arXiv subjects

Koray Karaca

Publications and source records attributed to Koray Karaca.

4 recordsLinked to original sources

arXiv2014

Philosophical perspectives on ad hoc hypotheses and the Higgs mechanism

We examine physicists' charge of ad hocness against the Higgs mechanism in the standard model of elementary particle physics. We argue that even though this charge never rested on a clear-cut and well-entrenched definition of "ad hoc", it is based on conceptual and methodological assumptions and principles that are well-founded elements of the scientific practice of high-energy particle physics. We further evaluate the implications of the recent discovery of a Higgs-like particle at the CERN's Large Hadron Collider for the charge of ad hocness against the Higgs mechanism.

physics.hist-ph↗

arXiv2005

An Open Inflationary Model for Dimensional Reduction and its Effects on the Observable Parameters of the Universe

Assuming that higher dimensions existed in the early stages of the universe where the evolution was inflationary, we construct an open, singularity-free, spatially homogeneous and isotropic cosmological model to study the effects of dimensional reduction that may have taken place during the early stages of the universe. We consider dimensional reduction to take place in a stepwise manner and interpret each step as a phase transition. By imposing suitable boundary conditions we trace their effects on the present day parameters of the universe.

astro-ph↗

arXiv2003

Inflation in Flat Universe

We started the evolution of a flat universe from a nonsingular state called prematter which is governed by an inflationary equation of state $P=(γ_{p}-1)ρ$ where $γ_{p}$ represents the initial vacuum dominance of the universe. The evolution of the universe-except in the prematter era-is affected neither by the initial vacuum dominance nor the initial expansion rate of the universe. On the other hand, present properties of the universe such as Hubble constant, age and density are sensitive to the temperature at the decoupling $(T_{m})$. Over a range between $3\cdot10^{4}$ and $5\cdot10^{4}$ K for $(T_{m})$, our model predicts a value between 50 and 80 $Km\cdot sec^{-1}\cdot Mpc^{-1}$ for the present value of the Hubble constant $(H_{0})$. Assuming that the thermal history of the universe is independent from its geometry, the above range could be considered as transition range for the decoupling temperature $(T_{m})$.

astro-ph↗

arXiv2003

An Open Singularity-Free Cosmological Model with Inflation

In the light of recent observations which point to an open universe $(Ω_{0}<1)$, we construct an open singularity-free cosmological model by reconsidering a model originally constructed for a closed universe. Our model starts from a nonsingular state called prematter, governed by an inflationary equation of state $P=(γ_{p}-1)ρ$ where $γ_{p}$ $(\simeq 10^{-3})$ is a small positive parameter representing the initial vacuum dominance of the universe. Unlike the closed models universe cannot be initially static hence, starts with an initial expansion rate represented by the initial value of the Hubble constant H(0). Therefore, our model is a two-parameter universe model $(γ_{p},H(0))$. Comparing the predictions of this model for the present properties of the universe with the recent observational results, we argue that the model constructed in this work could be used as a realistic universe model.

astro-ph↗