Energy spectrum and phase diagrams of two-sublattice hard-core boson model

The energy spectrum, spectral density and phase diagrams have been obtained for two-sublattice hard-core boson model in frames of random phase approximation approach. Reconstruction of boson spectrum at the change of temperature, chemical potential and energy difference between local positions in sublattices is studied. The phase diagrams illustrating the regions of existence of a normal phase which can be close to Mott-insulator (MI) or charge-density (CDW) phases as well as the phase with the Bose-Einstein condensate (SF phase) are built.Comment: 9 pages, 4 figure

Resonant Enhancement of Inelastic Light Scattering in Strongly Correlated Materials

We use dynamical mean field theory to find an exact solution for inelastic light scattering in strongly correlated materials such as those near a quantum-critical metal-insulator transition. We evaluate the results for $\textbf{q}=0$ (Raman) scattering and find that resonant effects can be quite large, and yield a triple resonance, a significant enhancement of nonresonant scattering peaks, a joint resonance of both peaks when the incident photon frequency is on the order of $U$, and the appearance of an isosbestic point in all symmetry channels for an intermediate range of incident photon frequencies.Comment: 5 pages RevTex, 4 Figures ep

Strong short-range interactions in one-dimensional proton conductor

The behaviour of one-dimensional proton conductor is investigated on the basis of orientational-tunnelling model. The previously proposed technique which permits the proton interactions to be taken into account in the zeroorder Hamiltonian, and is based on Green’s function’s expansion in terms of irreducible Green’s function parts, is generalized. The Larkin equation for the one-particle proton Green’s function is solved, while irreducible Larkin part is calculated within the framework of the first order approximation. The proton energy spectrum and chemical potential behaviour are investigated, and the results are compared with the ones previously obtained in the Hubbard-1 type approximation.В роботі вивчається поведінка одновимірного протонного провідника на основі орієнтаційно-тунельної моделі. Узагальнено запропоновану раніше схему, яка дозволяє точно враховувати протонні взаємодії в гамільтоніяні нульового наближення і базується на розкладах функції Гріна за незвідними частинами. Розв’язано рівняння Ларкі-на для одночастинкової функції Гріна у випадку, коли незвідна частина за Ларкіним була розрахована в першому наближенні. Досліджено протонний енергетичний спектр і поведінку хемічного потенціялу, проведено порівняння результатів з раніше отриманими в наближенні типу Габбард-1

Resonant electronic Raman scattering near a quantum critical point

We calculate the resonant electronic Raman scattering for the Falicov-Kimball model near the Mott transition on a hypercubic lattice. The solution is exact, and employs dynamical mean field theory.Comment: 2 pages, 2 figures, contribution to the SCES04 conferenc

First supernovae in dwarf protogalaxies

(Abridged) We explore numerically the chemical, thermal, and dynamical evolution of a shell formed by a high-energy supernova explosion ($10^{53}$ erg) in dwarf protogalaxies with total mass $10^7 M_\odot$ at a redshift $z=12$. We consider two initial configurations for the baryonic matter, one without rotation and the other having the ratio of rotational to gravitational energy $\beta=0.17$. The (non-rotating) dark matter halo is described by a quasi-isothermal sphere. We find that the dynamics of the shell is different in protogalaxies with and without rotation. For instance, the Rayleigh-Taylor instability in the shell develops faster in protogalaxies without rotation. The fraction of a blown-away baryonic mass is approximately twice as large in models with rotation ($\sim 20$) than in models without rotation. On the other hand, the chemical evolution of gas in protogalaxies with and without rotation is found to be similar. The relative number densities of molecular hydrogen and HD molecules in the cold gas ($T \le 10^3$ K) saturate at typical values of $10^{-3}$ and $10^{-7}$, respectively. The clumps formed in the fragmented shell move with velocities that are at least twice as large as the escape velocity. The mass of the clumps is \sim 0.1-10 \msun, which is lower than the Jeans mass. We conclude that the clumps are pressure supported. A supernova explosion with energy $10^{53}$ ergs destructs our model protogalaxy. The clumps formed in the fragmented shell are pressure supported. We conclude that protogalaxies with total mass $\sim 10^{7} M_\odot$ are unlikely to form stars due to high-energy supernova explosions of the first stars.Comment: 12 pages, 8 figures, accepted in A&

Infrared and sub-mm observations of outbursting young stars with Herschel and Spitzer

