75 research outputs found
Efimov physics from the functional renormalization group
Few-body physics related to the Efimov effect is discussed using the
functional renormalization group method. After a short review of
renormalization in its modern formulation we apply this formalism to the
description of scattering and bound states in few-body systems of identical
bosons and distinguishable fermions with two and three components. The Efimov
effect leads to a limit cycle in the renormalization group flow. Recently
measured three-body loss rates in an ultracold Fermi gas Li atoms are
explained within this framework. We also discuss briefly the relation to the
many-body physics of the BCS-BEC crossover for two-component fermions and the
formation of a trion phase for the case of three species.Comment: 28 pages, 13 figures, invited contribution to a special issue of
"Few-Body Systems" devoted to Efimov physics, published versio
Infrared behavior of interacting bosons at zero temperature
We review the infrared behavior of interacting bosons at zero temperature.
After a brief discussion of the Bogoliubov approximation and the breakdown of
perturbation theory due to infrared divergences, we present two approaches that
are free of infrared divergences -- Popov's hydrodynamic theory and the
non-perturbative renormalization group -- and allow us to obtain the exact
infrared behavior of the correlation functions. We also point out the
connection between the infrared behavior in the superfluid phase and the
critical behavior at the superfluid--Mott-insulator transition in the
Bose-Hubbard model.Comment: 8 pages, 4 figures. Proceedings of the 19th International Laser
Physics Workshop, LPHYS'10 (Foz do Iguacu, Brazil, July 5-9, 2010
Overview of the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES)
Substantial uncertainties still exist in the scientific understanding of the possible interactions between urban and natural (biogenic) emissions in the production and transformation of atmospheric aerosol and the resulting impact on climate change. The US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program\u27s Carbonaceous Aerosol and Radiative Effects Study (CARES) carried out in June 2010 in Central Valley, California, was a comprehensive effort designed to improve this understanding. The primary objective of the field study was to investigate the evolution of secondary organic and black carbon aerosols and their climate-related properties in the Sacramento urban plume as it was routinely transported into the forested Sierra Nevada foothills area. Urban aerosols and trace gases experienced significant physical and chemical transformations as they mixed with the reactive biogenic hydrocarbons emitted from the forest. Two heavily-instrumented ground sites-one within the Sacramento urban area and another about 40 km to the northeast in the foothills area-were set up to characterize the evolution of meteorological variables, trace gases, aerosol precursors, aerosol size, composition, and climate-related properties in freshly polluted and aged urban air. On selected days, the DOE G-1 aircraft was deployed to make similar measurements upwind and across the evolving Sacramento plume in the morning and again in the afternoon. The NASA B-200 aircraft, carrying remote sensing instruments, was also deployed to characterize the vertical and horizontal distribution of aerosols and aerosol optical properties within and around the plume. This overview provides: (a) the scientific background and motivation for the study, (b) the operational and logistical information pertinent to the execution of the study, (c) an overview of key observations and initial findings from the aircraft and ground-based sampling platforms, and (d) a roadmap of planned data analyses and focused modeling efforts that will facilitate the integration of new knowledge into improved representations of key aerosol processes and properties in climate models
A Hydrodynamic and Transport Model for Ultrarelativistic Heavy Ion Collisions at RHIC and LHC Energies
Combining the hydrodynamic model (Hydro code) and the transport model (PACIAE
model), we present the Hydro-PACIAE hybrid model. We use the Hydro-PACIAE
hybrid model to calculate Au+Au collisions at =130 GeV and Pb+Pb
collisions at =2.76 TeV. The obtained pseudo-rapidity and
transverse momentum distributions well reproduce the experimental data. This
shows that the Hydro-PACIAE hybrid model is useful to describe the
ultrarelativistic Heavy Ion Collisions at RHIC and LHC Energies. We used the
hybrid model to calculate the elliptical flow for the Pb+Pb collisions at
=2.76 TeV. The values are bigger than the experimental
data at high , and will become bigger when the Hydro evolution time is
longer. The results indicate that the selection of the transition hypersurface
has significant effect on the observable quantities.Comment: 8 pages, 8 figure
Fluctuations around Bjorken Flow and the onset of turbulent phenomena
We study how fluctuations in fluid dynamic fields can be dissipated or
amplified within the characteristic spatio-temporal structure of a heavy ion
