Astrophysics and Astronomy Commons^™

Measuring Cosmic Expansion From Early To Late Times Using Quasars, Galaxies, & Local Supernovae, Rajeev Vaisakh

Physics Theses and Dissertations

This dissertation investigates the evolution of cosmic expansion across a wide redshift ($z$) range by combining measurements from quasars \& galaxies in the distant universe $(z > 0.8)$ with those obtained from stripped-core collapse supernovae observations from the nearby universe $(z < 0.1)$. Using the DESI spectroscopic survey, we analyze large-scale clustering from quasars over $0.8 < z < 2.1$ and emission line galaxies over $0.8 < z < 1.6$, contributing to DESI DR2 BAO and full-shape measurements of cosmic expansion and structure growth. Combined with BBN in flat $\Lambda$CDM, DESI DR2 BAO gives $H_0 = 68.51 \pm 0.58$ km s$^{-1}$ Mpc$^{-1}$, while combinations of DESI BAO with CMB and supernova data show a preference for evolving dark energy, with representative constraints such as $w_0 = -0.752 \pm 0.057$ and $w_a = -0.86^{+0.23}_{-0.20}$ for DESI+CMB+DESY5. Using the ROTSE-III Supernova Survey and the expanding photosphere method (EPM), we measure distances to a sample of six supernovae for which the thermal phase can be clearly identified. This analysis focuses on testing whether reliable EPM distances can be obtained for this population. The resulting distances will eventually be compared with independent estimates from the literature. Establishing consistency with these external measurements represents an important step toward applying this methodology to larger samples, with the eventual goal of using ROTSE supernova distances to provide an independent measurement of the local Hubble constant.

Emergent De Sitter Expansion And Closed Topology From The Cosmic Fabric Model As An Open Thermodynamic System: Resolving The Negative Bulk Modulus Paradox, T G. Tenev, C B. Ward, T F. Tenev, M F. Horstemeyer

Faculty Publications and Presentations

The Cosmic Fabric Model establishes a continuum-mechanics isomorphism to General Relativity by representing physical space as an elastic three-dimensional hyperplate embedded in a four-dimensional spatial bulk. Reproducing vacuum kinematics requires a vanishing P-wave modulus, which in turn implies a negative bulk modulus—an apparent thermodynamic instability in a closed system. This paradox is resolved by recasting the framework as an open system: the instability is not pathological but instead drives cosmic expansion. In this interpretation, the observable universe is a lower-energy solid formed through continuous solidification from a higher-dimensional precursor fluid. Using multiplicative kinematics from finite-growth mechanics, the model shows that …

Universe Without A Cause: A Reply To David Lu, Daniel Linford

Philosophy Faculty Publications

David Lu has recently argued that denying the Modified Causal Principle (MCP)—that if the universe began to exist, then it has a cause—leads to the conclusion that we likely inhabit an Omphalos universe, one that began recently with the appearance of age. Lu goes on to argue that if the universe is likely Omphalos, then independent measurements of the universe’s age are unlikely to agree. I offer three families of objections. First, Lu’s probabilistic reasoning faces technical challenges and, even if those challenges are overcome, cannot rule out an Omphalos universe. Second, I propose an alternative hypothesis that does so. …

Gauge-Invariant Gravitational Wave Polarization In Metric F(R) Gravity With Cosmological Implications, Ramesh Radhakrishnan, David Mcnutt, Delaram Mirfendereski, Alejandro Pinero, Eric Davis, William Julius, Gerald Cleaver

Physics & Astronomy Faculty Publications

We develop a fully gauge-invariant analysis of gravitational-wave polarizations in metric 𝑓⁡(𝑅) gravity with a particular focus on the modified Starobinsky model 𝑓⁡(𝑅) =𝑅 +𝛼⁢𝑅2 −2⁢Λ, whose constant-curvature solution 𝑅𝑑 =4⁢Λ provides a natural de Sitter background for both early- and late-time cosmology. Linearizing the field equations around this background, we derive the Klein–Gordon equation for the curvature perturbation 𝛿⁢𝑅 and show that the scalar propagating mode acquires a mass 𝑚2𝜓 =1/(6⁢𝛼), highlighting how the same scalar degree of freedom governs inflationary dynamics at high curvature and the propagation of gravitational waves in the current accelerating Universe. Using the scalar–vector–tensor …

Cross-Correlation Studies Of The Cosmological 21 Cm Signal And High-Redshift Galaxy Distributions, Simon Matin

