1,642 research outputs found
Anatomy of Two Holographic Renormalization Group Flows
We derive and solve a subset of the fluctuation equations about two domain
wall solutions of D=5, N=8 gauged supergravity. One solution is dual to D=4,
N=4 SYM theory perturbed by an N=1, SO(3)-invariant mass term and the other to
a Coulomb branch deformation. In the first case we study all SO(3)-singlet
fields. These are assembled into bulk multiplets dual to the stress tensor
multiplet and to the N=1 chiral multiplets Tr Phi^2 and Tr W^2, the former
playing the role of anomaly multiplet. Each of these three multiplets has a
distinct spectrum of "glueball" states. This behavior is contrasted with the
Coulomb branch flow in which all fluctuations studied have a continuous
spectrum above a common mass gap, and spontaneous breaking of conformal
symmetry is driven by a bulk vector multiplet. R-symmetry is preserved in the
field theory, and correspondingly the bulk vector is dual to a linear anomaly
multiplet. Generic features of the fluctuation equations and solutions are
emphasized. For example, the transverse traceless modes of all fields in the
graviton multiplet can be expressed in terms of an auxiliary massless scalar,
and gauge fields associated with R-symmetry have a universal effective mass.Comment: 48 pages, no figures, LaTeX. v2: minor corrections, references added
v3: version submitted to JHE
Ground state and excitation dynamics in Ag doped helium clusters
We present a quantum Monte Carlo study of the structure and energetics of
silver doped helium clusters AgHe for up to 100. Our simulations show
the first solvation shell of the Ag atom to be composed by roughly 20 He atoms,
and to possess a structured angular distribution. Moreover, the electronic
PS and PS
electronic transitions of the embedded silver impurity have been studied as a
function of the number ofhelium atoms. The computed spectra show a redshift for
and an increasing blueshift for larger clusters, a feature
attributed to the effect of the second solvation shell of He atoms. For the
largest cluster, the computed excitation spectrum is found in excellent
agreement with the ones recorded in superfluid He clusters and bulk. No
signature of the direct formation of proposed AgHe exciplex is present in
the computed spectra of AgHe.Comment: 4 Pages, 3 Figures, submitted to Phys. Rev. Let
Theory of Interfacial Plasmon-Phonon Scattering in Supported Graphene
One of the factors limiting electron mobility in supported graphene is remote
phonon scattering. We formulate the theory of the coupling between graphene
plasmon and substrate surface polar phonon (SPP) modes, and find that it leads
to the formation of interfacial plasmon-phonon (IPP) modes, from which the
phenomena of dynamic anti-screening and screening of remote phonons emerge. The
remote phonon-limited mobilities for SiO, HfO, h-BN and
AlO substrates are computed using our theory. We find that h-BN
yields the highest peak mobility, but in the practically useful high-density
range the mobility in HfO-supported graphene is high, despite the fact
that HfO is a high- dielectric with low-frequency modes. Our
theory predicts that the strong temperature dependence of the total mobility
effectively vanishes at very high carrier concentrations. The effects of
polycrystallinity on IPP scattering are also discussed.Comment: 33 pages, 7 figure
Generating Tree Amplitudes in N=4 SYM and N=8 SG
We study n-point tree amplitudes of N=4 super Yang-Mills theory and N=8
supergravity for general configurations of external particles of the two
theories. We construct generating functions for n-point MHV and NMHV amplitudes
with general external states. Amplitudes derived from them obey SUSY Ward
identities, and the generating functions characterize and count amplitudes in
the MHV and NMHV sectors. The MHV generating function provides an efficient way
to perform the intermediate state helicity sums required to obtain loop
amplitudes from trees. The NMHV generating functions rely on the MHV-vertex
expansion obtained from recursion relations associated with a 3-line shift of
external momenta involving a reference spinor |X]. The recursion relations
remain valid for a subset of N=8 supergravity amplitudes which do not vanish
asymptotically for all |X]. The MHV-vertex expansion of the n-graviton NMHV
amplitude for n=5,6,...,11 is independent of |X] and exhibits the asymptotic
behavior z^{n-12}. This presages difficulties for n > 12. Generating functions
show how the symmetries of supergravity can be implemented in the quadratic map
between supergravity and gauge theory embodied in the KLT and other similar
relations between amplitudes in the two theories.Comment: 53 pages, 8 figures. v2: Added references, typos correcte
The production rate of the coarse grained Gibbs entropy and the Kolmogorov-Sinai entropy: a real connection ?
We discuss the connection between the Kolmogorov-Sinai entropy, , and
the production rate of the coarse grained Gibbs entropy, . Detailed
numerical computations show that the (often accepted) identification of the two
quantities does not hold in systems with intermittent behavior and/or very
different characteristic times and in systems presenting pseudo-chaos. The
basic reason of this fact is in the asymptotic (with respect to time) nature of
, while is a quantity related to short time features of a system.Comment: 8 pages, 5 figures Submitted to PR
Structure Of The Photochemical Reaction Path Populated Via Promotion Of Cf2i2 Into Its First Excited State
The photochemical reaction path following the promotion of CF2I2 into its lowest-lying excited electronic singlet state has been modeled using ab initio multiconfigurational quantum chemical calculations. It is found that a conical intersection drives the electronically excited CF2I2* species either to the CF2I + I radical pair or back to the starting CF2I2 structure. The structures of the computed relaxation pathways explain the photoproduct selectivity previously observed in the gas phase. Furthermore, the results provide the basis for explaining the condensed-phase photochemistry of CF2I2
The expansion of murine bone marrow cells preincubated in hypoxia as an in vitro indicator of their marrow-repopulating ability.
Dense dielectric ceramics with local graded structure from core-shell particles: preparation and properties
The modification of the surface properties of particles by coating with a different material, resulting in the formation of core-shell structures, is a well-known process. However, the consolidation of core-shell particles in bulk ceramics has not been extensively investigated yet, mainly because of the difficulty in controlling interdiffusion and interface reactions. In this study, we have coated BaTiO(3) spherical templates with SrTiO(3) and BaZrO(3) using a precipitation process from inorganic precursors. The size of the particles as well as the overall composition can be tailored over a wide range. Densification of the resulting core-shell particles was accomplished either using conventional sintering or spark plasma sintering. Dense ceramics with a graded composition at the level of the single grains could only be obtained by careful choice of the sintering conditions. The final ceramics show strongly modified dielectric properties in comparison to both the parent compounds and the homogeneous solid solutions. The proposed approach is quite generic and suggests new possibilities for the realization of polycrystalline materials with local graded structure by the controlled sintering of core-shell particles
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