Interference effects in two-photon ATI by multiple orders high harmonics with random or locked phases

We numerically study 2-photon processes using a set of harmonics from a Ti:Sapphire laser and in particular interference effects in the Above Threshold Ionization spectra. We compare the situation where the harmonic phases are assumed locked to the case where they have a random distribution. Suggestions for possible experiments, using realistic parameters are discussed.Comment: 11 pages, 13 figures, LaTe

Global Examination of the 12^{12}C+12^{12}C Reaction Data at Low and Intermediate Energies

We examine the $^{12}$C+$^{12}$C elastic scattering over a wide energy range from 32.0 to 70.7 MeV in the laboratory system within the framework of the Optical model and the Coupled-Channels formalism. The $^{12}$C+$^{12}$C system has been extensively studied within and over this energy range in the past. These efforts have been futile in determining the shape of the nuclear potential in the low energy region and in describing the individual angular distributions, single-angle 50$^{0}$ to 90$^{0}$ excitation functions and reaction cross-section data simultaneously. In order to address these problems systematically, we propose a potential that belongs to a family other than the one used to describe higher energy experimental data and show that it is possible to use it over this wide energy range. This potential also predicts the resonances at correct energies with reasonable widths.Comment: 30 pages with 13 eps figues and 3 tables, LaTeX-Revtex

Dynamics of coupled bosonic systems with applications to preheating

Coupled, multi-field models of inflation can provide several attractive features unavailable in the case of a single inflaton field. These models have a rich dynamical structure resulting from the interaction of the fields and their associated fluctuations. We present a formalism to study the nonequilibrium dynamics of coupled scalar fields. This formalism solves the problem of renormalizing interacting models in a transparent way using dimensional regularization. The evolution is generated by a renormalized effective Lagrangian which incorporates the dynamics of the mean fields and their associated fluctuations at one-loop order. We apply our method to two problems of physical interest: (i) a simple two-field model which exemplifies applications to reheating in inflation, and (ii) a supersymmetric hybrid inflation model. This second case is interesting because inflation terminates via a smooth phase transition which gives rise to a spinodal instability in one of the fields. We study the evolution of the zero mode of the fields and the energy density transfer to the fluctuations from the mean fields. We conclude that back reaction effects can be significant over a wide parameter range. In particular for the supersymmetric hybrid model we find that particle production can be suppressed due to these effects.Comment: 23 pages, 16 eps-figures, minor changes in the text, references added, accepted for publication in PR

A milestone toward understanding PDR properties in the extreme environment of LMC-30Dor

More complete knowledge of galaxy evolution requires understanding the process of star formation and interaction between the interstellar radiation field and the interstellar medium in galactic environments traversing a wide range of physical parameter space. Here we focus on the impact of massive star formation on the surrounding low metallicity ISM in 30 Doradus in the Large Magellanic Cloud. A low metal abundance, as is the case of some galaxies of the early universe, results in less ultra-violet shielding for the formation of the molecular gas necessary for star formation to proceed. The half-solar metallicity gas in this region is strongly irradiated by the super star cluster R136, making it an ideal laboratory to study the structure of the ISM in an extreme environment. Our spatially resolved study investigates the gas heating and cooling mechanisms, particularly in the photo-dissociation regions where the chemistry and thermal balance are regulated by far-ultraviolet photons (6 eV< h\nu <13.6 eV). We present Herschel observations of far-infrared fine-structure lines obtained with PACS and SPIRE/FTS. We have combined atomic fine-structure lines from Herschel and Spitzer observations with ground-based CO data to provide diagnostics on the properties and the structure of the gas by modeling it with the Meudon PDR code. We derive the spatial distribution of the radiation field, the pressure, the size, and the filling factor of the photodissociated gas and molecular clouds. We find a range of pressure of ~ 10^5 - 1.7x10^6 cm^{-3} K and a range of incident radiation field G_UV ~ 10^2 - 2.5x10^4 through PDR modeling. Assuming a plane-parallel geometry and a uniform medium, we find a total extinction of 1-3 mag , which correspond to a PDR cloud size of 0.2 to 3pc, with small CO depth scale of 0.06 to 0.5pc. We also determine the three dimensional structure of the gas. (Abridged)Comment: 20 pages, 23 figures, accepted in A&

