Mott-insulator phases of non-locally coupled 1D dipolar Bose gases

We analyze the Mott-insulator phases of dipolar bosonic gases placed in neighboring but unconnected 1D traps. Whereas for short-range interactions the 1D systems are independent, the non-local dipole-dipole interaction induces a direct Mott-insulator to pair-superfluid transition which significantly modifies the boundaries of the lowest Mott-insulator phases. The lowest boundary of the lowest Mott regions becomes progressively constant as a function of the hopping rate, eventually inverting its slope, leading to a re-entrant configuration which is retained in 2D. We discuss the consequences of this effect on the spatial Mott-insulator plateaux in experiments with additional harmonic confinement, showing that anti-intuitively the plateaux may become wider for increasing hopping. Our results are also applicable to non-dipolar boson-boson mixtures.Comment: 4 pages, 4 eps figures; minor changes, reference adde

Influence of Grain Size Distribution on Ultrasonic Scattering

Elastic wave scattering at grain boundaries in polycrystalline media can be quantified to determine microstructural properties. The amplitude drop observed for coherent wave propagation (attenuation) as well as diffuse-field scattering events (such as the single-scattering response) have been extensively studied. In all cases, the scattering shows a clear dependence on grain size, grain geometric morphology, and material texture (i.e., macroscale anisotropy). Scattering models used to quantify such scattering experiments are often developed under the assumption of a single effective grain diameter implying a very narrow distribution of grain size throughout the sample. However, several microscopy studies suggest that most metals have a log normal distribution of grain sizes with distribution widths as large as σ = 0.75, where eσ represents the standard deviation of the distribution. In this presentation grain size distribution is discussed within the context of previous attenuation and single scattering response models. Results are presented for several example metals using reported experimental values of distribution means and widths assuming spherically-shaped grains and no material texture. The longitudinal and shear attenuations are shown to vary with respect to their frequency dependence for varying distribution widths even when the mean grain size is held constant. A similar effect is observed for diffuse ultrasonic backscatter (DUB) predictions. These results suggest that grain size estimates based on DUB can have large errors if the distribution is neglected. A multi-frequency analysis approach is discussed based on a log normal distribution in order to reduce grain size estimate errors. This work is anticipated to play an important role in microstructural characterization research associated with ultrasonic scattering

An effective many-body theory for strongly interacting polar molecules

We derive a general effective many-body theory for bosonic polar molecules in strong interaction regime, which cannot be correctly described by previous theories within the first Born approximation. The effective Hamiltonian has additional interaction terms, which surprisingly reduces the anisotropic features of dipolar interaction near the shape resonance regime. In the 2D system with dipole moment perpendicular to the plane, we find that the phonon dispersion scales as \sqrt{|\bfp|} in the low momentum (\bfp) limit, showing the same low energy properties as a 2D charged Bose gas with Coulomb ($1/r$) interactions.Comment: Same as published version (11 pages, 2 figure

Baryon-induced collapse of dark matter cores into supermassive black holes

Non-linear structure formation for fermionic dark matter particles leads to dark matter density profiles with a degenerate compact core surrounded by a diluted halo. For a given fermion mass, the core has a critical mass that collapses into a supermassive black hole (SMBH). Galactic dynamics constraints suggest a $\sim 100$ keV/$c^2$ fermion, which leads to $\sim 10^7 M_\odot$ critical core mass. Here, we show that baryonic (ordinary) matter accretion drives an initially stable dark matter core to SMBH formation and determine the accreted mass threshold that induces it. Baryonic gas density $\rho_b$ and velocity $v_b$ inferred from cosmological hydro-simulations and observations produce sub-Eddington accretion rates triggering the baryon-induced collapse in less than a Gyr. This process produces active galactic nuclei in galaxy mergers and the high-redshift Universe. For TXS 2116-077, merging with a nearby galaxy, the observed $3\times 10^7 M_\odot$ SMBH, for $Q_b = \rho_b/v_b^3 = 0.125 M_\odot/(100 \text{km/s pc})^3$, forms in $\approx 0.6$ Gyr, consistent with the $0.5$-$2$ Gyr merger timescale and younger jet. For the farthest central SMBH detected by the \textit{Chandra} X-ray satellite in the $z=10.3$ UHZ1 galaxy observed by the James Webb Space Telescope (\textit{JWST}), the mechanism leads to a $4\times 10^7 M_\odot$ SMBH in $87$-$187$ Myr, starting the accretion at $z=12$-$15$. The baryon-induced collapse can also explain the $\approx 10^7$-$10^8 M_\odot$ SMBHs revealed by the JWST at $z\approx 4$-$6$. After its formation, the SMBH can grow to a few $10^9 M_\odot$ in timescales shorter than a Gyr via sub-Eddington baryonic mass accretion.Comment: Accepted for publication in The Astrophysical Journal Letter

