arXiv subjects

D. Cormier

Publications and source records attributed to D. Cormier.

72 records · Page 4Linked to original sources

arXiv2010

The effects of star formation on the low-metallicity ISM: NGC4214 mapped with Herschel/PACS spectroscopy

We present Herschel/PACS spectroscopic maps of the dwarf galaxy NC4214 observed in 6 far infrared fine-structure lines: [C II] 158mu, [O III] 88mu, [O I] 63mu, [O I] 146mu, [N II] 122mu, and [N II] 205mu. The maps are sampled to the full telescope spatial resolution and reveal unprecedented detail on ~ 150 pc size scales. We detect [C II] emission over the whole mapped area, [O III] being the most luminous FIR line. The ratio of [O III]/[C II] peaks at about 2 toward the sites of massive star formation, higher than ratios seen in dusty starburst galaxies. The [C II]/CO ratios are 20 000 to 70 000 toward the 2 massive clusters, which are at least an order of magnitude larger than spiral or dusty starbursts, and cannot be reconciled with single-slab PDR models. Toward the 2 massive star-forming regions, we find that L[CII] is 0.5 to 0.8% of the LTIR . All of the lines together contribute up to 2% of LTIR . These extreme findings are a consequence of the lower metallicity and young, massive-star formation commonly found in dwarf galaxies. These conditions promote large-scale photodissociation into the molecular reservoir, which is evident in the FIR line ratios. This illustrates the necessity to move to multiphase models applicable to star-forming clusters or galaxies as a whole.

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arXiv2010

The dust morphology of the elliptical Galaxy M86 with SPIRE

We present Herschel-SPIRE observations at 250-500um of the giant elliptical galaxy M86 and examine the distribution of the resolved cold dust emission and its relation with other galactic tracers. The SPIRE images reveal three dust components: emission from the central region; a dust lane extending north-south; and a bright emission feature 10kpc to the south-east. We estimate that approximately 10^6 solar masses of dust is spatially coincident with atomic and ionized hydrogen, originating from stripped material from the nearby spiral NGC4438 due to recent tidal interactions with M86. The gas-to-dust ratio of the cold gas component ranges from ~20-80. We discuss the different heating mechanisms for the dust features.

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arXiv2010

FIR colours and SEDs of nearby galaxies observed with Herschel

We present infrared colours (in the 25-500 mic spectral range) and UV to radio continuum spectral energy distributions of a sample of 51 nearby galaxies observed with SPIRE on Herschel. The observed sample includes all morphological classes, from quiescent ellipticals to active starbursts. Active galaxies have warmer colour temperatures than normal spirals. In ellipticals hosting a radio galaxy, the far-infrared (FIR) emission is dominated bynthe synchrotron nuclear emission. The colour temperature of the cold dust is higher in quiescent E-S0a than in star-forming systems probably because of the different nature of their dust heating sources (evolved stellar populations, X-ray, fast electrons) and dust grain properties. In contrast to the colour temperature of the warm dust, the f350/f500 index sensitive to the cold dust decreases with star formation and increases with metallicity, suggesting an overabundance of cold dust or an emissivity parameter beta<2 in low metallicity, active systems.

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arXiv2010

SPIRE imaging of M82: cool dust in the wind and tidal streams

M82 is a unique representative of a whole class of galaxies, starbursts with superwinds, in the Very Nearby Galaxy Survey with Herschel. In addition, its interaction with the M81 group has stripped a significant portion of its interstellar medium from its disk. SPIRE maps now afford better characterization of the far-infrared emission from cool dust outside the disk, and sketch a far more complete picture of its mass distribution and energetics than previously possible. They show emission coincident in projection with the starburst wind and in a large halo, much more extended than the PAH band emission seen with Spitzer. Some complex substructures coincide with the brightest PAH filaments, and others with tidal streams seen in atomic hydrogen. We subtract the far-infrared emission of the starburst and underlying disk from the maps, and derive spatially-resolved far-infrared colors for the wind and halo. We interpret the results in terms of dust mass, dust temperature, and global physical conditions. In particular, we examine variations in the dust physical properties as a function of distance from the center and the wind polar axis, and conclude that more than two thirds of the extraplanar dust has been removed by tidal interaction, and not entrained by the starburst wind.

