New Physics and the Proton Radius Problem

Background: The recent disagreement between the proton charge radius extracted from Lamb shift measurements of muonic and electronic hydrogen invites speculation that new physics may be to blame. Several proposals have been made for new particles that account for both the Lamb shift and the muon anomalous moment discrepancies. Purpose: We explore the possibility that new particles' couplings to the muon can be fine-tuned to account for all experimental constraints. Method: We consider two fine-tuned models, the first involving new particles with scalar and pseudoscalar couplings, and the second involving new particles with vector and axial couplings. The couplings are constrained by the Lamb shift and muon magnetic moments measurements while mass constraints are obtained by kaon decay rate data. Results: For the scalar-pseudoscalar model, masses between 100 to 200 MeV are not allowed. For the vector model, masses below about 200 MeV are not allowed. The strength of the couplings for both models approach that of electrodynamics for particle masses of about 2 GeV. Conclusions: New physics with fine tuned couplings may be entertained as a possible explanation for the Lamb shift discrepancy.Comment: 6 pages, 6 figures, v2 contains revised comment on competing model of Lamb Shift discrepanc

Resonance Region Structure Functions and Parity Violating Deep Inelastic Scattering

The primary motive of parity violating deep inelastic scattering experiments has been to test the standard model, particularly the axial couplings to the quarks, in the scaling region. The measurements can also test for the validity of models for the off-diagonal structure functions $F_{1,2,3}^{\gamma Z}(x,Q^2)$ in the resonance region. The off-diagonal structure functions are important for the accurate calculation of the $\gamma Z$-box correction to the weak charge of the proton. Currently, with no data to determine $F_{1,2,3}^{\gamma Z}(x,Q^2)$ directly, models are constructed by modifying existing fits to electromagnetic data. We present the asymmetry value for deuteron and proton target predicted by several different $F_{1,2,3}^{\gamma Z}(x,Q^2)$ models, and demonstrate that there are notable disagreements.Comment: 6 pages, 3 figures. New version contains additional descriptions of competing structure function model

Gamma-Z box contributions to parity violating elastic e-p scattering

Parity-violating (PV) elastic electron-proton scattering measures Q-weak for the proton, $Q_W^p$. To extract $Q_W^p$ from data, all radiative corrections must be well-known. Recently, disagreement on the gamma-Z box contribution to $Q_W^p$ has prompted the need for further analysis of this term. Here, we support one choice of a debated factor, go beyond the previously assumed equality of electromagnetic and gamma-Z structure functions, and find an analytic result for one of the gamma-Z box integrals. Our numerical evaluation of the gamma-Z box is in agreement within errors with previous reports, albeit somewhat larger in central value, and is within the uncertainty requirements of current experiments.Comment: 4 pages, 4 figures, v2: reference added, typo fixe

Dynamic Doorways: Overdoor Sculpture in Renaissance Genoa

Soprapporte--rectangular, overdoor lintels sculpted from marble or slate--were a prominent feature of both private residential and ecclesiastic portals in the Ligurian region in northwest Italy, and in particular its capital city Genoa, during the second half of the fifteenth and early sixteenth centuries. Sculpted site- or city-specific religious narratives occupy the centers of most soprapporte, and are typically framed with the coats of arms or the initials of their patrons. As this study demonstrates, soprapporte were not merely ornamental, for they acted as devotional objects and protective devices while connecting the citizens who commissioned them to the city, neighborhoods, and religious complexes whose portals they decorated. With a few exceptions, the literature on soprapporte is confined to scholarship produced by a limited circle of Ligurian scholars, and it is not part of the wider discourse of Italian Renaissance sculpture. By adopting an interdisciplinary approach to the relationship between these prominent and expensive objects and the history of ritual, patronage, and religious and domestic art in Genoa, this study represents the first comprehensive examination of these objects in English. In doing so, it also aims to reinstate Genoa into the dialogue of students and scholars of Renaissance politics, society, culture, religion, and art. The dissertation is composed of an introduction that examines traditions in ecclesiastic and domestic façade decorations and considers the sculptors, placement, developments, prevalence, preservation, and materials involved in creating soprapporte. This essential background information is followed by four chapters, which serve as case studies for the various functions, imagery, and dissemination of overdoor sculptures throughout Genoa and the rest of the Ligurian region. The over 350 examples of this sculptural type that I have encountered in my field research and consultation of secondary sources are included in an appendix. The result is a study that broadens the understanding of Ligurian, and especially Genoese, Renaissance art as well as provides a more coherent picture of the appearance and function of soprapporte and the ways in which they helped forge familial, communal, and devotional identities

Review of two-photon exchange in electron scattering

We review the role of two-photon exchange (TPE) in electron-hadron scattering, focusing in particular on hadronic frameworks suitable for describing the low and moderate Q^2 region relevant to most experimental studies. We discuss the effects of TPE on the extraction of nucleon form factors and their role in the resolution of the proton electric to magnetic form factor ratio puzzle. The implications of TPE on various other observables, including neutron form factors, electroproduction of resonances and pions, and nuclear form factors, are summarized. Measurements seeking to directly identify TPE effects, such as through the angular dependence of polarization measurements, nonlinear epsilon contributions to the cross sections, and via e+ p to e- p cross section ratios, are also outlined. In the weak sector, we describe the role of TPE and gamma-Z interference in parity-violating electron scattering, and assess their impact on the extraction of the strange form factors of the nucleon and the weak charge of the proton.Comment: 73 pages, 40 figures, review article for Prog. Part. Nucl. Phys. (dedicated to the memory of John A. Tjon

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe

Sculpting Public Presence in Early Modern Genoa: Overdoor Imagery in the Doria Family Neighborhood

ABSTRACT In fifteenth-century Genoa, the illustrious Doria family sought to augment their neighborhood with at least nine soprapporte, a lintel relief type particular to the Ligurian region. Adorned with Genoese and Doria patron saints and framed by the family’s coats of arms, these overdoor sculptures acted as both protective devices and also as promotional place markers visible to the frequent processions and celebrations along the public streets and piazza they faced. This essay posits that the Doria used soprapporte to not only endorse a unified Genoa but also to advance their individual family agenda on an international stage.</jats:p