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Florian Kuhnel

Publications and source records attributed to Florian Kuhnel.

45 records · Page 3Linked to original sources

Decay of Graviton Condensates and their Generalizations in Arbitrary Dimensions

Classicalons are self-bound classical field configurations, which include black holes in General Relativity. In quantum theory, they are described by condensates of many soft quanta. In this work, their decay properties are studied in arbitrary dimensions. It is found that generically the decays of other classicalons are enhanced compared to pure graviton condensates, ie. black holes. The evaporation of higher dimensional graviton condensates turns out to match Hawking radiation solely due to non-linearites captured by the classicalon picture. Although less stable than black holes, all self-bound condensates are shown to be stable in the limit of large mass. Like for black holes, the effective coupling always scales as the inverse of the number of constituents, indicating that these systems are at critical points of quantum phase transitions. Consequences for cosmology, astro- and collider physics are briefly discussed.

hep-th↗

Bose-Einstein Condensates with Derivative and Long-Range Interactions as Set-Ups for Analog Black Holes

General types of Bose-Einstein condensates are considered. The formation of black-hole analogues is examined for both short- and long-range interactions for arbitrary spatial dimensions greater than two. The former case includes non-linear derivative terms plus an inevitable external potential, while the latter one consists solely of gravity-like self-interactions for which intrinsic formation of analogue Schwarzschild-type background space-times is possible. The corresponding geometries are studied, and it is shown how they can be made stable. Their Hawking temperature is estimated, and it is found that in certain set-ups it can be significantly increased, thus providing better detectability.

gr-qc↗

High-Energy Gravitational Scattering and Bose-Einstein Condensates of Gravitons

Quantum black holes are difficult to describe. We consider two seemingly divergent approaches, high-energy scattering and the proposal to regard black holes as Bose-Einstein condensates of gravitons, and establish a connection between them. High-energy scattering is studied in the eikonal approximation, which is processed further by a saddle-point approximation. The dominant contribution to the scattering amplitude comes from a ladder diagram with the exchange of N gravitons, and the number of gravitons follows a Poisson distribution. This approximation supports the picture of a graviton Bose-Einstein condensate with an extent equal the Schwarzschild radius, which grows with N in a way determined by the saddle point. The approach permits calculations of 1 / N corrections from the fluctuations around the saddle points and we comment on these. Scattering methods might be useful probes of quantum black holes, especially when interpreted in terms of condensates.

hep-th↗

Modified Bose-Einstein Condensate Black Holes in d Dimensions

[Remark: Much more natural and important models are studied in arXiv:1405.2083. Furthermore, the physical picture given there is much more complete.] The quantum N-portrait -- black holes pictured as Bose-Einstein condensates -- is studied for a special class of models in arbitrary dimensions. In the presence of extra dimensions, the depletion rate is shown to be significantly enhanced in these models as compared to standard semi-classical results. Consequences for large as well as micro condensates are discussed. Speculations are made on a possible connection of higher-dimensional graviton condensates, strings and branes.

hep-th↗

On Instability of Certain Bi-Metric and Massive-Gravity Theories

Stability about cosmological background solutions to the bi-metric Hassan-Rosen theory is studied. The results of this analysis are presented, and it is shown that a large class of cosmological backgrounds is classically unstable. This sets serious doubts on the physical viability of the Hassan-Rosen theory - and in turn also of the de Rham-Gadabaze-Tolley model, to which the mentioned theory is parent. A way to overcome this instability by means of curvature-type deformations is discussed.

gr-qc↗

Axion arising from warped extra-dimensional gauge fields

We present a connection between two known solutions to the strong-CP problem: the standard introduction of axions and the extra-dimensional one, relying on topological arguments. Using an equivalent lower-dimensional set-up with a warped extra-dimension but without adding any new fields, it is shown that an additional light degree of freedom appears. Like an axion, it couples to the topological charge density via Fermionic loop corrections. Its decay constant is related to the geometry of the extra dimension and is suppressed by the warping scale.

hep-th↗

Large-Scale Suppression from Stochastic Inflation

We show non-perturbatively that the power spectrum of a self-interacting scalar field in de Sitter space-time is strongly suppressed on large scales. The cut-off scale depends on the strength of the self-coupling, the number of e-folds of quasi-de Sitter evolution, and its expansion rate. As a consequence, the two-point correlation function of field fluctuations is free from infra-red divergencies.

hep-ph↗

Stochastic Inflation and Dimensional Reduction

We present a replica field-theoretic approach to stochastic inflation in which a manifestation of dimensional reduction is found. The scale above which the latter dominates grows exponentially fast with time and thus affects largest super-horizon scales. We find inevitable modifications of the spectral index on those scales. An explicit relation between the noise correlator and the non-gaussianity parameter f_NL is found.

gr-qc↗

Stochastic Inflation and Replica Field Theory

We adopt methods from statistical field theory to stochastic inflation. For the example of a free test field in de Sitter and power-law inflation, the power spectrum of long-wavelength fluctuations is computed. We study its dependence on the shape of the filter that separates long from short wavelength modes. While for filters with infinite support the phenomenon of dimensional reductions is found on large super-horizon scales, filters with compact support return a scale-invariant power spectrum in the infra-red. Features of the power spectrum, induced by the filter, decay within a few e-foldings. Thus the late-time power spectrum is independent of the filter details.

gr-qc↗