20,201 research outputs found
The scalar complex potential and the Aharonov-Bohm effect
The Aharonov-Bohm effect is traditionally attributed to the effect of the
electromagnetic 4-potential , even in regions where both the electric field
and the magnetic field are zero. The AB effect
reveals that multiple-valued functions play a crucial role in the description
of an electromagnetic field. We argue that the quantity measured by AB
experiments is a difference in values of a multiple-valued complex function,
which we call a complex potential or {pre-potential. We show that any
electromagnetic field can be described by this pre-potential, and give an
explicit expression for the electromagnetic field tensor through this
potential. The pre-potential is a modification of the two scalar potential
functions.Comment: 10 pages 2 figure
Consenting agents: semi-autonomous interactions for ubiquitous consent
Ubiquitous computing, given a regulatory environment that seems to favor consent as a way to empower citizens, introduces the possibility of users being asked to make consent decisions in numerous everyday scenarios such as entering a supermarket or walking down the street. In this note we outline a model of semi-autonomous consent (SAC), in which preference elicitation is decoupled from the act of consenting itself, and explain how this could protect desirable properties of informed consent without overwhelming users. We also suggest some challenges that must be overcome to make SAC a reality
Identifying Identical Distributed Lag Structures by the Use of Prior SumConstraints
This paper derives an estimation procedure which, when the same distributed lag appears twice in an equation to be estimated by least-squares regression, identifies all of the relevant coefficients and lag weights and also constrains the two sets of individual lag weights to be identical. The procedure for solving this identification-constraint problem involves prior imposition of a restriction on the lag weight sum -- i.e., it is necessary to impose the sum restriction before estimating the equation. A further useful feature of the derived procedure is that it facilitates conveniently imposing the sum restriction on all of the weights in a distributed lag even if the leading weight is independent of a polynomial restriction imposed on the others.
Aspects of Investor Behavior Under Risk
The three sections of this paper support three related conclusions. First, asset demands with the familiar properties of wealth homogeneity and linearity in expected returns follow as close approximations from expected utility maximizing behavior under the assumptions of constant relative risk aversion and joint normally distributed asset returns. Second, although such asset demands exhibit a symmetric coefficient matrix with respect to the relevant vector of expected asset returns, symmetry is not a general property, and the available empirical evidence warrants rejecting it for both institutional and individual investors in the United States. Finally, in a manner analogous to the finite maximum exhibited by quadratic utility, a broad class of mean-variance utility functions also exhibits a form of wealth satiation which necessarily restricts it range of applicability.
A Note on the Derivation of Linear Homogeneous Asset Demand Functions
Among the numerous familiar sets of specific assumptions sufficient to derive mean-variance portfolio behavior from more general expected utility maximization in continuous time, the assumptions of constant relative risk aversion and joint normally distributed asset return assessments are also jointly sufficient to derive asset demand functions with the two desirable (and frequently simply assumed) properties of wealth homogeneity and linearity in expected returns. In addition, in discrete time constant relative risk aversion and joint normally distributed asset return assessments are sufficient to yield linear homogeneous asset demands as approximations if the time unit is small.
Phenomenology of D-Brane Inflation with General Speed of Sound
A characteristic of D-brane inflation is that fluctuations in the inflaton
field can propagate at a speed significantly less than the speed of light. This
yields observable effects that are distinct from those of single-field slow
roll inflation, such as a modification of the inflationary consistency relation
and a potentially large level of non-Gaussianities. We present a numerical
algorithm that extends the inflationary flow formalism to models with general
speed of sound. For an ensemble of D-brane inflation models parameterized by
the Hubble parameter and the speed of sound as polynomial functions of the
inflaton field, we give qualitative predictions for the key inflationary
observables. We discuss various consistency relations for D-brane inflation,
and compare the qualitative shapes of the warp factors we derive from the
numerical models with analytical warp factors considered in the literature.
Finally, we derive and apply a generalized microphysical bound on the inflaton
field variation during brane inflation. While a large number of models are
consistent with current cosmological constraints, almost all of these models
violate the compactification constraint on the field range in four-dimensional
Planck units. If the field range bound is to hold, then models with a
detectable level of non-Gaussianity predict a blue scalar spectral index, and a
tensor component that is far below the detection limit of any future
experiment.Comment: 23 pages, 11 figures, v2: version accepted by PRD; minor
clarifications and references added to the text. Higher resolution figures
are available in the published version. v3: post-publication correction of
typo in Eq. 87. No results/conclusions change
Realistic calculations of nuclear disappearance lifetimes induced by neutron-antineutron oscillations
Realistic calculations of nuclear disappearance lifetimes induced by
neutron-antineutron oscillations are reported for oxygen and iron, using
antineutron nuclear potentials derived from a recent comprehensive analysis of
antiproton atomic X-ray and radiochemical data. A lower limit of 3.3 x 10E8 s
on the neutron-antineutron oscillation time is derived from the
Super-Kamiokande I new lower limit of 1.77 x 10E32 yr on the neutron lifetime
in oxygen. Antineutron scattering lengths in carbon and nickel, needed in trap
experiments using ultracold neutrons, are calculated from updated antinucleon
optical potentials at threshold, with results shown to be largely model
independent.Comment: version matching PRD publication, typos and references correcte
- …