22 research outputs found
Quantum Inflation of Classical Shapes
I consider a quantum system that possesses key features of quantum shape
dynamics and show that the evolution of wave-packets will become increasingly
classical at late times and tend to evolve more and more like an expanding
classical system. At early times however, semiclassical effects become large
and lead to an exponential mismatch of the apparent scale as compared to the
expected classical evolution of the scale degree of freedom. This quantum
inflation of an emergent and effectively classical system, occurs naturally in
the quantum shape dynamics description of the system, while it is unclear
whether and how it might arise in a constrained Hamiltonian quantization.Comment: 14 pages, Late
Can chaos be observed in quantum gravity?
Full general relativity is almost certainly 'chaotic'. We argue that this
entails a notion of nonintegrability: a generic general relativistic model, at
least when coupled to cosmologically interesting matter, likely possesses
neither differentiable Dirac observables nor a reduced phase space. It follows
that the standard notion of observable has to be extended to include
non-differentiable or even discontinuous generalized observables. These cannot
carry Poisson-algebraic structures and do not admit a standard quantization;
one thus faces a quantum representation problem of gravitational observables.
This has deep consequences for a quantum theory of gravity, which we
investigate in a simple model for a system with Hamiltonian constraint that
fails to be completely integrable. We show that basing the quantization on
standard topology precludes a semiclassical limit and can even prohibit any
solutions to the quantum constraints. Our proposed solution to this problem is
to refine topology such that a complete set of Dirac observables becomes
continuous. In the toy model, it turns out that a refinement to a polymer-type
topology, as e.g. used in loop gravity, is sufficient. Basing quantization of
the toy model on this finer topology, we find a complete set of quantum Dirac
observables and a suitable semiclassical limit. This strategy is applicable to
realistic candidate theories of quantum gravity and thereby suggests a solution
to a long-standing problem which implies ramifications for the very concept of
quantization. Our work reveals a qualitatively novel facet of chaos in physics
and opens up a new avenue of research on chaos in gravity which hints at deep
insights into the structure of quantum gravity.Comment: 6 pages + references -- matches published version (clarifications
added for why GR with cosmologically interesting matter likely fails our
notion of weak-integrability
Functional Renormalization of Noncommutative Scalar Field Theory
In this paper we apply the Functional Renormalization Group Equation (FRGE)
to the non-commutative scalar field theory proposed by Grosse and Wulkenhaar.
We derive the flow equation in the matrix representation and discuss the theory
space for the self-dual model. The features introduced by the external
dimensionful scale provided by the non-commutativity parameter, originally
pointed out in \cite{Gurau:2009ni}, are discussed in the FRGE context. Using a
technical assumption, but without resorting to any truncation, it is then shown
that the theory is asymptotically safe for suitably small values of the
coupling, recovering the result of \cite{disertori:2007}. Finally, we
show how the FRGE can be easily used to compute the one loop beta-functions of
the duality covariant model.Comment: 38 pages, no figures, LaTe
The Link between General Relativity and Shape Dynamics
We show that one can construct two equivalent gauge theories from a linking
theory and give a general construction principle for linking theories which we
use to construct a linking theory that proves the equivalence of General
Relativity and Shape Dynamics, a theory with fixed foliation but spatial
conformal invariance. This streamlines the rather complicated construction of
this equivalence performed previously. We use this streamlined argument to
extend the result to General Relativity with asymptotically flat boundary
conditions. The improved understanding of linking theories naturally leads to
the Lagrangian formulation of Shape Dynamics, which allows us to partially
relate the degrees of freedom.Comment: 19 pages, LaTeX, no figure
Einstein gravity as a 3D conformally invariant theory
We give an alternative description of the physical content of general
relativity that does not require a Lorentz invariant spacetime. Instead, we
find that gravity admits a dual description in terms of a theory where local
size is irrelevant. The dual theory is invariant under foliation preserving
3-diffeomorphisms and 3D conformal transformations that preserve the 3-volume
(for the spatially compact case). Locally, this symmetry is identical to that
of Horava-Lifshitz gravity in the high energy limit but our theory is
equivalent to Einstein gravity. Specifically, we find that the solutions of
general relativity, in a gauge where the spatial hypersurfaces have constant
mean extrinsic curvature, can be mapped to solutions of a particular gauge
fixing of the dual theory. Moreover, this duality is not accidental. We provide
a general geometric picture for our procedure that allows us to trade foliation
invariance for conformal invariance. The dual theory provides a new proposal
for the theory space of quantum gravity.Comment: 27 pages. Published version (minor changes and corrections
Genome-Wide Association Study Identifies Two Novel Regions at 11p15.5-p13 and 1p31 with Major Impact on Acute-Phase Serum Amyloid A
Elevated levels of acute-phase serum amyloid A (A-SAA) cause amyloidosis and are a risk factor for atherosclerosis and its clinical complications, type 2 diabetes, as well as various malignancies. To investigate the genetic basis of A-SAA levels, we conducted the first genome-wide association study on baseline A-SAA concentrations in three population-based studies (KORA, TwinsUK, Sorbs) and one prospective case cohort study (LURIC), including a total of 4,212 participants of European descent, and identified two novel genetic susceptibility regions at 11p15.5-p13 and 1p31. The region at 11p15.5-p13 (rs4150642; p = 3.20×10−111) contains serum amyloid A1 (SAA1) and the adjacent general transcription factor 2 H1 (GTF2H1), Hermansky-Pudlak Syndrome 5 (HPS5), lactate dehydrogenase A (LDHA), and lactate dehydrogenase C (LDHC). This region explains 10.84% of the total variation of A-SAA levels in our data, which makes up 18.37% of the total estimated heritability. The second region encloses the leptin receptor (LEPR) gene at 1p31 (rs12753193; p = 1.22×10−11) and has been found to be associated with CRP and fibrinogen in previous studies. Our findings demonstrate a key role of the 11p15.5-p13 region in the regulation of baseline A-SAA levels and provide confirmative evidence of the importance of the 1p31 region for inflammatory processes and the close interplay between A-SAA, leptin, and other acute-phase proteins