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Item Numerical methods for rotating compact objects in modified gravity theories(Montana State University - Bozeman, College of Letters & Science, 2020) Sullivan, Andrew Patrick Kyung; Chairperson, Graduate Committee: Neil J. Cornish and Nicolas Yunes (co-chair); Nicolas Yunes was a co-author of the article, 'Slowly-rotating neutron stars in massive bigravity' in the journal 'Classical and quantum gravity' which is contained within this dissertation.; Nicolas Yunes, and Thomas Sotiriou were co-authors of the article, 'Numerical black hole solutions in modified gravity theories: spherical symmetry case' in the journal 'Physical review D' which is contained within this dissertation.; Nicolas Yunes, and Thomas Sotiriou were co-authors of the article, 'Numerical black hole solutions in modified gravity theories: axial symmetry case' submitted to the journal 'Physical review D' which is contained within this dissertation.Detailed observations of phenomena involving compact objects will provide us with a new avenue to test general relativity in the strong field regime. So as to not bias our analysis of these new experiments, we require knowledge of the spacetimes around these objects both within and beyond general relativity. Here I will describe work that applies two specific methods to solve the modified Einstein's equations that describe the exotic spacetimes beyond general relativity for neutron stars and black holes. The first method is a fourth-order Runge-Kutta-Fehlberg ordinary differential equation numerical integrator method. The second method is a relaxed Newton- Raphson method applied to a system of nonlinear partial differential equations. Using these methods, we solve for the spacetimes of slowly rotating neutron stars in massive bigravity and rotating black holes in scalar Gauss-Bonnet gravity in a theory independent methodology. We validate our numerical methods by applying them to compact objects in general relativity and using them to recover known perturbative solutions. We can then compare the fully nonlinear solutions to these perturbative solutions and comment on their differences. We then use these numerical solutions to calculate the physical observables of these systems and finally construct analytic fitted models that can be used in rapid computation methods that future experiments may use to constrain the free parameters in these theories.Item Towards a precision measurement of the Newtonian constant of gravitation and accelerometry with a levitated microsphere in a magneto-gravitational trap(Montana State University - Bozeman, College of Letters & Science, 2020) Lewandowski, Charles Wayne; Chairperson, Graduate Committee: Brian D'UrsoSince the theory of gravity was published by Issac Newton in the seventeenth century, scientists have studied its strength, originally for the purpose of astronomy and measuring the density of the Earth. After centuries of research and measurements, G remains the least precisely known fundamental constant. A new method for a time-of-swing measurement of G, developed a the National Bureau of Standards 1930, is proposed using a levitated microsphere in a magneto-gravitational trap. A new magneto-gravitational trap based on a previous system from our laboratory has been developed for a measurement of G. This trap has been designed to load large particles with low oscillation frequencies with large amplitudes of motion to improve sensitivity to G. Because of the weak trap, a loading method has been developed utilizing electric fields to help balance the force of gravity. A stable and variable high voltage reference has been developed to provide the necessary electric field. Camera-based feedback control has been implemented for cooling the center-of-mass motion or heating the motion in a controlled way. To limit errors due to equilibrium shifts of the particle in the trap from tilt, a simple modification was made to an optical table to actively stabilize the tilt. A measurement of G requires high sensitivity to accelerations and forces. The parameters achieved towards the measurement of G makes this system sensitive to acceleration. The first direct use of a room temperature levitated optomechanical system as an accelerometer has been achieved, with the best sensitivity to accelerations of any room temperature levitated optomechanical system. The sensitivity was measured to be 3:6 x 10 -8 g / square root of Hz.Item Perceptual interference(Montana State University - Bozeman, College of Arts & Architecture, 2019) Willard, Alyssa Riann; Chairperson, Graduate Committee: Jim ZimpelWhen I explore my surroundings, I often wonder about what we can never truly know. My studio practice serves as an outlet for my questions, and I expect it to generate more questions than answers. I have questions about origins, the unknown future, and the interactions between matter and energy. In conjunction with this written thesis I created works that will be displayed as my MFA thesis show in the Helen E. Copeland Gallery. These works are responses to my research into various energy forces, which stems from my collaborations with Montana State University's Physics Department. My primary interest this year has been electromagnetism which is the study of the interactions between electricity, magnetism and light. But I am also interested in how electromagnetism connects to other forces such as gravity and sound, and how these various systems follow patterns that are very similar to fractal patterns found in nature. There is a lack of knowledge when it comes to what connects various forces to others, which stimulates my interest in the interactions between them. My current questions have led me to the conclusion that invisible forces connect and influence all things.Item Testing alternative theories of gravity using low frequency gravitational waves(Montana State University - Bozeman, College of Letters & Science, 2019) O'Beirne, Logan Tyler; Chairperson, Graduate Committee: Neil J. Cornish; Bennett Link (co-chair); Logan O'Beirne, Stephen R. Taylor and Nicolas Yunes were co-authors of the article, 'Constraining alternative theories of gravity using pulsar timing arrays' in the