Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article Citation - WoS: 6Citation - Scopus: 5A Mechanism for Formation of Bose-Einstein Condensation in Cosmology(IOP Publishing, 2019) Erdem, Recai; Gültekin, KemalWe introduce a toy model of scalar particles with a trilinear scalar coupling in cosmology. The trilinear coupling phi(2)chi causes production of non-relativistic phi particles through the process chi chi -> phi phi where, initially, only relativistic chi particles are present. We consider the initial times of chi chi -> phi phi and observe that the curved space effects promote formation of Bose-Einstein condensate of phi particles.Article Citation - WoS: 607Citation - Scopus: 736Black Holes, Gravitational Waves and Fundamental Physics: a Roadmap(IOP Publishing, 2019) Barack, Leor; Cardoso, Vitor; Nissanke, Samaya; Sotiriou, Thomas P.; Askar, Abbas; Belczynski, Chris; Erdem, RecaiThe grand challenges of contemporary fundamental physics dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'.Article Citation - WoS: 9Citation - Scopus: 9Is It Possible To Obtain Cosmic Accelerated Expansion Through Energy Transfer Between Different Energy Densities?(Elsevier Ltd., 2017) Erdem, RecaiThe equation of state of an energy density may be significantly modified by coupling it to another energy density. In the light of this observation we check the possibility of producing cosmic accelerated expansion in this way. In particular we consider the case where matter is converted to radiation (or vice versa by particle physics processes). We find that cosmic accelerated expansion can be obtained in this way only if an intermediate state with negative equation of state forms during the conversion.Article Citation - WoS: 14Citation - Scopus: 15A Symmetry for Vanishing Cosmological Constant: Another Realization(Elsevier Ltd., 2006) Erdem, RecaiA more conventional realization of a symmetry which had been proposed towards the solution of cosmological constant problem is considered. In this study the multiplication of the coordinates by the imaginary number i in the literature is replaced by the multiplication of the metric tensor by minus one. This realization of the symmetry as well forbids a bulk cosmological constant and selects out 2 (2 n + 1)-dimensional spaces. On contrary to its previous realization the symmetry, without any need for its extension, also forbids a possible cosmological constant term which may arise from the extra-dimensional curvature scalar provided that the space is taken as the union of two 2 (2 n + 1)-dimensional spaces where the usual 4-dimensional space lies at the intersection of these spaces. It is shown that this symmetry may be realized through space-time reflections that change the sign of the volume element. A possible relation of this symmetry to the E-parity symmetry of Linde is also pointed out.Conference Object Citation - WoS: 22Citation - Scopus: 23A Symmetry for Vanishing Cosmological Constant in an Extra-Dimensional Toy Model(Elsevier, 2005) Erdem, RecaiWe introduce a symmetry principle that forbids a bulk cosmological constant in six and ten dimensions. Then the symmetry is extended in six dimensions so that it insures absence of 4-dimensional cosmological constant induced by the six-dimensional curvature scalar, at least, for a class of metrics. A small cosmological constant may be induced in this scheme by breaking of the symmetry by a small amount.