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 ${10^{-15}}$ induced in linearly polarized laser field per pass through a magnetic field having an amplitude and length ${B^{2}L=100\,\mathrm{T}^{2}\mathrm{m}}$. 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

Optical spectroscopy of a microsized Rb vapour sample in magnetic fields up to 58 tesla

We use a magnetometer probe based on the Zeeman shift of the rubidium resonant optical transition to explore the atomic magnetic response for a wide range of field values. We record optical spectra for fields from few tesla up to 60 tesla, the limit of the coil producing the magnetic field. The atomic absorption is detected by the fluorescence emissions from a very small region with a submillimiter size. We investigate a wide range of magnetic interactions from the hyperfine Paschen-Back regime to the fine one, and the transitions between them. The magnetic field measurement is based on the rubidium absorption itself. The rubidium spectroscopic constants were previously measured with high precision, except the excited state Land\'e $g$-factor that we derive from the position of the absorption lines in the transition to the fine Paschen-Back regime. Our spectroscopic investigation, even if limited by the Doppler broadening of the absorption lines, measures the field with a 20 ppm uncertainty at the explored high magnetic fields. Its accuracy is limited to 75 ppm by the excited state Land\'e $g$-factor determination

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

Chemical evolution in the environment of intermediate mass young stellar objects: NGC7129--FIRS2 and LkHα\alpha234

We have carried out a molecular survey of the Class 0 IM protostar NGC 7129 -- FIRS 2 (hereafter FIRS 2) and the Herbig Be star LkH$\alpha$ 234 with the aim of studying the chemical evolution of the envelopes of intermediate-mass (IM) young stellar objects (YSOs). Both objects have similar luminosities (~500 Lsun) and are located in the same molecular cloud which minimizes the chemical differences due to different stellar masses or initial cloud conditions. Moreover, since they are located at the same distance, we have the same spatial resolution in both objects. A total of 17 molecular species (including rarer isotopes) have been observed in both objects and the structure of their envelopes and outflows is determined with unprecedent detail. Our results show that the protostellar envelopes are dispersed and warmed up during the evolution to become a pre-main sequence star. In fact, the envelope mass decreases by a factor >5 from FIRS 2 to LkH$\alpha$234, while the kinetic temperature increases from ~13K to 28K. On the other hand, there is no molecular outflow associated with LkH$\alpha$234. The molecular outflow seems to stop before the star becomes visible. These physical changes strongly affect the chemistry of their envelopes. Based on our results in FIRS2 and LkH$\alpha$ 234, we propose some abundance ratios that can be used as chemical clocks for the envelopes of IM YSOs. The SiO/CS, CN/N2H+, HCN/N2H+, DCO+/HCO+ and D2CO/DCO+ ratios are good diagnostics of the protostellar evolutionary stage.Comment: 24 pages, 17 figure

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

Large Extra Dimensions at Linear Colliders

In this talk, I first present the motivation for theories wherein extra spacetime dimensions can be compactified to have large magnitudes. In particular, I discuss the Arkani-Hamed, Dimopoulos, Dvali (ADD) scenario. I present the constraints that have been derived on these models from current experiments and the expectations from future colliders. I concentrate particularly on the possibilities of probing these extra dimensions at future linear colliders.Comment: Talk given at the Third International Workshop on Electron-Electron Interactions at TeV Energies (e- e- 99), Santa Cruz, California, 10-12 Dec 1999. 7 pages, LaTeX, style files attache

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}$presented in this paper was obtained with about 200 magnetic pulses and a maximum field of 6.5\,T, giving a noise floor of about$8 \times 10^{-21}$\,T$^{-2}$at$3\sigma$ confidence level

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