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Manuel Kramer - One of the best experts on this subject based on the ideXlab platform.
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quantum Gravitational Effects on gauge invariant scalar and tensor perturbations during inflation the slow roll approximation
Physical Review D, 2016Co-Authors: David Brizuela, Claus Kiefer, Manuel KramerAbstract:We continue our study on corrections from canonical quantum gravity to the power spectra of gauge-invariant inflationary scalar and tensor perturbations. A direct canonical quantization of a perturbed inflationary universe model is implemented, which leads to a Wheeler-DeWitt equation. For this equation, a semiclassical approximation is applied in order to obtain a Schroedinger equation with quantum-Gravitational correction terms, from which we calculate the corrections to the power spectra. We go beyond the de Sitter case discussed earlier and analyze our model in the first slow-roll approximation, considering terms linear in the slow-roll parameters. We find that the dominant correction term from the de Sitter case, which leads to an enhancement of power on the largest scales, gets modified by terms proportional to the slow-roll parameters. A correction to the tensor-to-scalar ratio is also found at second order in the slow-roll parameters. Making use of the available experimental data, the magnitude of these quantum-Gravitational corrections is estimated. Finally, the Effects for the temperature anisotropies in the cosmic microwave background are qualitatively obtained.
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quantum Gravitational Effects on gauge invariant scalar and tensor perturbations during inflation the de sitter case
Physical Review D, 2016Co-Authors: David Brizuela, Claus Kiefer, Manuel KramerAbstract:We present detailed calculations for quantum-Gravitational corrections to the power spectra of gauge-invariant scalar and tensor perturbations during inflation. This is done by performing a semiclassical Born-Oppenheimer type of approximation to the Wheeler-DeWitt equation, from which we obtain a Schr\"odinger equation with quantum-Gravitational correction terms. As a first step, we perform our calculation for a de Sitter universe and find that the correction terms lead to an enhancement of power on the largest scales.
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quantum Gravitational Effects for inflationary perturbations and the fate of mild singularities in quantum cosmology
2015Co-Authors: Manuel KramerAbstract:In this dissertation, we investigate cosmological models within the framework of canonical quantum gravity based on the Wheeler–DeWitt equation with regard to whether it is possible to observe Effects of quantum gravity in the Cosmic Microwave Background radiation and whether a specific class of mild singularities can be resolved by quantizing classical cosmological models in which they appear. The first part is motivated by the fact that there are several candidates for a theory of quantum gravity and it is therefore crucial to find tests in order to figure out which theory is closest to the truth. The main problem here is that quantum-Gravitational Effects are highly suppressed at the energy scales one can nowadays probe in experiments. However, the inflationary phase of the universe takes place at an energy scale where Effects of quantum gravity could be sizeable. During inflation one can investigate primordial cosmological perturbations that are thought to be the seed for structure formation in the early universe as well as for primordial Gravitational waves. Thus they have left their imprints in the anisotropies and the polarization of the Cosmic Microwave Background radiation, which have been measured by the space observatories COBE, WMAP and Planck. We investigate to which extent quantum-Gravitational Effects influence these perturbations by canonically quantizing inflationary models, in which a scalar inflaton field drives the exponential expansion of the universe. At first, we analyze a simplified model, where we only add perturbations to the scalar field. Secondly, we consider scalar and tensor perturbations in a gauge-invariant way for a de Sitter universe and a generic quasi-de Sitter slow-roll model. We perform a semiclassical Born–Oppenheimer type of approximation to the Wheeler–DeWitt equation of each model and recover a Schrodinger equation for the perturbation modes as well as a modified Schrodinger equation with a quantum-Gravitational correction term. From the uncorrected Schrodinger equation, we derive the usual slow-roll power spectra. The quantum-Gravitational correction term leads to a modification of the power spectra on the largest scales. This effect is, however, too small to be measurable, especially in light of the statistical uncertainty due to cosmic variance, which is most prominent on large scales. We also obtain a quantum-Gravitational correction to the tensor-to-scalar ratio, which is, however, much more suppressed than the second-order slow-roll corrections. Finally, we compare our results to other methods in Wheeler–DeWitt quantum cosmology and to findings in other approaches to quantum gravity. The second part of this dissertation is based on the expectation that a quantum theory of gravity should resolve the singularities appearing in general relativity and in classical cosmology. We will focus on a specific set of cosmological singularities called type IV singularities that are of a mild nature in the sense that only higher derivatives of the Hubble parameter diverge. We model a universe with such a singularity by introducing a perfect fluid described by a generalized Chaplygin gas in the form of a scalar field, for which we consider both a standard as well as a phantom field with negative energy. After discussing the classical behavior, we can solve the Wheeler–DeWitt equation of this model analytically for a special case and can draw conclusions for the general case. We use the criterion that a singularity is avoided if the wave function vanishes in the region where the classical singularity is located. However, we obtain as a result that only particular solutions of the Wheeler–DeWitt equation of our model fulfill this criterion and therefore avoid the appearance of a type IV singularity. Lastly, we compare this result to earlier results finding an avoidance of other types of singularities and we discuss singularity resolution in other quantum gravity theories.
