosmology raises novel philosophical questions regarding the use of probabilities in inference. This work aims at identifying and assessing lines of arguments and problematic principles in probabilistic reasoning in cosmology.

The first, second, and third papers deal with the intersection of two distinct problems: accounting for selection effects, and representing ignorance or indifference in probabilistic inferences. These two problems meet in the cosmology literature when anthropic considerations are used to predict cosmological parameters by conditionalizing the distribution of, e.g., the cosmological constant on the number of observers it allows for. However, uniform probability distributions usually appealed to in such arguments …

Testing Lorentz Symmetry With Planetary Orbital Dynamics, A. Hees, Q. G. Bailey, C. Le Poncin-Lafitte, A. Bourgoin, A. Rivoldini, B. Lamine, F. Meynadier, C. Guerlin, P. Wolf

Publications

Planetary ephemerides are a very powerful tool to constrain deviations from the theory of general relativity (GR) using orbital dynamics. The effective field theory framework called the Standard-Model Extension (SME) has been developed in order to systematically parametrize hypothetical violations of Lorentz symmetry (in the Standard Model and in the gravitational sector). In this communication, we use the latest determinations of the supplementary advances of the perihelia and of the nodes obtained by planetary ephemerides analysis to constrain SME coefficients from the pure gravity sector and also from gravity-matter couplings. Our results do not show any deviation from GR and …

Stability Bounds On Compact Astrophysical Objects From Information-Entropic Measure, Marcelo Gleiser, Nan Jiang

Dartmouth Scholarship

We obtain bounds on the stability of various self-gravitating astrophysical objects using a new measure of shape complexity known as configurational entropy. We apply the method to Newtonian polytropes, neutron stars with an Oppenheimer-Volkoff equation of state, and to self-gravitating configurations of complex scalar field (boson stars) with different self couplings, showing that the critical stability region of these stellar configurations obtained from traditional perturbation methods correlates well with critical points of the configurational entropy with accuracy of a few percent or better.

On The Existence And Uniqueness Of Static, Spherically Symmetric Stellar Models In General Relativity, Josh Michael Lipsmeyer

Masters Theses

The "Fluid Ball Conjecture" states that a static stellar model is spherically symmetric. This conjecture has been the motivation of much work since first mentioned by Kunzle and Savage in 1980. There have been many partial results( ul-Alam, Lindblom, Beig and Simon,etc) which rely heavily on arguments using the positive mass theorem and the equivalence of conformal flatness and spherical symmetry. The purpose of this paper is to outline the general problem, analyze and compare the key differences in several of the partial results, and give existence and uniqueness proofs for a particular class of equations of state which represents …

High Gravitational Waveform Accuracy At Null Infinity, Maria Babiuc-Hamilton

Maria C. Babiuc-Hamilton

The aim of Cauchy-characteristic extraction is to provide a standardized waveform extraction tool for the numerical relativity community. The new extraction tool contains major improvements and corrections to previous versions and displays convergence. The error introduced by CCE satisfies the time domain criteria required for advanced LIGO data analysis. The importance of accurate waveforms to the gravitational wave astronomy has created an urgency for tools like CCE. The source code has been released to the public and is available as part of the Einstein Toolkit. We welcome applications to a variety of generic Cauchy codes implementing Einstein Equations of General …

Geometrization Conditions For Perfect Fluids, Scalar Fields, And Electromagnetic Fields, Charles G. Torre, Dionisios Krongos

Charles G. Torre

Rainich-type conditions giving a spacetime “geometrization” of matter fields in general relativity are reviewed and extended. Three types of matter are considered: perfect fluids, scalar fields, and electromagnetic fields. Necessary and sufficient conditions on a spacetime metric for it to be part of a perfect fluid solution of the Einstein equations are given. Formulas for constructing the fluid from the metric are obtained. All fluid results hold for any spacetime dimension. Geometric conditions on a metric which are necessary and sufficient for it to define a solution of the Einstein-scalar field equations and formulas for constructing the scalar field from …

Models Of Time Travel And Their Consequences, Antonio M. Mantica

Oglethorpe Journal of Undergraduate Research

How do we travel through time? We know that we can move forward in it (we have no choice), but can we jump forward in time? Can we go backward in time? It also gives rise to other troubling questions: is time measurable in distinct increments, or does it flow continuously? In "Models of Time Travel and their Consequences," Antonio Mantica walks the reader through current understandings of how time functions in Einstein's universe and proposes three distinct models to explain it. Following that, he provides a list of experiments to credit or discredit the models. Appropriate for audiences of …

Chiral Imprint Of A Cosmic Gauge Field On Primordial Gravitational Waves, Jannis Bielefeld, Robert R. Caldwell

Dartmouth Scholarship

A cosmological gauge field with isotropic stress-energy introduces parity violation into the behavior of gravitational waves. We show that a primordial spectrum of inflationary gravitational waves develops a preferred handedness, left or right circularly polarized, depending on the abundance and coupling of the gauge field during the radiation era. A modest abundance of the gauge field would induce parity-violating correlations of the cosmic microwave background temperature and polarization patterns that could be detected by current and future experiments.

