Motion-Induced Radiation Due to an Atom in the Presence of a Graphene Plane

We study the motion-induced radiation due to the non-relativistic motion of an atom, coupled to the vacuum electromagnetic field by an electric dipole term, in the presence of a static graphene plate. After computing the probability of emission for an accelerated atom in empty space, we evaluate the corrections due to the presence of the plate. We show that the effect of the plate is to increase the probability of emission when the atom is near the plate and oscillates along a direction perpendicular to it. On the contrary, for parallel oscillations, there is a suppression. We also evaluate the quantum friction on an atom moving at constant velocity parallel to the plate. We show that there is a threshold for quantum friction: friction occurs only when the velocity of the atom is larger than the Fermi velocity of the electrons in graphene.

Observations of GRO J1744–28 in quiescence with XMM-Newton

We report on the deep observations of the “bursting pulsar” GRO J1744–28, which were performed with XMM-Newton and aimed to clarify the origin of its X-ray emission in quiescence. We detect the source at a luminosity level of ∼1034 erg s−1 with an X-ray spectrum that is consistent with the power law, blackbody, or accretion-heated neutron star atmosphere models. The improved X-ray localization of the source allowed us to confirm the previously identified candidate optical counterpart as a relatively massive G/K III star at 8 kpc close to the Galactic center, implying an almost face-on view of the binary system. Although we could only find a nonrestricting upper limit on the pulsed fraction of ∼20%, the observed hard X-ray spectrum and strong long-term variability of the X-ray flux suggest that the source is also still accreting when not in outburst. The luminosity corresponding to the onset of centrifugal inhibition of accretion is thus estimated to be at least two orders of magnitude lower than previously reported. We discuss this finding in the context of previous studies and argue that the results indicate a multipole structure in the magnetic field with the first dipole term of ∼1010 G, which is much lower than previously assumed.

Shot noise in multitracer constraints on fNL and relativistic projections: Power spectrum

ABSTRACT Multiple tracers of the same surveyed volume can enhance the signal-to-noise on a measurement of local primordial non-Gaussianity and the relativistic projections. Increasing the number of tracers comparably increases the number of shot noise terms required to describe the stochasticity of the data. Although the shot noise is white on large scales, it is desirable to investigate the extent to which it can degrade constraints on the parameters of interest. In a multitracer analysis of the power spectrum, a marginalization over shot noise does not degrade the constraints on fNL by more than ∼30 per cent so long as haloes of mass $M\lesssim 10^{12}\, \mathrm{M}_\odot$ are resolved. However, ignoring cross shot noise terms induces large systematics on a measurement of fNL at redshift z < 1 when small mass haloes are resolved. These effects are less severe for the relativistic projections, especially for the dipole term. In the case of a low and high mass tracer, the optimal sample division maximizes the signal-to-noise on fNL and the projection effects simultaneously, reducing the errors to the level of ∼10 consecutive mass bins of equal number density. We also emphasize that the non-Poissonian noise corrections that arise from small-scale clustering effects cannot be measured with random dilutions of the data. Therefore, they must either be properly modelled or marginalized over.

τ−→ ℓi−ℓi+ℓj−ν̄jντ decays with a magnetic dipole term

Using the massive helicity formalism, we calculate the five-body average square amplitude of the decays [Formula: see text] [Formula: see text] within the Standard Model (SM), we then introduce a dimension-five effective vertex [Formula: see text] in order to determine the feasibility of imposing limits on the tau anomalous magnetic dipole moment [Formula: see text] via the current or future experimental measurements of the branching ratio for the decay [Formula: see text].

Virial coefficients of nitrogen from a quadrupolar site–site potential function

This work describes a procedure for the numerical calculation of third virial coefficients of simple linear molecules. The method is applied to nitrogen using a site–site model pair-potential and the triple dipole term. Values of volumetric and acoustic second and third virial coefficients of nitrogen are reported over a wide range of temperature and compared with experimental data of several authors. The effect of including the quadrupole–quadrupole energy to the pair potential is investigated and the results suggest that the contributions of the quadrupole moment to second and third virial coefficients are non-negligible at low temperatures.

Geometry and mechanics of two-dimensional defects in amorphous materials

We study the geometry of defects in amorphous materials and their elastic interactions. Defects are defined and characterized by deviations of the material’s intrinsic metric from a Euclidian metric. This characterization makes possible the identification of localized defects in amorphous materials, the formulation of a corresponding elastic problem, and its solution in various cases of physical interest. We present a multipole expansion that covers a large family of localized 2D defects. The dipole term, which represents a dislocation, is studied analytically and experimentally. Quadrupoles and higher multipoles correspond to fundamental strain-carrying entities. The interactions between those entities, as well as their interaction with external stress fields, are fundamental to the inelastic behavior of solids. We develop analytical tools to study those interactions. The model, methods, and results presented in this work are all relevant to the study of systems that involve a distribution of localized sources of strain. Examples are plasticity in amorphous materials and mechanical interactions between cells on a flexible substrate.