[Theory-seminars] Theory Seminar. Monday June 2. 1pm Room L102. Paul Hoyer

[Cesar Fernandez-Ramirez]

Dear all,

Please find enclosed the announcement of our next seminar.

Best,

Cesar


Date:    1 pm on Monday, June 2
Place:   Room L102
Speaker: Paul Hoyer (University of Helsinki)
Title:   Bound states -- from QED to QCD

Abstract: The hadron spectrum is characterized by the valence quark degrees of freedom, even though scattering (DIS) data shows that hadrons also have sea quarks and gluon constituents. The Dirac equation demonstrates that these two features can coexist for relativistic dynamics. Dirac bound states of an electron have an unlimited number of electron-positron pair constituents, while the spectrum is determined by a single electron equation. 

Confined fermion-antifermion states can be realized in gauge theory by imposing a non-vanishing boundary condition on Gauss' law. Only the simplest homogeneous solution, $A^0(\boldsymbol{x}) \propto \boldsymbol{x}$, is compatible with translation invariance, and then only for neutral states. This results in a linear instantaneous potential, similar to the ${\mathcal O}(\alpha_s^0)$ potential of the quark model. The bound states are described by equal-time wave functions in all frames, are rotationally invariant in the rest frame and have a dynamically realized boost covariance. Their electromagnetic form factors are gauge invariant and their parton distributions have contributions from sea quarks at low $x_{Bj}$. The boost from the rest frame to the infinite momentum frame reveals an interesting difference wrt. wave functions defined at equal light-cone time. The states thus constructed are candidates for ${\mathcal O}(\alpha_s^0)$ asymptotic ($in$ and $out$) states of the QCD $S$-matrix.

This approach is described in the lecture notes of arXiv:1402.5005.


-- 
César Fernández-Ramírez

Theory Center -- Jefferson Lab
12000 Jefferson Ave., Newport News, VA 23606, USA

Phone: (+1) 757-269-7844
Fax: (+1) 757-269-7002
E-mail: cesar at jlab.org