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arXiv2010

The Herschel Reference Survey

The Herschel Reference Survey is a guaranteed time Herschel key project and will be a benchmark study of dust in the nearby universe. The survey will complement a number of other Herschel key projects including large cosmological surveys that trace dust in the distant universe. We will use Herschel to produce images of a statistically-complete sample of 323 galaxies at 250, 350 and 500 micron. The sample is volume-limited, containing sources with distances between 15 and 25 Mpc and flux limits in the K-band to minimize the selection effects associated with dust and with young high-mass stars and to introduce a selection in stellar mass. The sample spans the whole range of morphological types (ellipticals to late-type spirals) and environments (from the field to the centre of the Virgo Cluster) and as such will be useful for other purposes than our own. We plan to use the survey to investigate (i) the dust content of galaxies as a function of Hubble type, stellar mass and environment, (ii) the connection between the dust content and composition and the other phases of the interstellar medium and (iii) the origin and evolution of dust in galaxies. In this paper, we describe the goals of the survey, the details of the sample and some of the auxiliary observing programs that we have started to collect complementary data. We also use the available multi-frequency data to carry out an analysis of the statistical properties of the sample.

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arXiv2001

Out of Equilibrium Dynamics of Supersymmetry at High Energy Density

We investigate the out of equilibrium dynamics of global chiral supersymmetry at finite energy density. We concentrate on two specific models. The first is the massive Wess-Zumino model which we study in a selfconsistent one-loop approximation. We find that for energy densities above a certain threshold, the fields are driven dynamically to a point in field space at which the fermionic component of the superfield is massless. The state, however is found to be unstable, indicating a breakdown of the one-loop approximation. To investigate further, we consider an O(N) massive chiral model which is solved exactly in the large $N$ limit. For sufficiently high energy densities, we find that for late times the fields reach a nonperturbative minimum of the effective potential degenerate with the perturbative minimum. This minimum is a true attractor for O(N) invariant states at high energy densities, and this provides a mechanism for determining which of the otherwise degenerate vacua is chosen by the dynamics. The final state for large energy density is a cloud of massless particles (both bosons and fermions) around this new nonperturbative supersymmetric minimum. By introducing boson masses which softly break the supersymmetry, we demonstrate a see-saw mechanism for generating small fermion masses. We discuss some of the cosmological implications of our results.

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arXiv2001

Dynamics of O(N) chiral supersymmetry at finite energy density

We consider an O(N) version of a massive, interacting, chiral supersymmetry model solved exactly in the large N limit. We demonstrate that the system approaches a stable attractor at high energy densities, corresponding to a non-perturbative state for which the relevant field quanta are massless. The state is one of spontaneously broken O(N), which, due to the influence of supersymmetry, does not become restored at high energies. Introducing soft supersymmetry breaking to the Lagrangian results in scalar masses at the soft breaking scale m_s independent of the mass scale of supersymmetry mu, with even smaller masses for the fermions.

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arXiv2000

Spinodal Instabilities and the Dark Energy Problem

The accelerated expansion of the Universe measured by high redshift Type Ia Supernovae observations is explained using the non-equilibrium dynamics of naturally soft boson fields. Spinodal instabilities inevitably present in such systems yield a very attractive mechanism for arriving at the required equation of state at late times, while satisfying all the known constraints on models of quintessence.

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arXiv2000

Metric Perturbations and Inflationary Phase Transitions

We study the out of equilibrium dynamics of inflationary phase transitions and compute the resulting spectrum of metric perturbations relevant to observation. We show that simple single field models of inflation may produce an adiabatic perturbation spectrum with a blue spectral tilt and that the precise spectrum depends on initial conditions at the outset of inflation.

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arXiv1999

Spinodal Decomposition and Inflation: Dynamics and Metric Perturbations

We analyse the dynamics of spinodal decomposition in inflationary cosmology using the closed time path formalism of out of equilibrium quantum field theory combined with the non-perturbative Hartree approximation. In addition to a general analysis, we compute the detailed evolution of two inflationary models of particular importance: lambda Phi^4 new inflation and natural inflation. We compute the metric fluctuations resulting from inflationary phase transitions in the slow roll approximation, showing that there exists a regime for which quantum fluctuations of the inflaton field result in a significant deviation in the predictions of the spectrum of primordial density perturbations from standard results. We provide case examples for which a blue tilt to the power spectrum (i.e. n_s > 1) results from the evolution of a single inflaton field, and demonstrate that field fluctuations may result in a scalar amplitude of fluctuations significantly below standard predictions, resulting in a slight alleviation of the inflationary fine tuning problem. We show explicitly that the metric perturbation spectrum resulting from inflation depends upon the state at the outset of the inflationary phase.

