1,322 research outputs found
Vacuum energy sequestering and graviton loops
We recently formulated a local mechanism of vacuum energy sequester. This mechanism automatically removes all matter loop contributions to vacuum energy from the stress energy tensor which sources the curvature. Here we adapt the local vacuum energy sequestering mechanism to also cancel all the vacuum energy loops involving virtual gravitons, in addition to the vacuum energy generated by matter fields alone
Towards Atomic Level Simulation of Electron Devices Including the Semiconductor-Oxide Interface
We report a milestone in device modeling whereby a planar MOSFET with extremely thin silicon on insulator channel is simulated at the atomic level, including significant parts of the gate and buried oxides explicitly in the simulation domain, in ab initio fashion, i.e without material or geometrical parameters. We use the density-functional-based tight-binding formalism for constructing the device Hamiltonian, and non-equilibrium Green's functions formalism for calculating electron current. Simulations of Si/SiO2 super-cells agree very well with experimentally observed band-structure phenomena in SiO2-confined sub-6 nm thick Si films. Device simulations of ETSOI MOSFET with 3 nm channel length and sub-nm channel thickness also agree well with reported measurements of the transfer characteristics of a similar transistor.published_or_final_versio
Permittivity of oxidized ultra-thin silicon films from atomistic simulations
We establish the dependence of the permittivity of oxidized ultra-thin silicon films on the film thickness by means of atomistic simulations within the density-functional-based tight-binding theory (DFTB). This is of utmost importance for modeling ultra- and extremely-thin silicon-on-insulator MOSFETs, and for evaluating their scaling potential. We demonstrate that electronic contribution to the dielectric response naturally emerges from the DFTB Hamiltonian when coupled to Poisson equation solved in vacuum, without phenomenological parameters, and obtain good agreement with available experimental data. Comparison to calculations of H-passivated Si films reveals much weaker dependence of permittivity on film thickness for the SiO2-passivated Si, with less than 18% reduction in the case of 0.9 nm silicon-on-insulator.published_or_final_versio
Hawking radiation of nonsingular black holes in two dimensions
In this letter we study the process of Hawking radiation of a black hole
assuming the existence of a limiting physical curvature scale. The particular
model is constructed using the Limiting Curvature Hypothesis (LCH) and in the
context of two-dimensional dilaton gravity. The black hole solution exhibits
properties of the standard Schwarzschild solution at large values of the radial
coordinate. However, near the center, the black hole is nonsingular and the
metric becomes that of de Sitter spacetime. The Hawking temperature is
calculated using the method of complex paths. We find that such black holes
radiate eternally and never completely evaporate. The final state is an
eternally radiating relic, near the fundamental scale, which should make a
viable dark matter candidate. We briefly comment on the black hole information
loss problem and the production of such black holes in collider experiments.Comment: 8 pages, 4 figures; minor revisions; references added; version to
appear in JHE
A Cosmological Theory without Singularities
A theory of gravitation is constructed in which all homogeneous and isotropic
solutions are nonsingular, and in which all curvature invariants are bounded.
All solutions for which curvature invariants approach their limiting values
approach de Sitter space. The action for this theory is obtained by a higher
derivative modification of Einstein's theory. We expect that our model can
easily be generalized to solve the singularity problem also for anisotropic
cosmologies.Comment: 25 pages, 11 figures (available as hard copies from the authors),
uses phyzzx, BROWN-HET-89
Parity violating cylindrical shell in the framework of QED
We present calculations of Casimir energy (CE) in a system of quantized
electromagnetic (EM) field interacting with an infinite circular cylindrical
shell (which we call `the defect'). Interaction is described in the only
QFT-consistent way by Chern-Simon action concentrated on the defect, with a
single coupling constant .
For regularization of UV divergencies of the theory we use % physically
motivated Pauli-Villars regularization of the free EM action. The divergencies
are extracted as a polynomial in regularization mass , and they renormalize
classical part of the surface action.
