1,721,029 research outputs found
Redundancy in the parity-violating 2-nucleon contact Lagrangian
No full textIt is shown that the number of independent operators in the nucleon-nucleon parity violating contact Lagrangian at the leading order in the low-momentum expansion can be reduced to five by using Fierz rearrangements of the nucleon fields
Double chiral logarithms of generalized chiral perturbation theory for low-energy pi pi scattering
No full textWe express the two-massless-flavor Gell-Mann-Oakes-Renner ratio in terms of low-energy pi pi observables including the O(p(6)) double chiral logarithms of generalized chiral perturbation theory. Their contribution is sizeable and tends to compensate the one from the single chiral logarithms. However it is not large enough to spoil the convergence of the chiral expansion. As a signal of reduced theoretical uncertainty, we find that the scale dependence from the one-loop single logarithms is almost completely canceled by the one from the two-loop double logarithms
Symmetries and fundamental interactions: Theory
No full textThese are the notes of a lecture given at the Pisa summer school on Basic nuclear interactions and their link to nuclear processes in the cosmos and on earth. Taking a historical perspective we will describe the gauge principle, which lies at the basis of all known fundamental interactions
Relationship between the quark condensate and low-energy pi pi observables beyond O(p4)
No full textThe two-flavor GellMann-Oakes-Renner ratio is expressed in terms of low-energy observables including the O(p6) double chiral logarithms, computed in Generalized Chiral Perturbation Theory. It is found that their contribution is important and tends to compensate the one from the single chiral logarithms
Echoes from the Moon
No full textWe report on a determination of the Earth-Moon distance, performed by students of an Italian high school, based on measurements of the time delay of the "echo" in the radio communications between NASA mission control in Houston and the Apollo astronauts on the lunar surface. By using open-source audio-editing software, the distance can be determined with a similar to 0.1% accuracy, allowing us to observe the effect of the eccentricity of the orbit of the Moon
Measuring the quark condensate from the decays tau -> 3 pi+nu(tau)
No full textThe possibility of detect the S-wave of the decays tau --> 3 pi+nu(tau) in the threshold region is explored, with emphasis on the sensitivity to the size of the quark antiquark condensate
The decay tau -> 3 pi nu(tau), as a probe of the mechanism of dynamical chiral symmetry breaking
No full textThe decays tau --> 3 pi + nu(tau) are analyzed at one loop order in the framework of Generalized Chiral Perturbation Theory, in order to test the sensitivity to the size of spontaneous chiral symmetry breaking parameters, contained in the S-wave. The latter, due to a kinematical suppression, at threshold, of the P-wave, is relatively large enough to be detectable at high-energy machines, through azimuthal left-right asymmetries. This quantity (for the pi(-) pi(-) pi(+) mode), integrated from threshold to Q(2) = 0.35 GeV2, varies from (17 +/- 3)% in the standard case of large condensate up to (40 +/- 5)% in the extreme case of tiny condensate. The feasibility of such measurement at high luminosity colliders (e.g., CLEO) is discussed. This method provides an independent cross-check of forthcoming experimental determination of the two-light-flavor chiral condensate, based on low-energy pi pi scattering
Relativistic Covariance of the 2-Nucleon Contact Interactions
No full textRelativistic covariance restricts the number of two-nucleon contact operators. We show that these constraints can be implemented starting from a complete set of relativistically invariant contact operators up to order Q in the parity-violating sector and order Q2 in the parity-conserving one
All'origine della massa: la QCD e il suo vuoto
Full text linkLa Cromodinamica Quantistica (QCD) è la moderna teoria delle interazioni forti tra i costituenti fondamentali della materia, il cui stato fondamentale, o stato di minima energia, si chiama tecnicamente vuoto. Le sue complesse proprietà determinano per più del 95% l'intera massa visibile dell'Universo. In questo contributo si illustrano le ragioni teoriche e fenomenologiche che hanno portato alla formulazione della QCD, evidenziando in particolare il meccanismo di generazione della massa
The pi-nucleus optical potential to O(p(5)) in Chiral Perturbation Theory
No full textWe describe the calculation of the pi-nucleus optical potential to NLO in Chiral Perturbation Theory (ChPT) within a new formulation of the effective theory in the presence of a nuclear background, characterized by a static, non-uniform distribution of the baryon number, describing the finite nucleus. This formulation reduces to the conventional In-medium ChPT in the case of a uniform distribution. In this way we are able to identify unambiguously the nuclear finite size effects and disentangle the S-, P- and D-wave contributions to the optical potential without invoking the local density approximation
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