Search results for "Quantum Field Theory"
showing 9 items of 489 documents
From a causal representation of multiloop scattering amplitudes to quantum computing in the Loop-Tree Duality
2023
La teoría cúantica de campos con enfoque perturbativo ha logrado de manera exitosa proporcionar predicciones teóricas increíblemente precisas en física de altas energías. A pesar del desarrollo de diversas técnicas con el objetivo de incrementar la eficiencia de estos cálculos, algunos ingredientes continuan siendo un verdadero reto. Este es el caso de las amplitudes de dispersión con lazos múltiples, las cuales describen las fluctuaciones cuánticas en los procesos de dispersión a altas energías. La Dualidad Lazo-Árbol (LTD) es un método innovador, propuesto con el objetivo de afrontar estas dificultades abriendo las amplitudes de lazo a amplitudes conectadas de tipo árbol. En esta tesis pr…
The Principles of Quantum Theory
2013
This chapter develops the formal framework of quantum mechanics: the mathematical tools, generalization and abstraction of the notion of state, representation theory, and a first version of the postulates on which quantum theory rests.
Observation of the rare decay K-S -> pi(0)e(+)e(-)
2003
A search for the decay Ks->pi0e+e- has been made by the NA48/1 experiment at the CERN SPS accelerator. Using data collected during 89 days in 2002 with a high-intensity Ks beam, 7 events were found with a background of 0.15 events. The branching fraction BR(Ks->pi0e+e-, m(ee) > 0.165 GeV/c^2) = (3.0^{+1.5}_{-1.2}(stat) +/-0.2 (syst)) x 10^{-9} has been measured. Using a vector matrix element and a form factor equal to one, the measurement gives BR(Ks->pi0e+e-) = (5.8^{+2.9}_{-2.4}) x 10^{-9}.
Open-source QCD analysis of nuclear parton distribution functions at NLO and NNLO
2019
We present new sets of nuclear parton distribution functions (nPDFs) at next-to-leading order (NLO) and next-to-next-to-leading order (NNLO). Our analyses are based on deeply inelastic scattering data with charged-lepton and neutrino beams on nuclear targets. In addition, a set of proton baseline PDFs is fitted within the same framework with the same theoretical assumptions. The results of this global QCD analysis are compared to existing nPDF sets and to the fitted cross sections. Also, the uncertainties resulting from the limited constraining power of the included experimental data are presented. The published work is based on an open-source tool, xFitter, which has been modified to be ap…
Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment
2017
The OLYMPUS collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, $R_{2\gamma}$, a direct measure of the contribution of hard two-photon exchange to the elastic cross section. In the OLYMPUS measurement, 2.01~GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of $\approx 20\degree$ to $80\degree$. The relative luminosity between the two beam species was mo…
Four-dimensional representation of scattering amplitudes and physical observables through the application of the Loop-Tree Duality theorem
2019
Las últimas dos décadas han sido testigo de un tremendo progreso en la física teórica de alta precisión. Muchos avances han sido hechos, en particular, en la evaluación de diagramas multi-loop, pero el principal desafío yace en el tratamiento de las divergencias IR a través de eficientes esquemas de substracción. Con la complejidad del procedimiento incrementándose exponencialmente con el número de escalas, se ha hecho necesario tratar la cuestión desde un ángulo diferente, invocando así al desarrollo de nuevas técnicas. La Dualidad Lazo-Árbol (LTD, por sus siglas en inglés) provee de un nuevo marco para el cómputo de amplitudes con loops. A través de la modificación de la prescripción está…
Quantum aspects originated by Gravitation: from cosmology to astrophysics
2018
El estudio de campos cuánticos que se propagan en espacio-tiempos clásicos, curvos y dinámicos, ofrece una primera manera de evaluar las consecuencias de la teoría cuántica cuando los fenómenos gravitatorios no son despreciables. Esta es una cuestión importante que debe ser abordada cuando un campo gravitatorio intenso juega un papel principal en la dinámica de un sistema físico, tal como ocurre durante el universo temprano (inflación cósmica) o en la formación de agujeros negros astrofísicos. Una de las características más sorprendentes de esta materia es quizás el hecho de que el cálculo de observables físicos, incluso para campos sin interacción, frecuentemente involucra operadores cuadr…
Applications in Mathematical Physics
2009
It turns out that pip-space methods have many applications in physics, although they are seldom mentioned as such. To draw on a literary analogy, like Moliere’s Monsieur Jourdain speaking in prose without knowing so, many authors have been using pip-space language without realizing it. In particular, chains or lattices of Hilbert spaces are quite common in many fields of mathematical physics. Some of these applications will be discussed at length in this chapter. To mention a few examples: quantum mechanics, in particular singular interactions (Section 7.1.3), scattering theory (Section 7.2), quantum field theory (Section 7.3), representations of Lie groups (Section 7.4), etc.
Search for the Decay of the Higgs Boson to Charm Quarks with the ATLAS Experiment
2018
A direct search for the standard model Higgs boson decaying to a pair of charm quarks is presented. Associated production of the Higgs and Z bosons, in the decay mode ZH→ℓ+ℓ−c¯c is studied. A data set with an integrated luminosity of 36.1 fb−1 of pp collisions at √s=13TeV recorded by the ATLAS experiment at the LHC is used. The H→c¯c signature is identified using charm-tagging algorithms. The observed (expected) upper limit on σ(pp→ZH)×B(H→c¯c) is 2.7 (3.9+2.1−1.1) pb at the 95% confidence level for a Higgs boson mass of 125 GeV, while the standard model value is 26 fb.