Randall J. Scalise

Infrared Kuiper belt constraints

We compute the temperature and IR signal of particles of radius a and albedo α at heliocentric distance R, taking into account the emissivity effect, and give an interpolating formula for the result. We compare with analyses of COBE DIRBE data by others (including recent detection of the cosmic IR background) for various values of heliocentric distance R, particle radius a, and particle albedo α. We then apply these results to a recently developed picture of the Kuiper belt as a two-sector disk with a nearby, low-density sector (40<R<50-90 AU) and a more distant sector with a higher density. We consider the case in which passage through a molecular cloud essentially cleans the solar system of dust. We apply a simple model of dust production by comet collisions and removal by the Poynting-Robertson effect to find limits on total and dust masses in the near and far sectors as a function of time since such a passage. Finally, we compare Kuiper belt IR spectra for various parameter values. Results of this work include: (1) numerical limits on Kuiper belt dust as a function of (R, a, α) on the basis of four alternative sets of constraints, including those following from recent discovery of the cosmic IR background by Hauser et al.; (2) application to the two-sector Kuiper belt model, finding mass limits and spectrum shape for different values of relevant parameters including dependence on time elapsed since last passage through a molecular cloud cleared the outer solar system of dust; and (3) potential use of spectral information to determine time since last passage of the Sun through a giant molecular cloud.

Predictions for neutrino structure functions.

The first measurements of Delta- xF3 are higher than current theoretical predictions. We investigate the sensitivity of these theoretical predictions upon a variety of factors including: renormalization scheme and scale, quark mass effects, higher twist, isospin violation, and PDF uncertainties.

Regularization, renormalization, and dimensional analysis: Dimensional regularization meets freshman E&M

We illustrate the dimensional regularization technique using a simple example from electrostatics. This example illustrates the virtues of dimensional regularization without the complications of a full quantum field theory calculation. We contrast the dimensional regularization approach with the cutoff regularization approach, and demonstrate that dimensional regularization preserves translational symmetry. We then introduce minimal subtraction and modified minimal subtraction schemes to renormalize the result. Finally, we consider dimensional transmutation as encountered in the case of compact “extra dimensions.”

Heavy quark parton distributions: Mass-dependent or mass-independent evolution?

In a consistently formulated pQCD framework incorporating nonzero mass heavy quark partons, there is still the freedom to define parton distributions obeying either mass-independent or mass-dependent evolution equations, contrary to statements made in a recent paper by MRRS. With properly matched hard cross-sections, different choices merely correspond to different factorization schemes, and they yield the same physical cross-sections. We demonstrate this principle in a concrete order αs calculation of the DIS charm structure function. We also examine the proper matching between parton definitions and subtractions in the hard cross-section near threshold where the calculation is particularly sensitive to mass effects of the heavy quark. The results obtained from the general-mass formalism are quite stable against different choices of scale and exhibit a smooth transition in the threshold region (using either mass-independent or mass-dependent evolution), in contrast to results of ref. [3].

On the Mass of the Kuiper Belt

Evidence for the Kuiper Belt (of cometary material just past Neptune) and the processes that shape it are briefly reviewed. A summary of selected estimates of its mass is given. A two-sector model for the belt is summarized. A limit is placed on the amount of mass that could be present in the Kuiper Belt in the form of objects with sizes around a centimeter, from survival of the Pioneer 10 spacecraft’s propellant tank during a dozen years in the belt. Work in progress on the belt’s IR signal is reviewed: A useful formula is given for the IR signal from dust particles as a function of albedo, radius and heliocentric distance. Preliminary results are given for limits on the sector masses, in the two-sector model, as a function of time since last passage of the Sun through a giant molecular cloud. Possible indication for the time since such passage and possible support for the existence of a more massive outer sector are found in preliminary results for the ratios of the IR signal in the four different COBE DIRBE bands.