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Popular misconceptions and outright myths about gravity and tides are illustrated by examples recently found in magazines and newspapers, and then discussed.

A spinning motion of a compact disc in a CD player offers an interesting and challenging problem in rotational kinematics with a nonconstant angular acceleration that can be incorporated into a typical introductory physics class for engineers and scientists. It can be used either as an example presented during the lecture, emphasizing application of calculus, or as a homework assignment that could be handled easily with the help of a spreadsheet, thus eliminating the calculus aspect altogether. I tried both approaches, and the spreadsheet study was favored by my students.

A tautochrone is a curve down where a bead will slide to the bottom under the influence of gravity in the same amount of time regardless of where you initially place it. Huygens was first to prove that such a curve is an arc of an inverted cycloid.1

Elongation of a vertically suspended Slinky under its own weight and a weight hung from it is discussed using elementary considerations. Displacement of the center of mass of Slinky is also found. The results are verified experimentally using a $1 apparatus.

Using the Weinberg-Soper formalism we construct the front-form $(j, 0)\ensuremath{\bigoplus}(0, j)$ spinors. Explicit expressions for the generalized Melosh transformations up to spin two are obtained. The formalism, without explicitly invoking any wave equations, reproduces the spin-\textonehalf{} front-form results of Melosh, Lepage and Brodsky, and Dziembowski.

We identify the source of a discrepancy between ${F}_{\ensuremath{\pi}}^{\mathrm{soft}}|\mathrm{long}$ and ${F}_{\ensuremath{\pi}}^{\mathrm{soft}}|\mathrm{trans}$ found by Isgur and Llewellyn Smith. We find that the discrepancy disappears when virtual $q\overline{q}$ pair production for longitudinal-momentum transfers is included. Our result rectifies the discussion by Isgur and Llewellyn Smith of soft nonperturbative effects at presently available values of ${Q}^{2}$.

The “instant” and “light front” forms of relativistic dynamics postulated by Dirac refer to physical conditions on flat spacelike surfaces in the Minkowski space. We consider another flat surface in the Minkowski space that upon parametric rotation interpolates between “instant” and “light front” surfaces. A projection of the covariant perturbation theory on the new surface is then considered. One limit of the theory reproduces the usual instant dynamics, whereas a different limit gives a light front dynamics. Neither infinite momemtum frame limit nor infinite momenta are involved. Although the interpolating surface is the “instant” surface in the moving system of reference, we argue why our procedure should not be associated with a Lorentz transformation.

The relativistic two-body bound-state form factor, recently calculated by Mankiewicz and Sawicki from a light-front formula involving analytic solutions to the Weinberg equation in a (1+1)-dimensional model field theory, is compared with the form factor obtained from the Mandelstam formula using analytic solutions to the corresponding Bethe-Salpeter equation. The results are different, since the former formula does not include the contribution of pair-creation diagrams which are included in the latter. When the pair-creation diagrams are included in the light-front formula in 1+1 dimensions, both approaches yield a numerically identical form factor, not having the strange properties described by Mankiewicz and Sawicki.

We show that under the operation of parity the {\it front-form} $(1/2,\,0)$ and $(0,\,1/2)$ Weyl spinors (massive or massless) do not get interchanged. This has the important consequence that if a front-form theory containing $(1/2,\,0)\oplus(0,\,1/2)$ representation space has to be parity covariant then one must study the evolution of a physical system not only along $x^+$ but also along the $x^-$ direction. As a result of our analysis, we find an indication that there may be no halving of the degrees of freedom in the front form of field theories., LAUR-93-4317-REV, 10 pages, Revtex Version 3.0 (Accepted for publication in Phys. Lett. B)

We argue that off-shell corrections to the parton model may account for a significant part of the reported violation of the Gottfried sum rule in deep inelastic scattering as well as for a relative depletion of Drell-Yan pairs at high [ital x][sub [ital F]] in nuclear targets.

We consider paths to the observation of the ultraheavy, negatively charged particle, a possible remnant from the early Universe. In particular, we study the reactions in a deuterium environment.

