Related papers: Dispersion relations and soft pion theorems for K …
We use a dispersion representation based on unitarity and analyticity to study the low energy $\gamma^* N\rightarrow \pi N$ process in the $S_{11}$ channel. Final state interactions among the $\pi N$ system are critical to this analysis.…
An overview is presented about old and recent methods to compute the $K\to \pi \pi$ decay amplitude.
We consider pion pair production in two-photon collisions, gamma* gamma -> pi+ pi-, at large photon virtuality Q^2 and center-of-mass energy \sqrt{s} in the hard-scattering picture. In the limit where s is large but s << Q^2 we derive an…
We match the results for the subthreshold parameters of pion-nucleon scattering obtained from a solution of Roy-Steiner equations to chiral perturbation theory up to next-to-next-to-next-to-leading order, to extract the pertinent low-energy…
A reanalysis of $\pi\pi$ amplitudes for all important partial-waves below about 2 GeV is presented. A set of once subtracted dispersion relations with imposed crossing symmetry condition is used to modify unitary multi-channel amplitudes in…
We evaluate the amplitude for gamma gamma --> pi^+ pi^- to two loops in the framework of chiral perturbation theory.The three new coupling constants that enter the result at this order in the low-energy expansion are estimated via resonance…
In order to directly compute physical two-pion K-decay amplitudes using lattice methods we must prepare a two-pion state with non-zero relative momentum. Building upon a proposal of Lellouch and L\"uscher, we describe a finite-volume method…
A simple matching procedure is proposed to extract constraints on effective meson theories. In this way, a QCD prediction for the pion decay constant is found, F(pi)=2 m(pi)/pi, i.e. approximately 90MeV. The same procedure also determines…
An effective theory for the soft field modes in hot QCD has been obtained recently by integrating out the field modes of momenta of order T and g T. The mean hard particle distribution obeys a transport equation with a collision term. The…
We match the known chiral perturbation theory representation of the pi pi scattering amplitude to two loops with a phenomenological description that relies on the Roy equations. On this basis, the corrections to Weinberg's low energy…
We compute the strong coupling constant $g_{P^* P \pi}$, with $P$ and $P^*$ respectively pseudoscalar and vector heavy mesons by using the QCD sum rules approach. Our computation is based on the evaluation of the time ordered product of…
Following the Gauge Theory Bootstrap method proposed in our previous work [arXiv:2309.12402], we compute pion scattering phase shifts for all partial waves with angular momentum $\ell\le 3$ up to 2 GeV and calculate the low energy $\chi$PT…
We present a set of once subtracted dispersion relations which implement crossing symmetry conditions for the $\pi\pi$ scattering amplitudes below 1 GeV. We compare and discuss the results obtained for the once and twice subtracted…
We study the correspondence between models of a self-interacting canonical complex scalar field and P(X)-theories/shift-symmetric k-essence. Both describe the same background cosmological dynamics, provided that the amplitude of the complex…
We investigate pion photoproduction off the proton in a manifestly gauge-invariant chiral unitary extension of chiral perturbation theory. In a first step, we consider meson-baryon scattering taking into account all next-to-leading order…
We revisit the information on the two lightest $a_0$ resonances and $S$-wave $\pi\eta$ scattering that can be extracted from photon-photon scattering experiments. For this purpose we construct a model for the $S$-wave photon-photon…
The s-wave correlated $\pi$-$\pi$ strength distribution in cold nuclear matter is investigated. The in-medium single pions are renormalized by means of the usual p-wave couplings to nucleons and $\Delta$'s. Two groups of models for the…
In this paper, we present a dispersive analysis of the double-virtual photon-photon scattering to two pions up to 1.5 GeV. Through unitarity, this process is very sensitive to hadronic final state interaction. For the $s$-wave, we use a…
We present a determination of the mass, width and coupling of the strange resonances appearing in pion-kaon scattering below 1.8 GeV, namely the much debated $K^*_0(800)$ or $\kappa$, the scalar $K^*_0(1430)$, the $K^*(892)$ and $K^*(1410)$…
Explicit expressions for pion correlators are derived in position-space, employing Chiral Perturbation Theory (ChPT). Resonance exchange contributions are included to test the range of applicability of the leading-order ChPT expressions.…