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arXiv1998

Spinodal Inflation

Out-of-equilibrium, non-perturbative, quantum effects significantly modify the standard picture of inflation in a wide class of models including new, natural, and hybrid inflation. We find that the quantum evolution of a single real inflaton field may be modeled by a classical theory of two homogeneous scalar fields. We briefly discuss the important observational consequences that are expected to result.

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arXiv1998

Non-Equilibrium Field Theory Dynamics in Inflationary Cosmology

For simple inflationary models, we provide a consistent and complete scheme by which the macro-physical details of early universe inflation may be determined explicitly from the underlying micro-physical theory. We examine inflationary dynamics within the context of a fully renormalized, non-perturbative, and non-equilibrium quantum field theory using the closed time path formalism. We study the non-perturbative dynamics using the self-consistent Hartree approximation and the large N limit. In addition, we include gravitation dynamically by means of the semi-classical approximation to Einstein gravity, allowing the cosmological geometry to be determined self-consistently by the evolution of the particle fields. We develop a simple and numerically implementable regularization and renormalization scheme for which the renormalization counterterms contain no explicit dependence on the initial state. We concern ourselves first with the dynamics of new inflation models, showing how the dynamics become quantum fluctuation driven. We then describe how these quantum fluctuations may be reassembled into an effective field which behaves classically and acts as the source for the gravitational background. This allows us to determine the spectrum of primordial density perturbations in a consistent manner. We also examine explosive particle production after inflation through the processes of spinodal decomposition and parametric amplification, showing that the non-perturbative backreaction on the inflaton field prevents catastrophic particle production. We find a strong dependence of particle production on the expansion rate and on the symmetry properties of the inflaton.

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arXiv1998

Out of Equilibrium Fields in Inflationary Dynamics. Density Fluctuations

The energy and time scales during the inflationary stage of the universe calls for an out of equilibrium quantum field treatment. Moreover, the high energy densities involved make necessary the use of non-perturbative approaches as large N and Hartree methods. We start these lectures by introducing such non-perturbative out of equilibrium methods in cosmological universes. We discuss the renormalization procedure and the choice of initial conditions. We then study the nonlinear dynamics of quantum fields in matter and radiation dominated FRW and de Sitter universes. For a variety of initial conditions, we compute the evolution of the inflaton,its quantum fluctuations and the equation of state. We investigate the explosive particle production due to spinodal unstabilities and parametric amplification in FRW and de Sitter universes with and without symmetry breaking.We find that the particle production is sensitive to the expansion of the universe.For symmetry breaking scenarios, we determine generic late time fields behavior for FRW and deSitter cosmologies.We find that quantum fluctuations damp in FRW as the square of the scale factor while the order parameter approaches a minimum of the potential at the same rate.We con- sider an O(N) inflaton model coupled self-consistently to gravity in the semi- classical approximation for a `new inflation' scenario. We find that spinodal instabilities drive the growth of non-perturbatively large quantum fluctuations which shut off inflation. These fluctuations assemble with the inflaton zero mode yielding a new effective field that actually rolls down behaving classi- cally. We compute the amplitude and index for scalar density and tensor perturbations. In all models of this type the spinodal instabilities produce a `red' spectrum of primordial scalar density perturbations.

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arXiv1997

Non-Perturbative Quantum Dynamics of a New Inflation Model

We consider an O(N) model coupled self-consistently to gravity in the semiclassical approximation, where the field is subject to `new inflation' type initial conditions. We study the dynamics self-consistently and non-perturbatively with non-equilibrium field theory methods in the large N limit. We find that spinodal instabilities drive the growth of non-perturbatively large quantum fluctuations which shut off the inflationary growth of the scale factor. We find that a very specific combination of these large fluctuations plus the inflaton zero mode assemble into a new effective field. This new field behaves classically and it is the object which actually rolls down. We show how this reinterpretation saves the standard picture of how metric perturbations are generated during inflation and that the spinodal growth of fluctuations dominates the time dependence of the Bardeen variable for superhorizon modes during inflation. We compute the amplitude and index for the spectrum of scalar density and tensor perturbations and argue that in all models of this type the spinodal instabilities are responsible for a `red' spectrum of primordial scalar density perturbations. A criterion for the validity of these models is provided and contact with the reconstruction program is established validating some of the results within a non-perturbative framework. The decoherence aspects and the quantum to classical transition through inflation are studied in detail by following the full evolution of the density matrix and relating the classicality of cosmological perturbations to that of long-wavelength matter fluctuations.

