1,519 research outputs found
The Lorentz and CPT violating effects on the Z\to l^+ l^- decay
We study the Lorentz and CPT violating effects on the branching ratio BR, the
CPT violating asymmetry A_{CPT} and the ratio of the decay width, including
only the Lorentz violating effects, to the one obtained in the standard model,
for the flavor dependent part of the lepton flavor conserving Z\to l^+ l^-
(l=e,\mu,\tau) decay. The inclusion of the Lorentz and CPT violating effects to
the standard model contribution is too small to be detected, since the
corresponding coefficients are highly suppressed at the low energy scale.Comment: 11 pages, 6 figure
CPT and Lorentz-invariance violation
The largest gap in our understanding of nature at the fundamental level is
perhaps a unified description of gravity and quantum theory. Although there are
currently a variety of theoretical approaches to this question, experimental
research in this field is inhibited by the expected Planck-scale suppression of
quantum-gravity effects. However, the breakdown of spacetime symmetries has
recently been identified as a promising signal in this context: a number of
models for underlying physics can accommodate minuscule Lorentz and CPT
violation, and such effects are amenable to ultrahigh-precision tests. This
presentation will give an overview of the subject. Topics such as motivations,
the SME test framework, mechanisms for relativity breakdown, and experimental
tests will be reviewed. Emphasis is given to observations involving antimatter.Comment: 6 page
When the Milky Way turned off the lights: APOGEE provides evidence of star formation quenching in our Galaxy
Quenching, the cessation of star formation, is one of the most significant
events in the life cycle of galaxies. We show here the first evidence that the
Milky Way experienced a generalised quenching of its star formation at the end
of its thick disk formation 9 Gyr ago. Elemental abundances of stars
studied as part of the APOGEE survey reveal indeed that in less than 2
Gyr the star formation rate in our Galaxy dropped by an order-of-magnitude.
Because of the tight correlation between age and alpha abundance, this event
reflects in the dearth of stars along the inner disk sequence in the
[Fe/H]-[/Fe] plane. Before this phase, which lasted about 1.5 Gyr, the
Milky Way was actively forming stars. Afterwards, the star formation resumed at
a much lower level to form the thin disk. These events are very well matched by
the latest observation of MW-type progenitors at high redshifts. In late type
galaxies, quenching is believed to be related to a long and secular exhaustion
of gas. In our Galaxy, it occurred on a much shorter time scale, while the
chemical continuity before and after the quenching indicates that it was not
due to the exhaustion of the gas. While quenching is generally associated with
spheroids, our results show that it also occurs in galaxies like the Milky Way,
possibly when they are undergoing a morphological transition from thick to thin
disks. Given the demographics of late type galaxies in the local universe, in
which classical bulges are rare, we suggest further that this may hold true
generally in galaxies with mass lower than or approximately , where
quenching could be directly a consequence of thick disk formation. We emphasize
that the quenching phase in the Milky Way could be contemporaneous with, and
related to, the formation of the bar. We sketch a scenario on how a strong bar
may inhibit star formation.Comment: 17 pages, 8 figures. Published versio
Vacuum Cherenkov radiation
Within the classical Maxwell-Chern-Simons limit of the Standard-Model
Extension (SME), the emission of light by uniformly moving charges is studied
confirming the possibility of a Cherenkov-type effect. In this context, the
exact radiation rate for charged magnetic point dipoles is determined and found
in agreement with a phase-space estimate under certain assumptions.Comment: 4 pages, REVTeX
Protecting backaction-evading measurements from parametric instability
Noiseless measurement of a single quadrature in systems of parametrically
coupled oscillators is theoretically possible by pumping at the sum and
difference frequencies of the two oscillators, realizing a backaction-evading
(BAE) scheme. Although this would hold true in the simplest scenario for a
system with pure three-wave mixing, implementations of this scheme are hindered
by unwanted higher-order parametric processes that destabilize the system and
add noise. We show analytically that detuning the two pumps from the sum and
difference frequencies can stabilize the system and fully recover the BAE
performance, enabling operation at otherwise inaccessible cooperativities. We
also show that the acceleration demonstrated in a weak signal detection
experiment [PRX QUANTUM 4, 020302 (2023)] was only achievable because of this
detuning technique.Comment: 7 pages, 3 figure
Reconstructing the star formation history of the Milky Way disc(s) from chemical abundances
We develop a chemical evolution model in order to study the star formation
history of the Milky Way. Our model assumes that the Milky Way is formed from a
closed box-like system in the inner regions, while the outer parts of the disc
