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Articles 1 - 12 of 12
Full-Text Articles in Other Physics
Measuring Cosmic Expansion From Early To Late Times Using Quasars, Galaxies, & Local Supernovae, Rajeev Vaisakh
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.
Probability Distributions Of The Scalar Potential, Candace Mathews
Probability Distributions Of The Scalar Potential, Candace Mathews
Legacy Theses & Dissertations (2009 - 2024)
In the study of cosmological inflation, string theory and supersymmetry have motivated a wide range of possible inflationary models. These models can be parameterized by a scalar potential V, which is a function of N scalar fields, and determines cosmological parameters such as the vacuum stability and energy density. In principle, we can determine V through high energy physics, such as string theory. In practice, though we may not know the details of V we might have clues about a distribution of plausible V’s, which we can build statistics on to further analyze. The purpose of this thesis defense is …
Effective Computational Cosmology, Eva Nesbit
Effective Computational Cosmology, Eva Nesbit
Dissertations - ALL
Effective Field Theories (EFTs) provide a unique framework in which to attempt to answer outstanding questions in cosmology (and all field of physics, for that matter). This work investigates how the use of both EFTs and computational tools can help us to advance our knowledge of how the universe evolved and formed over time. Specifically, we review the successful EFT of Inflation, the EFT of Dark Energy (EFTDE), and introduce the EFT of Reheating as a generalized model of particle formation after inflation. In this way, we show how effective EFTs are at quantifying physical phenomenology at many different energy …
Stability Of A Regular Black Holes Thin-Shell Wormhole In Reissner-Nordstrom - De Sitter Space-Time, A. Eid
Stability Of A Regular Black Holes Thin-Shell Wormhole In Reissner-Nordstrom - De Sitter Space-Time, A. Eid
Applications and Applied Mathematics: An International Journal (AAM)
The dynamics regular black holes thin shell wormhole with a phantom energy equation of state in Reissner-Nordstrom - De sitter space-time is studied using the Darmois-Israel formalism. A mechanical stability analysis is carried out by using the standard perturbation method. The stable and unstable static solution depends on the suitable value of parameters.
Non-Inflationary Bianchi Type Vi0 Model In Rosen’S Bimetric Gravity, M. S. Borkar, N. P. Gaikwad
Non-Inflationary Bianchi Type Vi0 Model In Rosen’S Bimetric Gravity, M. S. Borkar, N. P. Gaikwad
Applications and Applied Mathematics: An International Journal (AAM)
In this paper, we have present the solution of Bianchi type VI0 space-time by solving the Rosen’s field equations with massless scalar field φ and with constant scalar potential V(φ) for flat region. It is observed that the scalar field φ is an increasing function of time and affects the physical parameters of the model and leads to non-inflationary type solution of model, which contradicts the inflationary scenario. Other geometrical and physical properties of the model in relation to this non-inflationary model are also studied.
Lrs Bianchi Type-Ii Cosmological Model With String Bulk Viscous Fluid And Magnetic Field In Barber’S Second Self Creation Theory, M. S. Borkar, N. K. Ashtankar
Lrs Bianchi Type-Ii Cosmological Model With String Bulk Viscous Fluid And Magnetic Field In Barber’S Second Self Creation Theory, M. S. Borkar, N. K. Ashtankar
Applications and Applied Mathematics: An International Journal (AAM)
We present a solution of LRS Bianchi type-II space-time with string viscous fluid and magnetic field by solving the Barber’s field equations of self-creation theory of gravitation and it is seen that Barber scalar function 𝜙 affects the other physical parameters of the model and contributes a very high matter density, with high particle density at early stage of the universe and also it contributes the negative role of bulk viscous fluid in the evolution. Other geometrical and physical aspects of the model are also studied.