David Brizuela - One of the best experts on this subject based on the ideXlab platform.
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quantum Gravitational Effects on gauge invariant scalar and tensor perturbations during inflation the slow roll approximation
Physical Review D, 2016Co-Authors: David Brizuela, Claus Kiefer, Manuel KramerAbstract:We continue our study on corrections from canonical quantum gravity to the power spectra of gauge-invariant inflationary scalar and tensor perturbations. A direct canonical quantization of a perturbed inflationary universe model is implemented, which leads to a Wheeler-DeWitt equation. For this equation, a semiclassical approximation is applied in order to obtain a Schroedinger equation with quantum-Gravitational correction terms, from which we calculate the corrections to the power spectra. We go beyond the de Sitter case discussed earlier and analyze our model in the first slow-roll approximation, considering terms linear in the slow-roll parameters. We find that the dominant correction term from the de Sitter case, which leads to an enhancement of power on the largest scales, gets modified by terms proportional to the slow-roll parameters. A correction to the tensor-to-scalar ratio is also found at second order in the slow-roll parameters. Making use of the available experimental data, the magnitude of these quantum-Gravitational corrections is estimated. Finally, the Effects for the temperature anisotropies in the cosmic microwave background are qualitatively obtained.
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quantum Gravitational Effects on gauge invariant scalar and tensor perturbations during inflation the de sitter case
Physical Review D, 2016Co-Authors: David Brizuela, Claus Kiefer, Manuel KraemerAbstract:We present detailed calculations for quantum-Gravitational corrections to the power spectra of gauge-invariant scalar and tensor perturbations during inflation. This is done by performing a semiclassical Born-Oppenheimer type of approximation to the Wheeler-DeWitt equation, from which we obtain a Schroedinger equation with quantum-Gravitational correction terms. As a first step, we perform our calculation for a de Sitter universe and find that the correction terms lead to an enhancement of power on the largest scales.
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quantum Gravitational Effects on gauge invariant scalar and tensor perturbations during inflation the de sitter case
Physical Review D, 2016Co-Authors: David Brizuela, Claus Kiefer, Manuel KramerAbstract:We present detailed calculations for quantum-Gravitational corrections to the power spectra of gauge-invariant scalar and tensor perturbations during inflation. This is done by performing a semiclassical Born-Oppenheimer type of approximation to the Wheeler-DeWitt equation, from which we obtain a Schr\"odinger equation with quantum-Gravitational correction terms. As a first step, we perform our calculation for a de Sitter universe and find that the correction terms lead to an enhancement of power on the largest scales.
Detlef Lohse - One of the best experts on this subject based on the ideXlab platform.
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Gravitational effect in evaporating binary microdroplets
Physical Review Letters, 2019Co-Authors: Detlef Lohse, Christian Diddens, Herman Wijshoff, Michel VersluisAbstract:The flow in an evaporating glycerol-water binary submillimeter droplet with a Bond number $\mathrm{Bo}\ensuremath{\ll}1$ is studied both experimentally and numerically. First, we measure the flow fields near the substrate by microparticle image velocimetry for both sessile and pendant droplets during the evaporation process, which surprisingly show opposite radial flow directions---inward and outward, respectively. This observation clearly reveals that in spite of the small droplet size, Gravitational Effects play a crucial role in controlling the flow fields in the evaporating droplets. We theoretically analyze that this gravity-driven effect is triggered by the lower volatility of glycerol which leads to a preferential evaporation of water then the local concentration difference of the two components leads to a density gradient that drives the convective flow. We show that the Archimedes number Ar is the nondimensional control parameter for the occurrence of the Gravitational Effects. We confirm our hypothesis by experimentally comparing two evaporating microdroplet systems, namely, a glycerol-water droplet and a 1,2-propanediol-water droplet. We obtain different Ar, larger or smaller than a unit by varying a series of droplet heights, which corresponds to cases with or without Gravitational Effects, respectively. Finally, we simulate the process numerically, finding good agreement with the experimental results and again confirming our interpretation.
