Search results for "QCD"
showing 4 items of 614 documents
Balitsky-Kovchegov equation
2011
In high-energy particle physics the energy evolution of various quantities can be calculated from the Balitsky-Kovchegov (BK) equation. Depending on the frame that is used to describe the process, the BK equation can be seen to describe either the energy evolution of the virtual photon wave function or the gluon distribution function of a hadron. In this work the BK equation is derived at leading logarithm accuracy from QCD and solved analytically in some special cases. In order to derive it the quantum field theory on the light cone is introduced. Part of the higher order corrections to the BK equation, namely the running strong coupling constant and the kinematical constraint effects, are…
Hadronic light-by-light contribution to $(g-2)_\mu$ from lattice QCD with SU(3) flavor symmetry
2020
We perform a lattice QCD calculation of the hadronic light-by-light contribution to $(g-2)_\mu$ at the SU(3) flavor-symmetric point $m_\pi=m_K\simeq 420\,$MeV. The representation used is based on coordinate-space perturbation theory, with all QED elements of the relevant Feynman diagrams implemented in continuum, infinite Euclidean space. As a consequence, the effect of using finite lattices to evaluate the QCD four-point function of the electromagnetic current is exponentially suppressed. Thanks to the SU(3)-flavor symmetry, only two topologies of diagrams contribute, the fully connected and the leading disconnected. We show the equivalence in the continuum limit of two methods of computin…
K°- K°, - D° and B° - B° oscillations in the Standard Model and beyond from unquenched Twisted Mass Lattice QCD
2013
El análisis del triángulo de unitariedad y la búsqueda de cotas restrictivas sobre las escala de nueva física requiere medidas precisas de las amplitudes de mezcla de las oscilaciones de mesones. El retículo proporciona una óptima herramienta no perturbativa para el cálculo de dichos elementos de matriz con incertidumbres del 1% y errores sistemáticos bajo control. La tesis se centra en el cálculo de los parámetros B, que controlan las oscilaciones de mesones, la masa del quark b y las constantes de desintegración fB y fBs a partir de QCD simulada en el retículo con fermiones Twisted Mass e incluyendo los efectos cuánticos de quarks dinámicos en el mar. A lo largo de esta tesis, a partir de…
QCD bremsstrahlung at high energy
2017
Tämän työn tavoitteena on laskea kahdella tavalla puutason differentiaalisen vaikutusalan korkeaenergiaraja jarrutussäteilyprosessille, jossa kvarkki siroaa ulkoisesta Coulombin kentästä ja emittoi gluonin. Ensin vaikutusala lasketaan käyttämällä "tavallista" perturbatiivista kvanttiväridynamiikkaa tapauksessa, jossa ulkoista kenttää vastaa sironta leptonista. Sirontaan liittyvä matriisielementti rakennetaan prosessiin liittyvistä kahdesta Feynmanin diagrammista, ja differentiaalisen vaikutusalan laskeminen tästä on suoraviivaista tavallisen hiukkasfysiikan alkeiskurssin tiedoilla. Korkeaenergiaraja saadaan poimimalla matriisielementistä vain voimakkaimmin massakeskipisteliikeemäärästä riip…