Bianchi Type-I Hyperbolic Models With Perfect Fluid And Dark Energy In Bimetric Theory Of Gravitation, M. S. Borkar, S. S. Charjan, V. V. Lepse
Bianchi Type-I Hyperbolic Models With Perfect Fluid And Dark Energy In Bimetric Theory Of Gravitation, M. S. Borkar, S. S. Charjan, V. V. Lepse
Applications and Applied Mathematics: An International Journal (AAM)
Three different Bianchi type-I cosmological models as related to perfect fluid, with quintessence and with Chaplygin gas, in bimetric theory of gravitation have been deduced. The perfect fluid model has hyperbolic geometry and all its physical parameters are also hyperbolic in nature and therefore they have been studied from hyperbolic geometric view point. All these models are isotropize and shear-less. Other geometrical and physical behaviors of the models have also been studied. The hyperbolic geometric view point of the models will be helpful to the people who use observational data to search for such type of geometry.
Kaluza-Klein Type Cosmological Model Of The Universe With Inhomogeneous Equation Of State, G. S. Khadekar, Rajani Shelote
Kaluza-Klein Type Cosmological Model Of The Universe With Inhomogeneous Equation Of State, G. S. Khadekar, Rajani Shelote
Applications and Applied Mathematics: An International Journal (AAM)
In this paper we study Kaluza-Klein type cosmological model of the universe filled with an ideal fluid obeying an inhomogeneous equation of state depending on time. It is shown that there appears a quasi-periodic universe, which repeats the cycles of phantom type space acceleration.
Λcdm Cosmology + Chaotic Inflation, Peter A. Farago
Λcdm Cosmology + Chaotic Inflation, Peter A. Farago
Theses and Dissertations
ΛCDM cosmology is described in terms of general relativity and the Robertson-Walker metric. The evolution of the observable universe, currently dominated by dark energy (Λ) and cold dark matter (CDM), is presented in terms of its thermal history. CDM is extended to include an inflation epoch that accelerates the early expansion rate to near exponential levels. It is shown that inflation solves several problems in CDM and produces perturbations in the metric that lead to the observed anisotropies in the Cosmic Microwave Background and the formation of large scale cosmological structures. Various theories of inflation are explored. Predictions of inflation …
String Fluid Cosmological Model With Magnetic Field In Bimetric Theory Of Gravitation, M. S. Borkar, N. P. Gaikwad
String Fluid Cosmological Model With Magnetic Field In Bimetric Theory Of Gravitation, M. S. Borkar, N. P. Gaikwad
Applications and Applied Mathematics: An International Journal (AAM)
In this paper, LRS Bianchi type I string fluid cosmological model with magnetic field in bimetric theory of gravitation is investigated by assuming barotropic equation of state for pressure and density and assuming the bulk viscosity to be inversely proportional to the scalar expansion. The source of energy momentum tensor is a bulk viscous fluid containing one dimensional string with electromagnetic field. The physical and geometrical properties of the model are discussed. The bulk viscosity affected the whole properties of the model.
Bianchi Type I Magnetized Cosmological Model With Λ-Term In Bimetric Theory Of Gravitation, M. S. Borkar, S. S. Charjan
Bianchi Type I Magnetized Cosmological Model With Λ-Term In Bimetric Theory Of Gravitation, M. S. Borkar, S. S. Charjan
Applications and Applied Mathematics: An International Journal (AAM)
In this paper, we investigated Bianchi Type I magnetized cosmological model with cosmological constant in Rosen’s bimetric theory of gravitation by using the techniques of Letelier and Stachel. The nature of the model is discussed in presence as well as in absence of the magnetic field and cosmological constant. Our model exists and it never goes to vacuum if cosmological constant is not equal to zero and for finite value of cosmic time. In the presence of magnetic field, our model goes to vacuum when the cosmic time tends to minus infinity. Further in the absence of magnetic field the …
Oscillons: Resonant Configurations During Bubble Collapse, E J. Copeland, M Gleiser, H R. Müller
Oscillons: Resonant Configurations During Bubble Collapse, E J. Copeland, M Gleiser, H R. Müller
Dartmouth Scholarship
Oscillons are localized, non-singular, time-dependent, spherically-symmetric solutions of nonlinear scalar field theories which, although unstable, are extremely long-lived. We show that they naturally appear during the collapse of subcritical bubbles in models with symmetric and asymmetric double-well potentials. By a combination of analytical and numerical work we explain several of their properties, including the conditions for their existence, their longevity, and their final demise. We discuss several contexts in which we expect oscillons to be relevant. In particular, their nucleation during cosmological phase transitions may have wide-rangingconsequences.