4,983 research outputs found
Observable consequences of quantum gravity: Can light fermions exist?
Any theory of quantum gravity must ultimately be connected to observations.
This demand is difficult to be met due to the high energies at which we expect
the quantum nature of gravity to become manifest. Here we study, how viable
quantum gravity proposals can be restricted by investigating the interplay of
gravitational and matter degrees of freedom. Specifically we demand that a
valid quantum theory of gravity must allow for the existence of light (compared
to the Planck scale) fermions, since we observe these in our universe. Within
the effective theory framework, we can thus show that UV completions for
gravity are restricted, regardless of the details of the microscopic theory.
Specialising to asymptotically safe quantum gravity, we find indications that
universes with light fermions are favoured within this UV completion for
gravity.Comment: 4 pages, based on a talk given at Loops '11, Madrid, to appear in
Journal of Physics: Conference Series (JPCS
Renormalization Flow of Axion Electrodynamics
We study the renormalization flow of axion electrodynamics, concentrating on
the non-perturbative running of the axion-photon coupling and the mass of the
axion (like) particle. Due to a non-renormalization property of the
axion-photon vertex, the renormalization flow is controlled by photon and axion
anomalous dimensions. As a consequence, momentum-independent axion
self-interactions are not induced by photon fluctuations. The non-perturbative
flow towards the ultraviolet exhibits a Landau-pole-type behavior, implying
that the system has a scale of maximum UV extension and that the renormalized
axion-photon coupling in the deep infrared is bounded from above. Even though
gauge invariance guarantees that photon fluctuations do not decouple in the
infrared, the renormalized couplings remain finite even in the deep infrared
and even for massless axions. Within our truncation, we also observe the
existence of an exceptional RG trajectory, which is extendable to arbitrarily
high scales, without being governed by a UV fixed point.Comment: 12 pages, 4 figure
The (Non-)Effect of Unemployment Benefits:Variations in the effect of unemployment on life-satisfaction between EU countries
Quantum-gravity-induced matter self-interactions in the asymptotic-safety scenario
We investigate the high-energy properties of matter theories coupled to
quantum gravity. Specifically, we show that quantum gravity fluctuations
generically induce matter self-interactions in a scalar theory. Our
calculations apply within asymptotically safe quantum gravity, where our
results indicate that the UV is dominated by an interacting fixed point, with
non-vanishing gravitational as well as matter couplings. In particular,
momentum-dependent scalar self-interactions are non-zero and induce a
non-vanishing momentum-independent scalar potential. Furthermore we point out
that terms of this type can have observable consequences in the context of
scalar-field driven inflation, where they can induce potentially observable
non-Gaussianities in the CMB.Comment: 15 + 8 pages, 8 figures, extended truncation, version to be published
in PR
Intrinsic Ratchets
We present a generic formalism to describe Brownian motion of particles with
intrinsic asymmetry and give predictions for the drift behavior in unbiased
time-dependent force fields. Our findings are supported by molecular dynamics
simulations.Comment: 6 pages, 6 figure
The Thermodynamic Cost of Erasing Information in Finite-time
The Landauer principle sets a fundamental thermodynamic constraint on the
minimum amount of heat that must be dissipated to erase one logical bit of
information through a quasi-statically slow protocol. For finite time
information erasure, the thermodynamic costs depend on the specific physical
realization of the logical memory and how the information is erased. Here we
treat the problem within the paradigm of a Brownian particle in a symmetric
double-well potential. The two minima represent the two values of a logical
bit, 0 and 1, and the particle's position is the current state of the memory.
The erasure protocol is realized by applying an external time-dependent tilting
force. We derive analytical tools to evaluate the work required to erase a
classical bit of information in finite time via an arbitrary continuous erasure
protocol, which is a relevant setting for practical applications. Importantly,
our method is not restricted to the average work, but instead gives access to
the full work distribution arising from many independent realizations of the
erasure process. Using the common example of an erasure protocol that changes
linearly with time acting on a double-parabolic potential, we explicitly
calculate all relevant quantities and verify them numerically.Comment: 21 pages, 8 figure
Evolutionary multi-stage financial scenario tree generation
Multi-stage financial decision optimization under uncertainty depends on a
careful numerical approximation of the underlying stochastic process, which
describes the future returns of the selected assets or asset categories.
Various approaches towards an optimal generation of discrete-time,
discrete-state approximations (represented as scenario trees) have been
suggested in the literature. In this paper, a new evolutionary algorithm to
create scenario trees for multi-stage financial optimization models will be
presented. Numerical results and implementation details conclude the paper
Thermocurrents and their Role in high Q Cavity Performance
Over the past years it became evident that the quality factor of a
superconducting cavity is not only determined by its surface preparation
procedure, but is also influenced by the way the cavity is cooled down.
Moreover, different data sets exists, some of them indicate that a slow
cool-down through the critical temperature is favourable while other data
states the exact opposite. Even so there where speculations and some models
about the role of thermo-currents and flux-pinning, the difference in behaviour
remained a mystery. In this paper we will for the first time present a
consistent theoretical model which we confirmed by data that describes the role
of thermo-currents, driven by temperature gradients and material transitions.
We will clearly show how they impact the quality factor of a cavity, discuss
our findings, relate it to findings at other labs and develop mitigation
strategies which especially addresses the issue of achieving high quality
factors of so-called nitrogen doped cavities in horizontal test
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