Imaging Galactic Dark Matter with High-Energy Cosmic Neutrinos

We show that the high-energy cosmic neutrinos seen by the IceCube Neutrino Observatory can be used to probe interactions between neutrinos and the dark sector that cannot be reached by current cosmological methods. The origin of the observed neutrinos is still unknown, and their arrival directions are compatible with an isotropic distribution. This observation, together with dedicated studies of Galactic plane correlations, suggests a predominantly extragalactic origin. Interactions between this isotropic extragalactic flux and the dense dark matter (DM) bulge of the Milky Way would thus lead to an observable imprint on the distribution, which would be seen by IceCube as (i) slightly suppressed fluxes at energies below a PeV and (ii) a deficit of events in the direction of the Galactic center. We perform an extended unbinned likelihood analysis using the four-year high-energy starting event data set to constrain the strength of DM-neutrino interactions for two model classes. We find that, in spite of low statistics, IceCube can probe regions of the parameter space inaccessible to current cosmological methods.National Science Foundation (U.S.) (Grant PHY-1505858)National Science Foundation (U.S.) (Grant PHY-1505855

Acoustoelasticity of Polycrystalline Materials; a Formalism based on the Self-Consistent Elastic Constants

Elastic constants of polycrystalline materials can be obtained through methods of ensemble averages of the elastic constants belonging to individual grains. Assumptions are often made to relate the local strains (stresses) within individual grains as a result of a macroscopic strain (stress) on the polycrystal. The different assumptions lead to different estimates for the elastic constants of polycrystals. However, an exact formulation is possible, which enforces continuity (at the grain boundaries) between the macroscopic strain (stress) and the strain (stress) in the grain. The resulting estimates of the polycrystal’s elastic constants are known as selfconsistent because either a stress or strain formalism leads to the same estimates. This presentation extends the idea of macroscopic and local continuity of stress and strain and applies it to the theory of acoustoelasticity. Acoustoelasticity describes the dependence of the properties of an elastic wave on the stress state in the material supporting the wave. The selfconsistent formalism enters the elastic constitutive relation developed by C.-S. Man and coworkers. Such a constitutive relation is a function of initial stress, which can be either residual stress resulting from a series of inhomogeneous plastic deformations or generated from external mechanisms. The constitutive relation is used to derive the stress-dependent Christoffel equations for the polycrystal. Solutions to the Christoffel equation yield expressions for the phase velocities and displacement directions of elastic waves in a stressed polycrystal. A comparison is made between phase velocity values based on ensemble averaging originating from the self-consistent formalism and the phase velocities arriving from previous models. The cases in which the present model shows considerable differences from the previous models are presented. This overall goal of this work is to provide a better understanding of the influence of polycrystalline microstructure on acoustoelasticit

Life cycle assessment of hot mix asphalt with recycled concrete aggregates for road pavements construction

In this study a comparative life cycle assessment (LCA) was conducted according to a ‘cradle-to-laid’ approach to evaluate the potential environmental impacts related to the use of recycled concrete aggregates (RCAs) as a partial replacement of coarse natural aggregates in the production of Hot Mix Asphalt (HMA). Specifically, three percentages of RCA replacements were analyzed: 15, 30 and 45%. Primary data collected mainly through surveys performed in Colombian contractors from the region of Barranquila were used to model the foreground system. The SimaPro 8.4.0 software was used for modelling the processes analyzed in the case study and all the life cycle inputs and outputs related to the functional unit were characterised during life cycle impact assessment (LCIA) phase into potential impacts according to the TRACI v.2.1 impact assessment methodology. The results of the case study showed that the mixtures incorporating 15 and 30% of RCA can be considered as eco-friendly alternatives to the conventional mixture (i.e. no RCA content), as both allow reductions in all impact categories scores. On the contrary, the mixture that contains 45% of RCA denoted a lower environmental performance than that of the conventional mixture

Search for Lorentz Violation in km(3)-Scale Neutrino Telescopes

Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 2016Presented at the Seventh Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, June 20-24, 2016G.C., C.A., and J.C. are supported by NSF grants 1505858 and 1505855. T.K. is supported by the Science and Technology Facilities Council, UK. A.K. was supported in part by the NSF under grants 0937462 and 1306958 and by the University of Wisconsin Research Committee