The surface brightness profile of the remote cluster NGC 2419

It is well known that the bright and remote Galactic globular cluster NGC2419 has a very peculiar structure. In particular its half-light radius is significantly larger than that of ordinary globular clusters of similar luminosity, being as large as that of the brightest nuclei of dwarf elliptical galaxies. In this context it is particularly worth to check the reliability of the existing surface brightness profiles for this cluster and of the available estimates of its structural parameters. Combining different datasets I derive the surface brightness profile going from the cluster center out to ~ 480 arcsec, i.e. ~25 core radii. (Abridged). The newly obtained surface brightness profile is in excellent agreement with that provided by Trager, King & Djorgovski for r>= 4 arcsec; it is best fitted by a King model having r_c=0.32 arcmin, mu_V(0)=19.55 and C=1.35. Also new independent estimates of the total integrated V magnitude (V_t=10.47 +/- 0.07) and of the half-light radius (r_h=0.96 arcmin +/- 0.2 arcmin) have been obtained. (Abridged). The structure of NGC2419 is now reliably constrained by (at least) two fully independent observational profiles that are in good agreement one with the other. Also the overall agreement between structural parameters independently obtained by different authors is quite satisfying.Comment: Research Note, accepted for publication by A&A. 6 pages with 4 figures + 3 pages of Online Material (table

Max-Min characterization of the mountain pass energy level for a class of variational problems

We provide a max-min characterization of the mountain pass energy level for a family of variational problems. As a consequence we deduce the mountain pass structure of solutions to suitable PDEs, whose existence follows from classical minimization argument

Effective perfect fluids in cosmology

We describe the cosmological dynamics of perfect fluids within the framework of effective field theories. The effective action is a derivative expansion whose terms are selected by the symmetry requirements on the relevant long-distance degrees of freedom, which are identified with comoving coordinates. The perfect fluid is defined by requiring invariance of the action under internal volume-preserving diffeomorphisms and general covariance. At lowest order in derivatives, the dynamics is encoded in a single function of the entropy density that characterizes the properties of the fluid, such as the equation of state and the speed of sound. This framework allows a neat simultaneous description of fluid and metric perturbations. Longitudinal fluid perturbations are closely related to the adiabatic modes, while the transverse modes mix with vector metric perturbations as a consequence of vorticity conservation. This formalism features a large flexibility which can be of practical use for higher order perturbation theory and cosmological parameter estimation.Comment: Matches JCAP versio

Measurement of the position resolution of the Gas Pixel Detector

The Gas Pixel Detector was designed and built as a focal plane instrument for X-ray polarimetry of celestial sources, the last unexplored subtopics of X-ray astronomy. It promises to perform detailed and sensitive measurements resolving extended sources and detecting polarization in faint sources in crowded fields at the focus of telescopes of good angular resolution. Its polarimetric and spectral capability were already studied in earlier works. Here we investigate for the first time, with both laboratory measurements and Monte Carlo simulations, its imaging properties to confirm its unique capability to carry out imaging spectral-polarimetry in future X-ray missions.Comment: Submitted to Nuclear Instruments and Methods in Physics Research Section A; 15 figures, 3 table

Symmetries, Sum Rules and Constraints on Effective Field Theories

Using unitarity, analyticity and crossing symmetry, we derive universal sum rules for scattering amplitudes in theories invariant under an arbitrary symmetry group. The sum rules relate the coefficients of the energy expansion of the scattering amplitudes in the IR to total cross sections integrated all the way up to the UV. Exploiting the group structure of the symmetry, we systematically determine all the independent sum rules and positivity conditions on the expansion coefficients. For effective field theories the amplitudes in the IR are calculable and hence the sum rules set constraints on the parameters of the effective Lagrangian. We clarify the impact of gauging on the sum rules for Goldstone bosons in spontaneously broken gauge theories. We discuss explicit examples that are relevant for WW-scattering, composite Higgs models, and chiral perturbation theory. Certain sum rules based on custodial symmetry and its extensions provide constraints on the Higgs boson coupling to the electroweak gauge bosons.Comment: 50 pages, 5 figures, 5 appendices; several typos fixed, discussions improved, references added; results unchange