Covariant perturbation theory is formulated using a new set of space-time coordinates. This corresponds to a quantization on any flat spacelike surface in Minkowski space. One limit of the theory reproduces the usual instant (equal-time) dynamics, whereas a different limit gives light-front dynamics. Neither the infinite-momentum frame nor infinite momenta are involved. In particular a smooth parametric transformation from the instant to light-front picture is given for a system at rest.

Ever since the first successful Quantum Teleportation experiment was performed at the University of Innsbruck and subsequently repeated by numerous groups worldwide, the subject of Quantum Teleportation has been a big hit not only in the physics journals, but even more so in mass media.

The $\mathrm{VNN}$ sector of the nonstatic Lee model is investigated as a prototype of the three-nucleon $\mathrm{pnn}$ system, leading to an effective three-body Hamiltonian with a new kind of disconnected three-body force. The solution of the disconnectedness problem is presented in terms of modified Faddeev equations. The state vectors of the deuteron and triton are constructed and scattering amplitudes for reactions $n+p\ensuremath{\rightarrow}n+p$, $n+p\ensuremath{\rightarrow}n+n+{\ensuremath{\pi}}^{+}$, and $n+d\ensuremath{\rightarrow}n+d$ are derived. All effects of off-shell renormalization are included in a complete and consistent way.

We calculate the differential cross sections at various angles for reactions 3 He(p, pp)d and 3 He(p, pd)p at 35 MeV and 45 MeV incident proton laboratory energy, solving the integral equations of four-body theory with separable, S-wave, spin-dependent two body forces.

Generalized separable potential model of Alt, Grassberger and Sandhas is applied to 4-N system with the use of Bateman method and unitary pole approximation (UPA). Our principal aim is the evaluation of cross sections for processes like p 3He → p 3He and dd → pt. Bound states for 2-, 3-, and 4-body systems turned out to be very close to the experimental data either by input or by accident. However, the good fit at the negative energy, combined with the UPA method gave us a very good agreement for scattering processes at laboratory energies 9.75, 13.8, 25.3 and 51.5 MeV.

The ladder approximation to the bound-state equation at equal light-cone time is investigated in the framework of a scalar field theory. With the help of the Fock transformation the equation is reduced to an eigenvalue problem for a compact operator. Eigensolutions for lowest-energy levels are found and compared with the results of the covariant ladder approximation. In the positronium region both schemes yield equivalent eigenvalues, in agreement with predictions of perturbation theory. For strongly bound systems, however, both schemes give different results. The eigenfunctions are explicitly given and their asymptotic behavior is analyzed.

where R(t) is e i ther a cons tan t or a l inear funct ion, is appl ied to the charged-pion photoproduct ion processes ,/p -> u+n and yn -~ ~-p . We consider the z~, A s and p Regge exchanges and the appropr ia te absorpt ion cuts, s t rongly enhanced by coherent inelast ic factors ~'s. Our ampl i tudes are wr i t t en in the s-channel hel ic i ty formalism of COnENTANNOUDJI et al. (~). The A factors appear expl ic i t ly in the following formula for the full ampl i tude

Within a relativistically correct yet analytically solvable model of light-front quantum mechanics we construct the electromagnetic form factor of the two-body bound state and we study the validity of the static approximation to the full form factor. Upon comparison of full form factors calculated for different values of binding energy we observe an unexpected effect that for very strongly bound states further increase in binding leads to an increase in the size of the bound system. A similar effect is found for another quantum-mechanical model of relativistic dynamics.

We investigate the evolution equation for distribution amplitudes in the framework of a scalar theory quantized on the light cone. We find general solutions for the cases of 4 and 6 dimensions and use them to reconstruct two-body relativistic bound-state wave functions at small distances. The relation between the light-cone bound-state equation and the Bethe-Salpeter equation is discussed.

The bound-state equation at equal light-front time is investigated in the framework of a scalar field model in one space and one time dimension in the limit of an infinitely massive exchanged boson. Analytic expressions for the bound-state mass and form factor are obtained. In a weak-binding limit the results for mass and wave function coincide with those based on the nonrelativistic Schroedinger equation with delta-type potential. For weakly bound systems the form factor reduces to the proper static limit in the whole domain of momentum transfers. In general, the quality of the static approximation is controlled by a dimensionless parameter (B-bar/m) that characterizes the strength of the binding.