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Publication Metadata only Accelerated expansion of the universe `a la the Stueckelberg mechanism(Iop Publishing Ltd, 2014) Arik, Metin; Katirci, Nihan; Kavuk, Mehmet; Department of Physics; Akarsu, Özgür; Researcher; Department of Physics; College of Sciences; N/AWe investigate a cosmological model in which the Stueckelberg fields are nonminimally coupled to the scalar curvature in a gauge invariant manner. We present not only a solution that can be considered in the context of the late time acceleration of the universe but also a solution compatible with the inflationary cosmology. Distinct behaviors of the scalar and vector fields together with the real valued mass gained by the Stueckelberg mechanism lead the universe to go through the two different accelerated expansion phases with a decelerated expansion phase between them. On the other hand, in the solutions we present, if the mass is null then the universe is either static or exhibits a simple power law expansion due to the vector field potential.Publication Metadata only Comment on the possibility of a geometric constraint in the Schrodinger quantum mechanics(World Scientific Publ Co Pte Ltd, 2000) Department of Mathematics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; College of Sciences; 4231It is shown that the geometric constraint advocated in [R. S. Kaushal, Mod. Phys. Lett.A15, 1391 (2000)] is trivially satisfied. Therefore, such a constraint does not exist. We also point out another flaw in Kaushal's paper.Publication Metadata only Cosmology with hybrid expansion law: scalar field reconstruction of cosmic history and observational constraints(Institute of Physics (IOP) Publishing, 2014) Kumar, Suresh; Myrzakulov, R.; Sami, M.; Xu, Lixin; Department of Physics; Akarsu, Özgür; Researcher; Department of Physics; College of Sciences; N/AIn this paper, we consider a simple form of expansion history of Universe referred to as the hybrid expansion law − a product of power-law and exponential type of functions. The ansatz by construction mimics the power-law and de Sitter cosmologies as special cases but also provides an elegant description of the transition from deceleration to cosmic acceleration. We point out the Brans-Dicke realization of the cosmic history under consideration. We construct potentials for quintessence, phantom and tachyon fields, which can give rise to the hybrid expansion law in general relativity. We investigate observational constraints on the model with hybrid expansion law applied to late time acceleration as well as to early Universe a la nucleosynthesis.Publication Metadata only Entropy of the quantum fluctuations of fermionic instantons in the universe(World Scientific Publishing Co Pte Ltd, 2022) Akilli, Mahmut; Department of Physics; Yılmaz, Nazmi; Teaching Faculty; Department of Physics; College of Sciences; 178427The aim of this paper is to study the entropy of quantum fluctuations of fermionic instantons. For this purpose, we focus on the spinor-type instanton solution family of the massless pure fermionic Thirring model because it is a well-known quantized toy model in the quantum field theory since 1958. We calculate the Boltzmann-Gibbs-Shannon (BGS) entropy of the Thirring model by the normalized inner scalogram (NIS) and find that the entropy of quantum fluctuations of Thirring fermionic instantons increase slightly just after the big bang. This result leads us to discuss the relation between the increasing entropy in the Universe due to quantum fluctuations of the fermionic Thirring instantons during the creation of fermionic type particles.Publication Metadata only Exact solutions in five-dimensional axi-dilaton gravity with euler-poincare term(Iop Publishing Ltd, 2007) Aliev, A. N.; Cebeci, H.; Department of Physics; Dereli, Tekin; Faculty Member; Department of Physics; College of Sciences; 201358We examine the effective field equations that are obtained from the axi-dilaton gravity action with a second-order Euler-Poincare term and a cosmological constant in all higher dimensions. We solve these equations for five-dimensional-spacetimes possessing homogeneity and isotropy in their three-dimensional subspaces. For a number of interesting special cases, we show that the solutions fall into two main classes: the first class consists of time-dependent solutions with spherical or hyperboloidal symmetry which require certain fine-tuning relations between the coupling constants of the model and the cosmological