journal 'Physical review letters' which is contained within this thesis.; Neil J. Cornish were co-authors of the article, 'Constraining the polarization content of gravitational waves with astrometry' in the journal 'Physical review D' which is contained within this thesis.; Neil J. Cornish, Sarah J. Vigeland and Stephen R. Taylor were co-authors of the article, 'Constraining alternative polarizations of continuous gravitational waves using pulsar timing arrays' submitted to the journal 'Physical review D' which is contained within this thesis.General Relativity aptly describes current gravitational observations. However, there is great theoretical interest in its validity in untested regimes. Alternative theories of gravity attempt to relax some of the assumptions made, leaving distinct signatures that are absent in Einstein's theory, namely the presence of alternative polarizations of gravitational waves that manifest from the emission of gravitational scalar and vector dipole radiation in black hole binaries. To study this lower order multipole of radiation, it is desirable to work in a regime where the quadrupolar tensor radiation of general relativity is as quiet as possible. This motivates working with supermassive black hole binaries in their slowly evolving inspiral phase, when they are well separated from merger, emitting low frequency gravitational waves. Using a frequentist framework, we study the detectability of a stochastic background of each polarization using pulsar timing arrays, which is currently the most technically developed and viable method for studying low frequency gravitational waves, correlating the observed time delays of pulsars. We also find that astrometry, which measures transverse displacements of the apparent position of stars, turns out to have a very similar correlation structure as the time delays measured by pulsar timing arrays. We lastly study how effective using a pulsar timing array is at studying a loud, foreground binary with these alternative polarizations, using a Bayesian framework. Low frequency gravitational wave astronomy proves advantageous for studying these exotic signatures.Item Constraining scalar-tensor theories of gravity through observations(Montana State University - Bozeman, College of Letters & Science, 2018) Anderson, David Sutton; Chairperson, Graduate Committee: Nicolas Yunes; Nicolas Yunes and Enrico Barausse were co-authors of the article, 'The effect of cosmological evolution on solar system constraints and on the scalarization of neutron stars in massless scalar-tensor theories' in the journal 'American physical society' which is contained within this thesis.; Nicolas Yunes was a co-author of the article, 'Solar system constraints on massless scalar-tensor gravity with positive coupling constant upon cosmological evolution of the scalar field' in the journal 'American physical society' which is contained within this thesis.; Nicolas Yunes was a co-author of the article, 'Scalar charges and scaling relations in massless scalar-tensor theories' submitted to the journal 'Classical quantum gravity' which is contained within this thesis.; Paulo Freire and Nicolas Yunes were co-authors of the article, 'Binary pulsar constraints on massless scalar-tensor theories using bayesian statistics' submitted to the journal 'Classical quantum gravity' which is contained within this thesis.Scalar-tensor theories of gravity have been among the most popular and well-studied alternatives to Einstein's General Relativity. These theories of gravity contain an extra scalar degree of freedom that allows them to rectify some of the limitations of General Relativity but also fail some of the cornerstone tests of gravity that General Relativity passes with flying colors. Because of these conflicting features, it becomes necessary to investigate if scalar-tensor theories can pass current tests of gravity while still allowing for possible deviations from General Relativity in regimes that are not as highly constrained. In this thesis, we present the first self-consistent study of scalar-tensor theories in which we study the effects and constraints from Solar System observations, cosmological evolution of the universe, and the precise timing of binary pulsar systems. We constrain the free parameters of a certain class of massless-scalar-tensor theories first through cosmology and Solar System tests, in which we investigate the consistency between cosmological evolution scenarios and current Solar System observations. We then study strong field tests involving binary pulsar systems and investigate the various constraints that can be placed from measurements of the Keplerian and post-Keplerian parameters that determine the orbits.Item Multivariate Classification with Random Forests for Gravitational Wave Searches of Black Hole Binary Coalescence(2015-03) Baker, Paul T.; Caudill, Sarah; Hodge, Kari A.; Talukder, Dipongkar; Capano, Collin; Cornish, Neil J.Searches for gravitational waves produced by coalescing black hole binaries with total masses ≳25M⊙ use matched filtering with templates of short duration. Non-Gaussian noise bursts in gravitational wave detector data can mimic short signals and limit the sensitivity of these searches. Previous searches have relied on empirically designed statistics incorporating signal-to-noise ratio and signal-based vetoes to separate gravitational wave candidates from noise candidates. We report on sensitivity improvements achieved using a multivariate candidate ranking statistic derived from a supervised machine learning algorithm. We apply the random forest of bagged decision trees technique to two separate searches in the high mass (≳25M⊙) parameter space. For a search which is sensitive to gravitational waves from the inspiral, merger, and ringdown (IMR) of binary black holes with total mass between 25M⊙ and 100M⊙, we find sensitive volume improvements as high as 70±13−109±11\% when compared to the previously used ranking statistic. For a ringdown-only search which is sensitive to gravitational waves from the resultant perturbed intermediate mass black hole with mass roughly between 10M⊙ and 600M⊙, we find sensitive volume improvements as high as 61±4−241±12\% when compared