Search results for "Strong Interaction"
showing 10 items of 77 documents
The rho NN coupling with direct coupling and loops
2002
Starting from a gauge formalism of $\rho$ mesons, pions and baryons we evaluate the $\rho$ coupling to the nucleon, including the direct coupling provided by the Lagrangians, plus contributions from loops with the virtual pion cloud. We find a contribution to the magnetic $\rho$ coupling to the nucleon from pionic loops of the same size as the direct coupling, which is, however, still small compared to the empirical values. This finding goes in line with chiral formulations of the strong interaction of mesons at low energies where, unlike the scalar mesons which are mostly built of a pion (kaon) cloud, the $\rho$ meson stands as a genuine QCD state with intrinsic properties not tied to thos…
Lattice QCD and the anomalous magnetic moment of the muon
2019
The anomalous magnetic moment of the muon, a_mu, has been measured with an overall precision of 540 ppb by the E821 experiment at BNL. Since the publication of this result in 2004 there has been a persistent tension of 3.5 standard deviations with the theoretical prediction of a_mu based on the Standard Model. The uncertainty of the latter is dominated by the effects of the strong interaction, notably the hadronic vacuum polarisation (HVP) and the hadronic light-by-light (HLbL) scattering contributions, which are commonly evaluated using a data-driven approach and hadronic models, respectively. Given that the discrepancy between theory and experiment is currently one of the most intriguing …
Foundations of the Quantum Chromodynamics
2015
Quantum chromodynamics (QCD) is a theory to describe the strong interaction in hadrons. It was developed in the history of understanding the structure of the hadrons. In the 1950s, a large number of hadrons were discovered in experiments.
Transition form factors of theN*(1535)as a dynamically generated resonance
2008
We discuss how electromagnetic properties provide useful tests of the nature of resonances, and we study these properties for the ${N}^{*}(1535)$ that appears dynamically generated from the strong interaction of mesons and baryons. Within this coupled-channels chiral unitary approach, we evaluate the ${A}_{1/2}$ and ${S}_{1/2}$ helicity amplitudes as a function of ${Q}^{2}$ for the electromagnetic ${N}^{*}(1535)\ensuremath{\rightarrow}{\ensuremath{\gamma}}^{*}N$ transition. Within the same formalism we evaluate the cross section for the reactions $\ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\eta}N$. We find a fair agreement for the absolute values of the transition amplitudes, a…
A new state of hadronic matter at high density
1997
We propose in this article that if the chemical potential exceeds a critical value in dense hadronic medium, a first-order phase transition to a new state of matter with Lorentz symmetry spontaneously broken (in addition to the explicit breaking) takes place. As a consequence, light vector mesons get excited as ``almost'' Goldstone bosons. Since the light vector mesons dominantly couple to photons, the presence of these new vector mesons could lead to an enhancement in the dilepton production from dense medium at an invariant mass lower than the free-space vector-meson mass. We provide a low-energy quark model which demonstrates that the above scenario is a generic case for quark theories w…
Time-optimal control of the purification of a qubit in contact with a structured environment
2019
We investigate the time-optimal control of the purification of a qubit interacting with a structured environment, consisting of a strongly coupled two-level defect in interaction with a thermal bath. On the basis of a geometric analysis, we show for weak and strong interaction strengths that the optimal control strategy corresponds to a qubit in resonance with the reservoir mode. We investigate under which conditions qubit coherence and correlation between the qubit and the environment can speed up the control process.
Tunneling in a ?breathing? double well: Adiabatic and antiadiabatic limits and tunneling suppression
1995
Tunneling in a piecewise harmonic potential coupled to a harmonic oscillator is considered by means of the path integral technique. The reduced propagator for the tunneling particle is calculated explicitly and the tunneling splitting is found in semiclassical approximation. The result holds for arbitrary values of the parameters of the system. From this the adiabatic and antiadiabatic approximations are obtained as particular cases and compared with the results obtained differently. The limit of a strong interaction is also considered. It is found that for strong interaction or equivalently for the harmonic frequency tending to zero the preexponential factor in the tunneling splitting tend…
Time-dependent density-functional theory for strongly interacting electrons
2017
We consider an analytically solvable model of two interacting electrons that allows for the calculation of the exact exchange-correlation kernel of time-dependent density functional theory. This kernel, as well as the corresponding density response function, is studied in the limit of large repulsive interactions between the electrons and we give analytical results for these quantities as an asymptotic expansion in powers of the square root of the interaction strength. We find that in the strong interaction limit the three leading terms in the expansion of the kernel act instantaneously while memory terms only appear in the next orders. We further derive an alternative expansion for the ker…
Use of a running coupling in the NLO calculation of forward hadron production
2018
We address and solve a puzzle raised by a recent calculation [1] of the cross-section for particle production in proton-nucleus collisions to next-to-leading order: the numerical results show an un- reasonably large dependence upon the choice of a prescription for the QCD running coupling, which spoils the predictive power of the calculation. Specifically, the results obtained with a prescription formulated in the transverse coordinate space differ by one to two orders of magnitude from those obtained with a prescription in momentum space. We show that this discrepancy is an artefact of the interplay between the asymptotic freedom of QCD and the Fourier transform from coordinate space to mo…
Low energy structure of the nucleon from chiral effective field theory
2014
We present some updated results regarding the scalar and electromagnetic structure of the nucleon obtained by the relativistic formulation of chiral effective field theory with baryons. We compare them with previous determinations available in the literature, and show their relevance for searches of physics beyond the standard model in the low energy frontier. An accurate knowledge of the structure of the nucleon is important to improve our understanding of the funda- mental interactions and provide theoretical estimations of some important quantities with a small uncertainty. This is specially relevant for experiential searches of physics be- yond the standard model in the low energy front…