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Epoch of Reionization (EoR) marks a critical phase in cosmic history, during which time the first stars and galaxies ionized the surrounding neutral hydrogen gas. A powerful way to probe this period is by cross-correlating the 21 cm signal from neutral hydrogen with high-redshift galaxy distributions. In this study, we analyze the 21 cm-galaxy cross-power spectrum using simulated sky maps and explore its redshift evolution, revealing a transition from positive correlation at early times (high redshift) to anti-correlation at later stages of reionization (low redshift). Our results highlight the sensitivity of the cross-power spectrum to the evolving ionized structure …

How It Will End: Physical And Philosophical Implications Of The Fate Of Our Universe, Alex Bittle '26

Honor Scholar Theses

What does physics have to say about the end of our universe? And what does it mean for us, if anything? Answering these questions requires an understanding of the so-called "lambda-cold dark matter" (ΛCDM) model of cosmology, which models the universe as containing an expanding pressure, Λ or dark energy, in a battle with the gravitational attraction provided by dark and regular matter. First, the physics (including observations and theory) of the ΛCDM, including the Big Bang and CMB, the inflationary period, and equations that govern the way the size of the universe changes with respect to time for different …

On The Evidence For The Violation Of The Equivalence Principle In Disk Galaxies, Corey Sargent, William Clark, Antonia Seifert, Alicia Mand, Emerson Rogers, Adam Lane, Alexandre Deur, Balša Terzić

Physics Faculty Publications

We examine the claimed observations of a gravitational external field effect (EFE) reported by Chae et al. We show that observations suggestive of the EFE can be interpreted without violating Einstein’s equivalence principle, namely from known correlations between the morphology, the environment, and dynamics of galaxies. While Chae et al.’s analysis provides a valuable attempt at a clear test of modified Newtonian dynamics, an evidently important topic, a re-analysis of the observational data does not permit us to confidently assess the presence of an EFE or to distinguish this interpretation from that proposed in this article.

Source Anisotropies And Pulsar Timing Arrays, Bruce Allen, Deepali Agarwal, Joseph D. Romano, Serena Valtolina

Physics & Astronomy Faculty Publications

Pulsar timing arrays (PTAs) hunt for gravitational waves (GWs) by searching for the correlations that GWs induce in the time-of-arrival residuals from different pulsars. If the GW sources are of astrophysical origin, then they are located at discrete points on the sky. However, PTA data are often modeled, and subsequently analyzed, via a “standard Gaussian ensemble.” That ensemble is obtained in the limit of an infinite density of vanishingly weak, Poisson-distributed sources. In this paper, we move away from that ensemble, to study the effects of two types of “source anisotropy.” The first (a), which is often called “shot noise,” …

Hubble Tension And Gravitational Self-Interaction, Corey Sargent, William Clark, Alexander Deur, Balša Terzić

Physics Faculty Publications

One of the most important problems vexing the ΛCDM cosmological model is the Hubble tension. It arises from the fact that measurements of the present value of the Hubble parameter performed with low-redshift quantities, e.g. the Type IA supernova, tend to yield larger values than measurements from quantities originating at high-redshift, e.g. fits of cosmic microwave background radiation. It is becoming likely that the discrepancy, currently standing at 5σ, is not due to systematic errors in the measurements. Here we explore whether the self-interaction of gravitational fields in General Relativity, which are traditionally neglected when studying the evolution …

Tests Of General Relativity Through Searches For Lorentz And Cpt Symmetry Breaking, Kellie Ault

Doctoral Dissertations and Master's Theses

An effective field theory framework, the Standard Model Extension (SME), provides an agnostic, systematic test of General Relativity (GR) and its founding spacetime symmetries, Lorentz and CPT symmetry. Violating these symmetries may provide clues toward unifying the physics of the General Relativity and the Standard Model of particle physics. Part of this work involves the merge of theory, data analysis and experiments with gravitational wave (GW) signals from LIGO/Virgo/KAGRA (LVK) detectors. A modified dispersion relation derived from the SME of GWs is implemented into the LIGO Scientific Collaboration Algorithm Library Suite (LALSuite), where a joint Bayesian inference of the source …

