1,163 research outputs found
Entanglement and out-of-equilibrium dynamics in holographic models of de Sitter QFTs
In this paper we study various aspects of entanglement entropy in
strongly-coupled de Sitter quantum field theories in various dimensions. We
find gravity solutions that are dual to field theories in a fixed de Sitter
background, both in equilibrium and out-of-equilibrium configurations. The
latter corresponds to the Vaidya generalization of the AdS black hole solutions
with hyperbolic topology. We compute analytically the entanglement entropy of
spherical regions and show that there is a transition when the sphere is as big
as the horizon. We also explore thermalization in time-dependent situations in
which the system evolves from a non-equilibrium state to the Bunch-Davies
state. We find that the saturation time is equal to the light-crossing time of
the sphere. This behavior is faster than random walk and suggests the existence
of free light-like degrees of freedom.Comment: 39 pages, 11 figures; minor changes, conclusions unchange
Fluctuation and dissipation in de Sitter space
In this paper we study some thermal properties of quantum field theories in
de Sitter space by means of holographic techniques. We focus on the static
patch of de Sitter and assume that the quantum fields are in the standard
Bunch-Davies vacuum. More specifically, we follow the stochastic motion of a
massive charged particle due to its interaction with Hawking radiation. The
process is described in terms of the theory of Brownian motion in inhomogeneous
media and its associated Langevin dynamics. At late times, we find that the
particle undergoes a regime of slow diffusion and never reaches the horizon, in
stark contrast to the usual random walk behavior at finite temperature.
Nevertheless, the fluctuation-dissipation theorem is found to hold at all
times.Comment: 1+45 pages, 5 figures. v4: matches published versio
Structural development of laminar flow control aircraft chordwise wing joint designs
For laminar flow to be achieved, any protuberances on the surface must be small enough to avoid transition to turbulent flow. However, the surface must have joints between the structural components to allow assembly or replacement of damaged parts, although large continuous surfaces can be utilized to minimize the number the number of joints. Aircraft structural joints usually have many countersunk bolts or rivets on the outer surface. To maintain no mismatch on outer surfaces, it is desirable to attach the components from the inner surface. It is also desirable for the panels to be interchangeable, without the need for shims at the joint, to avoid surface discontinuities that could cause turbulence. Fabricating components while pressing their outer surfaces against an accurate mold helps to ensure surface smoothness and continuity at joints. These items were considered in evaluating the advantages and disadvantages of the joint design concepts. After evaluating six design concepts, two of the leading candidates were fabricated and tested using many small test panels. One joint concept was also built and tested using large panels. The small and large test panel deflections for the leading candidate designs at load factors up to +1.5 g's were well within the step and waviness requirements for avoiding transition.The small panels were designed and tested for compression and tension at -65 F, at ambient conditions, and at 160 F. The small panel results for the three-rib and the sliding-joint concepts indicated that they were both acceptable. The three-rib concept, with tapered splice plates, was considered to be the most practical. A modified three-rib joint that combined the best attributes of previous candidates was designed, developed, and tested. This improved joint met all of the structural strength, surface smoothness, and waviness criteria for laminar flow control (LFC). The design eliminated all disadvantages of the initial three-rib concept except for unavoidable eccentricity, which was reduced and reacted satisfactorily by the rib supports. It should also result in a relatively simple low-cost installation, and makes it easy to replace any panels damaged in the field
Accomplishments of participatory research for systems improvement in Iganga District, Uganda 1993 to 1997
Membrane nucleation rates from holography
Membrane nucleation, a higher dimensional analog of the Schwinger effect, is a useful toy model for vacuum decay. While a non-perturbative effect, the computation of nucleation rates has only been accomplished at weak coupling in the field theory. Here we compute the nucleation rates of spherical membranes using AdS/CFT duality, thus naturally including the effects of strong coupling. More precisely, we consider the nucleation of spherical membranes coupled to an antisymmetric tensor field, a process which renders the vacuum unstable above a critical value of the field strength. We analyze membrane creation in flat and de Sitter space using various foliations of AdS. This is accomplished via instanton methods, where the rate of nucleation is dominated by the semi-classical on-shell Euclidean action. Our findings generalize the holographic Schwinger effect and provide a step toward holographic false vacuum decay mediated by Coleman-De Luccia instantons
On the Anomalies and Schwinger Terms in Noncommutative Gauge Theories
Invariant (nonplanar) anomaly of noncommutative QED is reexamined. It is
found that just as in ordinary gauge theory UV regularization is needed to
discover anomalies, in noncommutative case, in addition, an IR regularization
is also required to exhibit existence of invariant anomaly. Thus resolving the
controversy in the value of invariant anomaly, an expression for the
unintergrated anomaly is found. Schwinger terms of the current algebra of the
theory are derived.Comment: LaTeX, axodraw.sty, 1 figure; v2: Typos corrected, References added,
Version to appear in Int. J. Mod. Phys. A (2006
Towards a microscopic construction of flavour vacua from a space-time foam model
The effect on flavour oscillations of simple expanding background
space-times, motivated by some D-particle foam models, is calculated for a
toy-model of bosons with flavour degrees of freedom. The presence of D-particle
defects in the space-time, which can interact non trivially (via particle
capture) with flavoured particles in a flavour non-preserving way, generates
mixing in the effective field theory of low-energy string excitations.
Moreover, the recoil of the D-particle defect during the capture/scattering
process implies Lorentz violation, which however may be averaged to zero in
isotropic D-particle populations, but implies non-trivial effects in
correlators. Both features imply that the flavoured mixed state sees a
non-trivial flavour (Fock-space) vacuum of a type introduced earlier by Blasone
and Vitiello in a generic context of theories with mixing. We discuss the
orthogonality of the flavour vacua to the usual Fock vacua and the effect on
flavour oscillations in these backgrounds. Furthermore we analyse the equation
of state of the Flavour vacuum, and find that, for slow expansion rates induced
by D particle recoil, it is equivalent to that of a cosmological constant. Some
estimates of these novel non-perturbative contribution to the vacuum energy are
made. The contribution vanishes if the mass difference and the mixing angle of
the flavoured states vanish.Comment: 27 pages RevTex, 2 eps figures incorporate
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