Ronald Bryan

Are quarks and leptons dynamically confined in four flat extra dimensions

Rubakov and Shaposhnikov have shown that the domain wall generated by real one-component φ4 theory extended to five flat (non-compact) dimensions can trap a massive bosonic excitation on the wall M4; adding LD = i Σμ=04 ψγμ∂μψ + gψφψ likewise traps a massless left-chiral Dirac particle on the wall. Independently, Kaplan has proposed this same mechanism to generate a massless chiral fermion to circumvent no-go theorems in lattice gauge theories. We show that if the Dirac field equation is extended to (7+1) flat dimensions and the classical domain wall replaced in the four extra dimensions R4 by a harmonic-oscillator potential plus a large constant, then “orbital” times “spin” solutions are generated in R4 which exhibit approximate SU(4) × SU(2) symmetry. In an SU(4) = SU(3) × U(1) decomposition, the 1 and 3 irreps of SU(3) resemble singlet and triplet color, respectively, while the U(1) symmetry yields replications suggesting generation number. Doublet representations of SU(2) resemble weak isospin. Thus these representations bear some resemblance to quarks and leptons. We indicate an SU(3)-invariant coupling of gluons to these “quarks”, and a left-right symmetric coupling of the proposed quarks and “leptons” to electroweak bosons. We suggest looking for an alternate mechanism to the HO well, perhaps a (Euclidean) instanton.

Comments on np elastic scattering, 142–800 MeV

Abstract Important new data of McNaughton et al. on np Wolfenstein parameters are added to NN phase-shift analysis. At 800 MeV, there is a dramatic improvement and one can see with confidence which way phase shifts are heading from 500 to 800 MeV. Dispersive effects in 3D1 and 3G3 herald the onset of I = 0 inelasticity. Phase shifts account naturally for the energy dependence of ΔσL and ΔσT for np scattering and do not support the claim of Beddo et al. for an I = 0 dibaryon resonance near 733 MeV.

Time-reversal noninvariance in nucleon-nucleon scattering. I. General formalism and zero-range parameterization

Abstract The observation that, in a time-irreversible one-boson-exchange nucleon-nucleon potential model due to Bryan and Gersten, T-violation occurs mostly in the lowest-permitted angular momentum states, leads us to construct a phase-shift parameterization of the 50 to 450 MeV NN data where T-violation takes place only in the lowest possible angular momentum states. The five ordinary (T-symmetric) Wolfenstein amplitudes are taken from phase shift analysis, and the sixth, T-asymmetric amplitude, t(θ), is parameterized by a single infinitesimal phase parameter λ1(λ2) in the case of np(pp) scattering. This leads to unique predictions for the relative angular distributions of time-reversal-asymmetric observables P − a and PA − PB, even though the absolute magnitudes remain undetermined. The model corresponds to an ordinary interaction that yields the usual experimental data, plus a superimposed very short-range T-noninvariant force. As such, it directs experimentalists to those angular regions of pp and np P − a and PA − PB measurements where T-violation due to short-range forces will be most strongly manifest. As the model incorporates isospin invariance, known to hold only at the few-percent level in np scattering, the predictions are likely to have greater significance in the case of pp scattering.

ONE-MESON-EXCHANGE CONTRIBUTIONS TO NUCLEON--NUCLEON SCATTERING BELOW 400 MeV AND RELATION TO SCATTERING AT HIGHER ENERGIES.

Abstract Nucleon-nucleon scattering is studied from the standpoint of meson resonances. The 0 to 400 MeV p-p and n-p data is fit by a sum of ρ, ω, π and e Born contributions in the geometric-unitarization model, with the S-wave phase-shift parameters searched phenomenologically as in phase-shift analysis. The correspondence of this model with ordinary phase-shift analysis, which incorporates just the pion pole term, is brought out. Evidence for multi-uncorrelated meson exchange effects is indirectly obtained in that the ρ, ω and e masses, when freed in the search, take on low values, much as the ρ and ω masses take on low values in single-pole fits to the nucleon electromagnetic form factors. However the π-mass, when freed, remains close to the physical mass. Thus a verification of the pion pole contribution to N-N scattering is provided by the lower partial waves. It is concluded that the muiti-pole, geometric-unitarization model correctly depicts the major features of the N-N interaction but must be augmented by uncorrelated meson-exchange contributions. Nucleon-nucleon scattering in the range 400 to 800 MeV is briefly touched upon. Several predictions are pointed out for high-energy, high orbital angular momentum states due to meson-exchange models which fit low-energy, low angular momentum states. A plea is made for experimental measurements to test time-reversal invariance and conservation of isotopic spin.

Why Shiny Metals Are Poor Emitters of Radiation

Students often wonder why polished metals are poor emitters of radiation when they are so shiny. Here I present a simple model that helps to explain this apparent paradox.

Some examples of centripetal acceleration

In lecturing to undergraduate students at Texas A&M University over the years, I have either come across or thought of problems in centripetal acceleration that I assign in an effort to make the subject more interesting. Here are four of my favorites.

Avogadro’s number and the kinetic theory of gases

Since the rms speed vrms of gas molecules in a container does not depend on the number of molecules but only on the pressure, the volume, and the total mass of the gas, Bernoulli probably knew that his kinetic theory required an atmospheric vrms is approximately equal to 1100 mi/hr at STP. Concerns over such a high speed were no doubt lessened with measurement of Avogardo’s number some 170 years later.

Unique isospin-zero phase-shift solution for nucleon-nucleon scattering near 325 MeV

Abstract The recent measurement of D t in np scattering at 325 MeV by the BASQUE group permits a unique I = 0 phase shift solution to be determined, provided that the triplet G-wave phase shifts are constrained by theory.

Nucleon-Nucleon Scattering Phase Shifts

I present 0 to 800 MeV nucleon-nucleon elastic and inelastic phase parameters derived by several groups: Arndt & Roper; Hoshizaki; Bugg; Bystricky, Lechanoine, & Lehar; and Bryan, Clark, & VerWest. Resonant-like behavior appears in the 1D2 and 3F3 states above the inelastic threshold in Hoshizaki’s analysis but not in Arndt & Roper’s. The np data are inadequate to permit determination of the I = 0 phase parameters above 600 MeV.