collision. The initial conditions for a fluid dynamic evolution of heavy ion
collisions may contain significant fluctuations in all fluid dynamical fields,
including the velocity field and its vorticity components. We formulate and
analyze the theory of local fluctuations around average fluid fields described
by Bjorken's model. For conditions of laminar flow, when a linearized treatment
of the dynamic evolution applies, we discuss explicitly how fluctuations of
large wave number get dissipated while modes of sufficiently long wave-length
pass almost unattenuated or can even be amplified. In the opposite case of
large Reynold's numbers (which is inverse to viscosity), we establish that
(after suitable coordinate transformations) the dynamics is governed by an
evolution equation of non-relativistic Navier-Stokes type that becomes
essentially two-dimensional at late times. One can then use the theory of
Kolmogorov and Kraichnan for an explicit characterization of turbulent
phenomena in terms of the wave-mode dependence of correlations of fluid dynamic
fields. We note in particular that fluid dynamic correlations introduce
characteristic power-law dependences in two-particle correlation functions.Comment: 40 pages, 5 figures, published versio
Flow in heavy-ion collisions - Theory Perspective
I review recent developments in the field of relativistic hydrodynamics and
its application to the bulk dynamics in heavy-ion collisions at the
Relativistic Heavy- Ion Collider (RHIC) and the Large Hadron Collider (LHC). In
particular, I report on progress in going beyond second order relativistic
viscous hydrodynamics for conformal fluids, including temperature dependent
shear viscosity to entropy density ratios, as well as coupling hydrodynamic
calculations to microscopic hadronic rescattering models. I describe
event-by-event hydrodynamic simulations and their ability to compute higher
harmonic flow coefficients. Combined comparisons of all harmonics to recent
experimental data from both RHIC and LHC will potentially allow to determine
the desired details of the initial state and the medium properties of the
quark-gluon plasma produced in heavy-ion collisions.Comment: 8 pages, Invited plenary talk at the 22nd International Conference on
Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2011), May 23-28
2011, Annecy, Franc
Overview of the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES)
Substantial uncertainties still exist in the scientific understanding of the possible interactions between urban and natural (biogenic) emissions in the production and transformation of atmospheric aerosol and the resulting impact on climate change. The US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program's Carbonaceous Aerosol and Radiative Effects Study (CARES) carried out in June 2010 in Central Valley, California, was a comprehensive effort designed to improve this understanding. The primary objective of the field study was to investigate the evolution of secondary organic and black carbon aerosols and their climate-related properties in the Sacramento urban plume as it was routinely transported into the forested Sierra Nevada foothills area. Urban aerosols and trace gases experienced significant physical and chemical transformations as they mixed with the reactive biogenic hydrocarbons emitted from the forest. Two heavily-instrumented ground sites – one within the Sacramento urban area and another about 40 km to the northeast in the foothills area – were set up to characterize the evolution of meteorological variables, trace gases, aerosol precursors, aerosol size, composition, and climate-related properties in freshly polluted and "aged" urban air. On selected days, the DOE G-1 aircraft was deployed to make similar measurements upwind and across the evolving Sacramento plume in the morning and again in the afternoon. The NASA B-200 aircraft, carrying remote sensing instruments, was also deployed to characterize the vertical and horizontal distribution of aerosols and aerosol optical properties within and around the plume. This overview provides: (a) the scientific background and motivation for the study, (b) the operational and logistical information pertinent to the execution of the study, (c) an overview of key observations and initial findings from the aircraft and ground-based sampling platforms, and (d) a roadmap of planned data analyses and focused modeling efforts that will facilitate the integration of new knowledge into improved representations of key aerosol processes and properties in climate models.United States. Dept. of Energy. Atmospheric System Research Program (Contract DE-AC06-76RLO 1830)United States. National Oceanic and Atmospheric AdministrationUnited States. National Aeronautics and Space Administration. HQ Science Mission Directorate Radiation Sciences ProgramUnited States. National Aeronautics and Space Administration. CALIPSO ProgramUnited States. Dept. of Energy. Atmospheric Radiation Measurement Program (Interagency Agreement No. DE-AI02-05ER63985
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