Isocurvature bounds on axions revisited
The axion is one of the best motivated candidates for particle dark matter. We study and update the constraints imposed by the recent CMB and LSS experiments on the mass of axions produced by the misalignment mechanism, as a function of both the inflationary scale and the reheating temperature. Under some particular although not unconventional assumptions, the axion induces isocurvature perturbations with an amplitude too large to be compatible with observations. Specifically, for inflation taking place at intermediate energy scales, we derive some restrictive limits which can only be evaded by assuming an efficient reheating mechanism, with T{sub rh}>10{sup 11} GeV. Chaotic inflation with a quadratic potential is still compatible with the axion scenario, provided that the Peccei-Quinn scale f{sub a} is close to 10{sup 10} or 10{sup 11} GeV. Isocurvature bounds eliminate the possibility of a larger f{sub a} and a small misalignment angle. We find that isocurvature constraints on the axion scenario must be taken into account whenever the scale of inflation is above 10{sup 12} GeV; below this scale, axionic isocurvature modes are too small to be probed by current observations.

title: Squeezing the window on isocurvature modes with the Lyman-{alpha} forest
abstract: Various recent studies proved that cosmological models with a significant contribution from cold dark matter isocurvature perturbations are still compatible with most recent data on cosmic microwave background anisotropies and on the shape of the galaxy power spectrum, provided that one allows for a very blue spectrum of primordial entropy fluctuations (n{sub iso}>2). However, such models predict an excess of matter fluctuations on small scales, typically below 40h{sup -1} Mpc. We show that the proper inclusion of high-resolution high signal-to-noise Lyman-{alpha} forest data excludes most of these models. The upper bound on the isocurvature fraction {alpha}=f{sub iso}{sup 2}/(1+f{sub iso}{sup 2}), defined at the pivot scale k{sub 0}=0.05 Mpc{sup -1}, is pushed down to {alpha}<0.4, while n{sub iso}=1.9{+-}1.0 (95% confidence limits). We also study the bounds on curvaton models characterized by maximal correlation between curvature and isocurvature modes, and a unique spectral tilt for both. We find that f{sub iso}<0.05 (95% C.L.) in that case. For double-inflation models with two massive inflatons coupled only gravitationally, the mass ratio should obey R<3 (95% C.L.)

title: Bayesian model selection and isocurvature perturbations
abstract: Present cosmological data are well explained assuming purely adiabatic perturbations, but an admixture of isocurvature perturbations is also permitted. We use a Bayesian framework to compare the performance of cosmological models including isocurvature modes with the purely adiabatic case; this framework automatically and consistently penalizes models which use more parameters to fit the data. We compute the Bayesian evidence for fits to a data set comprised of WMAP and other microwave anisotropy data, the galaxy power spectrum from 2dFGRS and SDSS, and Type Ia supernovae luminosity distances. We find that Bayesian model selection favors the purely adiabatic models, but so far only at low significance.

title: Isocurvature modes and Baryon Acoustic Oscillations
abstract: The measurement of Baryonic Acoustic Oscillations from galaxy surveys is well known to be a robust and powerful tool to constrain dark energy. This method relies on the knowledge of the size of the acoustic horizon at radiation drag derived from Cosmic Microwave Background Anisotropy measurements. In this paper we quantify the effect of non-standard initial conditions in the form of an isocurvature component on the determination of dark energy parameters from future BAO surveys. In particular, if there is an isocurvature component (at a level still allowed by present data) but it is ignored in the CMB analysis, the sound horizon and cosmological parameters determination is biased, and, as a consequence, future surveys may incorrectly suggest deviations from a cosmological constant. In order to recover an unbiased determination of the sound horizon and dark energy parameters, a component of isocurvature perturbations must be included in the model when analyzing CMB data. Fortunately, doing so does not increase parameter errors significantly.

title: Isocurvature, non-Gaussianity, and the curvaton model
abstract: Recent analyses of the statistical distribution of the temperature anisotropies in the cosmic microwave background do not rule out the possibility that there is a large non-Gaussian contribution to the primordial power spectrum. This fact motivates the reanalysis of the curvaton scenario, paying special attention to the compatibility of large non-Gaussianity of the local type with the current detection limits on the isocurvature amplitude in the cosmic microwave background. We find that if the curvaton mechanism generates a primordial power spectrum with an important non-Gaussian component, any residual isocurvature imprint originated by the curvaton, would have an amplitude too big to be compatible with the current bounds. This implies that the isocurvature mode should be equal to zero in this scenario and we explore the consequences of this inference. In order to prevent the generation of a such a signal, the cold dark matter (CDM) must be created at a late stage, after the curvaton decays completely. This is used to constrain the nature of the CDM, arriving at a general relation between the temperature of the universe at CDM creation and the scale of inflation. It is possible to find an absolute maximum for the temperature at CDM creation,more » which is dependent on the particular inflationary potential. For a quadratic potential, we find T{sub cdm}<1.7x10{sup 6} GeV.« less

title: INTERFEROMETRIC OBSERVATIONS OF NITROGEN-BEARING MOLECULAR SPECIES IN THE STAR-FORMING CORE AHEAD OF HH 80N
abstract: We present Very Large Array NH3 and Plateau de Bure Interferometer NH2D and HN13C observations of the star-forming core ahead of HH 80N, the optically obscured northern counterpart of the Herbig-Haro objects HH 80/81. The main goal is to determine the kinematical information of the high density regions of the core (n 105 cm–3) missed in previous works due to the depletion of the species observed (e.g., CS). The obtained maps show different kinematical signatures between the eastern and western parts of the core, suggesting a possible dynamical interaction of the core with the HH 80/81/80N outflow. The analysis of the position-velocity (P-V) plots of these species rules out a previous interpretation of having a molecular ring-like structure with a radius of 6 × 104 AU traced by CS infalling onto a central protostar found in the core (IRS1). A high degree of NH3 deuteration, with respect to the central part of the core harboring IRS1, is derived in the eastern part, where a dust condensation (SE) is located. This deuteration trend of NH3 suggests that SE is in a pre-stellar evolutionary stage, earlier than that of IRS1. Since SE is the closest condensation to the HH 80N/81/80N outflow, in a case of outflow-core dynamical interaction, it should be perturbed first and be the most evolved condensation in the core. Therefore, the derived evolutionary sequence for SE and IRS1 makes outflow triggered star formation on IRS1 unlikely.