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- Berlin.de

Quantum Phenomena in the Realm of Cosmology and Astrophysics

10 Part I. Introduction matter are estimated **in** **the** analysis **of** **the** Planck collaboration as Ω M = 31.75%, **and** **the** cosmological constant is assumed to make up about Ω Λ = 68.25%. The equation **of** state **of** **the** universe **in** **the** ΛCDM model can be given consider**in**g **the**se contributions as 1 ω = − , (1.35) 1 + Ω M /Ω Λ a−3 which for **the** above values results **in** ω ≃ −0.68. The cosmological constant postulated **in** **the** ΛCDM model doesn’t conta**in** any **in**formation on its micro-physical background or orig**in**, it is a phenomenological quantity motivated by observed features **of** **the** universe **and** requires yet to be derived **and** justified from a microphysical **the**ory. Some constra**in**ts on its physical nature can be obta**in**ed from experiments, but s**in**ce **the** only **in**formation comes from **in**direct observations **of** its consequences, our knowledge about **the** orig**in** **of** **the** effect st**and**s on shaky grounds. Many **the**ories put forward as its expla**in**ation are **in** accordance with observations, s**in**ce **the** parameters to compare with **the** data are few, **and** this leads to a large degeneracy **of** models. Correspond**in**gly, **the**re has been an animated discourse **and** prosperous growth **of** **the** number **of** **the**ories about **the** possible expla**in**ation to **the** phenomenon, **and** a fair evaluation **of** **the** models at h**and** **and** **the**ir success is def**in**itely necessary, **and** may be provided by cosmography. 1.2. Contents In this dissertation, we thus address some **of** **the** major concerns **of** modern cosmology. On **the** **the**oretical side, we successfully develop a model to expla**in** dark energy by connect**in**g it to a quantum **the**oretical phenomenon which has led to puzzles **in** quantum field **the**ories. Among **the** abundance **of** models try**in**g to expla**in** this k**in**ematic feature **of** **the** universe, one **of** **the**m is to consider **the** vacuum fluctuations **of** quantum fields, an energy density constant **in** space as **the** orig**in** **of** this expansion. The vacuum energy is a divergent quantity however, **and** is thus usually discarded as a possible expla**in**ation for dark energy. The huge discrepancy between an **in**f**in**ite value **of** **the** vacuum energy, or a very large f**in**ite value achieved by some k**in**d **of** renormalization technique, **and** **the** t**in**y constant energy density driv**in**g **the** cosmic expansion, is termed **the** hirarchy problem. By balanc**in**g contributions **of** different quantum fields, a small f**in**ite value **of** **the** vacuum energy can be achieved, which can correctly account for **the** expansion **of** **the** universe. In this way, we f**in**d an expla**in**ation to **the** question **of** dark energy as well as manage to resolve **the** hirarchy problem **in** this context.

1. Basic Foundations **and** Outlook 11 To complement this part **of** **the** work, we **in**vestigate **the** issue **of** **the** accelerated re-expansion **of** **the** universe from an observational po**in**t **of** view **and** improve conventional methods **of** data analysis to be able to extract **the** universe’s k**in**ematical properties from experimental results **in** **the** most **in**dependent way, **in** order to give **the** constra**in**ts that any viable **the**ory **of** cosmology has to fulfill. We **in**vestigate observational data **of** **the** lum**in**osity **of** type Ia supernovae events **in** order to obta**in** numerical fits for **the** parameters **of** **the** so-called cosmographic series, consist**in**g **of** **the** Hubble parameter H 0 , **the** acceleration parameter q 0 , **and** fur**the**r higher-order parameters describ**in**g **the** k**in**ematical evolution **of** **the** universe. The conventional approach utilizes Taylor expansions **of** **the** relevant quantities for data fitt**in**g. We extend **the** exist**in**g analyses for several orders **in** **the** expansion, **and** suggest improvements to conventional cosmography by construct**in**g alternatives to **the** commonly used redshift variable z, as well as by propos**in**g a new method **of** expansion substitut**in**g **the** usual Taylor approach. Our results confirm **the** validity **of** **the** **in**troduced modifications, as well as yield constra**in**ts on **the** k**in**ematical properties **of** our universe, affirm**in**g **the** ΛCDM model to be **in** accordance with observations. Yet ano**the**r connection **of** a quantum phenomenon to large scale scenarios is **the** **the**ory **of** **the** occurrence **of** a Bose-E**in**ste**in** condensate **in** compact objects. We will **in**vestigate **the** impact **of** **the** occurrence **of** a BEC on **the** properties **of** objects such as white dwarfs, where conditions allow for **the** formation **of** BECs due to a favourable comb**in**ation **of** temperature **and** density. Thus it is **of** **in**terest to **in**vestigate **the** condensation **of** bosonic particles under **the** **in**fluence **of** hard-sphere scatter**in**g **and** gravitational **in**teractions **in** **the** framework **of** a Hartree-Fock **the**ory at f**in**ite temperatures. Results can be compared to observations through **the** computed density pr**of**iles **and** masses **of** **the** objects. We will draw conclusions **and** ultimately summarize **the** work presented **in** **the** respective project at **the** end **of** each part, **and** comment on its significance **and** possible fur**the**r extensions.

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Bibliography 167 Bibliography [1] A

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Bibliography 169 [27] V. Vitagliano

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Bibliography 171 [58] L. E. Parker

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Bibliography 173 [87] R. R. Caldwel

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Bibliography 175 [116] R. C. Tolman

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Bibliography 177 [143] P. Oehberg a

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Acknowledgments 181 Acknowledgments