constant. Solutions in the second class are locally static and prove the validity of Birkhoff's staticity theorem in the axi-dilaton gravity. We also give a class of static solutions, among them the well known charged black hole solutions with a cosmological constant in which the usual electric charge is superseded by an axion charge.Publication Metadata only On the detection of scalar field induced space-time torsion(World Scientific Publishing Co Pte Ltd, 2002) Tucker, RW; Department of Physics; Dereli, Tekin; Faculty Member; Department of Physics; College of Sciences; 201358We argue that the geodesic hypothesis based on autoparallels of the Levi-Civita connection may need refinement in the scalar-tensor theories of gravity. Based on a reformulation of the Brans-Dicke theory in terms of a connection with torsion determined dynamically in terms of the gradient of the Brans-Dicke scalar field, we compute the perihelion shift in the orbit of Mercury on the alternative hypothesis that its worldline is an autoparallel of a connection with torsion. If the Brans-Dicke scalar field couples significantly to matter and test particles move on such worldlines, the current time keeping methods based on the conventional geodesic hypothesis may need refinement.Publication Metadata only On the pseudo-hermiticity of a class of PT-symmetric Hamiltonians in one dimension(World Scientific Publ Co Pte Ltd, 2002) Department of Mathematics; Mostafazadeh, Ali; Faculty Member; Department of Mathematics; College of Sciences; 4231For a given standard Hamiltonian H = [p - A(x)]2/(2m) + V(x) with arbitrary complex scalar potential V and vector potential A, with x ∈ ℝ, we construct an invertible antilinear operator τ such that H is τ-anti-pseudo-hermitian, i.e. H† = τHτ-1. We use this result to give the explicit form of a linear hermitian invertible operator with respect to which any standard PT-symmetric Hamiltonian with a real degree of freedom is pseudo-hermitian. Our results do not make use of the assumption that H is diagonalizable or that its spectrum is discrete.Publication Metadata only Supersymmetry of PT-symmetric tridiagonal hamiltonians(World Scientific Publ Co Pte Ltd, 2021) N/A; Almasri, Mohammad Walid; PhD Student; Graduate School of Sciences and Engineering; N/AWe extend the study of supersymmetric tridiagonal Hamiltonians to the case of non-Hermitian Hamiltonians with real or complex conjugate eigenvalues. We find the relation between matrix elements of the non-Hermitian Hamiltonian H and its supersymmetric partner H+ in a given basis. Moreover, the orthogonal polynomials in the eigenstate expansion problem attached to H+ can be recovered from those polynomials arising from the same problem for H with the help of kernel polynomials. Besides its generality, the developed formalism in this work is a natural home for using the numerically powerful Gauss quadrature techniques in probing the nature of some physical quantities such as the energy spectrum of PT-symmetric complex potentials. Finally, we solve the shifted PT-symmetric Morse oscillator exactly in the tridiagonal representation.Publication Metadata only The micro-broadband receiver (MU BBR) on the very-low-frequency propagation mapper cubesat(American Geophysical Union, 2021) Marshall, Robert A.; Sousa, Austin; Reid, Riley; Wilson, Gordon; Starks, Michael; Ramos, Daniel; Ballenthin, John; Quigley, Steven; Kay, Ron; Patton, James; Coombs, Joseph; Fennelly, Judy; Linscott, Ivan; Department of Electrical and Electronics Engineering; İnan, Umran Savaş; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; 177880The very low frequency (VLF) propagation mapper (VPM) is a 6U CubeSat designed to measure VLF radio waves in Low-Earth Orbit. The science goals of the VPM mission are to measure VLF signals broadcast by the DSX mission, and to study natural and anthropogenic signals (from lightning and VLF transmitters) in the near-Earth space environment. The primary payload consists of an electric field dipole antenna deployed to 2 meters in length, and a magnetic search coil deployed 50 cm from the spacecraft. Signals from these two sensors are conditioned by analog electronics, sampled, and then processed digitally into downloadable data products. The VPM mission was launched in January 2020; science operations began in March 2020 and continued through September, when contact with the spacecraft was lost. This paper describes the mission goals and instrument designs in detail, as well as some examples of the VPM data se