12,467 research outputs found
Limits on Non-Linear Electrodynamics
In this paper we set a framework in which experiments whose goal is to test
QED predictions can be used in a more general way to test non-linear
electrodynamics (NLED) which contains low-energy QED as a special case. We
review some of these experiments and we establish limits on the different free
parameters by generalizing QED predictions in the framework of NLED. We finally
discuss the implications of these limits on bound systems and isolated charged
particles for which QED has been widely and successfully tested
Characterization of the Vacuum Birefringence Polarimeter at BMV: Dynamical Cavity Mirror Birefringence
We present the current status and outlook of the optical characterization of
the polarimeter at the Bir\'{e}fringence Magn\'etique du Vide (BMV) experiment.
BMV is a polarimetric search for the QED predicted anisotropy of vacuum in the
presence of external electromagnetic fields. The main challenge faced in this
fundamental test is the measurement of polarization ellipticity on the order of
induced in linearly polarized laser field per pass through a
magnetic field having an amplitude and length
. This challenge is addressed by
understanding the noise sources in precision cavity-enhanced polarimetry. In
this paper we discuss the first investigation of dynamical birefringence in the
signal-enhancing cavity as a result of cavity mirror motion.Comment: To appear in the 2019 CPEM special issue of IEEE Transactions on
Instrumentation and Measuremen
Noise characterization for resonantly-enhanced polarimetric vacuum magnetic-birefringence experiments
In this work we present data characterizing the sensitivity of the
Bir\'{e}fringence Magnetique du Vide (BMV) instrument. BMV is an experiment
attempting to measure vacuum magnetic birefringence (VMB) via the measurement
of an ellipticity induced in a linearly polarized laser field propagating
through a birefringent region of vacuum in the presence of an external magnetic
field. Correlated measurements of laser noise alongside the measurement in the
main detection channel allow us to separate measured sensing noise from the
inherent birefringence noise of the apparatus. To this end we model different
sources of sensing noise for cavity-enhanced polarimetry experiments, such as
BMV. Our goal is to determine the main sources of noise, clarifying the
limiting factors of such an apparatus. We find our noise models are compatible
with the measured sensitivity of BMV. In this context we compare the phase
sensitivity of separate-arm interferometers to that of a polarimetry apparatus
for the discussion of current and future VMB measurements
Zero-Temperature Limit of the SUSY-breaking Complexity in Diluted Spin-Glass Models
We study the SUSY-breaking complexity of the Bethe Lattice Spin-Glass in the
zero temperature limit. We consider both the Gaussian and the bimodal
distribution of the coupling constants. For the SUSY breaking
theory yields fields distributions that concentrate on integer values at low
temperatures, at variance with the unbroken SUSY theory. This concentration
takes place both in the quenched as well as in the simpler annealed
formulation.Comment: 4 pages, 2 figure
Vacuum magnetic linear birefringence using pulsed fields: the BMV experiment
We present the current status of the BMV experiment. Our apparatus is based
on an up-to-date resonant optical cavity coupled to a transverse magnetic
field. We detail our data acquisition and analysis procedure which takes into
account the symmetry properties of the raw data with respect to the orientation
of the magnetic field and the sign of the cavity birefringence. The measurement
result of the vacuum magnetic linear birefringence k_\mathrm{CM}8 \times 10^{-21}^{-2}3\sigma$ confidence level
The Dynamical Dipole Mode in Fusion Reactions with Exotic Nuclear Beams
We report the properties of the prompt dipole radiation, produced via a
collective bremsstrahlung mechanism, in fusion reactions with exotic beams. We
show that the gamma yield is sensitive to the density dependence of the
symmetry energy below/around saturation. Moreover we find that the angular
distribution of the emitted photons from such fast collective mode can
represent a sensitive probe of its excitation mechanism and of fusion dynamics
in the entrance channel.Comment: 5 pages, 3 figures, to appear in Phys.Rev.
Observation of the Inverse Cotton-Mouton Effect
We report the observation of the Inverse Cotton-Mouton Effect (ICME) i.e. a
magnetization induced in a medium by non resonant linearly polarized light
propagating in the presence of a transverse magnetic field. We present a
detailed study of the ICME in a TGG crystal showing the dependence of the
measured effect on the light intensity, the optical polarization, and on the
external magnetic field. We derive a relation between the Cotton-Mouton and
Inverse Cotton-Mouton effects that is roughly in agreement with existing
experimental data. Our results open the way to applications of the ICME in
optical devices
Collider Production of TeV Scale Black Holes and Higher-Curvature Gravity
We examine how the production of TeV scale black holes at colliders is
influenced by the presence of Lovelock higher-curvature terms in the action of
models with large extra dimensions. Such terms are expected to arise on rather
general grounds, e.g., from string theory and are often used in the literature
to model modifications to the Einstein-Hilbert action arising from quantum
and/or stringy corrections. While adding the invariant which is quadratic in
the curvature leads to quantitative modifications in black hole properties,
cubic and higher invariants are found to produce significant qualitative
changes, e.g., classically stable black holes. We use these higher-order
curvature terms to construct a toy model of the black hole production cross
section threshold. For reasonable parameter values we demonstrate that detailed
measurements of the properties of black holes at future colliders will be
highly sensitive to the presence of the Lovelock higher-order curvature terms.Comment: 37 pages, 11 figures, references adde
Ammonia observations in the LBV nebula G79.29+0.46. Discovery of a cold ring and some warm spots
The surroundings of Luminous Blue Variable (LBV) stars are excellent
laboratories to study the effects of their high UV radiation, powerful winds,
and strong ejection events onto the surrounding gas and dust. The LBV
G79.29+0.46 powered two concentric infrared rings which may interact with the
infrared dark cloud (IRDC) G79.3+0.3. The Effelsberg 100m telescope was used to
observe the NH_3 (1,1), (2,2) emission surrounding G79.29+0.46 and the IRDC. In
addition, we observed particular positions in the (3,3) transition toward the
strongest region of the IRDC. We report here the first coherent shell-like
structure of dense NH_3 gas associated with an evolved massive star. The shell,
two or three orders of magnitude more tenuous than the IRDC, is well traced in
both ammonia lines, and surrounds the ionized nebula. The NH_3 emission in the
IRDC is characterized by a low and uniform rotational temperature (T_rot ~ 10
K) and moderately high opacities in the (1,1) line. The rest of the observed
field is spotted by warm or hot zones (T_rot > 30 K) and characterized by
optically thin emission of the (1,1) line. The NH_3 abundances are about
10^{-8} in the IRDC, and 10^{-10}-10^{-9} elsewhere. The warm temperatures and
low abundances of NH_3 in the shell suggest that the gas is being heated and
photo-dissociated by the intense UV field of the LBV star. An outstanding
region is found to the south-west (SW) of the LBV star within the IRDC. The
NH_3 (3,3) emission at the centre of the SW region reveals two velocity
components tracing gas at temperatures > 30K. The northern edge of the SW
region agrees with the border of the ring nebula and a region of continuum
enhancement; here, the opacity of the (1,1) line and the NH_3 abundance do not
decrease as expected in a typical clump of an isolated cold dark cloud. This
strongly suggests some kind of interaction between the ring nebula and the
IRDC.Comment: 15 pages, 13 figures, accepted by A&A. Note the change of title with
respect to previous versio
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