[Theory-seminars] Theory Center Seminar - P. Hoyer - L102 2:00pm

[Andrea Signori]

Reminder

> Theory Center Seminar
> Friday, May 11, 2018
> 2:00 p.m. (coffee at 1:45 p.m.)
> CEBAF Center, Room L102
> 
> Paul Hoyer
> University of Helsinki
> 
> Bound States and QCD
> 
> There are many formally equivalent perturbative approaches to QED bound states (atoms), 
> because even a first approximation has a non-polynomial wave function. Requiring that the 
> gauge field be classical at lowest order selects the \hbar expansion with a stationary action. 
> This principle allows to derive the SchrÃdinger equation from QED. Higher order corrections 
> are defined as in the Interaction Picture, but with the in- and out-states being eigenstates of 
> the Hamiltonian that includes the classical field. Features of hadron data indicate that the \hbar 
> expansion is relevant also for QCD bound states. The QCD scale can arise from a homogeneous, 
> O(\alpha_s^0) solution of the field equations. Given basic physical requirements the solution 
> appears to be unique (up to the scale). It implies a linear potential for mesons and a related 
> confining potential for baryons. At lowest order in 1/N_c mesons lie on linear Regge trajectories
> and their daughters. There are massless (M=0) states which allow an explicit realization of 
> spontaneous chiral symmetry breaking, through mixing of the 0^{++} sigma state with the 
> perturbative vacuum. Chiral transformations of the sigma condensate generate massless 0^{-+}
> pions. For a small quark mass m the pion gets a mass M \propto \sqrt{m}. The pion is annihilated 
> by the axial vector current as expected for a Goldstone boson.
> 
> 
> The link to attend remotely via BlueJeans is available at https://www.jlab.org/div_dept/theory/seminars/2018-spring-cake-seminar.html <https://www.jlab.org/div_dept/theory/seminars/2018-spring-cake-seminar.html>_______________________________________________

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