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arXiv1997

Self-Consistent Dynamics of Inflationary Phase Transitions

The physics of the inflationary universe requires the study of the out of equilibrium evolution of quantum fields in curved spacetime. We present the evolution for both the geometry and the matter (described by the quantum inflaton field) by means of the non-perturbative large N limit combined with semi-classical gravitational dynamics including the back-reaction of quantum fluctuations self-consistently for a new inflation scenario. We provide a criterion for the validity of the classical approximation and a full analysis of the case in which spinodal quantum fluctuations drive the evolution of the scale factor. Under carefully determined conditions, we show that the full field equations may be well approximated by those of a single composite field which obeys the classical equation of motion in all cases. The de Sitter stage is found to be followed by a matter dominated phase. We compute the spectrum of scalar density perturbations and argue that the spinodal instabilities are responsible for a `red' spectrum with more power at longer wavelengths. A criterion for the validity of these models is provided and contact with the reconstruction program is established.

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arXiv1997

Out of Equilibrium Dynamics of an Inflationary Phase Transition

We study the non-linear dynamics of an inflationary phase transition in a quartically self coupled inflaton model within the framework of a de Sitter background. Large N and Hartree non-perturbative approximations combined with non-equilibrium field theory methods are used to study the self-consistent time evolution including backreaction effects. We find that when the system cools down from an initial temperature T_i > T_c to below T_c with the initial value of the zero mode of the inflaton phi(0) << m lambda^{-1/4}, the dynamics is determined by the growth of long-wavelength quantum fluctuations. For phi(0) >> m lambda^{-1/4} the dynamics is determined by the evolution of the classical zero mode. In the regime where spinodal quantum fluctuations give the most important contribution to the non-equilibrium dynamics, we find that they modify the equation of state providing a graceful exit from the inflationary stage. Inflation ends through this new mechanism at a time scale t_s >= [H/m^2]ln[lambda^{-1}] which for H >= m and very weak coupling allows over one hundred e-folds during the de Sitter phase. Spatially correlated domains grow to be of horizon-size and quantum fluctuations ``freeze-out'' for times t> t_s.

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arXiv1997

Scalar Field Dynamics in Friedman Robertson Walker Spacetimes

We study the non-linear dynamics of quantum fields in matter and radiation dominated universes, using the non-equilibrium field theory approach combined with the non-perturbative Hartree and the large N approximations. We examine the phenomenon of explosive particle production due to spinodal instabilities and parametric amplification in expanding universes with and without symmetry breaking. For a variety of initial conditions, we compute the evolution of the inflaton, its quantum fluctuations, and the equation of state. We find explosive growth of quantum fluctuations, although particle production is somewhat sensitive to the expansion of the universe. In the large N limit for symmetry breaking scenarios, we determine generic late time solutions for any flat Friedman-Robertson-Walker cosmology. We also present a complete and numerically implementable renormalization scheme for the equation of motion and the energy momentum tensor in flat FRW cosmologies. In this scheme the renormalization constants are independent of time and of the initial conditions.

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arXiv1996

Preheating in FRW Universes

The nonlinear time evolution of the quantum fields is studied in the O(N) model for large N in a radiation dominated FRW universe, with a view towards the phenomenon of explosive particle production due to either spinodal instabilities or parametric amplification, i.e. preheating. Quantum backreaction effects due to the produced particles are included consistently within the large N approximation. We find that preheating persists when the expansion is included, although the amount of particle production is reduced compared to the values found in Minkowski space. We also see that the behavior of the evolving zero mode is very different from that in Minkowski space, though the late time behavior in all cases is determined by a sum rule that implies the existence of Goldstone bosons in the final state.

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