[en] In a 6D model, where the extra dimensions form a discretized curved disc, we investigate the mass spectra and profiles of gravitons and Dirac fermions. The discretization is performed in detail leading to a star-like geometry. In addition, we use the curvature of the disc to obtain the mass scales of this model in a more flexible way. We also discuss some applications of this setup such as generating small fermion masses

[en] We demonstrate that by employing the correspondence between gauge theories in geometric and in deconstructed extra dimensions, it is possible to transfer the methods for calculating finite Casimir energy densities in higher dimensions to the four-dimensional deconstruction setup. By this means, one obtains an unambiguous and well-defined prescription to determine finite vacuum energy contributions of four-dimensional quantum fields which have a higher-dimensional correspondence. Thereby, large kink masses lead to an exponentially suppressed Casimir effect. For a specific model we hence arrive at a small and positive contribution to the cosmological constant in agreement with observations. (author)

[en] We study the renormalization group running of the cosmological and the Newton constants, where the renormalization scale is given by the inverse of the radius of the cosmological event horizon. In this framework, we discuss the future evolution of the universe, where we find stable de Sitter solutions, but also 'big crunch'-like and 'big rip'-like events, depending on the choice of the parameters in the model

[en] We describe the software chain for the Atlas muon optical alignment system, dedicated to the measurement of geometry corrections for the Muon Spectrometer chambers positions. The corrections are then used inside the reconstruction software. We detail in particular the architecture of the monitoring application, deployed in a J2EE server, and the monitoring tools that have been developed for the daily follow up. The system has been in production during the whole Run 1 period (2010-2013).

[en] We establish an indirect link between relic neutrinos and the dark energy sector which originates from the vacuum energy contributions of the neutrino quantum fields. Via renormalization group effects they induce a running of the cosmological constant with time which dynamically influences the evolution of the cosmic neutrino background. We demonstrate that the resulting reduction of the relic neutrino abundance allows us to largely evade current cosmological neutrino mass bounds and discuss how the scenario might be probed with the help of future large scale structure surveys and Planck data

[en] We study the role of the cosmological constant (CC) as a component of dark energy (DE). It is argued that the cosmological term is in general unavoidable and it should not be ignored even when dynamical DE sources are considered. From the theoretical point of view quantum zero-point energy and phase transitions suggest a CC of large magnitude in contrast to its tiny observed value. Simply relieving this disaccord with a counterterm requires extreme fine-tuning which is referred to as the old CC problem. To avoid it, we discuss some recent approaches for neutralising a large CC dynamically without adding a fine-tuned counterterm. This can be realised by an effective DE component which relaxes the cosmic expansion by counteracting the effect of the large CC. Alternatively, a CC filter is constructed by modifying gravity to make it insensitive to vacuum energy.

[en] Recently, a mechanism for relaxing a large cosmological constant (CC) has been proposed by Bauer et al (2009 Phys. Lett. B 678 427), which permits solutions with low Hubble rates at late times without fine-tuning. The setup is implemented in the ΛXCDM framework, and we found a reasonable cosmological background evolution similar to the ΛCDM model with a fine-tuned CC. In this work, we analyse analytically the perturbations in this relaxation model, and we show that their evolution is also similar to the ΛCDM model, especially in the matter era. Some tracking properties of the vacuum energy are discussed, too.

[en] We analyze non-minimally coupled scalar field theories in metric (second-order) and Palatini (first-order) formalisms in a comparative fashion. After contrasting them in a general setup, we specialize to inflation and find that the two formalisms differ in their predictions for various cosmological parameters. The main reason is that dependencies on the non-minimal coupling parameter are different in the two formalisms. For successful inflation, the Palatini approach prefers a much larger value for the non-minimal coupling parameter than the Metric approach. Unlike the Metric formalism, in Palatini, the inflaton stays well below the Planck scale whereby providing a natural inflationary epoch

[en] We propose a lower limit on the size of a single discrete gravitational extra dimension in the context of an effective field theory for massive gravitons. The limit arises in this setup from the requirement that the Casimir energy density of quantum fields is in agreement with the observed dark energy density of the universe ρ_obs∼10^-47GeV⁴. The Casimir energy densities can be exponentially suppressed to an almost arbitrarily small value by the masses of heavy bulk fields, thereby allowing a tiny size of the extra dimension. This suppression is only restricted by the strong coupling scale of the theory, which is known to be related to the compactification scale via an UV/IR connection for local gravitational theory spaces. We thus obtain a lower limit on the size of the discrete gravitational extra dimension in the range (10¹²GeV)^-1...(10⁷GeV)^-1, while the strong coupling scale is by a factor ∼10² larger than the compactification scale. We also comment on a possible cancelation of the gravitational contribution to the quantum effective potential

[en] In order to deal with a large cosmological constant a relaxation mechanism based on modified gravity has been proposed recently. By virtue of this mechanism the effect of the vacuum energy density of a given quantum field/string theory (no matter how big is its initial value in the early universe) can be neutralized dynamically, i.e. without fine tuning, and hence a Big Bang-like evolution of the cosmos becomes possible. Remarkably, a large class (Fⁿ_m) of models of this kind, namely capable of dynamically adjusting the vacuum energy irrespective of its value and size, has been identified. In this paper, we carefully put them to the experimental test. By performing a joint likelihood analysis we confront these models with the most recent observational data on type Ia supernovae (SNIa), the Cosmic Microwave Background (CMB), the Baryonic Acoustic Oscillations (BAO) and the high redshift data on the expansion rate, so as to determine which ones are the most favored by observations. We compare the optimal relaxation models Fⁿ_m found by this method with the standard or concordance ΛCDM model, and find that some of these models may appear as almost indistinguishable from it. Interestingly enough, this shows that it is possible to construct viable solutions to the tough cosmological fine tuning problem with models that display the same basic phenomenological features as the concordance model