Harald W. Grießhammer

Signatures of chiral dynamics in low-energy Compton scattering off the nucleon

Abstract.We present a projection formalism which allows us to define dynamical polarizabilities of the nucleon from a multipole expansion of the nucleon Compton amplitudes. We give predictions for the energy dependence of these dynamical polarizabilities both from Dispersion Theory and from leading-one-loop Chiral Effective Field Theory. Based on the good agreement between the two theoretical frameworks, we conclude that the energy dependence of the dynamical polarizabilities is dominated by chiral dynamics, except in those multipole channels where the first nucleon resonance

Naïve dimensional analysis for three-body forces without pions

Delta

Nucleon polarisabilities from Compton scattering on the deuteron

(1232) can be excited. Both the Dispersion Theory framework and a Chiral Effective Field Theory with explicit

Spin polarizabilities of the nucleon from polarized low-energy Compton scattering

Delta

Measurement of compton scattering from the deuteron and an improved extraction of the neutron electromagnetic polarizabilities.

(1232) degrees of freedom lead to a very good description of the available low-energy proton Compton data. We discuss the sensitivity of the proton Compton cross-section to dynamical polarizabilities of different multipole content and present a fit of the static electric and magnetic dipole polarizabilities from low-energy Compton data up to

Dispersion effects in nucleon polarizabilities

omega sim 170;mathrm{MeV}

Explicit Δ(1232) degrees of freedom in Compton scattering off the deuteron

, finding

Pion Deuteron Scattering Length in Effective Field Theory

bar{alpha}_{E} = (11.04pm1.36)cdot 10^{-4};mathrm{fm}^3,; bar{beta}_{M} = (2.76mp1.36)cdot 10^{-4};mathrm{fm}^3

Compton scattering from the deuteron below pion-production threshold

.

Nucleon polarisabilities from Compton scattering off the one- and few-nucleon system

Abstract For systems of three identical particles in which short-range forces produce shallow two-particle bound states, and in particular for the “pionless” effective field theory of nuclear physics, I extend and systematise the power-counting of three-body forces to all partial waves and orders, including external currents. With low-energy observables independent of the details of short-distance dynamics, the typical strength of a three-body force is determined from the superficial degree of divergence of the three-body diagrams which contain only two-body forces. This naive dimensional analysis must be amended as the asymptotic solution to the leading-order Faddeev equation depends for large off-shell momenta crucially on the partial wave and spin combination of the system. It is shown by analytic construction to be weaker than expected in most channels with angular momentum smaller than 3. This demotes many three-nucleon forces to high orders. Observables like the 4 S 3/2 -scattering length are less sensitive to three-nucleon forces than guessed. I also comment on the Efimov effect and limit-cycle for non-zero angular momentum.