Reheating in the Presence of Noise

Explosive particle production due to parametric resonance is a crucial feature of reheating in inflationary cosmology. Coherent oscillations of the inflaton field act as a periodically varying mass in the evolution equation for matter fields which couple to the inflaton. This in turn results in the parametric resonance instability. Thermal and quantum noise will lead to a nonperiodic perturbation in the mass. We study the resulting equation for the evolution of matter fields and demonstrate that noise (at least if it is temporally uncorrelated) will increase the rate of particle production. We also estimate the limits on the magnitude of the noise for which the resonant behavior is qualitatively unchanged.Comment: 26 pages, 2 figures, uses LATE

Mass distribution and structural parameters of Small Magellanic Cloud star clusters

In this work we estimate, for the first time, the total masses and mass function slopes of a sample of 29 young and intermediate-age SMC clusters from CCD Washington photometry. We also derive age, interstellar reddening and structural parameters for most of the studied clusters by employing a statistical method to remove the unavoidable field star contamination. Only these 29 clusters out of 68 originally analysed cluster candidates present stellar overdensities and coherent distribution in their colour-magnitude diagrams compatible with the existence of a genuine star cluster. We employed simple stellar population models to derive general equations for estimating the cluster mass based only on its age and integrated light in the B, V, I, C and T1 filter. These equations were tested against mass values computed from luminosity functions, showing an excellent agreement. The sample contains clusters with ages between 60 Myr and 3 Gyr and masses between 300 and 3000 Mo distributed between ~0.5 deg. and ~2 deg. from the SMC optical centre. We determined mass function slopes for 24 clusters, of which 19 have slopes compatible with that of Kroupa IMF (2.3 +/- 0.7), considering the uncertainties. The remaining clusters - H86-188, H86-190, K47, K63 and NGC242 - showed flatter MFs. Additionally, only clusters with masses lower than ~1000 Mo and flatter MF were found within ~0.6 deg. from the SMC rotational centre.Comment: 12 pages, 19 figures. Includes another 29 full-page figures of supplementary material. Accepted for publication in the MNRA

GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle

Physical properties were derived for the candidate open cluster La Serena 94, recently unveiled by the VVV collaboration. Thanks to the exquisite angular resolution provided by GeMS/GSAOI, we could characterize this system in detail, for the first time, with deep photometry in JHK$_{s}$ - bands. Decontaminated JHK$_{s}$ diagrams reach about 5 mag below the cluster turnoff in H. The locus of red clump giants in the colour - colour diagram, together with an extinction law, was used to obtain an average extinction of $A_V =14.18 \pm 0.71$. The same stars were considered as standard - candles to derive the cluster distance, $8.5 \pm 1.0$ kpc. Isochrones were matched to the cluster colour - magnitude diagrams to determine its age, $\log{t(yr)}=9.12\pm 0.06$, and metallicity, $Z=0.02\pm0.01$. A core radius of $r_{c}=0.51\pm 0.04$ pc was found by fitting King models to the radial density profile. By adding up the visible stellar mass to an extrapolated mass function, the cluster mass was estimated as $M=(2.65\pm0.57) \times 10^3$ M$_{\odot}$, consistent with an integrated magnitude of $M_{K}=-5.82\pm0.16$ and a tidal radius of $r_{t}=17.2\pm2.1$ pc. The overall characteristics of La Serena 94 confirm that it is an old open cluster located in the Crux spiral arm towards the fourth Galactic quadrant and distant $7.30\pm 0.49$ kpc from the Galactic centre. The cluster distorted structure, mass segregation and age indicate that it is a dynamically evolved stellar system.Comment: 16 pages, 24 figures, 2 Tables, accepted by MNRAS; corrected typo

Magnetic Monopoles Without String In The Kähler-clifford Algebra Bundle: A Geometrical Interpretation

In substitution for Dirac monopoles with string (and for topological monopoles), "monopoles without string" have recently been introduced on the basis of a generalized potential, the sum of a vector A, and a pseudovector γ5 B potential. By making recourse to the Clifford bundle script c sign(τM,g) [ ( TxM,g) = ℝ1,3; script c sign(TxM,g) = ℝ1,3 ], which just allows adding together for each x∈M tensors of different ranks, in a previous paper a Lagrangian and Hamiltonian formalism was constructed for interacting monopoles and charges that can be regarded as satisfactory from various points of view. In the present article, after having "completed" the formalism, a purely geometrical interpretation of it is put forth within the Kähler-Clifford bundle script K(τ*M,ĝ) of differential forms, essential ingredients being a generalized curvature and the Hodge decomposition theorem. Thus the way is paved for the extension of our "monopoles without string" to non-Abelian gauge groups. The analogy with supersymmetric theories is apparent. © 1990 American Institute of Physics.31250250

The Deformable Universe

The concept of smooth deformations of a Riemannian manifolds, recently evidenced by the solution of the Poincar\'e conjecture, is applied to Einstein's gravitational theory and in particular to the standard FLRW cosmology. We present a brief review of the deformation of Riemannian geometry, showing how such deformations can be derived from the Einstein-Hilbert dynamical principle. We show that such deformations of space-times of general relativity produce observable effects that can be measured by four-dimensional observers. In the case of the FLRW cosmology, one such observable effect is shown to be consistent with the accelerated expansion of the universe.Comment: 20 pages, LaTeX, 3 figure