Detection Of Baryonic Acoustic Oscillations In The Matter Power Spectrum, Spencer Everett, Ian Johnson, Jon Murphy, Mary Tarpley

DePaul Discoveries

Using the spectra of 22,923 high-redshift quasars from the Baryon Oscillation Spectrosocpic Survey (BOSS) subset of the Sloan Digital Sky Survey (SDSS), the authors detect evidence of the primordial baryonic acoustic oscillations (BAOs) in the matter power spectrum. The detection further endorses the currently accepted Lambda-CDM model of cosmology based upon the existence of dark energy (Lambda) and cold dark matter (CDM). Additionally, the use of the continuous wavelet transform to calculate the power spectrum has many advantages over traditional Fourier methods and independently corroborates previous detections.

Fermi-Bounce Cosmology And The Fermion Curvaton Mechanism, Stephon Alexander, Yi-Fu Cai, Antonino Marcianò

Dartmouth Scholarship

A nonsingular bouncing cosmology can be achieved by introducing a fermion field with BCS condensation occurring at high energy scales. In this paper we are able to dilute the anisotropic stress near the bounce by means of releasing the gap energy density near the phase transition between the radiation and condensate states. In order to explain the nearly scale-invariant CMB spectrum, another fermion field is required. We investigate one possible curvaton mechanism by involving one another fermion field without condensation where the mass is lighter than the background field. We show that, by virtue of the fermion curvaton mechanism, our …

Gravitational Waves: A New Window Into The Cosmos, Jeffrey S. Hazboun

Jeffrey Hazboun

No abstract provided.

Logarithmic Spiral Arm Pitch Angle Of Spiral Galaxies: Measurement And Relationship To Galactic Structure And Nuclear Supermassive Black Hole Mass, Benjamin Lee Davis

Graduate Theses and Dissertations

In this dissertation, I explore the geometric structure of spiral galaxies and how the visible structure can provide information about the central mass of a galaxy, the density of its galactic disk, and the hidden mass of the supermassive black hole in its nucleus. In order to quantitatively measure the logarithmic spiral pitch angle (a measurement of tightness of the winding) of galactic spiral arms, I led an effort in our research group (the Arkansas Galaxy Evolution Survey) to modify existing two-dimensional fast Fourier transform software to increase its efficacy and accuracy. Using this software, I was able to lead …

Schwarzschild Spacetime And Friedmann-Lemaitre-Robertson-Walker Cosmology, Zachary Cohen

Honors Scholar Theses

The advent of General Relativity via Einstein's field equations revolutionized our understanding of gravity in our solar system and universe. The idea of General Relativity posits that gravity is entirely due to the geometry of the universe -- that is, the mass distribution throughout the universe results in the "curving" of spacetime, which gives us the physics we see on a large scale. In the framework of General Relativity, we find that the universe behaves differently than was predicted in the model of gravitation developed by Newton. We will derive the general relativistic model for a simple system near a …

Supernatural Cosmic Origins: Challenging The Reigning Paradigm, Rachel Blattner

Senior Honors Theses

Contemporary scientific study primarily uses a paradigm based upon naturalism, materialism, and empiricism on which to base research. The widely accepted cosmological model the big bang theory adheres to this paradigm. Despite many weaknesses in this model and in the paradigm itself, researchers continue to favor the modification of the accepted model over the adoption of other more comprehensive models. The paradigm from which the models proposed by Russell Humphries, John Hartnett, and Jason Lisle come justifies the six-day creation young-earth biblical account and better fits observational evidence with fewer arbitrary assumptions than the paradigm from which the big bang …

Gravitational-Wave Mediated Preheating, Stephon Alexander, Sam Cormack, Antonino Marcianò, Nicolás Yunes

Dartmouth Scholarship

We propose a new preheating mechanism through the coupling of the gravitational field to both the inflaton and matter fields, without direct inflaton–matter couplings. The inflaton transfers power to the matter fields through interactions with gravitational waves, which are exponentially enhanced due to an inflation–graviton coupling. One such coupling is the product of the inflaton to the Pontryagin density, as in dynamical Chern–Simons gravity. The energy scales involved are constrained by requiring that preheating happens fast during matter domination.

The Ptolemaic System: A Detailed Synopsis, John Cramer Dr.

Oglethorpe Journal of Undergraduate Research

The Ptolemaic System, constructed by Claudius Ptolemeus (the Latin form of his name), was the most influential of all Earth centered cosmological systems. His ingenious and creative work is primarily recorded in his book The Mathematical Systematic Treatise which the Arabs characterized as “the greatest” and, in so doing, gave the book its most used name, Almagest.

The Copernican System: A Detailed Synopsis, John Cramer Dr.

