scholarly journals Electroweak reactions in the non-perturbative regime of QCD

2005 ◽  
pp. 147-174
Author(s):  
Ulf-G. Meißner
Keyword(s):  
Perturbative Regime

scholarly journals Highly efficient THz four-wave mixing in doped silicon

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Nils Dessmann ◽  
Nguyen H. Le ◽  
Viktoria Eless ◽  
Steven Chick ◽  
Kamyar Saeedi ◽  
...  
Keyword(s):  
Four Wave Mixing ◽  
Wave Mixing ◽  
Optical Nonlinearities ◽  
Third Order ◽  
Picosecond Pulses ◽  
Light Pulses ◽  
A Value ◽  
Doped Silicon ◽  
Perturbative Regime ◽  
Silicon Doped

AbstractThird-order non-linearities are important because they allow control over light pulses in ubiquitous high-quality centro-symmetric materials like silicon and silica. Degenerate four-wave mixing provides a direct measure of the third-order non-linear sheet susceptibility χ(3)L (where L represents the material thickness) as well as technological possibilities such as optically gated detection and emission of photons. Using picosecond pulses from a free electron laser, we show that silicon doped with P or Bi has a value of χ(3)L in the THz domain that is higher than that reported for any other material in any wavelength band. The immediate implication of our results is the efficient generation of intense coherent THz light via upconversion (also a χ(3) process), and they open the door to exploitation of non-degenerate mixing and optical nonlinearities beyond the perturbative regime.

Topologically massive chromodynamics in the perturbative regime

1985 ◽  
Vol 32 (8) ◽  
pp. 2081-2096 ◽  
Author(s):  
Robert D. Pisarski ◽  
Sumathi Rao
Keyword(s):  
Perturbative Regime

scholarly journals Future Measurements of the Nucleon Elastic Electromagnetic Form Factors at Jefferson Lab

2018 ◽  
Vol 172 ◽  
pp. 02004 ◽  
Author(s):  
Gerard Gilfoyle
Keyword(s):  
United States ◽  
Electron Beam ◽  
Form Factors ◽  
The United States ◽  
Precision Measurements ◽  
Electromagnetic Form Factors ◽  
Jefferson Lab ◽  
Atomic Nuclei ◽  
Perturbative Regime ◽  
Nucleon Form Factors

The elastic, electromagnetic form factors are fundamental observables that describe the internal structure of protons, neutrons, and atomic nuclei. Jefferson Lab in the United States has completed the 12 GeV Upgrade that will open new opportunities to study the form factors. A campaign to measure all four nucleon form factors (electric and magnetic ones for both proton and neutron) has been approved consisting of seven experiments in Halls A, B, and C. The increased energy of the electron beam will extend the range of precision measurements to higher Q2 for all four form factors together. This combination of measurements will allow for the decomposition of the results into their quark components and guide the development of a QCD-based understanding of nuclei in the non-perturbative regime. I will present more details on the 12 GeV Upgrade, the methods used to measure the form factors, and what we may learn.

scholarly journals Recent results from the CBELSA/TAPS experiment at ELSA

2020 ◽  
Vol 241 ◽  
pp. 01001
Author(s):  
Farah Afzal
Keyword(s):  
Final States ◽  
Excitation Spectra ◽  
Unpolarized Cross Section ◽  
Polarized Target ◽  
Double Polarization ◽  
Perturbative Regime ◽  
Measured Polarization ◽  
Polarization Observables ◽  
The Impact ◽  
Photoproduction Reactions

In order to gain a better understanding of the dynamics inside the nucleon and of the non-perturbative regime of QCD, the nucleon excitation spectra and the properties of nucleon resonances are investigated. An essential experimental tool to achieve this goal is the study of different photoproduction reactions. Partial wave analyses are performed in order to obtain information about the contributing resonances. A complete experiment is needed to extract the underlying amplitudes unambiguously, which requires the measurement of carefully chosen single and double polarization observables in addition to the unpolarized cross section. The CBELSA/TAPS experiment in Bonn offers the possibility to measure several polarization observables using a linearly or circularly polarized photon beam and with a longitudinally or transversely polarized target. This contribution gives an overview of recently measured polarization observables in different final states. The impact of the new data is discussed.

scholarly journals Nonsmooth and level-resolved dynamics illustrated with a periodically driven tight-binding model

2015 ◽  
Author(s):  
Masudul Haque ◽  
jiang min zhang
Keyword(s):  
Perturbation Theory ◽  
Transition Probability ◽  
Tight Binding ◽  
Coarse Graining ◽  
Sinc Function ◽  
Tight Binding Model ◽  
Binding Model ◽  
Periodically Driven ◽  
Perturbative Regime ◽  
Simple Equality

Abstract We point out that in the first-order time-dependent perturbation theory, the transition probability may behave nonsmoothly in time and have kinks periodically. Moreover, the detailed temporal evolution can be sensitive to the exact locations of the eigenvalues in the continuum spectrum, in contrast to coarse-graining ideas. Underlying this nonsmooth and level-resolved dynamics is a simple equality about the sinc function sinc x ≡ sin x/x. These physical effects appear in many systems with approximately equally spaced spectra, and are also robust for larger amplitude coupling beyond the domain of perturbation theory. We use a one-dimensional periodically driven tight-binding model to illustrate these effects, both within and outside the perturbative regime.

Molecular annihilation dynamics measured in the perturbative regime of excitation

2020 ◽  
Author(s):  
Pavel Malevich ◽  
Constantin Heshmatpour ◽  
Harald Ceymann ◽  
Maximilian Hubert Schreck ◽  
Juergen Hauer
Keyword(s):  
Perturbative Regime

scholarly journals ON UNITARITY OF A LINEARIZED YANG–MILLS FORMULATION FOR MASSLESS AND MASSIVE GRAVITY WITH PROPAGATING TORSION

2010 ◽  
Vol 25 (26) ◽  
pp. 4911-4932
Author(s):  
ROLANDO GAITAN DEVERAS
Keyword(s):  
Degrees Of Freedom ◽  
Dimensional Space ◽  
Massive Gravity ◽  
Dynamical Variable ◽  
General Covariance ◽  
Yang Mills ◽  
Dimensional Space Time ◽  
Perturbative Regime ◽  
Massive Theory ◽  
Extended Theories

A perturbative regime based on contortion as a dynamical variable and metric as a (classical) fixed background, is performed in the context of a pure Yang–Mills formulation for gravity in a (2+1)-dimensional space–time. In the massless case, we show that the theory contains three degrees of freedom and only one is a nonunitary mode. Next, we introduce quadratical terms dependent on torsion, which preserve parity and general covariance. The linearized version reproduces an analogue Hilbert–Einstein–Fierz–Pauli unitary massive theory plus three massless modes, two of them represents nonunitary ones. Finally, we confirm the existence of a family of unitary Yang–Mills-extended theories which are classically consistent with Einstein's solutions coming from nonmassive and topologically massive gravity. The unitarity of these Yang–Mills-extended theories is shown in a perturbative regime. A possible way to perform a nonperturbative study is remarked.

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