We reveal the dependence of CE on the coupling constant . Corresponding
Casimir force is attractive for all values of . For we
reproduce the known results for CE for perfectly conducting cylindrical shell
first obtained by DeRaad and Milton.Comment: Typos corrected. Some references adde
Classical model of elementary particle with Bertotti-Robinson core and extremal black holes
We discuss the question, whether the Reissner-Nordstr\"{o}m RN) metric can be
glued to another solutions of Einstein-Maxwell equations in such a way that (i)
the singularity at r=0 typical of the RN metric is removed (ii), matching is
smooth. Such a construction could be viewed as a classical model of an
elementary particle balanced by its own forces without support by an external
agent. One choice is the Minkowski interior that goes back to the old Vilenkin
and Fomin's idea who claimed that in this case the bare delta-like stresses at
the horizon vanish if the RN metric is extremal. However, the relevant entity
here is the integral of these stresses over the proper distance which is
infinite in the extremal case. As a result of the competition of these two
factors, the Lanczos tensor does not vanish and the extremal RN cannot be glued
to the Minkowski metric smoothly, so the elementary-particle model as a ball
empty inside fails. We examine the alternative possibility for the extremal RN
metric - gluing to the Bertotti-Robinson (BR) metric. For a surface placed
outside the horizon there always exist bare stresses but their amplitude goes
to zero as the radius of the shell approaches that of the horizon. This limit
realizes the Wheeler idea of "mass without mass" and "charge without charge".
We generalize the model to the extremal Kerr-Newman metric glued to the
rotating analog of the BR metric.Comment: 23 pages. Misprints correcte
3D-4D Interlinkage Of qqq Wave Functions Under 3D Support For Pairwise Bethe-Salpeter Kernels
Using the method of Green's functions within a Bethe-Salpeter framework
characterized by a pairwise qq interaction with a Lorentz-covariant 3D support
to its kernel, the 4D BS wave function for a system of 3 identical relativistic
spinless quarks is reconstructed from the corresponding 3D form which satisfies
a fully connected 3D BSE. This result is a 3-body generalization of a similar
2-body result found earlier under identical conditions of a 3D support to the
corresponding qq-bar BS kernel under Covariant Instaneity (CIA for short). (The
generalization from spinless to fermion quarks is straightforward).
To set the CIA with 3D BS kernel support ansatz in the context of
contemporary approaches to the qqq baryon problem, a model scalar 4D qqq BSE
with pairwise contact interactions to simulate the NJL-Faddeev equations is
worked out fully, and a comparison of both vertex functions shows that the CIA
vertex reduces exactly to the NJL form in the limit of zero spatial range. This
consistency check on the CIA vertex function is part of a fuller accounting for
its mathematical structure whose physical motivation is traceable to the role
of `spectroscopy' as an integral part of the dynamics.Comment: 20 pages, Latex, submitted via the account of K.-C. Yan
Radiation of Charged Particles by Charged Black Hole
The probability of a charged particle production by the electric field of a
charged black hole depends essentially on the particle energy. This probability
is found in the nonrelativistic and ultrarelativistic limits. The range of
values for the mass and charge of a black hole is indicated where the discussed
mechanism of radiation is dominating over the Hawking one.Comment: 10 pages, latex, 4 ps-figure
Radio-Frequency Measurements of Coherent Transition and Cherenkov Radiation: Implications for High-Energy Neutrino Detection
We report on measurements of 11-18 cm wavelength radio emission from
interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield
Accelerator. The electrons were observed both in a configuration where they
produced primarily transition radiation from an aluminum foil, and in a
configuration designed for the electrons to produce Cherenkov radiation in a
silica sand target. Our aim was to emulate the large electron excess expected
to develop during an electromagnetic cascade initiated by an ultra high-energy
particle. Such charge asymmetries are predicted to produce strong coherent
radio pulses, which are the basis for several experiments to detect high-energy
neutrinos from the showers they induce in Antarctic ice and in the lunar
regolith. We detected coherent emission which we attribute both to transition
and possibly Cherenkov radiation at different levels depending on the
experimental conditions. We discuss implications for experiments relying on
radio emission for detection of electromagnetic cascades produced by ultra
high-energy neutrinos.Comment: updated figure 10; fixed typo in equation 2.2; accepted by PR
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