experience some accretion. Unlike the usual procedure, we do not fix the star
formation prescription (e.g. Kennicutt law) in order to reproduce the chemical
abundance trends. Instead, we fit the abundance trends with age in order to
recover the star formation history of the Galaxy. Our method enables one to
recover with unprecedented accuracy the star formation history of the Milky Way
in the first Gyrs, in both the inner (R9-10kpc) discs as
sampled in the solar vicinity. We show that, in the inner disc, half of the
stellar mass formed during the thick disc phase, in the first 4-5 Gyr. This
phase was followed by a significant dip in the star formation activity (at 8-9
Gyr) and a period of roughly constant lower level star formation for the
remaining 8 Gyr. The thick disc phase has produced as many metals in 4 Gyr as
the thin disc in the remaining 8 Gyr. Our results suggest that a closed box
model is able to fit all the available constraints in the inner disc. A closed
box system is qualitatively equivalent to a regime where the accretion rate, at
high redshift, maintains a high gas fraction in the inner disc. In such
conditions, the SFR is mainly governed by the high turbulence of the ISM. By
z~1 it is possible that most of the accretion takes place in the outer disc,
while the star formation activity in the inner disc is mostly sustained by the
gas not consumed during the thick disc phase, and the continuous ejecta from
earlier generations of stars. The outer disc follows a star formation history
very similar to that of the inner disc, although initiated at z~2, about 2 Gyr
before the onset of the thin disc formation in the inner disc.Comment: 30 pages, 18 figures, 3 tables, accepted by A&A - minor stylistic
change
Concerns of Ageing and Interest in Assistive Technologies – Convenience Sampling of Attendees at an Aged Care Technology Exhibition in China
Part 7: e-Health, the New Frontier of Service Science InnovationInternational audienceAs in many countries, ageing and aged care in China is an important issue. There is a need for more research on the potential for technology to assist older people and their families, particularly given the disappointing levels of adoption in developed countries. Accordingly this paper aims to gain insight into the perceptions of older people and stakeholders in relation to issues of ageing and their interest in adoption of technology. Using convenience sampling, the authors surveyed 277 participants to understand peoples concerns concerning ageing and use of technologies. Results from this study provide a basis for discussion with stakeholders, particularly concerning ageing in China
Smart Focal Plane Technologies for VLT Instruments
As we move towards the era of ELTs, it is timely to think about the future
role of the 8-m class telescopes. Under the OPTICON programme, novel
technologies have been developed that are intended for use in multi-object and
integral-field spectrographs. To date, these have been targeted at instrument
concepts for the European ELT, but there are also significant possibilities for
their inclusion in new VLT instruments, ensuring the continued success and
productivity of these unique telescopes.Comment: 5 pages, to appear in the proceedings of the ESO Workshop "Science
with the VLT in the ELT era
Synchronisation in networks of delay-coupled type-I excitable systems
We use a generic model for type-I excitability (known as the SNIPER or SNIC
model) to describe the local dynamics of nodes within a network in the presence
of non-zero coupling delays. Utilising the method of the Master Stability
Function, we investigate the stability of the zero-lag synchronised dynamics of
the network nodes and its dependence on the two coupling parameters, namely the
coupling strength and delay time. Unlike in the FitzHugh-Nagumo model (a model
for type-II excitability), there are parameter ranges where the stability of
synchronisation depends on the coupling strength and delay time. One important
implication of these results is that there exist complex networks for which the
adding of inhibitory links in a small-world fashion may not only lead to a loss
of stable synchronisation, but may also restabilise synchronisation or
introduce multiple transitions between synchronisation and desynchronisation.
To underline the scope of our results, we show using the Stuart-Landau model
that such multiple transitions do not only occur in excitable systems, but also
in oscillatory ones.Comment: 10 pages, 9 figure
Single-shot measurement of the Josephson charge qubit
We demonstrate single-shot readout of quantum states of the Josephson charge
qubit. The quantum bits are transformed into and stored as classical bits
(charge quanta) in a dynamic memory cell - a superconducting island. The
transformation of state |1> (differing form state |0> by an extra Cooper pair)
is a result of a controllable quasiparticle tunneling to the island. The charge
is then detected by a conventional single-electron transistor,
electrostatically decoupled from the qubit. We study relaxation dynamics in the
system and obtain the readout efficiency of 87% and 93% for |1> and |0> states,
respectively.Comment: submitted to Rapid Communications of Phys. Rev. B (february 2004
- …