164 research outputs found
On gravitational interactions for massive higher spins in
In this paper we investigate gravitational interactions of massive higher
spin fields in three dimensional space with arbitrary value of
cosmological constant including flat Minkowski space. We use frame-like gauge
description for such massive fields adopted to three-dimensional case. At
first, we carefully analyze the procedure of switching on gravitational
interactions in the linear approximation on the example of massive spin-3 field
and then proceed with the generalization to the case of arbitrary integer spin
field. As a result we construct a cubic interaction vertex linear in spin-2
field and quadratic in higher spin field on background. As in the
massless case the vertex does not contain any higher derivative corrections to
the Lagrangian and/or gauge transformations. Thus, even after switching on
gravitational interactions, one can freely consider any massless or partially
massless limits as well as the flat one.Comment: 21 pages. Some clarifications and 1 new reference added. Version to
appear in the J.Phys.A special volume on "Higher Spin Theories and AdS/CFT"
edited by Matthias Gaberdiel and Mikhail Vasilie
Massive Gravity on de Sitter and Unique Candidate for Partially Massless Gravity
We derive the decoupling limit of Massive Gravity on de Sitter in an
arbitrary number of space-time dimensions d. By embedding d-dimensional de
Sitter into d+1-dimensional Minkowski, we extract the physical helicity-1 and
helicity-0 polarizations of the graviton. The resulting decoupling theory is
similar to that obtained around Minkowski. We take great care at exploring the
partially massless limit and define the unique fully non-linear candidate
theory that is free of the helicity-0 mode in the decoupling limit, and which
therefore propagates only four degrees of freedom in four dimensions. In the
latter situation, we show that a new Vainshtein mechanism is at work in the
limit m^2\to 2 H^2 which decouples the helicity-0 mode when the parameters are
different from that of partially massless gravity. As a result, there is no
discontinuity between massive gravity and its partially massless limit, just in
the same way as there is no discontinuity in the massless limit of massive
gravity. The usual bounds on the graviton mass could therefore equivalently
well be interpreted as bounds on m^2-2H^2. When dealing with the exact
partially massless parameters, on the other hand, the symmetry at m^2=2H^2
imposes a specific constraint on matter. As a result the helicity-0 mode
decouples without even the need of any Vainshtein mechanism.Comment: 30 pages. Some clarifications and references added. New subsection
'Symmetry and Counting in the Full Theory' added. New appendix 'St\"uckelberg
fields in the Na\"ive approach' added. Matches version published in JCA
Modeling of 3D microstructures produced by additive manufacturing
Two approaches to simulating microstructures typical of additively manufactured (AM) materials are presented. First approach relies on the mathematical description of the microstructure evolution during metal AM process, taking into account complex physical processes involved. The numerical solution is based on a combination of the finite difference method for modeling AM thermal processes and the cellular automata method for describing the grain growth. The other approach provides fast generation of artificial 3D microstructures similar to those produced by AM by geometrical characteristics of grains, using the step-by-step packing method
Cooperative Recombination of a Quantized High-Density Electron-Hole Plasma
We investigate photoluminescence from a high-density electron-hole plasma in
semiconductor quantum wells created via intense femtosecond excitation in a
strong perpendicular magnetic field, a fully-quantized and tunable system. At a
critical magnetic field strength and excitation fluence, we observe a clear
transition in the band-edge photoluminescence from omnidirectional output to a
randomly directed but highly collimated beam. In addition, changes in the
linewidth, carrier density, and magnetic field scaling of the PL spectral
features correlate precisely with the onset of random directionality,
indicative of cooperative recombination from a high density population of free
carriers in a semiconductor environment
Immunological context of brain injury
The parameters of several populations of immune cells (T cell populations, macrophage subpopulations) in peripheral blood and brain were studied in a clinically significant model of mild traumatic brain injury among rats. The population of resident cells of innate immunity of microglia and brain astrocytes with local tissue damage is involved in the implementation of the inflammatory response, it is also shown that in case of trauma, blood leukocytes can overcome the blood-brain barrier and penetrate the brain parenchyma. The methods of flow cytometry and immunofluorescence were used. An increase in the number of monocytes and neutrophils up to 1 day, after a mild traumatic brain injury (TBI) with a subsequent decrease to the end of the observation period was noticed. It was determined, that the number of CD45+ cells, CD3+T cells decreased at 1 days post-injury (dpi), and rose slightly by 14 dpi, the percentage of CD4+T cells continuously declined from 7 to 14 dpi, while the percentage of CD8+T cells increased from 7 to 14 dpi. With mild traumatic brain injury in animals, a significant (3-10 times) decrease in the number of microvessels with a positive reaction to the presence of SMI 71 on the 8th and 14th day after head injury was observed. Intensive staining of SMI 71 microvessels was sometimes observed with an increase in the area of a positive reaction. Thin positive deposits of the reaction product are observed in the brain of healthy animals around the wall of the microvessel. In the damaged brain, CD45high/CD11b+ positive macrophages of the M1 subpopulation appeared in the brain tissue on the 2nd day after TBI and a significant amount was observed on the 8-14th day. In the corpus callosum and ipsilateral region of the striatum, the content of cells expressing CD16/11b+ reached a maximum 8 days after TBI, which correlated with a decrease in the positive response to the presence of endothelial antigen SMI 71. Thus, in the acute period of mild TBI, the presence of neuroimmunopathological processes is determined in the brain, which can subsequently result to the dysregulation of neuroimmune connections
Peculiarities of phonon spectra and lattice heat capacity in Ir and Rh
A simple pseudopotential model is proposed, which allows the phonon spectra
and temperature dependence of the lattice heat capacity of Ir and Rh be
described with a high enough accuracy. A careful comparison of the calculated
and experimental values of the lattice heat capacity is carried out, with the
procedure of the identification of the phonon contribution to the heat capacity
and determination of the characteristics (momenta) of the phonon density of
states from the experimental values of the total heat capacity of metal at a
constant pressure being described in detail. The results of the theoretical
calculations explain, in particular, such peculiar feature of Ir and Rh,
unusual for cubic metals, as a sharp (more than by a factor of 1.5) decrease in
the effective Debye temperature with increasing termperature. The temperature
dependence of the mean square amplitude of atomic displacements in Ir and Rh
has been calculated. Basing on the band calculations the manifestation of the
Kohn singularities in the phonon spectra of Ir are discussed.Comment: 15 pages, LaTeX2e, 12 figures in postscrip
On the cubic interactions of massive and partially-massless higher spins in (A)dS
Cubic interactions of massive and partially-massless totally-symmetric
higher-spin fields in any constant-curvature background of dimension greater
than three are investigated. Making use of the ambient-space formalism, the
consistency condition for the traceless and transverse parts of the
parity-invariant interactions is recast into a system of partial differential
equations. The latter can be explicitly solved for given s_1-s_2-s_3 couplings
and the 2-2-2 and 3-3-2 examples are provided in detail for general choices of
the masses. On the other hand, the general solutions for the interactions
involving massive and massless fields are expressed in a compact form as
generating functions of all the consistent couplings. The St\"uckelberg
formulation of the cubic interactions as well as their massless limits are also
analyzed.Comment: 42 pages, 2 tables, LaTex. Comments on two-derivative couplings
involving partially-massless spin-2 fields added, typos corrected, references
added. v2: final version to appear in JHEP. v3: formulae (3.4) and (3.9)
correcte
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