13,886 research outputs found
Uncertainty relations for cosmological particle creation and existence of large fluctuations in reheating
We derive an uncertainty relation for the energy density and pressure of a
quantum scalar field in a time-dependent, homogeneous and isotropic, classical
background, which implies the existence of large fluctuations comparable to
their vacuum expectation values. A similar uncertainty relation is known to
hold for the field square since the field can be viewed as a Gaussian random
variable. We discuss possible implications of these results for the reheating
process in scalar field driven inflationary models, where reheating is achieved
by the decay of the coherently oscillating inflaton field. Specifically we
argue that the evolution after backreaction can seriously be altered by the
existence of these fluctuations. For example, in one model the coherence of the
inflaton oscillations is found to be completely lost in a very short time after
backreaction starts. Therefore we argue that entering a smooth phase in thermal
equilibrium is questionable in such models and reheating might destroy the
smoothness attained by inflation.Comment: 6 pages, essay written for the Gravity Research Foundation 2011
Awards for Essays on Gravitation, Received Honorable Mentio
Intensity-Resolved Above Threshold Ionization of Xenon with Short Laser Pulses
We present intensity-resolved above threshold ionization (ATI) spectra of
xenon using an intensity scanning and deconvolution technique. Experimental
data were obtained with laser pulses of 58 fs and central wavelength of 800 nm
from a chirped-pulse amplifier. Applying a deconvolution algorithm, we obtained
spectra that have higher contrast and are in excellent agreement with
characteristic 2 and 10 cutoff energies contrary to that found for
raw data. The retrieved electron ionization probability is consistent with the
presence of a second electron from double ionization. This recovered ionization
probability is confirmed with a calculation based on the PPT tunneling
ionization model [Perelomov, Popov, and Terent'ev, Sov. Phys. JETP 23, 924
(1966)]. Thus, the measurements of photoelectron yields and the proposed
deconvolution technique allowed retrieval of more accurate spectroscopic
information from the ATI spectra and ionization probability features that are
usually concealed by volume averaging.Comment: 21 pages, 7 figure
AdS/CFT and Randall-Sundrum Model Without a Brane
We reformulate the Randall-Sundrum (RS) model on the compactified AdS by
adding a term proportional to the area of the boundary to the usual gravity
action with a negative cosmological constant and show that gravity can still be
localized on the boundary without introducing singular brane sources. The
boundary conditions now follow from the field equations, which are obtained by
letting the induced metric vary on the boundary. This approach gives similar
modes that are obtained in [1] and clarifies the complementarity of the RS and
the AdS/CFT pictures. Normalizability of these modes is checked by an
inner-product in the space of linearized perturbations. The same conclusions
hold for a massless scalar field in the bulk.Comment: Comments and references added, to apear in JHE
Intrinsic parameter fluctuations in decananometer MOSFETs introduced by gate line edge roughness
In this paper, we use statistical three-dimensional (3-D) simulations to study the impact of the gate line edge roughness (LER) on the intrinsic parameters fluctuations in deep decananometer (sub 50 nm) gate MOSFETs. The line edge roughness is introduced using a Fourier synthesis technique based on the power spectrum of a Gaussian autocorrelation function. In carefully designed simulation experiments, we investigate the impact of the rms amplitude /spl Delta/ and the correlation length /spl Lambda/ on the intrinsic parameter fluctuations in well scaled, but simple devices with fixed geometry as well as the channel length and width dependence of the fluctuations at fixed LER parameters. For the first time, we superimpose in the simulations LER and random discrete dopants and investigate their relative contribution to the intrinsic parameter fluctuations in the investigated devices. For particular MOSFET geometries, we were able to identify the regions where each of these two sources of intrinsic parameter fluctuations dominates
Breakdown of universal mobility curves in sub-100-nm MOSFETs
We explore the breakdown of universal mobility behavior in sub-100-nm Si MOSFETs, using a novel three-dimensional (3-D) statistical simulation approach. In this approach, carrier trajectories in the bulk are treated via 3-D Brownian dynamics, while the carrier-interface roughness scattering is treated using a novel empirical model
Cosmological backreaction of a quantized massless scalar field
We consider the backreaction problem of a quantized minimally coupled
massless scalar field in cosmology. The adiabatically regularized stress-energy
tensor in a general Friedmann-Robertson-Walker background is approximately
evaluated by using the fact that subhorizon modes evolve adiabatically and
superhorizon modes are frozen. The vacuum energy density is verified to obey a
new first order differential equation depending on a dimensionless parameter of
order unity, which calibrates subhorizon/superhorizon division. We check the
validity of the approximation by calculating the corresponding vacuum energy
densities in fixed backgrounds, which are shown to agree with the known results
in de Sitter space and space-times undergoing power law expansions. We then
apply our findings to slow-roll inflationary models. Although backreaction
effects are found to be negligible during the near exponential expansion, the
vacuum energy density generated during this period might be important at later
stages since it decreases slower than radiation or dust.Comment: 20 pages, 2 figures, v2: comments and a reference added, to appear in
JCA
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