Nkx2-5 and Sarcospan genetically interact in the development of the muscular ventricular septum of the heart

The muscular ventricular septum separates the flow of oxygenated and de-oxygenated blood in air-breathing vertebrates. Defects within it, termed muscular ventricular septal defects (VSDs), are common, yet less is known about how they arise than rarer heart defects. Mutations of the cardiac transcription factor NKX2-5 cause cardiac malformations, including muscular VSDs. We describe here a genetic interaction between Nkx2-5 and Sarcospan (Sspn) that affects the risk of muscular VSD in mice. Sspn encodes a protein in the dystrophin-glycoprotein complex. Sspn knockout (Sspn(KO)) mice do not have heart defects, but Nkx2-5(+/−)/Sspn(KO) mutants have a higher incidence of muscular VSD than Nkx2-5(+/−) mice. Myofibers in the ventricular septum follow a stereotypical pattern that is disrupted around a muscular VSD. Subendocardial myofibers normally run in parallel along the left ventricular outflow tract, but in the Nkx2-5(+/−)/Sspn(KO) mutant they commonly deviate into the septum even in the absence of a muscular VSD. Thus, Nkx2-5 and Sspn act in a pathway that affects the alignment of myofibers during the development of the ventricular septum. The malalignment may be a consequence of a defect in the coalescence of trabeculae into the developing ventricular septum, which has been hypothesized to be the mechanistic basis of muscular VSDs

A Survey of Atomic Carbon [C I] in High-redshift Main-Sequence Galaxies

We present the first results of an ALMA survey of the lower fine structure line of atomic carbon [C I](^3P_1\,-\,^{3}P_0) in far infrared-selected galaxies on the main sequence at $z\sim1.2$ in the COSMOS field. We compare our sample with a comprehensive compilation of data available in the literature for local and high-redshift starbursting systems and quasars. We show that the [C I]($^3P_1$$\rightarrow$$^3P_0$) luminosity correlates on global scales with the infrared luminosity $L_{\rm IR}$ similarly to low-$J$ CO transitions. We report a systematic variation of L'_{\rm [C\,I]^3P_1\,-\, ^3P_0}/$L_{\rm IR}$ as a function of the galaxy type, with the ratio being larger for main-sequence galaxies than for starbursts and sub-millimeter galaxies at fixed $L_{\rm IR}$. The L'_{\rm [C\,I]^3P_1\,-\, ^3P_0}/$L'_{\rm CO(2-1)}$ and $M_{\rm{[C I]}}$/$M_{\rm dust}$ mass ratios are similar for main-sequence galaxies and for local and high-redshift starbursts within a 0.2 dex intrinsic scatter, suggesting that [C I] is a good tracer of molecular gas mass as CO and dust. We derive a fraction of $f_{\rm{[C\,I]}} = M_{\rm{[C\,I]}} / M_{\rm{C}}\sim3-13$% of the total carbon mass in the atomic neutral phase. Moreover, we estimate the neutral atomic carbon abundance, the fundamental ingredient to calibrate [C I] as a gas tracer, by comparing L'_{\rm [C\,I]^3P_1\,-\, ^3P_0} and available gas masses from CO lines and dust emission. We find lower [C I] abundances in main-sequence galaxies than in starbursting systems and sub-millimeter galaxies, as a consequence of the canonical $\alpha_{\rm CO}$ and gas-to-dust conversion factors. This argues against the application to different galaxy populations of a universal standard [C I] abundance derived from highly biased samples.Comment: 14 pages + Appendix. Accepted for publication in ApJ. All the data tables in Appendix will be also released in electronic forma

Two--Electron Atoms in Short Intense Laser Pulses

We discuss a method of solving the time dependent Schrodinger equation for atoms with two active electrons in a strong laser field, which we used in a previous paper [A. Scrinzi and B. Piraux, Phys. Rev. A 56, R13 (1997)] to calculate ionization, double excitation and harmonic generation in Helium by short laser pulses. The method employs complex scaling and an expansion in an explicitly correlated basis. Convergence of the calculations is documented and error estimates are provided. The results for Helium at peak intensities up to 10^15 W/cm^2 and wave length 248 nm are accurate to at least 10 %. Similarly accurate calculations are presented for electron detachment and double excitation of the negative hydrogen ion.Comment: 14 pages, including figure