15 research outputs found
Fixed-Functionals of three-dimensional Quantum Einstein Gravity
We study the non-perturbative renormalization group flow of f(R)-gravity in
three-dimensional Asymptotically Safe Quantum Einstein Gravity. Within the
conformally reduced approximation, we derive an exact partial differential
equation governing the RG-scale dependence of the function f(R). This equation
is shown to possess two isolated and one continuous one-parameter family of
scale-independent, regular solutions which constitute the natural
generalization of RG fixed points to the realm of infinite-dimensional theory
spaces. All solutions are bounded from below and give rise to positive definite
kinetic terms. Moreover, they admit either one or two UV-relevant deformations,
indicating that the corresponding UV-critical hypersurfaces remain finite
dimensional despite the inclusion of an infinite number of coupling constants.
The impact of our findings on the gravitational Asymptotic Safety program and
its connection to new massive gravity is briefly discussed.Comment: 34 pages, 14 figure
RG flows of Quantum Einstein Gravity on maximally symmetric spaces
We use the Wetterich-equation to study the renormalization group flow of
-gravity in a three-dimensional, conformally reduced setting. Building on
the exact heat kernel for maximally symmetric spaces, we obtain a partial
differential equation which captures the scale-dependence of for
positive and, for the first time, negative scalar curvature. The effects of
different background topologies are studied in detail and it is shown that they
affect the gravitational RG flow in a way that is not visible in
finite-dimensional truncations. Thus, while featuring local background
independence, the functional renormalization group equation is sensitive to the
topological properties of the background. The detailed analytical and numerical
analysis of the partial differential equation reveals two globally well-defined
fixed functionals with at most a finite number of relevant deformations. Their
properties are remarkably similar to two of the fixed points identified within
the -truncation of full Quantum Einstein Gravity. As a byproduct, we
obtain a nice illustration of how the functional renormalization group realizes
the "integrating out" of fluctuation modes on the three-sphere.Comment: 35 pages, 6 figure
Scheme dependence and universality in the functional renormalization group
We prove that the functional renormalization group flow equation admits a
perturbative solution and show explicitly the scheme transformation that
relates it to the standard schemes of perturbation theory. We then define a
universal scheme within the functional renormalization group.Comment: 5 pages, improved version; v2: published version; v3 and v4: fixed
various typos (final result is unaffected
RG flows of Quantum Einstein Gravity in the linear-geometric approximation
We construct a novel Wetterich-type functional renormalization group equation
for gravity which encodes the gravitational degrees of freedom in terms of
gauge-invariant fluctuation fields. Applying a linear-geometric approximation
the structure of the new flow equation is considerably simpler than the
standard Quantum Einstein Gravity construction since only transverse-traceless
and trace part of the metric fluctuations propagate in loops. The geometric
flow reproduces the phase-diagram of the Einstein-Hilbert truncation including
the non-Gaussian fixed point essential for Asymptotic Safety. Extending the
analysis to the polynomial -approximation establishes that this fixed
point comes with similar properties as the one found in metric Quantum Einstein
Gravity; in particular it possesses three UV-relevant directions and is stable
with respect to deformations of the regulator functions by endomorphisms.Comment: 32 pages, 4 figue
Macromolecular dynamics in red blood cells investigated using neutron spectroscopy
We present neutron scattering measurements on the dynamics of hemoglobin (Hb)
in human red blood cells in vivo. Global and internal Hb dynamics were measured
in the ps to ns time- and {\AA} length-scale using quasielastic neutron
backscattering spectroscopy. We observed the cross-over from global Hb
short-time to long-time self-diffusion. Both short- and long-time diffusion
coefficients agree quantitatively with predicted values from hydrodynamic
theory of non-charged hard-sphere suspensions when a bound water fraction of
around 0.23g H2O/ g Hb is taken into account. The higher amount of water in the
cells facilitates internal protein fluctuations in the ps time-scale when
compared to fully hydrated Hb powder. Slower internal dynamics of Hb in red
blood cells in the ns time-range were found to be rather similar to results
obtained with fully hydrated protein powders, solutions and E. coli cells