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Gravitational effect on the formation of surface nanodroplets
Langmuir, 2015Co-Authors: Detlef Lohse, Xuehua ZhangAbstract:Nanoscale droplets at a solid–liquid interface are of high relevance for many fundamental phenomena and applied processes. The solvent exchange process is a simple approach to produce, e.g., oil nanodroplets over a large surface area on a substrate, by exchange oil-saturated ethanol by oil-saturated water, which has a lower oil solubility than ethanol. In this process, the size of the nanodroplets is closely related to the flow conditions. To achieve control of the droplet size, it is essential to fully understand the nucleation and growth of nanodroplets under different flow conditions. In this work, we investigate the Gravitational effect on the droplet formation by the solvent exchange. We compared the droplet size as the substrate was placed on the upper or lower wall in a horizontal fluid channel or on the sides of a vertical channel with an upward or downward flow. We found significant difference in the droplet size for the three substrate positions in a wide channel with height h = 0.21 mm. The difference of droplet size was eliminated in a narrow channel with height h = 0.07 mm. The relevant dimensional control parameter for the occurrence of the Gravitational Effects is the Archimedes number Ar and these two heights correspond to Ar = 10 and Ar = 0.35, respectively. The Gravitational Effects lead to a nonsymmetric parabolic profile of the mixing front, with the velocity maximum being off-center and thus with different distances α(Ar)h and (1 – α(Ar))h to the lower and upper wall, respectively. The ratio of the total droplet volume on the lower and upper wall is theoretically found to be (α(Ar)/(1 – α(Ar)))3. This study thus improves our understanding of the mechanism of the solvent exchange process, providing guidelines for tailoring the volume of surface nanodroplets.
Claus Kiefer - One of the best experts on this subject based on the ideXlab platform.
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quantum Gravitational Effects on gauge invariant scalar and tensor perturbations during inflation the slow roll approximation
Physical Review D, 2016Co-Authors: David Brizuela, Claus Kiefer, Manuel KramerAbstract:We continue our study on corrections from canonical quantum gravity to the power spectra of gauge-invariant inflationary scalar and tensor perturbations. A direct canonical quantization of a perturbed inflationary universe model is implemented, which leads to a Wheeler-DeWitt equation. For this equation, a semiclassical approximation is applied in order to obtain a Schroedinger equation with quantum-Gravitational correction terms, from which we calculate the corrections to the power spectra. We go beyond the de Sitter case discussed earlier and analyze our model in the first slow-roll approximation, considering terms linear in the slow-roll parameters. We find that the dominant correction term from the de Sitter case, which leads to an enhancement of power on the largest scales, gets modified by terms proportional to the slow-roll parameters. A correction to the tensor-to-scalar ratio is also found at second order in the slow-roll parameters. Making use of the available experimental data, the magnitude of these quantum-Gravitational corrections is estimated. Finally, the Effects for the temperature anisotropies in the cosmic microwave background are qualitatively obtained.
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quantum Gravitational Effects on gauge invariant scalar and tensor perturbations during inflation the de sitter case
Physical Review D, 2016Co-Authors: David Brizuela, Claus Kiefer, Manuel KraemerAbstract:We present detailed calculations for quantum-Gravitational corrections to the power spectra of gauge-invariant scalar and tensor perturbations during inflation. This is done by performing a semiclassical Born-Oppenheimer type of approximation to the Wheeler-DeWitt equation, from which we obtain a Schroedinger equation with quantum-Gravitational correction terms. As a first step, we perform our calculation for a de Sitter universe and find that the correction terms lead to an enhancement of power on the largest scales.
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quantum Gravitational Effects on gauge invariant scalar and tensor perturbations during inflation the de sitter case
Physical Review D, 2016Co-Authors: David Brizuela, Claus Kiefer, Manuel KramerAbstract:We present detailed calculations for quantum-Gravitational corrections to the power spectra of gauge-invariant scalar and tensor perturbations during inflation. This is done by performing a semiclassical Born-Oppenheimer type of approximation to the Wheeler-DeWitt equation, from which we obtain a Schr\"odinger equation with quantum-Gravitational correction terms. As a first step, we perform our calculation for a de Sitter universe and find that the correction terms lead to an enhancement of power on the largest scales.
Alexandre Arbey - One of the best experts on this subject based on the ideXlab platform.
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dark fluid a complex scalar field to unify dark energy and dark matter
Physical Review D, 2006Co-Authors: Alexandre ArbeyAbstract:In this article, we examine a model which proposes a common explanation for the presence of additional attractive Gravitational Effects\char22{}generally considered to be due to dark matter\char22{}in galaxies and in clusters, and for the presence of a repulsive effect at cosmological scales\char22{}generally taken as an indication of the presence of dark energy. We therefore consider the behavior of a so-called dark fluid based on a complex scalar field with a conserved $U(1)$-charge and associated to a specific potential, and show that it can at the same time account for dark matter in galaxies and in clusters, and agree with the cosmological observations and constraints on dark energy and dark matter.
