279 research outputs found
Digital frequency synthesizer for radar astronomy
The digital frequency synthesizer (DFS) is an integral part of the programmable local oscillator (PLO) which is being developed for the NASA's Deep Space Network (DSN) and radar astronomy. Here, the theory of operation and the design of the DFS are discussed, and the design parameters in application for the Goldstone Solar System Radar (GSSR) are specified. The spectral purity of the DFS is evaluated by analytically evaluating the output spectrum of the DFS. A novel architecture is proposed for the design of the DFS with a frequency resolution of 1/2(exp 48) of the clock frequency (0.35 mu Hz at 100 MHz), a phase resolution of 0.0056 degrees (16 bits), and a frequency spur attenuation of -96 dBc
Playing Quantum Physics Jeopardy with zero-energy eigenstates
We describe an example of an exact, quantitative Jeopardy-type quantum
mechanics problem. This problem type is based on the conditions in
one-dimensional quantum systems that allow an energy eigenstate for the
infinite square well to have zero curvature and zero energy when suitable Dirac
delta functions are added. This condition and its solution are not often
discussed in quantum mechanics texts and have interesting pedagogical
consequences.Comment: 8 pages, 3 figures, requires graphicx and epsfig packages. Additional
information, including individual files containing the Worksheet and a
Worksheet template, are available at
http://webphysics.davidson.edu/mjb/jeopardy
Prominent Decay Modes of a Leptophobic Z'
An anomaly-free U(1) charge has recently been identified within the
group E for which the familiar leptons (the left- and right-handed electron
and the left-handed neutrino) have . It is pointed out that the
charges of several {\it exotic} leptons within E matter multiplets are
quite large, leading to the prediction that half of the decays of the so-called
``leptophobic'' bosons coupling to are to these exotic leptons. Other
large charges include those of standard up-type quarks and exotic
down-type quarks. Substantial forward-backward asymmetries are expected in channels when is a standard up-type quark, an
exotic down-type quark, or an exotic lepton.Comment: 7 pages, latex, no figures. Version to be published in Phys. Lett
Spatial oscillations in the spontaneous emission rate of an atom inside a metallic wedge
A method of images is applied to study the spontaneous emission of an atom
inside a metallic wedge with an opening angle of , where N is an
arbitrary positive integer. We show the method of images gives a rate formula
consistent with that from Quantum Electrodynamics. Using the method of images,
we show the correspondence between the oscillations in the spontaneous emission
rate and the closed-orbits of emitted photon going away and returning to the
atom inside the wedge. The closed-orbits can be readily constructed using the
method of images and they are also extracted from the spontaneous emission
rate.Comment: 8 figure
Slower-than-Light Spin-1/2 Particles Endowed with Negative Mass Squared
Extending in a straightforward way the standard Dirac theory, we study a
quantum mechanical wave-equation describing free spinning particles --which we
propose to call "Pseudotachyons" (PT's)-- which behave like tachyons in the
momentum space, but like subluminal particles (v<c) in the ordinary space. This
is allowed since, as it happens in every quantum theory for spin-1/2 particles,
the momentum operator (that is conserved) and the velocity operator (that is
not) are independent operators, which refer to independent quantities. As a
consequence, at variance with ordinary Dirac particles, for PT's the average
velocity is not equal to the classical velocity, but actually to the velocity
"dual" of the classical velocity. The speed of PT's is therefore smaller than
the speed of light. Since a lot of experimental data seems to involve a
negative mass squared for neutrinos, we suggest that these particles might be
PT's, travelling, because of their very small mass, at subluminal speeds very
close to c. The present theory is shown to be separately invariant under the C,
P, T transformations; the covariance under Lorentz transformations is also
proved. Furthermore, we derive the kinematical constraints linking 4-impulse,
4-velocity and 4-polarization of free PT'sComment: LaTeX; 20 page
Leptoquark production in ultrahigh-energy neutrino interactions revisited
The prospects for producing leptoquarks (LQs) in ultrahigh-energy (UHE)
neutrino nucleon collisions are re-examined in the light of recent
interpretations of HERA data in terms of leptoquark production. We update
predictions for cross-sections for the production of first- and
second-generation leptoquarks in UHE nu-N and nubar-N collisions including
(i) recent experimental limits on masses and couplings from the LEP and
TEVATRON colliders as well as rare processes,
(ii) modern parton distributions, and
(iii) radiative corrections to single leptoquark production.
If the HERA events are due to an SU(2) doublet leptoquark which couples
mainly to (e+,q) states, we argue that there are likely other LQ states which
couple to neutrinos which are close in mass, due to constraints from precision
electroweak measurements.Comment: 12 pages, LaTeX, 3 separate postscript figures. Added 1 reference
plus discussion, updated another referenc
Analytic results for Gaussian wave packets in four model systems: II. Autocorrelation functions
The autocorrelation function, A(t), measures the overlap (in Hilbert space)
of a time-dependent quantum mechanical wave function, psi(x,t), with its
initial value, psi(x,0). It finds extensive use in the theoretical analysis and
experimental measurement of such phenomena as quantum wave packet revivals. We
evaluate explicit expressions for the autocorrelation function for
time-dependent Gaussian solutions of the Schrodinger equation corresponding to
the cases of a free particle, a particle undergoing uniform acceleration, a
particle in a harmonic oscillator potential, and a system corresponding to an
unstable equilibrium (the so-called `inverted' oscillator.) We emphasize the
importance of momentum-space methods where such calculations are often more
straightforwardly realized, as well as stressing their role in providing
complementary information to results obtained using position-space
wavefunctions.Comment: 18 pages, RevTeX, to appear in Found. Phys. Lett, Vol. 17, Dec. 200
Forward-Backward Asymmetries in Hadronically Produced Lepton Pairs
It has now become possible to observe appreciable numbers of hadronically
produced lepton pairs in mass ranges where the contributions of the photon and
are comparable. Consequently, in the reaction , substantial forward-backward asymmetries can be seen. These
asymmetries provide a test of the electroweak theory in a new regime of
energies, and can serve as diagnostics for any new neutral vector bosons
coupling both to quarks and to charged lepton pairs.Comment: 11 pages, latex, 4 uuencoded figures sent separately, Fig. 2 revise
The Stark effect in linear potentials
We examine the Stark effect (the second-order shift in the energy spectrum
due to an external constant force) for two 1-dimensional model quantum
mechanical systems described by linear potentials, the so-called quantum
bouncer (defined by V(z) = Fz for z>0 and V(z) infinite for z<0) and the
symmetric linear potential (given by V(z) = F|z|). We show how straightforward
use of the most obvious properties of the Airy function solutions and simple
Taylor expansions give closed form results for the Stark shifts in both
systems. These exact results are then compared to other approximation
techniques, such as perturbation theory and WKB methods. These expressions add
to the small number of closed-form descriptions available for the Stark effect
in model quantum mechanical systems.Comment: 15 pages. To appear in Eur. J. Phys. Needs Institute of Physics
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