Episodic accretion plays an important role in the evolution of young stars. Although it has been under investigation for a long time, the origin of such episodic accretion events is not yet understood. We investigate the dust and gas emission of a sample of young outbursting sources in the infrared to get a better understanding of their properties and circumstellar material, and we use the results in a further work to model the objects. We used Herschel data, from our PI program of 12 objects and complemented with archival observations to obtain the spectral energy distributions (SEDs) and spectra of our targets. We report here the main characteristics of our sample, focussing on the SED properties and on the gas emission lines detected in the PACS and SPIRE spectra. The SEDs of our sample show the diversity of the outbursting sources, with several targets showing strong emission in the far-infrared from the embedded objects. Most of our targets reside in a complex environment, which we discuss in detail. We detected several atomic and molecular lines, in particular rotational CO emission from several transitions from J=38-37 to J=4-3. We constructed rotational diagrams for the CO lines, and derived in three domains of assumed local thermodynamic equilibrium (LTE) temperatures and column densities, ranging mainly between 0-100 K and 400-500K. We confirm correlation in our sample between intense CO $J=16-15$ emission and the column density of the warm domain of CO, N(warm). We notice a strong increase in luminosity of HH 381 IRS and a weaker increase for PP 13 S, which shows the beginning of an outburst.Comment: 23 pages, 17 figures, A&A accepte

Accretion bursts in high-mass protostars: a new testbed for models of episodic accretion

It is well known that low mass young stellar objects (LMYSOs) gain a significant portion of their final mass through episodes of very rapid accretion, with mass accretion rates up to $\dot M_* \sim 10^{-4} M_{\odot}$~yr$^{-1}$. Recent observations of high mass young stellar objects (HMYSO) with masses $M_* \gtrsim 10 M_{\odot}$ uncovered outbursts with accretion rates exceeding $\dot M_*\sim 10^{-3}M_{\odot}$~yr$^{-1}$. Here we examine which scenarios proposed in the literature so far to explain accretion bursts of LMYSOs can apply to the episodic accretion in HMYSOs. We utilise a 1D time dependent models of protoplanetary discs around HMYSOs to study burst properties. We find that discs around HMYSOs are much hotter than those around their low mass cousins. As a result, much more extended regions of the disc are prone to the thermal hydrogen ionisation and MRI activation instabilities. The former in particular is found to be ubiquitous in a very wide range of accretion rates and disc viscosity parameters. The outbursts triggered by these instabilities, however, always have too low $\dot M_*$, and are one to several orders of magnitude too long compared to those observed from HMYSOs so far. On the other hand, bursts generated by tidal disruptions of gaseous giant planets formed by the gravitational instability of the protoplanetary discs yield properties commensurate with observations, provided that the clumps are in the post-collapse configuration with planet radius $R_{\rm p} \gtrsim 10$ Jupiter radii. Furthermore, if observed bursts are caused by disc ionisation instabilities then they should be periodic phenomena with the duration of the quiescent phase comparable to that of the bursts. This may yield potentially observable burst periodicity signatures in the jets, the outer disc, or the surrounding diffuse material of massive HMYSOs. (abridged)Comment: 8 pages, 6 figures, Accepted to A&A Letter

Mass transport from the envelope to the disk of V346 Nor: a case study for the luminosity problem in an FUor-type young eruptive star

A long-standing open issue of the paradigm of low-mass star formation is the luminosity problem: most protostars are less luminous than theoretically predicted. One possible solution is that the accretion process is episodic. FU Ori-type stars (FUors) are thought to be the visible examples for objects in the high accretion state. FUors are often surrounded by massive envelopes, which replenish the disk material and enable the disk to produce accretion outbursts. However, we have insufficient information on the envelope dynamics in FUors, about where and how mass transfer from the envelope to the disk happens. Here we present ALMA observations of the FUor-type star V346 Nor at 1.3 mm continuum and in different CO rotational lines. We mapped the density and velocity structure of its envelope and analyze the results using channel maps, position-velocity diagrams, and spectro-astrometric methods. We found that V346 Nor is surrounded by gaseous material on 10000 au scale in which a prominent outflow cavity is carved. Within the central $\sim$700 au, the circumstellar matter forms a flattened pseudo-disk where material is infalling with conserved angular momentum. Within $\sim$350 au, the velocity profile is more consistent with a disk in Keplerian rotation around a central star of 0.1 $M_{\odot}$. We determined an infall rate from the envelope onto the disk of 6$\times$10$^{-6}\,M_{\odot}$yr$^{-1}$, a factor of few higher than the quiescent accretion rate from the disk onto the star, hinting for a mismatch between the infall and accretion rates as the cause of the eruption.Comment: 16 pages, 8 figures, published in Ap