R.L. Jaffe

Diquarks and exotic spectroscopy

We propose that the recently discovered Theta(+) baryon is a bound state of four quarks and an antiquark, containing two highly correlated ud pairs. If so, the theta(+) has positive parity, and it lies in an near-ideally mixed SU(3)(f) 10;(f) plus sign in circle 8(f). The Roper resonance and the P11(1710) fit naturally into this classification. We predict an isospin 3/2 multiplet of Xis (S=-2) with J(Pi)=1 / 2(+) around 1750 MeV. A search for manifestly exotic Xi(+) and Xi(--) in this mass range could provide a sharp test of our proposal. We predict that charm and bottom analogs of the Theta(+) may be stable against strong decays.

The g1 problem : deep inelastic electron scattering and the spin of the proton

Abstract A recent measurement of the spin-dependent structure function of the proton, g 1 p ( x , Q 2 ), suggest that the quarks spin accounts for little of the protons spin. We analyze several theoretical issues bearing on this result. We discuss the result expected in a variety of quark models. We examine the proposal that gluons contribute to the protons spin in an amount calculable (in terms of gluon distribution functions) in perturbative QCD. We examine the conserved currents associated with Lorentz transformations in QCD, derive sum rules and show that the anomalous (gluonic) U (1) A current, K μ , is not in general to be identified with the gluon spin. Finally, we discuss the ensemble of nucleon matrix elements of quark bilinear operators and urge an experimental and theoretical program to study them.

Chiral-odd parton distributions and Drell-Yan processes☆

Abstract We study the twist-two and twist-three chiral-odd parton distributions, h 1 ( x ), h L ( x ) and e ( x ), which appear in the quark density matrix of the nucleon. We explore the relationship between h 1 ( x ) and the spin properties of the nucleon; we unravel the twist structure of h L ( x ) and we emphasize the role of e ( x ) in studying the deep-inelastic structure function E 4 ν N ( x ) and the π N σ-term. We derive sum rules, make model estimates, and show that they all appear in Drell-Yan cross sections with polarized and unpolarized beams.

Unconventional states of confined quarks and gluons

Abstract The spectrum of confined colored quarks and gluons is studied in the bag. ta states are calculated: hadrons made of gluons alone; QQ Q Q exotics and QQQ or Q Q states with unconventional quantum numbers. Many of these states are in the mass range 600–1600 MeV. The known 0++ mesons may be members of a nonet of QQ Q Q exotics rather than P-wave Q Q states.

Pathways for solar photovoltaics

Solar energy is one of the few renewable, low-carbon resources with both the scalability and the technological maturity to meet ever-growing global demand for electricity. Among solar power technologies, solar photovoltaics (PV) are the most widely deployed, providing 0.87% of the worlds electricity in 2013 and sustaining a compound annual growth rate in cumulative installed capacity of 43% since 2000. Given the massive scale of deployment needed, this article examines potential limits to PV deployment at the terawatt scale, emphasizing constraints on the use of commodity and PV-critical materials. We propose material complexity as a guiding framework for classifying PV technologies, and we analyze three core themes that focus future research and development: efficiency, materials use, and manufacturing complexity and cost.

Strangeness Mixing and Quenching in the Nambu-Jona-Lasinio Model

Abstract We study the mixing of quarks of one flavor into the wavefunction of constituent quarks of a different flavor when chiral symmetry breaks dynamically in the Nambu-Jona-Lasinio model. First we generalize the Nambu-Jona-Lasino model to N ƒ flavors including U(1) A symmetry breaking by a 2N ƒ - fermion interaction. In the Hartree-Fock approximation, this term is entirely responsible for flavor mixing. We specialize to three flavors and use meson properties and vacuum quark condensates to fix the three parameters of the model. We show that there are generically two different regimes in the broken chiral symmetry phase. Non-linearities in the strange quark mass are strong in the “barely broken regime”, allowing for a large Σ-term and a small s-quark content of the proton. In the “firmly broken regime”, non-linearities in m s , are small, chiral perturbation theory is likely to be reliable and the Σ-term is small. We also study deep inelastic scattering and demonstrate that dynamical chiral symmetry breaking gives rise to a non-negligible s-parton distribution.

Parton distribution functions for twist 4

Abstract All O(1/Q2) corrections to leptoproduction are described by a small number of generalized multiparton distribution functions which depend only on the longitudinal momentum of the partons. We show that these functions can be represented (in A+ = 0 gauge) by sequential emission or absorption by the target of quarks, antiquarks and gluons where (i) all quanta move with 0 ⩽ k+/p+ ⩽ 1; (ii) all intermediate hadronic states are on-mass-shell; (iii) no graphs are semi-disconnected with respect to the target or the intermediate hadronic state. We show how all O(1/Q2) corrections to the forward virtual Compton amplitude can be represented in terms of these parton distributions.

Scattering theory approach to electrodynamic Casimir forces

We give a comprehensive presentation of methods for calculating the Casimir force to arbitrary accuracy, for any number of objects, arbitrary shapes, susceptibility functions, and separations. The technique is applicable to objects immersed in media other than vacuum, nonzero temperatures, and spatial arrangements in which one object is enclosed in another. Our method combines each objects classical electromagnetic scattering amplitude with universal translation matrices, which convert between the bases used to calculate scattering for each object, but are otherwise independent of the details of the individual objects. The method is illustrated by rederiving the Lifshitz formula for infinite half-spaces, by demonstrating the Casimir-Polder to van der Waals crossover, and by computing the Casimir interaction energy of two infinite, parallel, perfect metal cylinders either inside or outside one another. Furthermore, it is used to obtain new results, namely, the Casimir energies of a sphere or a cylinder opposite a plate, all with finite permittivity and permeability, to leading order at large separation.

Stranger than fiction: The strangeness radius and magnetic moment of the nucleon☆

Abstract The nucleon matrix elements of the operators r 2 s ≡s † (x)x 2 s(x) and μ s ≡ 1 2 x× s γs are estimated using dispersion theory fits to the nucleon isoscalar form factor, together with a standard treatment of θ-ω mixing and some mild assumptions on the asymptotic behavior (at large q2) of nucleon form factors. The results indicate a significant strange quark content in the nucleon.

Insight into the scalar mesons from a lattice calculation

Abstract We study the possibility that the light scalar mesons are q 2 q 2 states rather than q q . We perform a lattice QCD calculation of pseudoscalar meson scattering amplitudes, ignoring quark loops and quark annihilation, and find indications that for sufficiently heavy quarks there is a stable four-quark bound state with J PC =0 ++ and non-exotic flavor quantum numbers.