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Hey everyone,</div>
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Today we will be having a remote seminar by Yang Li (USTC) at 1pm. Please join us in F224-225 or on Zoom
<a id="LPlnk939741" href="https://jlab-org.zoomgov.com/j/1612031893?pwd=Q4KRMVsR2m27YbCgvPrZzbfClwqSLD.1">
https://jlab-org.zoomgov.com/j/1612031893?pwd=Q4KRMVsR2m27YbCgvPrZzbfClwqSLD.1</a></div>
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Title: Revisiting Hadron Structure in Three Dimensions: From Electromagnetic to Mechanical Densities</div>
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Abstract:</div>
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Understanding the three-dimensional structure of hadrons — such as the proton and pion — has become a central focus in modern nuclear and particle physics. Probes via electroweak currents (vector and axial) and the energy-momentum tensor have spurred significant
theoretical and experimental advances. Nevertheless, fundamental challenges remain, particularly in defining relativistic charge and mechanical distributions. A key issue is the breakdown of the traditional Sachs formalism, which relies on non-relativistic
assumptions ill-suited for hadrons whose size is comparable to their Compton wavelength (r ∼ λ). This limitation echoes a century-old problem in relativistic electromagnetism — the proper description of electromagnetic observables for moving bodies — studied
by Lorentz, Einstein, and Minkowski. </div>
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In this talk, I will show how a covariant formulation based on relativistic multipole expansions naturally resolves this issue, revealing that various proposed hadron density distributions emerge as multipole moment densities in a covariant macroscopic electrodynamics
framework. This approach not only clarifies the physical meaning of charge distributions in relativistic systems but also provides a unified foundation for interpreting experimental data from elastic and deep exclusive scattering. I will further extend this
framework to the mechanical structure of hadrons, including pressure and shear force distributions derived from the energy-momentum tensor, offering new insights into the internal forces that bind quarks and gluons. This perspective bridges historical foundations
in relativity with contemporary hadronic physics, paving the way for a consistent and observable-based understanding of hadron structure in three dimensions.</div>
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<span style="background-color: rgb(255, 255, 255);">--</span></div>
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Joe Karpie</div>
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Pronouns: He/His/Him</div>
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Postdoctoral Fellow</div>
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Theoretical and Computational Physics Center</div>
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Jefferson Lab</div>
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