T. Goldman

The Arguments against 'antigravity' and the gravitational acceleration of antimatter

Abstract In the 1950s interest arose in the science-fiction idea of “antigravity”. This concept was a speculation that matter and antimatter would repel each other in ordinary tensor (Einsteinian) gravity. (This was reminiscent of the Coulomb interaction between like charges.) Three types of arguments were raised to disprove “antigravity”: (i) violation of conservation of energy, (ii) violation of the principle of equivalence, (iii) anomalous regeneration of Ks mesons, all of which were unseen. Unfortunately, in the physics folklore these arguments came to be interpreted as ruling out any difference in the gravitational interaction of matter and antimatter to the earth, not just ruling out this “antigravity.” After reviewing the history behind the concept of antigravity, we discuss modern theoretical ideas and experiments which are relevant to the possibility that there exist static, non-Newtonian components of gravity. We then consider the arguments against antigravity, pointing out their regimes of applicability and inapplicability to modern quantum theories of gravity. We specifically show that, if these arguments are applied to the ongoing experiment to measure the gravitational acceleration of the antiproton, they do not rule out a large anomalous gravitational response for the antiproton. The antiproton gravity experiment is one of five types of experiments that we consider to be the most critical in testing for finite but long-range, non-Newtonian and non-Einsteinian gravity. We discuss how all five are related to each other and how their completion would improve our knowledge of gravitational forces.

RELATIVISTIC SYMMETRY SUPPRESSES QUARK SPIN-ORBIT SPLITTING

Experimental data indicate small spin-orbit splittings in hadrons. For heavy-light mesons we identify a relativistic symmetry that suppresses these splittings. We suggest an experimental test in electron-positron annihilation. Furthermore, we argue that the dynamics necessary for this symmetry are possible in QCD.

Spin and orbital angular momentum in gauge theories: nucleon spin structure and multipole radiation revisited.

We address and solve the long-standing gauge-invariance problem of the nucleon spin structure. Explicitly gauge-invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task and opens a more promising avenue towards the understanding of the nucleon spin. Our research also justifies the traditional use of the canonical, gauge-dependent angular momentum operators of photons and electrons in the multipole-radiation analysis and labeling of atomic states and sheds much light on the related energy-momentum problem in gauge theories, especially in connection with the nucleon momentum.Parallel to the construction of gauge invariant spin and orbital angular momentum for QED in paper (I) of this series, we present here an analogous but non-trivial solution for QCD. Explicitly gauge invariant spin and orbital angular momentum operators of quarks and gluons are obtained. This was previously thought to be an impossible task, and opens a more promising avenue towards the understanding of the nucleon spin structure.

Are antiprotons forever

Abstract Up to more than one million antiprotons from a single LEAR spill have been captured in a large Penning trap. Surprisingly, when the antiprotons are cooled to energies significantly below 1 eV, the annihilation rate falls below the background. Thus, very long storage times for antiprotons have been demonstrated in the trap, even at the compromised vacuum conditions imposed by the experimental setup. The significance for future ultra-low-energy experiments is discussed.

Do gluons carry half of the nucleon momentum

We examine the conventional picture that gluons carry about half of the nucleon momentum in the asymptotic limit. We show that this large fraction is due to an unsuitable definition of the gluon momentum in an interacting theory. If defined in a gauge-invariant and consistent way, the asymptotic gluon momentum fraction is computed to be only about one-fifth. This result suggests that the asymptotic limit of the nucleon spin structure should also be reexamined. A possible experimental test of our finding is discussed in terms of novel parton distribution functions.

The dark matter problem and quantum gravity

Abstract We explicitly solve the one-loop renormalization group equations for a particular higher derivative quantum gravity and obtain the induced r -dependence of Newtons constant due to quantum fluctuations of the geometry. We then show how, by considering these effects, it may be possible to (a) reconcile nucleosynthesis bounds on the density parameter of the Universe with the predictions of inflationary cosmology, and (b) reproduce the inferred variation of the density parameter with distance. Our calculation can be interpreted as a computation of the contribution of gravitons to the (local) energy density of the Universe.

Radiative leptonic decays of heavy mesons.

We compute the photon spectrum and the rate for the decays [ital B]([ital D])[r arrow][ital l][nu][sub [ital l]] [gamma]. These photonic modes constitute a potentially large background for the purely leptonic decays which are used to extract the heavy meson decay constants. While the rate for [ital D][r arrow][ital l][nu][gamma] is small, the radiative decay in the [ital B] meson case could be of comparable magnitude or even larger than [ital B][r arrow][mu][nu]. This would affect the determination of [ital f][sub [ital B]] if the [tau] channel cannot be identified. We obtain theoretical estimates for the photonic rates and discuss their possible experimental implications.

Open charm tomography of cold nuclear matter

We study the relative contribution of partonic subprocesses to D meson production and D meson-triggered inclusive di-hadrons to lowest order in perturbative QCD. While gluon fusion dominates the creation of large angle DD pairs, charm on light parton scattering determines the yield of single inclusive D mesons. The distinctly different nonperturbative fragmentation of c quarks into D mesons versus the fragmentation of quarks and gluons into light hadrons results in a strong transverse momentum dependence of anticharm content of the away side charm-triggered jet. In p+A reactions, we calculate and resum the coherent nuclear-enhanced power corrections from the final-state partonic scattering in the medium. We find that single and double inclusive open charm production can be suppressed as much as the yield of neutral pions from dynamical high-twist shadowing. Effects of energy loss in p+A collisions are also investigated phenomenologically and may lead to significantly weaker transverse momentum dependence of the nuclear attenuation.

Quark delocalization, color screening, and dibaryons

The quark delocalization and color screening model, a quark potential model, is used for a systematic search of dibaryon candidates in the {ital u}, {ital d}, and {ital s} three flavor world. Color screening, which appears in unquenched lattice gauge calculations, and quark delocalization (which is similar to electron delocalization in molecular physics) are both included. Flavor symmetry breaking and channel coupling effects are studied. The model is constrained not only by baryon ground state properties but also by the {ital N}-{ital N} scattering phase shifts. The deuteron and zero energy dinucleon resonance are both reproduced qualitatively. The model predicts two extreme types of dibaryonic systems: ``molecular`` like the deuteron, and highly delocalized six-quark systems among which only a few narrow dibaryon resonances occur in the {ital u}, {ital d}, and {ital s} three flavor world. Possible high spin dibaryon resonances are emphasized.

SYSTEMATIC THEORETICAL SEARCH FOR DIBARYONS IN A RELATIVISTIC MODEL

A relativistic quark potential model is used to do a systematic search for quasi-stable dibaryon states in the u, d and s three-flavor world. Flavor symmetry breaking and channel coupling effects are included and an adiabatic method and fractional parentage expansion technique are used in the calculations. The relativistic model predicts dibaryon candidates completely consistent with the nonrelativistic model.