Cosmological Vector Fields And Constraining The Neutrino Masses, Avery J. Tishue

Dartmouth College Ph.D Dissertations

In this thesis I explore two main topics: the role and consequences of cosmological vector fields, and new ideas for constraining fundamental physics with state-of-the-art experiments. These topics are disparate in content and technique but unified in their attempt to leverage novel approaches to better understand longstanding questions in cosmology. These questions, such as ``What is causing the universe to accelerate today?'' and ``What are the neutrino masses?'', underpin the modern cosmological paradigm. They play a key role in our understanding of cosmic history, the formation of structure, and the fate of our universe. Answers to or hints about these …

New Physics In The Age Of Precision Cosmology, Vivian I. Sabla

Dartmouth College Ph.D Dissertations

The Lambda-cold dark matter (LCDM) model has become the standard model of cosmology because of its ability to reproduce a vast array of cosmological observations, from the earliest moments of our Universe, to the current period of accelerated expansion, which it does with great accuracy. However, the success of this model only distracts from its inherent flaws and ambiguities. LCDM is purely phenomenological, providing no physical explanation for the nature of dark matter, responsible for the formation and evolution of large-scale structure, and giving an inconclusive explanation for dark energy, which drives the current period of accelerated expansion.

Furthermore, cracks …

Evolution Of Density And Velocity Perturbations In A Slowly Contracting Universe, Olivia R. Bitcon

Honors Undergraduate Theses

One focus of research in cosmology regards the growth of structure in the universe: how we end up with stars, galaxies, galaxy clusters, and large scale structure in a universe that appears homogeneous and isotropic on large scales. Using cosmological perturbation theory, we investigate the evolution of density and velocity perturbations corresponding to a universe that is slowly contracting (Ijjas and Steinhardt), testing with and comparing different values for the equation-of-state parameter. This allows for the comparison of the growth of large scale structure in scenarios including a matter-dominated expanding universe, a dark energy-dominated expanding universe, and now, an ekpyrotic …

Applications Of Digital Filters In Radio Astronomy, Joseph William Kania

Graduate Theses, Dissertations, and Problem Reports (ETD)

The radio sky spans tens of orders of magnitude in length, density, and time.
In this thesis, using novel filtering techniques and two different telescopes,
we investigate two tracers of cosmic structure: Baryon Acoustic Oscillations
(BAOs) and Fast Radio Bursts (FRBs). BAOs formed as the universe cooled
after the Big Bang. BAOs provide a fiducial length scale of the universe
throughout cosmic time and thus can be used to understand how the universe
is evolving. FRBs are very bright, short timescale, bursts of as-yet unknown
origin which occur uniformly on the sky at a rate of a few thousand per …

Targeted Search For The Kinematic Dipole Of The Gravitational-Wave Background, Adrian Ka-Wai Chung, Alexander C. Jenkins, Joseph D. Romano, Mairi Sakellariadou

Physics & Astronomy Faculty Publications

There is growing interest in using current and future gravitational-wave interferometers to search for anisotropies in the gravitational-wave background. One guaranteed anisotropic signal is the kinematic dipole induced by our peculiar motion with respect to the cosmic rest frame, as measured in other full-sky observables such as the cosmic microwave background. Our prior knowledge of the amplitude and direction of this dipole is not explicitly accounted for in existing searches by LIGO/Virgo/KAGRA but could provide crucial information to help disentangle the sources which contribute to the gravitational-wave background. Here, we develop a targeted search pipeline which uses this prior knowledge …

Astrophysics, Cosmology And Particle Phenomenology At The Energy Frontier, Jorge Fernandez Soriano

Dissertations, Theses, and Capstone Projects

This dissertation consists of two parts, treating significantly separated fields. Each part consists on several chapters, each treating a somewhat isolated topic from the rest. In each chapter, I present some of the work developed during my passage through the graduate program, which has mostly been published elsewhere.

Part I – Cosmic Rays and Particle Physics

• Chapter 1: In this chapter we present an introduction to the topic of cosmic ray physics, with an special focus on the so-called ultra high energy cosmic rays: their potential origins, effects during their propagation between their sources and Earth, the different techniques used …

Toward Deep Learning Emulators For Modeling The Large-Scale Structure Of The Universe, Neerav Kaushal

Dissertations, Master's Theses and Master's Reports

Multi-billion dollar cosmological surveys are being conducted almost every decade in today’s era of precision cosmology. These surveys scan vast swaths of sky and generate tons of observational data. In order to extract meaningful information from this data and test these observations against theory, rigorous theoretical predictions are needed. In the absence of an analytic method, cosmological simulations become the most widely used tool to provide these predictions in order to test against the observations. They can be used to study covariance matrices, generate mock galaxy catalogs and provide ready-to-use snapshots for detailed redshift analyses. But cosmological simulations of matter …

