Tensor Meson Production in Proton-Proton Collisions from the Color Glass Condensate

We compute the inclusive cross-section of $f_{2}$ tensor mesons production in proton-proton collisions at high-energy. We use an effective theory inspired from the tensor meson dominance hypothesis that couples gluons to $f_{2}$ mesons. We compute the differential cross-section in the $k_{\perp}$-factorization and in the Color Glass Condensate formalism in the low density regime. We show that the two formalisms are equivalent for this specific observable. Finally, we study the phenomenology of $f_{2}$ mesons by comparing theoretical predictions of different parameterizations of the unintegrated gluon distribution function. We find that $f_{2}$-meson production is another observable that can be used to put constraints on these distributions.Comment: 26 pages, 3 figures, to be submitted in Phys. Rev.

Penser la relation d’aide et de soin à partir du handicap: enjeux et ambivalences.

International audienceCet article est l'éditorial d'un premier numéro spécial de la revue Alter sur la thématique "Care et handicap". Un deuxième numéro suivra. Ces deux numéros spéciaux de la revue Alter autour de la thématique « care et handicap » ont pour objectif de prolonger le débat et le dialogue initiés entre différents courants de pensée sur la nature de la relation d’aide, sur ses effets en termes de qualification et de définition des personnes (aidantes comme aidées), sur ses ambivalences et tensions inhérentes. Ils reviennent notamment sur le débat entre Disability Studies et Ethique du care

Resonantly enhanced pair production in a simple diatomic model

A new mechanism for the production of electron-positron pairs from the interaction of a laser field and a fully stripped diatomic molecule in the tunneling regime is presented. When the laser field is turned off, the Dirac operator has resonances in both the positive and the negative energy continua while bound states are in the mass gap. When this system is immersed in a strong laser field, the resonances move in the complex energy plane: the negative energy resonances are pushed to higher energies while the bound states are Stark shifted. It is argued here that there is a pair production enhancement at the crossing of resonances by looking at a simple 1-D model: the nuclei are modeled simply by Dirac delta potential wells while the laser field is assumed to be static and of finite spatial extent. The average rate for the number of electron-positron pairs produced is evaluated and the results are compared to the single nucleus and to the free cases. It is shown that positrons are produced by the Resonantly Enhanced Pair Production (REPP) mechanism, which is analogous to the resonantly enhanced ionization of molecular physics. This phenomenon could be used to increase the number of pairs produced at low field strength, allowing the study of the Dirac vacuum.Comment: 11 pages, 4 figure

Magnetic properties of HO2 thin films

We report on the magnetic and transport studies of hafnium oxide thin films grown by pulsed-laser deposition on sapphire substrates under different oxygen pressures, ranging from 10-7 to 10-1 mbar. Some physical properties of these thin films appear to depend on the oxygen pressure during growth: the film grown at low oxygen pressure (P ~= 10-7 mbar) has a metallic aspect and is conducting, with a positive Hall signal, while those grown under higher oxygen pressures (7 x 10-5 <= P <= 0.4 mbar) are insulating. However, no intrinsic ferromagnetic signal could be attributed to the HfO2 films, irrespective of the oxygen pressure during the deposition.Comment: 1

Landau-Zener-St\"uckelberg interferometry in pair production from counterpropagating lasers

The rate of electron-positron pair production in linearly polarized counter-propagating lasers is evaluated from a recently discovered solution of the time-dependent Dirac equation. The latter is solved in momentum space where it is formally equivalent to the Schr\"odinger equation describing a strongly driven two-level system. The solution is found from a simple transformation of the Dirac equation and is given in compact form in terms of the doubly-confluent Heun's function. By using the analogy with the two-level system, it is shown that for high-intensity lasers, pair production occurs through periodic non-adiabatic transitions when the adiabatic energy gap is minimal. These transitions give rise to an intricate interference pattern in the pair spectrum, reminiscent of the Landau-Zener-St\"uckelberg phenomenon in molecular physics: the accumulated phase result in constructive or destructive interference. The adiabatic-impulse model is used to study this phenomenon and shows an excellent agreement with the exact result.Comment: 22 pages, 7 figure

Indirect ultraviolet photodesorption from CO:N2 binary ices - an efficient grain-gas process

UV ice photodesorption is an important non-thermal desorption pathway in many interstellar environments that has been invoked to explain observations of cold molecules in disks, clouds and cloud cores. Systematic laboratory studies of the photodesorption rates, between 7 and 14 eV, from CO:N2 binary ices, have been performed at the DESIRS vacuum UV beamline of the synchrotron facility SOLEIL. The photodesorption spectral analysis demonstrates that the photodesorption process is indirect, i.e. the desorption is induced by a photon absorption in sub-surface molecular layers, while only surface molecules are actually desorbing. The photodesorption spectra of CO and N2 in binary ices therefore depend on the absorption spectra of the dominant species in the subsurface ice layer, which implies that the photodesorption efficiency and energy dependence are dramatically different for mixed and layered ices compared to pure ices. In particular, a thin (1-2 ML) N2 ice layer on top of CO will effectively quench CO photodesorption, while enhancing N2 photodesorption by a factors of a few (compared to the pure ices) when the ice is exposed to a typical dark cloud UV field, which may help to explain the different distributions of CO and N2H+ in molecular cloud cores. This indirect photodesorption mechanism may also explain observations of small amounts of complex organics in cold interstellar environments.Comment: 21 pages 5 figure

Explicit volume-preserving numerical schemes for relativistic trajectories and spin dynamics

A class of explicit numerical schemes is developed to solve for the relativistic dynamics and spin of particles in electromagnetic fields, using the Lorentz-BMT equation formulated in the Clifford algebra representation of Baylis. It is demonstrated that these numerical methods, reminiscent of the leapfrog and Verlet methods, share a number of important properties: they are energy-conserving, volume-conserving and second order convergent. These properties are analysed empirically by benchmarking against known analytical solutions in constant uniform electrodynamic fields. It is demonstrated that the numerical error in a constant magnetic field remains bounded for long time simulations in contrast to the Boris pusher, whose angular error increases linearly with time. Finally, the intricate spin dynamics of a particle is investigated in a plane wave field configuration.Comment: 15 pages, 9 figure