Oglethorpe Journal of Undergraduate Research

Dissatisfied with the problems of the geocentric system inherited from Claudius Ptolemy, Nicholas Copernicus began the change from geocentrism to heliocentrism. His eponymous system was expounded first in the Commentariolus (written about 1508 and circulated privately in manuscript form) and then more fully and finally in his book, De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Orbs) published as he lay dying in 1543.

The Riemann Curvature Tensor, Its Invariants, And Their Use In The Classification Of Spacetimes, Jesse Hicks

Presentations and Publications

The equivalence problem in general relativity is to determine whether two solutions of the Einstein field equations are isometric. Petrov has given a classification of metrics according to their isometry algebras. This talk discusses the use of the Petrov classification scheme, together with the use of scalar curvature invariants, to address the equivalence problem. These are the slides for a presentation at the Mathematics Association of America Spring 2015 conference at Brigham Young University.

Geometrization Conditions For Perfect Fluids, Scalar Fields, And Electromagnetic Fields, Charles G. Torre, Dionisios Krongos

Presentations and Publications

Rainich-type conditions giving a spacetime “geometrization” of matter fields in general relativity are reviewed and extended. Three types of matter are considered: perfect fluids, scalar fields, and elec- tromagnetic fields. Necessary and sufficient conditions on a spacetime metric for it to be part of a perfect fluid solution of the Einstein equa- tions are given. Formulas for constructing the fluid from the metric are obtained. All fluid results hold for any spacetime dimension. Ge- ometric conditions on a metric which are necessary and sufficient for it to define a solution of the Einstein-scalar field equations and for- mulas for constructing …

What Do We Know About Lorentz Symmetry?, Q. G. Bailey

Publications

Precision tests of Lorentz symmetry have become increasingly of interest to the broader gravitational and high-energy physics communities. In this talk, recent work on violations of local Lorentz invariance in gravity is discussed, including recent analysis constraining Lorentz violation in a variety of gravitational tests. The arena of short-range tests of gravity is highlighted, demonstrating that such tests are sensitive to a broad class of unexplored signals that depend on sidereal time and the geometry of the experiment.

Short-Range Gravity And Lorentz Violation, Quentin G. Bailey, V. Alan Kostelecký, Rui Xu

Publications

Comparatively few searches have been performed for violations of local Lorentz invariance in the pure-gravity sector. We show that tests of short-range gravity are sensitive to a broad class of unconstrained and novel signals that depend on the experimental geometry and on sidereal time.

Rationality Of The Spectral Action For Robertson-Walker Metrics And The Geometry Of The Determinant Line Bundle For The Noncommutative Two Torus, Asghar Ghorbanpour

Electronic Thesis and Dissertation Repository

In noncommutative geometry, the geometry of a space is given via a spectral triple $(\mathcal{A,H},D)$. Geometric information, in this approach, is encoded in the spectrum of $D$ and to extract them, one should study spectral functions such as the heat trace $\Tr (e^{-tD^2})$, the spectral zeta function $\Tr(|D|^{-s})$ and the spectral action functional, $\Tr f(D/\Lambda)$.

The main focus of this thesis is on the methods and tools that can be used to extract the spectral information. Applying the pseudodifferential calculus and the heat trace techniques, in addition to computing the newer terms, we prove the rationality of the spectral action …

Void Cosmology-Better Explains What Happens First, Background Radiation, Voids In Space, Hydrogen Concentrations, James T. Struck

James T Struck

1

Void Cosmology better explains What Happened First, Cosmic

Microwave Background at around 4. 73 K, 150 Million Light

Year Diameter Largest Voids, Red shift at Distance through

Void Drifting/Void Expansion, Void Inflation, Gravitational

mass and Void Movement, and Helium at 25 % Versus

Hydrogen at 75 % Due to Particle Combination and less Higher

Element Concentrations

Abbe George Lemaitre 1894-1966 was a Belgian cosmologist,

mathematician, priest, physicist who postulated an explosive

beginning. In the 1940’s, George Gamow, Hans Bethe and

Ralph Alpher went from Lemaitre’s starting nuclear fission

ideas to ideas of nuclear fusion being responsible for the

Universe’s …

Evidence Of Attenuation Of Vhe Blazar Spectra By Extragalactic Background Light, Cameron Allen

Physics

The spectrum of two blazar objects, 1ES 1959+650 and 1ES 2344+514, are analyzed for evidence of interactions with the Extragalactic Background Light (EBL), using combined data from the Very Energetic Radiation Imaging Telescope Array System and the Fermi Gamma-ray Space Telescope, By analyzing the distinct curvature across the combined spectrum, we infer that the very-high energy (VHE) gamma-rays must be attenuated by interactions with the EBL. We also find that the measured 1ES 1959+650 spectrum is sensitive to the intrinsic blazar model, with a preference for a power-law with an exponential cutoff (EPWL). The measured curvature is a combination of …