Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article A Metric for Gravitational Collapse Around a Schwarzschild Black Hole(World Scientific Publishing, 2023) Erdem, Recai; Demirkaya, Betül; Gültekin, KemalWe consider the problem of gravitational collapse of a fluid under the effect of a small Schwarzschild black hole (e.g. a primordial one). We assume the fluid initially may be approximated by a uniform homogeneous dust. Starting from this configuration we obtain a class of metrics under some physically justified assumptions. We find that the metric we obtain includes the dust collapse as a subcase. After discussing some basic properties of the solution, we discuss the case of dust collapse in more detail. We find that the radial and tangential pressures outside the horizon may take positive or negative values depending on the values of the parameters.Article It Is Sufficient To Set the Cosmological Constant To Zero or To a Small Number at an Initial Time(TUBITAK, 2016) Erdem, RecaiI point out a simple but usually overlooked fact about the cosmological constant problem: to solve the cosmological constant problem it is sufficient to find a symmetry or mechanism that sets the cosmological constant to zero or to a tiny value at some time in the past, provided that general relativity is the relevant theory of gravity, and the energy-momentum tensor (excluding the part of the form of a cosmological constant) is conserved. The relevant symmetry or mechanism need not be applicable today. Any additional cosmological constant term induced by a phase transition in the energy-momentum tensor in this case is compensated by a shift in the cosmological constant term of gravitational origin.Conference Object Extra Dimensional Metric Reversal Symmetry and Its Prospect for Cosmological Constant and Zero-Point Energy Problems, Automatic Pauli-Villars Regularization, and an Interesting Kaluza-Klein Spectrum(2010) Erdem, RecaiThe metric reversal symmetry was introduced in the context of cosmological constant problem. Besides proposing a solution to the cosmological constant problem the metric reversal symmetry has also provided a framework for solution of the zero-point energy problem, an automatic Pauli-Villars-like regularization, and an interesting Kaluza- Klein spectrum with interesting phenomenological implications. In this talk I give a brief overall summary and discussion of these topics with their potential implications.Article Citation - WoS: 2Citation - Scopus: 2Single Scale Factor for the Universe From the Creation of Radiation and Matter Till the Present(Springer Verlag, 2014) Erdem, RecaiA scheme for incorporating the creation of radiation and matter into the cosmological evolution is introduced so that it becomes possible to merge the times before and after the creation of radiation and matter in a single scale factor in the Robertson–Walker metric. This scheme is illustrated through a toy model that has the prospect of constituting a basis for a realistic model.