702 research outputs found
Vacuum Energy Density and Cosmological Constant in dS Brane World
We discuss the vacuum energy density and the cosmological constant of dS
brane world with a dilaton field. It is shown that a stable AdS brane can
be constructed and gravity localization can be realized. An explicit relation
between the dS bulk cosmological constant and the brane cosmological constant
is obtained. The discrete mass spectrum of the massive scalar field in the
AdS brane is used to acquire the relationship between the brane
cosmological constant and the vacuum energy density. The vacuum energy density
in the brane gotten by this method is in agreement with astronomical
observations.Comment: 16 pages,4 figure
Orbital photogalvanic effects in quantum-confined structures
We report on the circular and linear photogalvanic effects caused by
free-carrier absorption of terahertz radiation in electron channels on
(001)-oriented and miscut silicon surfaces. The photocurrent behavior upon
variation of the radiation polarization state, wavelength, gate voltage and
temperature is studied. We present the microscopical and phenomenological
theory of the photogalvanic effects, which describes well the experimental
results. In particular, it is demonstrated that the circular (photon-helicity
sensitive) photocurrent in silicon-based structures is of pure orbital nature
originating from the quantum interference of different pathways contributing to
the absorption of monochromatic radiation.Comment: 8 pages, 5 figures, two culumne
Photoexcitation of valley-orbit currents in (111)-oriented silicon metal-oxide-semiconductor field-effect transistors
We demonstrate the injection of pure valley-orbit currents in multivalley semiconductors and present the phenomenological theory of this effect. We studied photoinduced transport in (111)-oriented silicon metaloxide-semiconductor field effect transistors at room temperature. By shining circularly polarized light on exact oriented structures with six equivalent valleys, nonzero electron fluxes within each valley are generated, which
compensate each other and do not yield a net electric current. By disturbing the balance between the valley fluxes, we demonstrate that the pure valley-orbit currents can be converted into a measurable electric current
The dual of Janus -:- an interface CFT
We propose and study a specific gauge theory dual of the smooth,
non-supersymmetric (and apparently stable) Janus solution of Type IIB
supergravity found in hep-th/0304129. The dual field theory is N=4 SYM theory
on two half-spaces separated by a planar interface with different coupling
constants in each half-space. We assume that the position dependent coupling
multiplies the operator L' which is the fourth descendent of the primary Tr(X^I
X^J) and closely related to the N=4 Lagrangian density. At the classical level
supersymmetry is broken explicitly, but SO(3,2) conformal symmetry is
preserved. We use conformal perturbation theory to study various correlation
functions to first and second order in the discontinuity of g^2_{YM},
confirming quantum level conformal symmetry. Certain quantities such as the
vacuum expectation value are protected to all orders in g^2_{YM}N, and we
find perfect agreement between the weak coupling value in the gauge theory and
the strong coupling gravity result. SO(3,2) symmetry requires vanishing vacuum
energy, =0, and this is confirmed in first order in the
discontinuity.Comment: 24 pages, 1 figure; references adde
Holography and Defect Conformal Field Theories
We develop both the gravity and field theory sides of the Karch-Randall
conjecture that the near-horizon description of a certain D5-D3 brane
configuration in string theory, realized as AdS_5 x S^5 bisected by an AdS_4 x
S^2 "brane", is dual to N=4 Super Yang-Mills theory in R^4 coupled to an R^3
defect. We propose a complete Lagrangian for the field theory dual, a novel
"defect superconformal field theory" wherein a subset of the fields of N=4 SYM
interacts with a d=3 SU(N) fundamental hypermultiplet on the defect preserving
conformal invariance and 8 supercharges. The Kaluza-Klein reduction of wrapped
D5 modes on AdS_4 x S^2 leads to towers of short representations of OSp(4|4),
and we construct the map to a set of dual gauge-invariant defect operators O_3
possessing integer conformal dimensions. Gravity calculations of and
are given. Spacetime and N-dependence matches expectations from dCFT,
while the behavior as functions of lambda = g^2 N at strong and weak coupling
is generically different. We comment on a class of correlators for which a
non-renormalization theorem may still exist. Partial evidence for the
conformality of the quantum theory is given, including a complete argument for
the special case of a U(1) gauge group. Some weak coupling arguments which
illuminate the duality are presented.Comment: 47 pages, LaTeX, 2 figures, feynmf. v2: fixed minor errors, added
references. v3: fixed more typo
Defect Conformal Field Theory and Locally Localized Gravity
Gravity may be "locally localized" over a wide range of length scales on a
d-dimensional anti-de Sitter (AdS) brane living inside AdS_{d+1}. In this paper
we examine this phenomenon from the point of view of the holographic dual
"defect conformal field theory". The mode expansion of bulk fields on the
gravity side is shown to be precisely dual to the "boundary operator product
expansion" of operators as they approach the defect. From the field theory
point of view, the condition for localization is that a "reduced operator"
appearing in this expansion acquires negative anomalous dimension. In
particular, a very light localized graviton exists when a mode arising from the
reduction of the ambient stress-energy tensor to the defect has conformal
dimension Delta ~ d-1. The part of the stress tensor containing the defect
dynamics has dimension Delta = d-1 in the free theory, but we argue that it
acquires an anomalous dimension in the interacting theory, and hence does not
participate in localization in the regime of small backreaction of the brane.
We demonstrate that such an anomalous dimension is consistent with the
conservation of the full stress-energy tensor. Finally, we analyze how to
compute the anomalous dimensions of reduced operators from gravity at leading
order in the interactions with the brane.Comment: 38 pages, LaTeX, 5 figures. v2: typos fixe
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