33 research outputs found
Lensing with generalized symmetrons
Generalized symmetrons are models that have qualitatively similar features to
the archetypal symmetron, but have barely been studied. In this article, we
investigate for what parameter values the fifth forces induced by disformally
coupling generalized symmetrons can provide an explanation for the difference
between baryonic and lens masses of galaxies. While it is known that the
standard symmetron struggles with providing an alternative source for the
lensing otherwise attributed to particle dark matter, we show that some
generalized symmetron models are more suitable for complying with existing
constraints on disformal couplings. This motivates future studies of these only
little explored models.Comment: 18 pages, 4 figure
Quantum simulation of dark energy candidates
Additional scalar fields from scalar-tensor, modified gravity or higher
dimensional theories beyond general relativity may account for dark energy and
the accelerating expansion of the Universe. These theories have lead to
proposed models of screening mechanisms, such as chameleon and symmetron
fields, to account for the tight experimental bounds on fifth-force searches.
Cold atom systems have been very successfully used to constrain the parameters
of these screening models, and may in future eliminate the interesting
parameter space of some models entirely. In this paper, we show how to
manipulate a Bose-Einstein condensate to simulate the effect of any screened
scalar field model coupled conformally to the metric. We give explicit
expressions for the simulation of various common models. This result may be
useful for investigating the computationally challenging evolution of particles
on a screened scalar field background, as well as for testing the metrology
scheme of an upcoming detector proposal.Comment: 26 pages, 3 figure
A new method for directly computing reduced density matrices
We demonstrate the power of a first principle-based and practicable method
that allows for the perturbative computation of reduced density matrix elements
of an open quantum system without making use of any master equations. The
approach is based on techniques from non-equilibrium quantum field theory like
thermo field dynamics, the Schwinger-Keldsyh formalism, and the Feynman-Vernon
influence functional. It does not require the Markov approximation and is
essentially a Lehmann-Szymanzik-Zimmermann-like reduction. In order to
illustrate this method, we consider a real scalar field as an open quantum
system interacting with an environment comprising another real scalar field. We
give a general formula that allows for the perturbative computation of density
matrix elements for any number of particles in a momentum basis. Finally, we
consider a simple toy model and use this formula to obtain expressions for some
of the system's reduced density matrix elements.Comment: 25 pages, 12 figure
Astro- and Quantum Physical Tests of Screened Scalar Fields
In general, modified gravity theories are modifications or extensions of
Einstein's general relativity. Some of them give rise to additional scalar
degrees of freedom in Nature. If these scalar fields exist and are light
enough, they should cause a gravity-like fifth force that could, in principle,
exceed gravity in its strength. However, there are tight constraints on fifth
forces from Solar System-based tests. Screening mechanisms are popular means
for avoiding these constraints by suppressing a fifth force in regions of high
environmental mass density but allowing for phenomenologically interesting
effects in environments of lower densities. In this thesis, scalar field models
with screening mechanisms will be discussed and some astro- and quantum
physical tests for their existence presented. At first, the impact of
disformally coupled symmetrons on gravitational lensing by galaxies will be
evaluated. Secondly, it will be shown how fluctuations of a chameleon scalar
field induce the open dynamics of a quantum test particle. For this, tools from
non-equilibrium quantum field theory will be introduced, developed and applied,
and a quantum master equation derived.Comment: PhD thesis; 140 page
Green's function analysis of the Neutron Lloyd interferometer
The neutron optical Lloyd interferometer can serve as a potent experiment for
probing fundamental physics beyond the standard models of particles and
cosmology. In this article, we provide a full Green's function analysis of a
Lloyd interferometer in the limit that the reflecting mirror extends to the
screen. We consider two distinct situations: first, we will review the
theoretical case of no external fields being present. Subsequently, we will
analyze the case in which a gravitational field is acting on the neutrons. The
latter case provides the theory necessary for using a Lloyd interferometer as a
probe of gravitational fields.Comment: 14 pages, 2 figures, as published in Zeitschrift f\"ur Naturforschung
Astro- and Quantum Physical Tests of Screened Scalar Fields
In general, modified gravity theories are modifications or extensions of Einstein's general relativity. Some of them give rise to additional scalar degrees of freedom in Nature. If these scalar fields exist and are light enough, they should cause a gravity-like fifth force that could, in principle, exceed gravity in its strength. However, there are tight constraints on fifth forces from Solar System based tests. Screening mechanisms are popular means for avoiding these constraints by suppressing a fifth force in regions of high environmental mass density but allowing for phenomenologically interesting effects in environments of lower densities.
In this thesis, scalar field models with screening mechanisms will be discussed and some astro- and quantum physical tests for their existence presented. At first, the impact of disformally coupled symmetrons on gravitational lensing by galaxies will be evaluated. Secondly, it will be shown how fluctuations of a chameleon scalar field induce the open dynamics of a quantum test particle. For this, tools from non-equilibrium quantum field theory will be introduced, developed and applied, and a quantum master equation derived
Quantum-enhanced screened dark energy detection
We propose an experiment based on a Bose–Einstein condensate interferometer for strongly constraining fifth-force models. Additional scalar fields from modified gravity or higher dimensional theories may account for dark energy and the accelerating expansion of the Universe. These theories have led to proposed screening mechanisms to fit within the tight experimental bounds on fifth-force searches. We show that our proposed experiment would greatly improve the existing constraints on these screening models by many orders of magnitude
Quantum-enhanced screened dark energy detection
We propose an experiment based on a Bose-Einstein condensate interferometer
for strongly constraining fifth-force models. Additional scalar fields from
modified gravity or higher dimensional theories may account for dark energy and
the accelerating expansion of the Universe. These theories have led to proposed
screening mechanisms to fit within the tight experimental bounds on fifth-force
searches. We show that our proposed experiment would greatly improve the
existing constraints on these screening models by many orders of magnitude,
entirely eliminating the remaining parameter space of the simplest of these
models.Comment: 20 pages, 6 figure