553 research outputs found
Strengthening extended Gravity constraints with combined systems:\\ \texorpdfstring{}{} bounds from Cosmology and the Galactic Center
MOdified Gravity (MoG)) is widely constrained in different astrophysical and
astronomical systems. Since these different systems are based on different
scales it is not trivial to get a combined constraint that is based on
different phenomenology. Here, for the first time (to the best of our
knowledge), we combine constraints for MoG from late time Cosmology and the
orbital motion of the stars around the galactic center. MoG give different
potentials that are tested directly in the galactic center. The cosmological
data set includes the type Ia supernova and baryon acoustic oscillations. For
the galactic star center data set we use the published orbital measurements of
the S2 star. The constraints on the universal parameter from the
combined system give: for the Hu-Sawicki model,
while for the Starobinsky model. These results
improve on the cosmological results we obtain. The results show that {{\it
combined constraint}} from different systems yields a stronger constraint for
different theories under consideration. Future measurements from the galactic
center and from cosmology will give better constraints on MoG.Comment: 8 pages, 2 figure
Carrier relaxation in GaAs v-groove quantum wires and the effects of localization
Carrier relaxation processes have been investigated in GaAs/AlGaAs v-groove
quantum wires (QWRs) with a large subband separation (46 meV). Signatures of
inhibited carrier relaxation mechanisms are seen in temperature-dependent
photoluminescence (PL) and photoluminescence-excitation (PLE) measurements; we
observe strong emission from the first excited state of the QWR below ~50 K.
This is attributed to reduced inter-subband relaxation via phonon scattering
between localized states. Theoretical calculations and experimental results
indicate that the pinch-off regions, which provide additional two-dimensional
confinement for the QWR structure, have a blocking effect on relaxation
mechanisms for certain structures within the v-groove. Time-resolved PL
measurements show that efficient carrier relaxation from excited QWR states
into the ground state, occurs only at temperatures > 30 K. Values for the low
temperature radiative lifetimes of the ground- and first excited-state excitons
have been obtained (340 ps and 160 ps respectively), and their corresponding
localization lengths along the wire estimated.Comment: 9 pages, 8 figures, submitted to Phys. Rev. B Attempted to correct
corrupt figure
Constraining Dark Energy from Local Group dynamics
This Letter develops a method to constrain the Cosmological Constant
from binary galaxies, focusing on the Milky Way and Andromeda. We
provide an analytical solution to the two-body problem with and show
that the ratio between the Keplerian period and Gyr controls the importance of effects from the
Cosmological Constant. The Andromeda-Milky Way orbit has a period of
Gyr and so Dark Energy has to be taken into account. Using the current best
mass estimates of the Milky Way and Andromeda galaxies, we find the
Cosmological Constant value based only on the Local Group dynamics to be lower
then times the value obtained by Planck. With future astrometric
measurements, the bound on the Cosmological Constant can be reduced to
. Our results offer the prospects
of constraints on over very different scales than previously. The
Local Group provides also a completely novel platform to test alternative
theories of gravity. We illustrate this by deriving bounds on scalar-tensor
theories of gravity over Megaparsec scales.Comment: ApJL, submitte
Quintessential inflation and cosmological seesaw Mechanism: reheating and observational constraints
Recently a new kind of quintessential inflation coming from the Lorentzian
distribution has been introduced in [1,2]. The model leads to a very simple
potential, which basically depends on two parameters, belonging to the class of
-attractors and depicting correctly the early and late time
accelerations of our universe. The potential emphasizes a {\it cosmological
seesaw mechanism} (CSSM) that produces a large inflationary vacuum energy in
one side of the potential and a very small value of dark energy on the right
hand side of the potential. {Here we show that the model agrees with the recent
observations and with the reheating constraints. Therefore the model gives a
reasonable scenario beyond the standard CDM that includes the
inflationary epoch.}Comment: 9 pages; 5 figures; accepted for publishing in JCA
An Inner Disk in the Large Gap of the Transition Disk SR 24S
We report new Atacama Large Millimeter/sub-millimeter Array (ALMA) Band 3
observations at 2.75 mm of the TD around SR 24S with an angular resolution of
0.11'' 0.09'' and a peak signal-to-noise ratio of . We
detect an inner disk and a mostly symmetric ring-like structure that peaks at
0.32'', that is 37 au at a distance of 114.4 pc. The full
width at half maximum of this ring is 28 au. We analyze the observed
structures by fitting the dust continuum visibilities using different models
for the intensity profile, and compare with previous ALMA observations of the
same disk at 0.45 mm and 1.30 mm. We qualitatively compare the results of these
fits with theoretical predictions of different scenarios for the formation of a
cavity or large gap. The comparison of the dust continuum structure between
different ALMA bands indicates that photoevaporation and dead zone can be
excluded as leading mechanisms for the cavity formation in SR 24S disk, leaving
the planet scenario (single or multiple planets) as the most plausible
mechanism. We compared the 2.75 mm emission with published (sub-)centimeter
data and find that the inner disk is likely tracing dust thermal emission. This
implies that any companion in the system should allow dust to move inwards
throughout the gap and replenish the inner disk. In the case of one single
planet, this puts strong constraints on the mass of the potential planet inside
the cavity and the disk viscosity of about 5 and
, respectively
Linear Potentials in Galaxy Halos by Asymmetric Wormholes
A spherically symmetric space-time solution for a diffusive two measures theory is studied. An asymmetric wormhole geometry is obtained where the metric coefficients has a linear term for galactic distances and the analysis of Mannheim and collaborators, can then be used to describe the galactic rotation curves. For cosmological distances a de-Sitter space-time is realized. Center of gravity coordinates for the wormhole are introduced which are the most suitable for the collective motion of a wormhole. The wormholes connect universes with different vacuum energy densities which may represent different universes in a “landscape scenario”. The metric coefficients depend on the asymmetric wormhole parameters. The coefficient of the linear potential is proportional to both the mass of the wormhole and the cosmological constant of the observed universe. Similar results are also expected in other theories like k-essence theories, that may support wormholes
Gap maps and intrinsic diffraction losses in one-dimensional photonic crystal slabs
A theoretical study of photonic bands for one-dimensional (1D) lattices
embedded in planar waveguides with strong refractive index contrast is
presented. The approach relies on expanding the electromagnetic field on the
basis of guided modes of an effective waveguide, and on treating the coupling
to radiative modes by perturbation theory. Photonic mode dispersion, gap maps,
and intrinsic diffraction losses of quasi-guided modes are calculated for the
case of self-standing membranes as well as for Silicon-on-Insulator structures.
Photonic band gaps in a waveguide are found to depend strongly on the core
thickness and on polarization, so that the gaps for transverse electric and
transverse magnetic modes most often do not overlap. Radiative losses of
quasi-guided modes above the light line depend in a nontrivial way on structure
parameters, mode index and wavevector. The results of this study may be useful
for the design of integrated 1D photonic structures with low radiative losses.Comment: 9 pages, 8 figures, submitted to Physical Review
Optically Driven Qubits in Artificial Molecules
We present novel models of quantum gates based on coupled quantum dots in
which a qubit is regarded as the superposition of ground states in each dot.
Coherent control on the qubit is performed by both a frequency and a
polarization of a monochromatic light pulse illuminated on the quantum dots. We
also show that a simple combination of two single qubit gates functions as a
controlled NOT gate resulting from an electron-electron interaction. To examine
the decoherence of quantum states, we discuss electronic relaxation contributed
mainly by LA phonon processes.Comment: 11 pages, 4 figures, submitted to Physical Review
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