Understanding The Physics Of Galaxy Clusters Out To Their Virial Radii And Beyond, Arnab Sarkar

Theses and Dissertations--Physics and Astronomy

In the hierarchical structure formation model, galaxy clusters grow and evolve via mergers and accretion from the surrounding cosmic web, leaving distinctive marks in the gas properties, metallicity, and dynamical state at the outskirts of clusters, which needs to be probed to better understand the growth of a cluster. I probed the gas properties of four nearby galaxy groups MKW4, Antlia, RXJ1159, and ESO3060170 out to their virial radii using deep Suzaku and mostly snapshot Chandra observations. I found the gas entropy profiles of MKW4 follow a power-law at its outskirts - as expected from purely gravitational structure formation model. …

Perturbative Unitarity And Nec Violation In Genesis Cosmology, Yong Cai, Ji Xu, Shuai Zhao, Siyi Zhou

Physics Faculty Publications

Explorations of the violation of null energy condition (NEC) in cosmology could enrich our understanding of the very early universe and the related gravity theories. Although a fully stable NEC violation can be realized in the “beyond Horndeski” theory, it remains an open question whether a violation of the NEC is allowed by some fundamental properties of UV-complete theories or the consistency requirements of effective field theory (EFT). We investigate the tree-level perturbative unitarity for stable NEC violations in the contexts of both Galileon and “beyond Horndeski” genesis cosmology, in which the universe is asymptotically Minkowskian in the past. We …

Testing Galaxy Formation And Dark Matter With Low Surface Brightness Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

Galaxies are the basic structural element of the universe; galaxy formation theory seeks to explain how these structures came to be. I trace some of the foundational ideas in galaxy formation, with emphasis on the need for non-baryonic cold dark matter. Many elements of early theory did not survive contact with observations of low surface brightness galaxies, leading to the need for auxiliary hypotheses like feedback. The failure points often trace to the surprising predictive successes of an alternative to dark matter, the Modified Newtonian Dynamics (MOND). While dark matter models are flexible in accommodating observations, they do not provide …

Searching For The Global 21 Cm Cosmic Dawn Absorption Signal With The Long Wavelength Array, Christopher Dilullo

Physics & Astronomy ETDs

The redshifted 21 cm signal from neutral hydrogen offers one of the best observational probes of Cosmic Dawn and the Epoch of Reionization. This dissertation presents an effort to detect the redshifted 21 cm signal using the Long Wavelength Array station located on the Sevilleta National Wildlife Refuge in New Mexico, USA (LWA-SV). The major goal is to validate the potential detection reported by the EDGES collaboration. This measurement requires a dynamic range on the order of 10⁵ in order to disentangle the cosmological signal from the Galactic foregrounds. The beamforming capability of LWA-SV is novel to this search. …

All-Sky Search In Early O3 Ligo Data For Continuous Gravitational-Wave Signals From Unknown Neutron Stars In Binary Systems, R. Abbott, T. D. Abbott, S. Abraham, F. Acernese, Teviet Creighton, Mario C. Diaz, Soma Mukherjee, Volker Quetschke, K. E. Ramirez, W. H. Wang

Physics & Astronomy Faculty Publications

Rapidly spinning neutron stars are promising sources of continuous gravitational waves. Detecting such a signal would allow probing of the physical properties of matter under extreme conditions. A significant fraction of the known pulsar population belongs to binary systems. Searching for unknown neutron stars in binary systems requires specialized algorithms to address unknown orbital frequency modulations. We present a search for continuous gravitational waves emitted by neutron stars in binary systems in early data from the third observing run of the Advanced LIGO and Advanced Virgo detectors using the semicoherent, GPU-accelerated, BinarySkyHough pipeline. The search analyzes the most sensitive frequency …

Redefining Nietzsche’S Greatest Weight Into Contemporary Cosmology, Christian E. Coffinet-Crean

Scholarly Horizons: University of Minnesota, Morris Undergraduate Journal

Friedrich Nietzsche’s theory of eternal recurrence and it’s cosmological value has been discredited and cast aside because of the lack of scientific backing the original theory had. In this essay, Nietzche’s eternal recurrence will be observed and analyzed through some of his major works and defended from outside criticism. Furthermore, Roger Penrose’s Conformal Cyclic Cosmology and Jean-Paul Luminet’s research are used in support for eternal recurrence as a cosmological theory. Luminet’s research of cosmic background radiation concludes that the universe has an odd but finite shape. Penrose’s research theorizes a sort of repeating universe, allowing time to be treated as …

