Related papers: The sigma -> gamma gamma Width from Nucleon Electr…
A non-zero signal $A_\gamma^\mathrm{np}=(-3.0\pm1.4\pm0.2)\times 10^{-8}$ of the gamma-ray asymmetry in the neutron-proton capture was recently reported by the NPDGamma Collaboration which provides the first determination of the $\Delta…
The gamma-ray strength function for gamma energies in the 1-7 MeV region has been measured for 161,162-Dy and 171,172-Yb using the (3-He,alpha gamma) reaction. Various models are tested against the observed gamma-ray strength functions. The…
Differential cross sections for elastic scattering of photons have been measured for $^{40}$Ca at energies of 58 and 74 MeV and for $^{16}$O and $^4$He at 61 MeV, in the angular range from 45$^o$ to 150$^o$. Evidence is obtained that there…
From a re-analysis of pi+ pi- -> pi+ pi- and pi+ pi- -> K K data, we found for pi-pi S-wave interaction below 2 GeV, sigma(400), f0(980), f0(1500) and f0(1780) clearly show up. f0(1370) can be included with a very small branching ratio to…
Results are presented for the medium-induced, soft coherent radiation spectrum for all $2\to 2$ partonic channels in QCD, at leading-order in $\alpha_s$ but beyond leading logarithmic accuracy. The general formula is valid in the full…
After a brief overview of the realization of chiral symmetry in hot and/or dense medium, the implications of the existence of a light scalar-isoscalar meson (which we call $\sigma$ throughout this report) are discussed in the vacuum and in…
In this thesis the polarized and unpolarized photon distributions of the nucleon (proton, neutron) $(\Delta)\gamma^N$, evaluated in the equivalent photon approximation (EPA), are computed theoretically and the possibility of their…
We present a critical analysis of Pade-based methods for the unitarization of low energy amplitudes. We show that the use of certain Pade Approximants to describe the resonance region may lead to inaccurate determinations. In particular, we…
The emission of the 4.438-MeV gamma-ray line in proton inelastic scattering off 12C has been investigated in detail. For this, two independent descriptions of the correlated scattering and emission process have been developed, one for the…
A method has been recently proposed to establish the geometry of the alpha-cluster arrangement in $^{12}$C making use of polarized gamma-rays. The ratio of intensities of scattered radiation at 90 degrees along and perpendicular to the…
We derive and analyse inequalities relating masses of the lightest pi-pi resonances (rho and sigma) to low energy couplings of the effective chiral Lagrangian in the limit of large number of colours.
We discuss how the lightest scalars, in particular the broad sigma resonance, can be understood as unitarized (qbar q) states within a unitarized quark model (UQM). The bare (qbar q) scalars are strongly distorted by hadronic mass shifts,…
We give some estimates for the light-quark mass dependence of the pole position of the sigma ($f_{0}(500)$) resonance in the complex energy plane, with the help of a chiral Lagrangian for the resonance field and some input from hadronic…
We present methods to measure the beam polarizations and the luminosity of $\gamma \gamma$ colliders at TeV energy scale. The beam polarizations of a $\gamma \gamma$ collider can easily be monitored by comparing the numbers of events of the…
Using the most general form of the interpolating currents, the coupling constants $g_{\Sigma_b\Sigma_b\pi}$ and $g_{\Sigma_c\Sigma_c\pi}$ are calculated within the light cone QCD sum rules approach. It is found that…
We discuss how the a_0(980), f_0(980), K^*_0(1430) and particularly the broad sigma resonance can be understood within a coupled channel framework, which includes all light two-pseudoscalar thresholds together with constraints from Adler…
We use dispersion relations to evaluate the gamma-Z box contribution to parity-violating electron scattering in the forward limit arising from the axial-vector coupling at the electron vertex. The calculation makes full use of the critical…
Measuring Compton scattered photons and recoil neutrons in coincidence, quasi-free Compton scattering by the neutron has been investigated at MAMI (Mainz) at $theta^{lab}_\gamma=136^o$ in an energy range from 200 to 400 MeV. From the data a…
We develop a field-theoretic model for the description of proton Compton scattering in which the proton and its excited state, the \Delta+ resonance, are described as part of one multiplet with a single Rarita-Schwinger wavefunction. In…
We revisit the measurement of the polarization fraction, $P$, and the measurement of the polarization angle of partially linearly-polarized gamma rays using their conversion to $e^+e^-$ pairs in the field of a nucleus. We show that an…