to the previously used ranking statistic. We also report how sensitivity improvements can differ depending on mass regime, mass ratio, and available data quality information. Finally, we describe the techniques used to tune and train the random forest classifier that can be generalized to its use in other searches for gravitational waves.Item Projected Constraints on Lorentz-Violating Gravity with Gravitational Waves(2015-04) Hansen, Devin; Yunes, Nicolás; Yagi, KentGravitational waves are excellent tools to probe the foundations of General Relativity in the strongly dynamical and non-linear regime. One such foundation is Lorentz symmetry, which can be broken in the gravitational sector by the existence of a preferred time direction, and thus, a preferred frame at each spacetime point. This leads to a modification in the orbital decay rate of binary systems, and also in the generation and chirping of their associated gravitational waves. We here study whether waves emitted in the late, quasi-circular inspiral of non-spinning, neutron star binaries can place competitive constraints on two proxies of gravitational Lorentz-violation: Einstein-\AE{}ther theory and khronometric gravity. We model the waves in the small-coupling (or decoupling) limit and in the post-Newtonian approximation, by perturbatively solving the field equations in small deformations from General Relativity and in the small-velocity/weak-gravity approximation. We assume a gravitational wave consistent with General Relativity has been detected with second- and third-generation, ground-based detectors, and with the proposed space-based mission, DECIGO, with and without coincident electromagnetic counterparts. Without a counterpart, a detection consistent with General Relativity of neutron star binaries can only place competitive constraints on gravitational Lorentz violation when using future, third-generation or space-based instruments. On the other hand, a single counterpart is enough to place constraints that are 10 orders of magnitude more stringent than current binary pulsar bounds, even when using second-generation detectors. This is because Lorentz violation forces the group velocity of gravitational waves to be different from that of light, and this difference can be very accurately constrained with coincident observations.Item The awful truth about zero-G(Montana State University - Bozeman, Graduate School, 2014) Dooling, Dave; Chairperson, Graduate Committee: Peggy Taylor.Zero-G is a concept that people think they know but usually misunderstand. To illustrate the effects that happen in free-fall, the proper term, NASA developed two different demonstration units based on drop towers it uses in microgravity research, and associated education materials. While highly valuable, their efficacy has never been tested to show that they lead to proper student understanding of gravity and free-fall rather than providing a classroom diversion. In preparation for employing the free-fall demonstrator in a museum, an informal education setting, I developed and tested an activity in which students are challenged to explain what is happening in free-fall and the apparent 0g of space, and lead them to discover that the "awful truth" that true 0g does not exist. The activity is targeted for grades 5-9, consistent with New Mexico education standards, but is applicable to a broad range of audiences. I describe common misperceptions, the apparatus used, and results of the activity with teachers and then with students in an after-school program.Item Development and calibration of a concept inventory to measure introductory college astronomy and physics students' understanding of Newtonian gravity(Montana State University - Bozeman, College of Letters & Science, 2013) Williamson, Kathryn Elizabeth; Chairperson, Graduate Committee: Shannon WilloughbyThe topic of Newtonian gravity offers a unique vantage point from which to investigate and encourage conceptual change because it is something with which everyone has daily experience, and because it is taught in two courses that reach a wide variety of students - introductory-level college astronomy ("Astro 101") and physics ("Phys 101"). Informed by the constructivist theory of learning, this study characterizes and measures Astro 101 and Phys 101 students' understanding of Newtonian gravity within four conceptual domains - Directionality, Force Law, Independence of Other Forces, and Threshold. A phenomenographic analysis of Astro 101 student-supplied responses to open-ended questions about gravity results in the characterization of students' alternative mental models and misapplications of the scientific model. These student difficulties inform the development of a multiple-choice assessment instrument, the Newtonian Gravity Concept Inventory (NGCI). Classical Test Theory (CTT) statistics, student interviews, and expert review show that the NGCI is a reliable and valid tool for assessing both Astro 101 and Phys 101 students' understanding of gravity. Furthermore, the NGCI can provide extensive and robust information about differences between Astro 101 and Phys 101 students and curricula. Comparing and contrasting the Astro 101 and Phys 101 CTT values and student response patterns shows qualitative differences in each of the four conceptual domains. Additionally, performing an Item Response Theory (IRT) analysis of NGCI student response data calibrates item parameters for all Astro 101 and Phys 101 courses and provides Newtonian gravity ability estimates for each student. Physics students show significantly higher pre-instruction and post-instruction IRT abilities than astronomy students, but they show approximately equal gains. To investigate the differential effect of Astro 101 compared to Phys 101 curricula on students' overall post-instruction Newtonian gravity ability, linear regression models control for student characteristics and classroom dynamics. Results show that differences in post-instruction abilities are most influenced by students' pre-instruction abilities and the level of interactivity in the classroom, rather than the astronomy curriculum compared to the physics curriculum. These analyses show that the NGCI has broad capabilities.