Using The Baryonic Tully–Fisher Relation To Measure Ho, Stacy S. Mcgaugh

Faculty Scholarship

We explore the use of the baryonic Tully-Fisher relation (bTFR) as a new distance indicator. Advances in near-IR imaging and stellar population models, plus precise rotation curves, have reduced the scatter in the bTFR such that distance is the dominant source of uncertainty. Using 50 galaxies with accurate distances from Cepheids or the tip magnitude of the red giant branch, we calibrate the bTFR on a scale independent of H o . We then apply this calibrated bTFR to 95 independent galaxies from the SPARC sample, using CosmicFlows-3 velocities, to deduce the local value of H o . We find …

Stability Of Regular Thin Shell Wormholes Supported By Vdw Quintessence, A. Eid

Applications and Applied Mathematics: An International Journal (AAM)

The dynamical equations of motion for a thin shell wormhole from regular black holes that are supported by Van der Waals (VDW) quintessence equation of state (EoS) are constructed, through cut and -paste technique. The linearized stability of regular wormhole is derived. The presences of unstable and stable static solutions with different value of some parameters are analyzed.

Aspects Of Quantum Theory In General Relativity And Cosmology, Eamon Mccaughey

Doctoral

After a brief introduction to Cosmology some quantum aspects of General Relativity and cosmology are presented. The radial motion of a massive particles in the ergosphere of the Kerr Black Hole is considered. Screening of Hawking radiation and shielding of the Penrose process is examined in the context of the region of negative energy inside the ergosphere. Tunnelling of such particles between the boundaries of the classically forbidden region will be considered and the transmission coefficient determined. The evolution of Primordial black holes in standard and Loop Quantum Cosmology is reviewed. A stability analysis of Einstein’s universe in both classical …

Magnetic Structure And Radiative Captures Of Few-Nucleon Systems: Status And Prospects, Laura Elisa Marcucci, Rocco Schiavilla, Alex Gnech, Michele Viviani

Physics Faculty Publications

We review the main ingredients for an ab-initio study of few-nucleon reactions of astrophysical interest within the chiral effective field theory approach, with particular attention to radiative captures relevant for Big Bang Nucleosynthesis and stellar evolution. We conclude with an outlook for ongoing and future work.

Dark Matter Production Beyond The Thermal Wimp Paradigm: An Exploration Of Early Matter Domination Scenarios, Jacek Ksawery Osinski

Physics & Astronomy ETDs

In the standard thermal history of the Universe, the energy density is dominated by radiation throughout the postinflationary era, until matter-radiation equality after big bang nucleosynthesis (BBN). However, we currently do not have any observational probes of the pre-BBN period, and radiation domination (RD) is therefore an assumption. Generic early Universe models predict the presence of additional components in the postinflationary Universe which can lead to periods of nonstandard evolution before the onset of BBN. A prominent example of such a period is a phase of early matter domination (EMD) in which the Universe undergoes matter-dominated expansion for a time, …

New Foundation In The Sciences: Physics Without Sweeping Infinities Under The Rug, Florentin Smarandache, Victor Christianto, Robert Neil Boyd

Branch Mathematics and Statistics Faculty and Staff Publications

It is widely known among the Frontiers of physics, that “sweeping under the rug” practice has been quite the norm rather than exception. In other words, the leading paradigms have strong tendency to be hailed as the only game in town. For example, renormalization group theory was hailed as cure in order to solve infinity problem in QED theory. For instance, a quote from Richard Feynman goes as follows: “What the three Nobel Prize winners did, in the words of Feynman, was "to get rid of the infinities in the calculations. The infinities are still there, but now they can …

One-Note-Samba Approach To Cosmology, Florentin Smarandache, Victor Christianto

Branch Mathematics and Statistics Faculty and Staff Publications

Inspired by One Note Samba, a standard jazz repertoire, we present an outline of Bose-Einstein Condensate Cosmology. Although this approach seems awkward and a bit off the wall at first glance, it is not impossible to connect altogether BEC, Scalar Field Cosmology and Feshbach Resonance with Ermakov-Pinney equation. We also briefly discuss possible link with our previous paper which describes Newtonian Universe with Vortex in terms of Ermakov equation.